Healthcare Reforms In Hawaii And Massachusetts Essay

Social insurance Reforms In Hawaii And Massachusetts - Essay Example Hawaii was the principal state to pass enactment, Hawaii’s Prepaid Health Care Act 1974, which expects businesses to give representatives medical coverage. The state has remained reliably ace wellbeing changes and this is apparent in the enactment that was passed in 2009 that made the Hawaii Health Authority. This authority has been ordered to get ready for social insurance needs of the state and to decide future limit requirements for the state’s wellbeing suppliers, bolster administrations, gear, and offices. Hawaii’s support for wellbeing changes is likewise found in Hawaii Health Authority’s undertaking of deciding, executing and keeping up the waivers that are accessible to the state’s occupants under government law. Correspondingly, Massachusetts has shown its help for wellbeing changes by embracing human services change laws like the one it received in 2006. This law expected inhabitants to have protection inclusion, bosses to furnish workers with medical coverage spread and swore that the state would give occupants acquiring beneath 150% of the government neediness level (FPL) with free medicinal services protection. The state revised this law in 2008 and 2010 so as to realign its wellbeing change objectives to those of the Federal Affordable Care Act. The Commonwealth Health Insurance Connector Authority is Massachusetts’ equality of Hawaii Health Authority (Bauer and Hollier, 2012). In spite of their help for wellbeing changes, there exist abberations in how these changes happen in the two states.

Ratio Analysis Annual Published Statements †MyAssignmenthelp.com

Question: Talk about the Ratio Analysis Annual Published Statements. Answer: Presentation: The present report depends on the investigation of the proportion for RIO Tinto and BHP Billiton. The proportions will be founded on the regions of benefit, dissolvability, liquidity and effectiveness proportion. Figures separated are from the yearly distributed proclamations of the particular organizations. As apparent the present proportion for Rio Tinto has spoken to a rising pattern as the organization in the year 2012 revealed current proportion of 1.42 though in the year 2017 the current expanded to 1.71 speaking to that Rio Tinto has been using its resources for meet its obligation commitments. Rio Tinto then again revealed a solid arrangement of results with higher working income of US $13.9 billion and mirrored a powerful operational exhibition. BHP Billiton in 2012 detailed a present proportion of 0.93 anyway over the range of six years the present proportion stood firmly to 1.85. This gives a diagram that BHP Billiton has had the option to pay its liabilities. The organization posted a solid monetary outcomes with positive working income of US $12.6 billion. In like manner, the speedy proportion for Rio Tinto in 2012 stood 0.96 which along these lines expanded to 1.32 in 2014. Despite the fact that the brisk proportion declined in 2016 to 1.27 anyway in 2017 the fast proportion expanded to 1.37. This mirrors the organization has adequate advantages for meet its transient commitments. The explanation behind increment in fast proportion is basically a result of solid hidden EBITDA of US $18.6 billion and with a multi year record edge of 44% in 2017. BHP announced a brisk proportion of 0.91 in 2012 which expanded over the range of five years to 1.76. BHP detailed a higher fast proportion than Rio Tinto as the organization has better figured out how to resources for pay momentary commitments. The explanation behind ascent in brisk proportion is fundamentally a result of $12.6 billion money showing a proceeded with progress in both the profitability and proficiency. Rio Tinto revealed an obligation proportion a lower obligation proportion of 0.47 in 2017 mirroring that the organization has lower extent of benefits financed by resources. The essential explanation behind lower obligation proportion is on the grounds that the organization took proportions of bringing down the obligation to US $3.8 billion out of 2017. BHP Billiton expressed an obligation proportion of moderately stable obligation proportion as the organization revealed obligation proportion of 0.46 in 2017. The obligation proportion of BHP Billiton spoke to a lower level of BHPs resources that is offered by obligation. Sensibly the lower obligation proportion is to a great extent a result of paid off net obligation to US $9.8 billion from US $16.8 billion. The obligation to value proportion speaks to the monetary proportion that mirrors the general extent of investors value and obligation utilized to back the benefits of organization (Scott, 2015). The obligation to value proportion for Rio Tinto throughout the years has generally been changing as in 2012 the organization announced an obligation proportion of 1.08 in 2013 and most minimal of 0.87 in 2017. There is higher level of obligation that is utilized by the organization to fund the benefits. Moreover, the expanding security yields and higher swelling with higher valuation of the US value advertise have diminished the unpredictability and fundamentally brought down obligation for the Rio Tinto. BHP Billiton announced a moderately lower obligation to value proportion as in 2012 the proportion stood 0.93 while in 2017 it diminished to 0.87 speaking to a lower extent of investors value and obligation utilized to back the benefits of organization. The fundamental value costs for BHP Billiton has altogether improved the edges and creates a solid income. BHP Billiton lower net obligation and in accordance with the solid money related execution of non-money alteration of US $0.6 billion. Stock Turnover Ratio: The stock turnover proportion can be characterized as the proportion that speaks to how well the association is adequately dealing with its stock (Weygandt et al., 2015). The stock turnover proportion for Rio Tinto in 2012 stood lower to 8.31 anyway over the range of six years it expanded to 11.53 in 2017. This speaks to Rio Tinto moderately more slow to change over its stock to the dollar sum. In spite of the more slow stock transformation rate the market suppositions for Rio Tinto chinas flexibly side renewal were actualized and drop in the worldwide stock by 10 percent. Besides, the market flexibly for titanium likewise improved in 2017 that was bolstered by lower stock and more tight gracefully. BHP Billiton detailed an improved stock turnover proportion of 0.56 in 2012 which further improved in 2017 with the organization revealing stock turnover of 0.33. This speaks to that the organization has been proficient in changing over its income rapidly than Rio Tinto to the dollar sum. The essential explanation behind diminished stock proportion is a result of decreased expense of Esconda unit by seven percent bringing about persistent efficiency and good developments in stock. The advantage turnover proportion is viewed as the productivity proportion that helps in estimating the capacity of the association in creating deals from its benefits by contrasting the net deals and the normal all out resources (Williams, 2014). Rio Tinto announced a generally steady resource turnover proportion of 0.44 in 2012. In spite of the fact that the proportion fell in 2015 to 0.38 anyway in 2017 it stood firmly to 0.46. The essential explanation behind improved resource turnover proportion is a direct result of solid monetary record, world-class resources and trained distribution of capital spots Rio Tinto in the one of a kind situation of having the option to put resources into higher worth development and give better come back from its benefits than investors. BHP Billiton detailed a declining pattern of advantage turnover proportion. The proportion in 2012 stood 0.65 while in 2017 it felled down to as low as 0.32. This speaks to that the organization has produced lower extent of deals from its benefits. In spite of the lower extent of focused deals, the five star resources produce huge measure of money from all the stages and with positive asset report and come back to investors of US $4.4 billion. The productivity proportion is utilized decide the capacity of the business in creating the income in contrast with the use and different business costs that are happened during the specific timespan (Weygandt et al., 2015). Net Profit Margin: The net overall revenue speaks to the level of income that is left over after the consumption are deducted from the deals. If there should be an occurrence of Rio Tinto, the overall revenue proportion over the range of five years stood moderately steady. The proportion in 2012 stood 17.56 while in 2017 it expanded imperceptibly to 20.25. The essential purpose behind improved net revenue is solid hidden income of US $8.6 billion and solid net profit of US $8.8 billion of every 2017. BHP Billiton announced an overall revenue proportion of 21.21 in 2012 though in 2016 the net revenue declined to - 19.80 mirroring a fall in the edge of benefit for the organization. In any case, in 2017 the edge improved decidedly to stand 15.95. The essential purpose behind ascent in benefit for BHP is a direct result of the US $5.9 billion of inferable benefit in 2017 while the basic inferable benefit was US $6.7 billion out of 2016. The arrival on resources shows how the organization is moderately producing benefit in regard its all out resources (Warren Jones, 2018). If there should arise an occurrence of Rio Tinto the arrival on resources stood moderately turbulent as in 2012 the proportion stood 17.56 while in 2015 it declined to 13.00. The proportion anyway improved to 20.25 in 2017. BHP detailed an arrival on resources of 13.69 in 2012 anyway in 2016 the advantage declined to - 5.19. In the ensuing year of 2017 the advantage has improved emphatically to 5.18. The organization has broadened arrangement of conveying innovation and applying capital control to remove most and better yield from its benefits. The RIO Tinto improve return on resources is principally a direct result of the organization US $50 billion resource with most worth imaginative projects to give come back from the advantages. End: On an indisputable note the examination can be finished up by expressing that Rio Tinto has generally detailed a solid budgetary exhibition in regard to BHP Billiton. The present proportion and speedy proportion remained steadfast for Rio Tinto and the net revenue mirrors that the organization has better capacity to created deals income from its advantages utilized. Reference List: Gitman, L. J., Juchau, R., Flanagan, J. (2015).Principles of administrative money. Pearson Higher Education AU. Henderson, S., Peirson, G., Herbohn, K., Howieson, B. (2015).Issues in monetary bookkeeping. Pearson Higher Education AU. Narayanaswamy, R. (2017).Financial bookkeeping: an administrative point of view. PHI Learning Pvt. Ltd.. Schaltegger, S., Burritt, R. (2017).Contemporary natural bookkeeping: issues, ideas and practice. Routledge. Scott, W. R. (2015).Financial bookkeeping theory(Vol. 2, No. 0, p. 0). Prentice Hall. Warren, C. S., Jones, J. (2018).Corporate money related bookkeeping. Cengage Learning. Weygandt, J. J., Kimmel, P. D., Kieso, D. E. (2015).Financial administrative bookkeeping. John Wiley Sons. Williams, J. (2014).Financial bookkeeping. McGraw-Hill Higher Education.

The Great Pueblo Revolt - Resisting Spanish Colonialism

The Great Pueblo Revolt - Resisting Spanish Colonialism The Great Pueblo Revolt, or Pueblo Revolt [AD 1680-1696], was a 16-year time frame throughout the entire existence of the American southwest when the Pueblo individuals toppled the Spanish conquistadors and started to remake their networks. The occasions of that period have been seen throughout the years as a bombed endeavor to for all time remove Europeans from the pueblos, an impermanent misfortune to Spanish colonization, a superb snapshot of freedom for the pueblo individuals of the American southwest, or some portion of a bigger development to cleanse the Pueblo universe of remote impact and come back to customary, pre-Hispanic lifestyles. It was no uncertainty a touch of every one of the four. The Spanish originally entered the northern Rio Grande locale in 1539 and its control was established set up by the 1599 attack of Acoma pueblo by Don Vicente de Zaldivar and a couple of score of fighter homesteaders from the undertaking of Don Juan de Oã ±ate. At Acomas Sky City, Oã ±ates powers murdered 800 peopleâ and caught 500 ladies and youngsters and 80 men. After a preliminary, everybody beyond 12 25 years old oppressed; all men more than 25 had a foot excised. Around 80 years after the fact, a mix of strict mistreatment and monetary persecution prompted a savage uprising in Santa Fe and different networks of what is today northern New Mexico. It was one of only a handful scarcely any successfulif temporaryforceful stoppages of the Spanish pioneer juggernaut in the New World. Life Under the Spanish As they had done in different pieces of the Americas, the Spanish introduced a mix of military and clerical initiative in New Mexico. The Spanish set up missions of Franciscan ministers in a few pueblos to explicitly separate the indigenous strict and mainstream networks, stamp out strict practices and supplant them with Christianity. As indicated by both Pueblo oral history and Spanish archives, simultaneously the Spanish requested that the pueblos render certain dutifulness and pay substantial tribute in merchandise and individual assistance. Dynamic endeavors to change over the Pueblo individuals to Christianity included pulverizing kivas and different structures, consuming formal stuff in open courts, and utilizing allegations of black magic to detain and execute customary stately pioneers. The legislature additionally settled an encomienda framework, permitting up to 35 driving Spanish pioneers to gather tribute from the family units of a specific pueblo. Hopi oral narratives report that the truth of the Spanish standard included constrained work, the enticement of Hopi ladies, assaulting of kivas and holy services, cruel discipline for neglecting to go to mass, and a few rounds of dry spell and starvation. Numerous records among Hopis and Zunis and other Puebloan individuals relate unexpected forms in comparison to that of the Catholics, including sexual maltreatment of Pueblo ladies by Franciscan clerics, a reality never recognized by the Spanish however refered to in case in later questions. Developing Unrest While the Pueblo Revolt of 1680 was the occasion that (incidentally) expelled the Spanish from the southwest, it was not the main endeavor. The pueblos had offered obstruction all through the 80-year time frame following the victory. Open changes didnt (consistently) lead to individuals surrendering their customs but instead drove the functions underground. The Jemez (1623), Zuni (1639) and Taos (1639) networks each independently (and ineffectively) revolted. There additionally were multi-town revolts which occurred during the 1650s and 1660s, yet in each caseâ , the arranged rebellions were found and the pioneers executed. The Pueblos were autonomous social orders before Spanish standard, and savagely so. What prompted the fruitful revolt was the capacity to beat that freedom and blend. A few researchers state that the Spanish accidentally gave the Pueblo individuals a lot of political organizations that they used to oppose pilgrim powers. Others think it was a millenarian development, and have highlighted a populace breakdown during the 1670s coming about because of a staggering scourge that executed off an expected 80% of the local populace, and it turned out to be evident that the Spanish couldn't clarify or forestall pandemic maladies or cataclysmic dry spells. In certain regards, the fight was one of whose god was on whose side: both Pueblo and Spanish sides recognized the legendary character of specific occasions, and the two sides accepted the occasions included heavenly intercession. In any case, the concealment of indigenous practices turned out to be especially exceptional somewhere in the range of 1660 and 1680, and one of the principle explanations behind the fruitful revolt seems to have happened in 1675â when then-representative Juan Francisco de Trevino captured 47 alchemists, one of whom was Popay of San Juan Pueblo. Initiative PoPay (or Popã ©) was a Tewa strict pioneer, and he was to turn into a key chief and maybe essential coordinator of the disobedience. PoPay may have been critical, however there were a lot of different pioneers in the insubordination. Domingo Naranjo, a man of blended African and Indian legacy, is regularly refered to, as are El Saca and El Chato of Taos, El Taque of San Juan, Francisco Tanjete of San Ildefonso, and Alonzo Catiti of Santo Domingo. Under the standard of pilgrim New Mexico, the Spanish conveyed ethnic classifications crediting pueblo to lump etymologically and socially assorted individuals into a solitary gathering, building up double and topsy-turvy social and financial connections between the Spanish and Pueblos. Popay and different pioneers appropriated this to assemble the unique and crushed towns against their colonizers. August 10-nineteenth, 1680 Following eight many years of living under outside guideline, Pueblo pioneers formed a military partnership that rose above longstanding competitions. For nine days, together they assaulted the capital of Santa Fe and different pueblos. In this underlying fight, more than 400 Spanish military work force and pioneers and 21 Franciscan ministers lost their lives: the quantity of Pueblo individuals who kicked the bucket is obscure. Senator Antonio de Otermin and his residual pilgrims withdrew in disgrace to El Paso del Norte (what is today Cuidad Juarez in Mexico). Â Witnesses said that during the revolt and a while later, PoPay visited the pueblos, lecturing a message of nativism and revivalism. He requested the pueblos to separate and consume the pictures of Christ, the Virgin Mary and different holy people, to consume the sanctuaries, crush the ringers, and separate from the spouses the Christian church had given them. Houses of worship were sacked in a considerable lot of the pueblos; symbols of Christianity were scorched, whipped and felled, pulled down from the square communities and dumped in burial grounds. Rejuvenation and Reconstruction Somewhere in the range of 1680 and 1692, regardless of the endeavors of the Spanish to recover the district, the Pueblo individuals reconstructed their kivas, resuscitated their functions and reconsecrated their places of worship. Individuals left their central goal pueblos at Cochiti, Santo Domingo and Jemez and assembled new towns, for example, Patokwa (set up in 1860 and comprised of Jemez, Apache/Navajos and Santo Domingo pueblo individuals), Kotyiti (1681, Cochiti, San Felipe and San Marcos pueblos), Boletsakwa (1680-1683, Jemez and Santo Domingo), Cerro Colorado (1689, Zia, Santa Ana, Santo Domingo), Hano (1680, for the most part Tewa), Dowa Yalanne (for the most part Zuni), Laguna Pueblo (1680, Cochiti, Cieneguilla, Santo Domingo and Jemez). There were numerous others. The design and settlement arranging at these new towns was another conservative, double court structure, a takeoff from the dissipated formats of mission towns. Liebmann and Pruecel have contended this new configuration is the thing that the developers considered a customary prehispanic town, in view of group moieties. A few potters chipped away at restoring conventional themes on their coating product earthenware production, for example, the multiplied headed key theme, which began AD 1400-1450. New social personalities were made, obscuring the customary phonetic ethnic limits that characterized Pueblo towns during the initial eight many years of colonization. Between pueblo exchange and different ties between pueblo individuals were built up, for example, new exchange connections among Jemez and Tewa individuals which got more grounded during the revolt time than they had been in the 300 years before 1680. Reconquest Endeavors by the Spanish to reconquer the Rio Grande area started as ahead of schedule as 1681â when the previous senator Otermin endeavored to reclaim Santa Fe. Others included Pedro Romeros de Posada in 1688 and Domingo Jironza Petris de Cruzate in 1689Cruzates reconquest was especially bleeding, his gathering obliterated Zia pueblo, executing several occupants. Be that as it may, the uncomfortable alliance of free pueblos wasnt great: without a shared adversary, the confederation broke into two groups: the Keres, Jemez, Taos and Pecos against the Tewa, Tanos, and Picuris. The Spanish exploited the disunity to make a few reconquest endeavors, and in August of 1692, the new legislative head of New Mexico Diego de Vargas, started his own reconquest, and this time had the option to arrive at Santa Fe and on August fourteenth announced the Bloodless Reconquest of New Mexico. A second fruitless revolt happened in 1696, however after it fizzled, the Spanish stayed in power until 1821 when Mexico announced freedom from Spain. Archeological and Historical Studies Archeological investigations of the Great Pueblo Revolt have been centered around a few strings, a considerable lot of which started as ahead of schedule as the 1880s. Spanish strategic has included uncovering the crucial; asylum site prehistoric studies centers around examinations of the new settlements made after the Pueblo Revolt; and Spanish site paleohistory, including the illustrious manor of Santa Fe and the governors castle which was widely reproduced by the pueblo individuals. Early examinations depended intensely on Spanish military diaries and Franciscan religious correspondence, yet since that time, oral accounts and dynamic

Christianity verses islam Essay

The mentalities of Christianity and Islam toward dealers and exchange are comparable yet unique. After some time Christian and Islamic mentalities towards the dealers and exchange have changed. The perspectives of Christianity and Islam toward shippers and brokers are comparable. A way that these two religions mentalities towards their vendors and exchange was that the two of them permitted being dealt with better under god simpler for shippers to accomplish in the event that they spoke the truth about what their exchange. In the Muslim Qur’an it states â€Å"On the day of judgment, the legit, honest Muslim trader will take rank with the saints of the faith† (Doc 2). This announcement demonstrates that dealers could be dealt with better under god on the off chance that they were straightforward. Likewise in the Christian Bible, New Testament (Matthew) it states â€Å"It is simpler for a camel to experience the opening of a needle, than for a rich man to go into the r ealm of god† (Doc 1). This implies it is simpler for the fair dealers to enter the realm of god than the rich high society Christians. With everything taken into account, the Christian and Islamic perspectives toward the vendors and exchange are comparative. Just as the perspectives of Christianity and Islam toward vendors and exchange being comparative they were extraordinary. A way that Christianity and Islam mentalities were various was that a few Christians felt that on the off chance that they parted with their cash earned to good cause they would have the option to turn out to be nearer to God by serving him, however in Islam they just idea that trustworthiness could get you closer to God. In The Life of St. Godric by Reginald it states â€Å"now he had lived sixteen years as a vendor, and suspected of spending on good cause, to God’s respect and service† (Doc 3). In spite of the fact that this announcement demonstrates the distinction it might be predisposition since it was composed by a partner of a shipper, this could imply that he was encountering things unique in relation to what they were truly expected to be by law. In the Qur’an it states â€Å"On the day of judgment, the fair, honest Muslim dealer wil l take rank with the saints of the faith† (Doc 2). The announcements from these two works together demonstrate that the mentalities towards vendors and exchange were diverse among Christianity and Islam. After some time both Christianity and Islam perspectives towards shippers and tradeâ changed. Christianity began with the Christian shippers not offering with the dealers to offering with the merchants. Thomas Aquinas composed â€Å"the vender must not force upon the bidder† (Doc 4). What's more, this change was introduced when a letter was composed putting in a request for English fleece saying â€Å"with god consistently before us, we will do your bidding† (Doc 6). Both these announcements could be predisposition because of the author, the primary statement from Aquinas could be inclination since he was a scholar which implies he contemplated divine beings thus he could have expounded more on what the book of scriptures states and not what really occurred. At that point the letter was composed by a dealer which implies they could have had various encounters with exchange than different shippers. Islam began with their vendors waiting be straightforward and wound up with their traders trying to make benefits and betting, and betting for more cash isn't honest. The Qur’an it states â€Å"On the day of judgment, the genuine, honest Muslim trader will take rank with the saints of the faith† (Doc 2). Ibn Khaldun a main Muslim researcher composed â€Å"We have just expressed that merchants must purchase and sell and look for profits† and he composed â€Å"they go under the heading of gambling† (Doc 5). With everything taken into account both Christianity and Islamic mentalities toward dealers and exchange changed after some time. Taking everything into account Christianity and Islam had perspectives toward vendors and exchange that were comparative and extraordinary, and that the two religions mentalities changed after some time. An archive that was absent that would have been useful would be a record composed by Muslim or Christian shippers in light of the fact that the reports that were composed by vendors were composed by British and Italian dealers.

Post-Colonialism: Trying To Regain Ethnic Individuality :: essays research papers fc

In fact, the outsider has bizarre traditions. The white man held the paper like a holy thing. His hands shook, and we doubted him... For what number of moons will the outsider be among us? (Vera 43) The more odd despite everything lives among the individuals of Zimbabwe, however the pilgrim political authority has left. However I wonder if the town senior talking in the above section from Yvonne Vera's Nehanda would perceive current Zimbabwean specialists as outsiders or comrades. Might he be able to identify with the present government authorities and comprehend the dialects which they talk? Would he feel comfortable in an African nation with outskirts characterized by European supreme forces regardless of the different ethnic countries included? Post-pilgrim hypothesis endeavors to clarify issues, for example, these, yet it does so solely in the dialects of the European frontier powers. Europeans even made the word Africa. "To name the world is to 'get' it, to know it and to have command over it" (Ashcroft 283). Since information is force, and words, regardless of whether composed or spoken, are the vehicle of trade, utilizing words brings about duty. One must utilize uncommon consideration with extensively characterized words and terms, for example, post-frontier. Post-frontier writing portrays a wide cluster of encounters set with regards to heterogeneous social orders which themselves speak to a wide range of ethnic gatherings. Ashcroft, Griffiths and Tiffin characterize post-frontier hypothesis as conversation of "migration, bondage, concealment, opposition, portrayal, contrast, race, sex, spot, and reactions to the persuasive ace talks of majestic Europe... furthermore, the essential encounters of talking and composing by which all these come into being" (Ashcroft 2). The wide-going nature of the term present pioneer compromises on debilitate its handiness by "diffusion... so outrageous that it is utilized to allude to immensely unique as well as even restricted activities" (Ashcroft 2). Post-imperialism incorporates a large number of the issues experienced in the work we have talked about up to this point in the semester. However in light of the fact that dubious and summed up hypotheses have cutoff points and will in general misrepresent, blurring over genuine issues, one must deal with the term with care. Ashcroft, Griffiths, and Tiffin recommend that we ought to confine the term present pioneer on mean after expansionism. "All post-pioneer social orders are as yet subject somehow to unmistakable or unobtrusive types of neo-pilgrim control, and autonomy has not fathomed the problem" (Ashcroft 2). After expansionism, new elites, regularly as despots, every now and again rose and still ascent to control in post-pilgrim nations.

Going for the Au

Going for the Au Today, MIT alum Pat Antaki 84 will compete in the Olympics. He will compete in the luge-like, super-crazy event of skeleton, where he will race down a pure ice track head first at 80 miles per hour. Since Antaki lives in the Dallas suburb of Plano, the Dallas Morning News has the full story. Images of Pat Antaki from skeletonsport.com, photos by Tea Karvinen (TsK) Antaki, who was born in and will compete for Lebanon, lived in Burton-Conner when he was an undergraduate. He was active in rugby, sailing, and, of course, UROP. Pat Antaki isnt the first MIT alum to go to the Olympics. Some others include: CREW Chet Riley 62, 1964, United States Gary Piantedosi 76, 1976, United States John Everett 76, 1980, United States Elizabeth Bradley 81, 1988, United States Steve Tucker 91, 2000 and 2004, mens lightweight double sculls, United States FENCING Joseph Levis 26, 1932, Foil, United States, Silver medalist Johan Harmenberg 81, 1980, Epee, Sweden, Gold medalist RIFLE Herb Voelcker 48, 1956, high-powered rifle, United States SAILING Ralph Evans, 1948, Firefly Dinghies, United States, Silver medalist Ed Melaika, 1952, Finn Dinghies, United States John Marvin 49, 1956, Finn Dinghies, United States Eric Olsen 41, 1956, Sharpie (two-man), United States John Bertrand, 1972, Finn Dinghies, Australia Paula Lewin, 1992 and 1996, Europe Dinghies; 2004, Ynglings, Bermuda SKIING Alexis Photoiades 91, 1988 and 1992, Cyprus TAEKWONDO Chinedum Osuji 03, 2004, Trinidad and Tobago TRACK AND FIELD Thomas Pelham Curtis 94, 1896, 110m hurdles, United States, Gold medalist Henry Steinbrenner 27, 1928, 220-yard hurdles, United States WRESTLING Nate Ackerman G, 2004, Freestyle 74kg, Great Britain And dont forget the cool ice skate research!

Prediction of Corrosion Rate - Free Essay Example

Prediction of Corrosion Rate and Its Affecting Factors on Surface Casing Abstract Corrosion is a physicochemical phenomenon affected by multiple factors. The effect of these factors on corrosion depends on their concentrations and interactions with each other. It is not possible to establish a direct one to one relationship between the values of a single parameter and the corrosion rate while neglecting other parameters. This requires calculation that considers interactions of different parameters with each other as well as their effect on the corrosion rate. As the impact of each parameter value on corrosion rate, considering value of other parameters, cannot be expressed with a simple equation, it is not possible to accurately and confidently generalize the effects of change in each parameter on the corrosion rate over an entire domain. Surface casing of the wells can cause serious hazards and possible blowout as a result of early corrosion. In different areas in the world, surface casing collapses as a result of downhole corrosion, casing cracking, and rupture under high-pressure-corrosion. Surface casings or conductor pipes cannot be excavated deep for repair because of safety concerns. Corrosion problems of the surface casing result from non-fined manufactured joints, presence of salt water in some formation beds, and the cement section that isolates formation from the casing. In the shallow part of the casing, corrosion can result from either local or areal electrochemical reaction. Keywords: CO2 Corrosion, Surface Casing, Corrosion Rate, NORSOK M-506. III List of Symbols A the cross sectional area in m2 B(index) the constant used in viscosity calculations C(index) the concentration of component CRT the corrosion rate at temperature T in mm/year D the pipe diameter in mm FH2O the water mass flow in humidity calculations Ftot the total mass flow in humidity calculations K(index) the equilibrium constant used in pH calculations KSP the equilibrium constant of iron carbonate KT the constant for the temperature T used in corrosion rate calculations LTR Linear Polarization Resistance OCTG Oil Country Tubular Goods P the total system pressure in bar QG the volumetric flow of gas in MSm3/d QL the volumetric flow of liquid (i.e. liquid hydrocarbons and water) in Sm3/d R w/o Re the Reynolds number S the wall shear stress in Pa T the temperature given in Kelvin. Tc the temperature given in C Tf the temperature given in F Tstd the temperature given in Kelvin at standard conditions (60 F/15.55 C) Z the compressibility of the gas a the fugacity coefficient f the friction factor fCO2 the fugacity of CO2 in bar f(pH)T the the pH factor at temperature T k the pipe roughness in m I the ionic strength given in molar pCO2 the CO2 partial pressure in bar pH2O the H2O vapour pressure in bar T the 20 C, 40 C, 60 C, 80 C, 90 C, 120 C or 150 C uGS the superficial velocities of gas in m/s uLS the superficial velocities of liquid in m/s um the mixed velocity (m/s) the liquid fraction o the viscosity of oil in Ns/m2 G the viscosity of gas in Ns/m2 L the viscosity of liquid in Ns/m2 m the mixed viscosity in Ns/m2 relmax the maximum relative viscosity (relative to the oil) w the viscosity of water in Ns/m2 G the gas density in kg/m3 L the liquid density in kg/m3 m the mixed density in kg/m3 o the oil density in kg/m3 w the water density kg/m3 the watercut c the watercut at inversion point III Prediction of Corrosion Rate and Its Affecting Factors Introduction 1. Introduction Corrosion is defined as the chemical degradation of metals by reaction with the environment. The destruction of metals by corrosion occurs either by direct chemical attack at elevated temperatures in a dry environment or by electrochemical processes at low temperature in a water-wet or moist environment. Corrosion is the main threat to the petroleum industry. Its enormous impact is shown in Table 1.1. The values in the table may be assumed as average ones, because they vary regarding to the country and region e.g. in Western Europe corrosion-related failures come to ca. 25%, in the Gulf of Mexico and Poland about 50%, while in India they reach 80% (1) Table 1.1 Failures in Oil and Gas Industry (2) Type of failure Number of Cases [%] Corrosion (all types) 33 Fatigue 18 Mechanical damage/overload 14 Brittle fracture 9 Fabrication defects (excluding welding defects) 9 Welding defects 7 Others 10 The surface casing of wells located varies from a few hundred feet to as much as 5000 ft is prone to external corrosion attack at the splash zone around the wellhead region. The principal functions of the surface casing string are to: hold back unconsolidated shallow formations that can slough into the hole and cause problems, isolate the freshwater-bearing formations and prevent their contamination by fluids from deeper formations and to serve as a base on which to set the blowout preventers. It is generally set in competent rocks, such as hard limestone or dolomite, so that it can hold any pressure that may be encountered between the surface casing seat and the next casing seat. The effect of corrosion in surface casing ultimately results in loss of load bearing capacity of the wellhead when the severity is very high. At rig based well reentry, collapse of the surface casing had occurred under the weight of the Blow Out Preventer (BOP) during its installation. Historical records, field investigation and lab results from a previous study (SPE Paper 100432 and 108698) indicate the near surface casing corrosion is a result of cyclic or consistent moisture ingress of oxygenated water with the annulus between the Surface Casing and Conductor Casing. Elevated well operating temperatures in conjunction with an extremely corrosive environment caused by the salts that leach from the cement create a very aggressive corrosion environment. Corrosion of Surface casing itself can be distinguished based on its environment conditions ( 1.1) 1. Corrosion due to atmospheric condition (Zone I) 2. Corrosion due to corrosive water (Zone II) 3. Corrosion due to cementing (Zone III) 4. Internal Corrosion Prediction of Corrosion Rate and Its Affecting Factors Types of Casing Corrosion 2. Types of Casing Corrosion Casing is made by steel consists of alloy of pure iron and small amounts of carbon present as Fe3C with trace amounts of other elements such as Manganese, Molybdenum, Chromium, Nickel, Copper with particular purposes. In the most steel corrosion problems, the important differences in reaction potentials are not those between dissimilar metals but those which exist between separate areas interspersed over all the surface of a single metal. These potential differences result from local chemical or physical differences within or on the metal, such variations in grain structure, stresses and scale, inclusions in the metal, grain boundaries, scratches or other surface conditions. Corrosion of surface casing is initiated by a wide variety of mechanisms. They can be grouped into three categories: electrochemical corrosion, chemical corrosion, and mechanical assisted corrosion (3). 2.1 Electrochemical Corrosion Corrosion of casing is mostly electrochemical reaction composed of two half cell reactions, an anodic reaction and a cathodic reaction. The anodic reaction releases electrons, while the cathodic reaction consumes electrons (2.1 and 2.2). There are three common cathodic reactions, oxygen reduction (fast), hydrogen evolution from neutral water (slow), and hydrogen evolution from acid (fast). The corrosion cell can be represented as follows: * Anodic reaction: Fe Fe2+ + 2e- * Cathodic reactions: O2 + 4 H+ + 4e- 2H2O (oxygen reduction in acidic solution) 1/2 O2 + H2O + 2e- 2OH- (oxygen reduction in neutral or basic solution) 2H+ + 2e- H2 (hydrogen evolution from acidic solution) 2H2O + 2e- H2 + 2OH- (hydrogen evolution from neutral water) Electrochemical corrosion occurs above all on the outer casing wall. This type of corrosion can be subdivided into the following three sub-groups. 2.1.1 Galvanic Corrosion Galvanic corrosion is the most widespread type of corrosion and comes into being when two different metals or alloys develop a potential difference between them in a conducting electrolyte ( 2.3). The metal with the lower positive electrochemical potential acts as an anode and corrodes metal ions away to balance the electron flow. The second metal with higher positive electrochemical potential acts as a cathode and is protected from corrosion. If there were no electrical contact, both metals would be uniformly attacked by the corrosion. The severity of galvanic corrosion depends primarily upon the difference in potentials (the ranking of metal in galvanic series), their surface areas and environment (conductivity of the corrosive medium). 2.1.2 Crevice Corrosion This is an example of localized attack in the shielded areas of metal assemblies, shielded areas of metal assemblies. Crevice corrosion is caused by concentration differences of a corrodant over a metal surface. Electrochemical potential differences result in selective crevice or pitting corrosion attack. This kind of corrosion occurs at casing in poorly cemented sections as well as at drillpipe joints, tubing and casing collars ( 2.4). 2.1.3 Pitting Corrosion Pitting corrosion is similar to crevice corrosion and indicates a localized attack ( 2.5). Pitts are caused by a scratch, defect or impurity in casing. Pitting is one of the most dangerous forms of corrosion, because the metal loss can be rapid (even several mm per year) and often results in fast penetration. This type of corrosion is strongly affected by temperature. 2.2 Chemical Corrosion Chemical corrosion occurs mainly on the inner casing wall. It is governed by the chemical reactions that can not generate the electrical current. Characteristic chemical attacks are primary encouraged by carbon dioxide, hydrogen sulphide and organic or inorganic acids. 2.2.1 CO2 Corrosion CO2 corrosion or Sweet corrosion results from the presence of water containing dissolved carbon dioxide. Dissolved carbon dioxide in water decreases the pH of the water and increases its corrosivity. The following shows how CO2 results in the corrosion of steel: CO2 (g) + H2O (l) H2CO3 (aq) (Carbonic Acid) Fe (s) + H2CO3 (aq) FeCO3 (aq) + H2 (g) (Iron Carbonate) CO2 Corrosion in surface casing usually takes the form of deep pits with steep, undercut sides. This is sometimes referred to as mesa corrosion due to the shape of the pitting profile, i.e. areas of unattacked metal adjacent to pitted areas. The pits may penetrate the wall completely in a relatively short period of time. This pitting is caused when the carbon dioxide dissolves in water droplets that condense on the casing wall ( 2.6). The most serious sweet oil corrosion problem can usually be found in gas lift wells. They are usually high water producers, and corrosion can be accelerated if the injected gas lift gas contains carbon dioxide and/or small amounts of oxygen. 2.2.2 H2S Corrosion H2S Corrosion or sour corrosion is caused by hydrogen sulphide dissolved in water, which reacts with metal. Hydrogen ions are produced, which results in a more acidic environment, and low pH accelerates corrosion (especially in deep wells, where pH is further reduced by the pressure). Additionally iron sulphide is created, which at higher temperatures is cathodic to iron and leads to galvanic corrosion. Below is the chemical reaction to describe reaction between iron and H2S. Fe (s) + H2S (g) FeS (s) +2H In the presence of an oxidizing agent, the iron sulphide (FeS) deposited is cathodic to the steel and a galvanic cell can be set up. This may result in pitting of areas where the iron sulphide film has bee partially detached from the surface of the steel. An iron sulphide film that is adherent and undamaged can actually provide protection to the steel. 2.2.3 Strong Acids Corrosion Strong Acids Corrosion results from acids, which are pumped into the wells. They are mostly used to stimulate production like HCl in limestone formations or hydrofluoric acid for sandstones reservoir. Furthermore, dissolved oxygen stimulates corrosion in the presence of H2S and CO2. 2.3 Mechanical Assisted Corrosion The surface casing is considered to have low load level. Since the setting depth of surface casing is low, its main load is produced by BOP during the drilling phase and by other casing string strings hanging on it during production. However the Stresses in surface casing can increase corrosion especially on the casing joints and collars. This type of corrosion can be divided into several groups 2.3.1 Corrosion Fatigue When surface casing is repeatedly stressed in a cyclic manner, it will fail in a brittle manner at stresses far below the yield or tensile strength of the material ( 2.8). There exists a limiting stress below which steel may be cyclically stressed indefinitely without failure. This stress is called the endurance limit and is always lower than the yield and tensile strengths. The fatigue life of casing is substantially reduced when the casing is cyclically stressed in a corrosive environment. The simultaneous occurrence of cyclic stress and corrosion is called corrosion fatigue, and the steel no longer exhibits an endurance limit. In corrosion fatigue, the corrosivity of the environment is extremely important. The presence of dissolved gases especially oxygen carbon dioxide or The presence of dissolved gases, especially oxygen, carbon dioxide or hydrogen sulphide, results in a pronounced reduction in fatigue life. Pitting or localized attack is most damaging to fatigue life, but even slight general corrosion will substantially reduce time to failure. 2.3.2 Sulphide Stress Cracking (SSC) Sulphide stress cracking is a spontaneous brittle failure that occurs in steels and high strength alloys when exposed to moist hydrogen sulphide. This phenomenon is also referred to as sulphide cracking, sulphide corrosion cracking, and sulphide stress corrosion cracking. All the names refer to the same corrosion phenomenon, hydrogen embrittlement, which requires that hydrogen sulphide be present, water (even in small quantities) a high strength material, and tensile stress (either applied or residual). Sulphide stress cracking (SSC) may occur very rapidly after exposure to a sour environment, or it may take place after considerable time has passed. 2.3.3 Stress Corrosion Cracking (SCC) Stress corrosion cracking is caused by the synergistic action of a corrosive medium and applied tensile stress; that is, the combined effect of the two is greater than the sum of the single effects. In absence of the corrodant, the alloy could easily support the stress. The stress is always a tensile stress and can be either applied or residual. When a casing suffers stress corrosion cracking, metal loss from corrosion is generally very low, although most likely, pits will occur and the cracks will develop in the base of the pits. Stress Corrosion Cracking (SCC) of high strength casing steels occurs in salt solutions, moist atmospheres, and even in tap water if the steel is ultra high strength steel. Cracking tendency increases with the strength of the steel. Experience or testing is necessary to determine the corrosive and conditions which will cause cracking of high strength steels ( 2.6). It has to be added that the pure hydrocarbons are not corrosive themselves, so the corrosion is always initiated by other factors (most important are mentioned above). The market shares of individual corrosion mechanisms are presented in Table 2.1, however naturally they may occur simultaneously. Table 2.1 Causes of corrosion-related failure within the oil and gas industry (2) Cause of failure Total failure [%] CO2 related 28 H2S related 18 Preferential weld 18 Pitting 12 Erosion corrosion 9 Galvanic 6 Crevice 3 Impingement 3 Stress corrosion 3 45 Prediction of Corrosion Rate and Its Affecting Factors Corrosion Aspects of OCTG Materials 3. Corrosion Aspects of OCTG Materials 3.1 Introduction of OCTG Materials In recent years, oil and gas wells have been developed in increasingly severe corrosion environment characterized by high temperature, high partial pressure of CO2 and high concentration of Chloride ions, and in some cases, also containing H2S. For this reason, the prevention of corrosion in Oil Country Tubular Goods (OCTG) has become important task. OCTG includes three types of seamless tubes, delivered in quenched and tempered condition: * Drillpipe heavy seamless tubes that rotate the drill bit and circulate the drilling fluid. Joint of pipe 30 ft (9m) long are coupled together with tool joints. * Casing pipe is used to line the hole. * Tubing a pipe through which the oil and gas is produced from the wellbore. Tubing joints are generally around 30 ft (9m) long with thread connection on each end. The corrosion aspects of OCTG materials depend on their material contents such as Carbon, Chromium, Manganese, Nickel, Molybdenum and Copper. The tables below (Table 3.1 and 3.2) show the chemical compositions for OCTG grades of low alloy grades and stainless steel. Traditionally the grades used for OCTG applications were Carbon Manganese steels (up to the 55 ksi strength level) or Mo containing up to 0.4% Mo. Nowadays, wells with contaminants causing corrosive attack have strong demand for higher strength materials resistant to Hydrogen Embrittlement and Sulphide Stress Cracking (SCC). Highly tempered martensite has been identified as the structure which most resistant to SCC at higher strength level, and 0.75% Mo has been found to be the Mo concentration to obtain the optimum combination of yield strength and resistance to SCC (10). This is reflected in the list of Mo containing low alloy API standard grades (Table 3.1). For the 75 ksi strength level 0.4% Mo is sufficient, while each of the higher strength grades up to 125 ksi show the optimum Mo level of 0.75 or 0.80% and for higher strength up to 140 ksi (yield strength 965-1171 MPa) precipitated has been introduced as an additional strengthening mechanism by the addition of Niobium (Columbium). Table 3.1 Chemical Composition and Strength Properties of Common Alloy OCTG Steels (9) Yield strength API Grade % Alloy content Tensile Strength (ksi) Code C Mn Ni Cr Mo Cu min (N/mm2) 40 H40 0.5 1.5 410 55 K55 0.5 1.5 655 75 C75-1 0.5 1.7 0.5 0.5 0.4 0.5 665 90 C90-1 0.35 1.9 0.9 1.2 0.75 690 95 T95-1 0.35 1.2 0.9 1.5 0.85 724 125 Q125 0.35 1 0.9 1.2 0.75 930 140 0.3 1 1.6 1.1 0.05 1034 Table 3.2 Chemical Composition and Strength Properties of OCTG Stainless Steels (9) Yield strength API Grade % Alloy content Tensile Strength (ksi) Code C Mn Ni Cr Mo Cu min (N/mm2) 9% Chromium 75 C75-9Cr 0.15 0.6 0.5 9 1 0.25 655 13% Chromium 80 L80-13Cr 0.22 16 0.5 13 0.25 655 95/110 0.04 0.6 4 13 1.5 95/111 0.04 0.6 5 13 2.5 For service in oil and gas fields with more aggressive corrosion environments stainless API grades are standardized with 9% Cr, 1% Mo and 13% Cr (without Mo). For high temperature environments with CO2 and H2S, the non API specialized grades shown in table 3.2 with improved corrosion and SCC resistance have been developed (11). The reduced Carbon content increases Cr in solid solution, which effectively improves the corrosion resistance. Ni and Mo secure both hot workability and corrosion resistance. In particular the addition of Mo improves the pitting corrosion resistance, thereby eliminating initiation sites for SCC. 3.2 Influence of Microstructure and Chemical Composition of Steel in Corrosion Behavior Steel is an alloy of iron (Fe) and carbon (C). Carbon is fairly soluble in liquid iron at steel making temperatures, however, it is practically insoluble in solid iron (0.02% at 7230C), and trace at room temperature. Pure iron is soft and malleable; small amounts carbon and manganese are added to give steel its strength and toughness. Most of the carbon is oxidized during steelmaking. The residual carbon and post-fabrication heat treatment determines the microstructure, therefore strength and hardness of steels. Carbon steels are then identified by their carbon contents, i.e., low-carbon or mild steel, medium carbon (0.2- 0.4 % C), high-carbon (up to 1% C) steels, and cast irons (2 % C). In a corrosive environment, either grains or the grain boundaries having different composition can become anodic or cathodic, thus forming the corrosion cells. Hydrogen evolution reaction can take place on iron carbide, and spheroidized carbon in steels, and graphite in cast irons, in acidic solutions with relative ease; areas denuded in carbon become anodic and corrode preferentially. Therefore, post-weld heat treatment of steels is critical in order to prevent corrosion of the heat affected zone (HAZ), sensitization and intergranular corrosion in stainless steels The final microstructure of carbon and low alloy carbon steel OCTG is determined by its chemical composition and the thermomechanical treatments used during the production processes. Although the design criteria are mainly focused on properties such as mechanical resistance, toughness, and weld ability, the corrosion resistance is also affected. The microstructure is considered to have an important effect on how firmly the corrosion scale sticks to the surface. The adherence of the corrosion product film, and hence its protectiveness, has often been related to the presence of iron carbide and its morphology (laminar, globular, etc.). The idea is that the carbide phase can strengthen the film and can anchor it to the steel substrate, and then the size and distribution of these carbides become very important. Table 3.3 shows the typical corrosion characteristics of different types of steel. The table indicates that metals which have similar chemical composition will have different behavior in corrosion depend on their microstructures. Table 3.3 Typical Corrosion Characteristics of Different Types of Steel. (12) Item Martensitic Ferritic Austenitic Duplex Corrosion resistance to General Corrosion Fair Excellent Excellent Excellent Corrosion resistance to SSC Poor Poor Excellent Fair Corrosion resistance to SCC Excellent Excellent Poor Fair Strength High Low Low High Weldability Fair Fair Excellent Fair In order to prevent possible stress corrosion cracking in sour gas and oil wells containing CO2 and H2S with specific partial pressure, it is necessary to use specially manufactured tubing and casing. 3.1 below is a concept for material selection according to CO2 and H2S partial Pressure. Prediction of Corrosion Rate and Its Affecting Factors Corrosion of Surface Casing and Affecting Factors 4. Corrosion of Surface Casing and Elements Affecting of Corrosion Rate 4.1 Corrosion due to Atmospheric Corrosion Atmospheres are often classified as being rural, industrial or marine in nature. Two decidedly rural environments can differ widely in average yearly temperature and rainfall patterns, mean temperature, and perhaps acid rain, can make extrapolations from past behavior less reliable. The corrosion of casing steel in the atmosphere and in many aqueous environments is best understood from a film formation and brake down standpoint. It is an inescapable fact that iron in the presence of oxygen and water is thermodynamically unstable with respect to its oxides. Because atmospheric corrosion is an electrolytic process, the presence of an electrolyte is required. This should not be taken to mean that the steel surface must be awash in water; a very thin adsorbed film of water is all that is required. During the actual exposure, the metal spends some portion of the time awash with water because of rain or splashing and a portion of the time covered with a thin adsorbed water film. The portion of time spent covered with the thin water film depends quite strongly on relative humidity at the exposure site. This fact has led many corrosion scientists to investigate the influence of the time of wetness on the corrosion rate. Rusting of iron depends on relative humidity and time of exposure in atmosphere containing 0.01% SO2. The increase in corrosion rate produced by the addition of SO2 is substantial. Oxides of nitrogen in the atmosphere would also exhibit an accelerating effect on the corrosion of steel. Indeed, any gaseous atmospheric constituent capable of strong electrolytic activity should be suspected as being capable of increasing the corrosion rate of steel. Because carbon steels are not very highly alloyed, it is not surprising that most grades do not exhibit large differences in atmospheric-corrosion rate. Nevertheless, alloying can make changes in the atmospheric-corrosion rate of carbon steel. The elements generally found to be most beneficial in this regard are copper, nickel, silicon, chromium and phosphorus. Of these, the most striking example is that of copper, increases from 0.01-0.05%, decrease the corrosion rate by a factor of two to three. 4.2 Corrosion due to Water Environment Carbon steel casing is often submerged in water to some extent during service. This exposure can be under conditions varying temperature, flow rate, pH, and other factors, all of which can alter the rate of corrosion. The relative acidity of the solution is probably the most important factor to be considered. At low pH the evolution of hydrogen tends to eliminate the possibility of protective film formation so that steel continues to corrode but in alkaline solutions, the formation of protective films greatly reduces the corrosion rate. The greater alkalinity, the slower the rate of attack becomes. In neutral solutions, other factors such as aeration became determining so that generalization becomes more difficult. The corrosion of steels in aerated seawater is about the same overall as in aerated fresh water, but this is somewhat misleading because the improved electrical conductivity of seawater can lead to increased pitting. The concentration cells can operate over long distance, and this leads to a more nonuniform attack than in fresh water. Alternate cycling through immersion and exposure to air produces more pitting attack than continuous immersion. The effect of various alloying addition and exposure conditions on the corrosion behavior is shown in Table 4.1. Table 4.1 Comparison of results under different type of exposure (13) Effects of alloy selection, chemical composition and alloy additions Sea air Freshwater Alternately wet with Seawater or Spray and dry Continuously wet with seawater Ferrous alloys Pockmarked Vermiform on cleaned bars Pitting, particularly on bars with scale Pitting, particularly on bars with scale Wrought iron versus carbon steel Steel superior to wrought and ingot irons Iron and steel equal in low-moor areas Low-moor iron superior to carbon steel Low-moor iron superior to carbon steel Sulfur and phosphorus content Best results when S and P are low Best results when S and P are low Best results when S and P are low Apparently little influence Addition of copper Beneficial: Effect increasing with copper content Beneficial: 0.635% Cu almost as good as 2.185% Cu Beneficial: 0.635% and 2.185% Cu much the same 0.635% Cu slightly beneficial: 2.185% Cu Addition of nickel 3.75% Ni Superior even to 2% Cu; 36% Ni almost Perfect after 15-year exposure 3.75%Ni Superior even to 2%Cu; 36%Ni excellent resistance 3.75%Ni beneficial usually more so than Cu: 36%Ni the best metal in the set 3.75% Ni slightly beneficial and slightly superior to Cu: 36% Ni the best metal in the set Addition of 13.5% Cr Excellent resistance to corrosion: cold blast metal perfect after 15-year exposure: equal to 36% Ni steel Excellent resistance to corrosion: equal to 36% Ni steel Subject to severe localized corrosion that virtually destroys the metal Subject to severe localized corrosion that virtually destroys the metal Behavior of cast irons Excellent resistance to corrosion: cold blast metal superior to hot: no graphitic corrosion Undergoes graphitic corrosion Undergoes graphitic corrosion Undergoes graphitic corrosion Interestingly, the corrosion rates of specimens completely immersed in seawater do not appear to depend on the geographical location of the test site; therefore, by inference, the mean temperature does not appear to play an important role. This constancy of the corrosion rate in seawater has been attributed to the more rapid fouling of the exposed steel by marine organisms, such as barnacles and algae, in warmer seas. It is further speculated that this fouling offsets that increases expected from the temperature rise. 4.3 Corrosion due to Cement Environment 4.3.1 Cement as an Environment for Casing Steel and the Role of Alkalinity Cementing is one of the fundamental techniques in oil and gas well design approach. It serves its purpose as a protective material in preventing the casing from corrosion. Environment formation characteristics such as mineral content, microorganisms, acidity lead to steel corrosion and this could be prevented by cementing. Cementing is one method to surround the steel with an alkaline environment having a pH value within the range 9.5 to 13. Hydrated cement provides such an environment, the normal pH value being 12.5, at which steel is protected in the absence of aggressive anions. At this pH value a passive film forms on the steel that reduces the rate of corrosion to a very low and harmless value (Fig 4.1). Thus, cement cover provides chemical as well as physical protection to the steel. However, circumstances do arise in which corrosion of reinforcement occurs. Since rust has a larger volume than the steel from which it is formed, the result can be cracking, rust-staining, or even spalling of the cement cover. Such occurrences usually arise from loss of alkalinity in the immediate vicinity of the steel or from the presence of excessive quantities of aggressive anions in the cement (normally chloride), or from a combination of both of these factors. 4.3.2 Loss of Alkalinity by Carbonation Alkalinity can be lost as a result of: * Reaction with acidic gases (such as carbon dioxide) in the atmosphere. The effects of sulphur dioxide are also included in the term carbonation. * Leaching by water from the surface. In practice both of these factors contribute to the reduction of alkalinity in the cement. Cement is permeable and allows the slow ingress of the atmosphere; the acidic gases react with the alkalis (usually calcium, sodium and potassium hydroxides), neutralizing them by forming carbonates and sulphates, and at the same time reducing the pH value. If the carbonated front penetrates sufficiently deeply into the cement to intersect with the cement reinforcement interface, protection is lost and, since both oxygen and moisture are available, the steel is likely to corrode. The extent of the advance of the carbonation front depends, to a considerable extent, on the porosity and permeability of the cement and on the conditions of the exposure. 4.3.3 The Effect of Chloride in The Cement The passivity provided by the alkaline conditions can also be destroyed by the presence of chloride ions, even though a high level of alkalinity remains in the cement. The chloride ion can locally de-passivity the metal and promote active metal dissolution. Chlorides react with the calcium aluminates and calcium aluminoferrites in the cement to form insoluble calcium chloroaluminates and calcium chloroferrites in which the chloride is bound in non-active form; however, the reaction is never complete and some active soluble chloride always remains in equilibrium in the aqueous phase in the cement. It is this chloride in solution that is free to promote corrosion of the steel. At low levels of chloride in the aqueous phase, the rate of corrosion is very small, but higher concentration increases the risks of corrosion. Thus the amount of chloride in the cement and, in turn, the amount of free chloride in the aqueous phase (which is partly a function of cement content and also of the cem ent type) will influence the risk of corrosion. While the cement remains in an uncarbonated state the level of free chloride in the aqueous phase remains low (perhaps 10% of the total Cl). However, the influence of severe carbonation is to break down the hydrated cement phases and, in the case of chloroaluminates, the effect is to release chloride. Thus more free chloride is available in carbonated cement than in uncarbonated materials. 4.4 Elements Affecting of Corrosion Rate 4.4.1 Water Chemistry Water chemistry is probably the most influential parameter affecting corrosion. The situation can vary from being very simple with only a few carbonic species present, as in the case with condensed water in gas pipelines, to being very complex with numerous species found for example in formation water emerging together with crude oil. In some cases the concentration of dissolved salts can be very high ( 10 wt %) making the solution non-ideal. Table 4.2 contains an overview over dissolved species can be found in formation water. Table 4.2 Dissolved Species that can be found in Formation Water (13) Specie Description CO2 Dissolved carbon dioxide H2CO3 Carbonic acid HCO3- Bicarbonate ion CO3- Carbonate ion H+ Hydrogen ion OH- Hydroxide ion Fe2+ Iron ion CH3COOH (HAc) Acetic acid H2S Dissolved hydrogen sulphide S- Sulphide ion SO4- Sulphate ion Cl- Chloride ion Na+ Sodium ion K+ Potassium ion Ca2+ Calcium ion Mg2+ Magnesium ion Ba2+ Barium ion CH3COO- (Ac-) Acetate ion HSO4- Bisulphate ion O2 Dissolved Oxygen Understanding the brine chemistry is important to be able to predict corrosion rate since pH is one of the most important parameters when calculating the corrosion rate. pH depends strongly on the water chemistry. 4.4.2 The Effect of pH Experience has shown that pH has a strong influence on the corrosion rate. Typical pH in pure water is about 4, while pH in buffered brines normally is in the range 5 7. At pH 4 (and lower) direct reduction of H+ ions is important particular at lower partial pressure of CO2 and the pH has a direct affect on the corrosion rate. However, the most important effect of pH is indirect and relates to how pH affects conditions for formation of iron carbonate films. High pH results in a decreased solubility of iron carbonate and lead to an increased precipitation rate and higher scaling tendency; reflected by a rapid decrease of the corrosion rate with time. When calculating corrosion rates, it is of vital importance to have as accurate as possible pH value for the actual exposure condition either from: * Direct measured values (easy in lab, difficult in the field) * pH calculation tool in addition to reliable water chemistry analysis 4.4.3 The effect of CO2 Partial Pressure In case of film-free CO2 corrosion, an increase in partial CO2 pressure (PCO2) typically leads to an increase in the corrosion rate. The commonly accepted theory is that with PCO2 the concentration of H2CO3 increases and accelerates the cathodic reaction, and ultimately the corrosion rate. At a constant pH, higher PCO2 leads to an increase in CO32- concentration and a higher supersaturation, which accelerates precipitation and film formation. 4.4.4 The effect of HAc Since acetic acid HAc is a stronger acid than carbonic acid (H2CO3), it is the main source of hydrogen ions when the two acid concentrations are similar. The effect of HAc is particularly pronounced at higher temperatures where the presence of HAc can increase the corrosion rate dramatically. 4.4.5 The effect of Temperature Temperature accelerates all the processes involved in corrosion. One would expect that the corrosion rate steadily increases with temperature. This is the case at low pH when precipitation of iron carbonate or other protective films does not occur. The situation changes markedly when solubility of iron carbonate (or other salt) is exceeded, typically at high pH. In that case, increased temperature accelerates rapidly the kinetics of precipitation and protective film formation, decreasing the corrosion rate. The peak in the corrosion rate is usually seen between 60 and 800C depending on water chemistry and flow conditions; see 4.2 as an example. Prediction of Corrosion Rate and Its Affecting Factors Corrosion Model and Calculation of Corrosion Rate 5. Corrosion Model and Calculation of Corrosion rate 5.1 Introduction of Corrosion Model Corrosion of carbon steel alloys has been, and remains, a major cause of corrosion damage in oil and gas field operations. The industry relies heavily on the extensive use of these materials, and thus there is a desire to predict the corrosivity of CO2-H2S containing hydrocarbons when designing wellbore, production equipment and transportation facilities. A true industry standard approach to predict CO2-H2S corrosion does not exist although there are aspects of commonality between the approaches/models offered by the industry and the research organizations. The Shell equation or nomogram was developed as an engineering tool. It presents, in a simple form, the relationship between potential corrosivity of aqueous media for a given level of dissolved CO2-H2S, defined by its partial pressure, at any given temperature. The NORSOK M-506 model is an empirical model mainly base don laboratory data at low temperature and a combination of lab and field data at temperatures above 1000C. The NORSOK model takes larger account for the effect of protective corrosion films and therefore predicts lower corrosion rates at high temperature and high pH than other models. The model does not take any effect of oil wetting. The model has been developed by Statoil, Hydro Oil Energy and Saga Petroleum, and has been issued as a NORSOK standard for the Norwegian Oil industry. The spreadsheet with the model is openly available on its website. 5.2 Corrosion Model based on NORSOK M-506 rev.2 The model is an empirical corrosion rate model for carbon steel in water containing CO2-H2S with particular ratio at different temperatures, pHs, CO2-H2S fugacities and wall shear stresses. It is based on flow-loop experiments at temperatures from 5C to 150C. A large amount of data at various temperatures, CO2-H2S fugacities, pHs and wall shear stresses are used. The following general equation of the CO2-H2S corrosion rate for carbon steel at each of the temperatures (T); * 20C, 40C, 60C, 80C, 90C, 120C and 150C is used: CRT = KT x fCO2 0.62 x (S/19) 0.146 + 0.0324 log (fCO2) x f(pH)T (mm/year) (5.1) * The following equation is used at temperature 15C: CRT = KT x fCO2 0.36 x (S/19) 0.146 + 0.0324 log (fCO2) x f(pH)T (mm/year) (5.2) * The following equation is used at temperature 5C: CRT = KT x fCO2 0.36 x f(pH)T (mm/year) (5.3) The corrosion rate between temperatures where a constant Kt has been generated is found by a linear extrapolation between the calculated corrosion rate at the temperature above and below the desired temperature. The constant KT is given in the table below Table 5.1 Constant KT Temperature KT C 5 0.42 15 1.59 20 4.762 40 9 60 11 80 10 90 6 120 8 150 5 When the pH in the water increases the corrosion rate will decrease due to the reduction of the H+- ions in the water. In addition to this protective corrosion films may be formed on the steel surface and reduce the corrosion rate even more. It has not been distinguished between these two effects on the general corrosion rate in this study. The effect of pH is included in equation (5.4): * CRT = KT x fCO2 0.6 x f(S) x f(pH)T (mm/year) (5.4) Where f(pH)T is the effect of pH on the corrosion rate for each temperature T. The effect of pH was found by plotting measured corrosion rate divided by the product of KT, fCO20.6 and f(S). The effect of pH on corrosion rate at various temperatures is described by the functions in Table 5.2. The effect of pH on corrosion rate is different for all the temperatures. The effect of pH is given in Table 5.2. Table 5.2 pH Function Temperature pH f(pH) C 5 3,5 pH 4,6 f(pH) = 2,0676 (0,2309 x pH) 5 4,6 pH 6,5 f(pH) = 4,342 (1,051 x pH) + (0,0708 x pH2) 15 3,5 pH 4,6 f(pH) = 2,0676 (0,2309 x pH) 15 4,6 pH 6,5 f(pH) = 4,986 (1,191 x pH) + (0,0708 x pH2) 20 3,5 pH 4,6 f(pH) = 2,0676 (0,2309 x pH) 20 4,6 pH 6,5 f(pH) = 5,1885 (1,2353 x pH) + (0,0708 x pH2) 40 3,5 pH 4,6 f(pH) = 2,0676 (0,2309 x pH) 40 4,6 pH 6,5 f(pH) = 5,1885 (1,2353 x pH) + (0,0708 x pH2) 60 3,5 pH 4,6 f(pH) = 1,836 (0,1818 x pH) 60 4,6 pH 6,5 f(pH) = 15,444 (6,1291 x pH) + (0,8204 x pH2) (0,0371 x pH3) 80 3,5 pH 4,6 f(pH) = 2,6727 (0,3636 x pH) 80 4,6 pH 6,5 f(pH) = 331,68 x e(-1,2618 x pH) 90 3,5 pH 4,57 f(pH) = 3,1355 (0,4673 x pH) 90 4,57 pH 5,62 f(pH) = 21254 x e(-2,1811 x pH) 90 5,62 pH 6,5 f(pH) = 0,4014 (0,0538 x pH) 120 3,5 pH 4,3 f(pH) = 1,5375 (0,125 x pH) 120 4,3 pH 5 f(pH) = 5,9757 (1,157 x pH) 120 5 pH 6,5 f(pH) = 0,546125 (0,071225 x pH) 150 3,5 pH 3,8 f(pH) = 1 150 3,8 pH 5 f(pH) = 17,634 (7,0945 x pH) + (0,715 x pH2) 150 5 pH 6,5 f(pH) = 0,03 The corrosion rates at temperatures between 20 and 400C, 40 and 600C, 60 and 800C and so on should be calculated by linear interpolation between the corrosion rates calculated with equation (5.4) at these temperatures. The pH has a significant effect on the corrosion rate for all the temperatures. One interesting observation is that the maximum corrosion rates vary between 40 and 90C depending on the pH. To predict the pH in the condensed water or formation water, the parameters given in Table 5.3 are needed. Table 5.3 Input Parameters for pH Calculation Parameter Unit Range Default values Comments Temperature C 5 to 150 F 41 to 302 Total pressure bar 1 to 1000 psi 14,5 to 14500 Total mass flow kmole/h 10 to 106 Only relevant when CO2 is given in kmole/h CO2 fugacity bar 0 to 10 The CO2 partial pressure shall be lower than the psi 0 to 145 total pressure.The allowed ranges of mole% and mole% variable kmole/h CO2 are dependent on the total pressure. kmole/h variable Bicarbonate (HCO3-) mg/l 0 to 20000 0 Default values for formation water. mM 0 to 327 Ionic strength/salinity g/l 0 to 175 50 Default values for formation water. M 0 to 3 The routine for calculation of pH is based on the following chemical reactions and equilibrium constants: The system has to be electro-neutral, which can be described by the following equation: (5.5) It is assumed that bicarbonate is added as sodium bicarbonate (NaHCO3). It is also assumed that no other salts than sodium bicarbonate and sodium chloride (NaCl) are present in the solution. These salts will dissolve as follows: Based on these assumptions, the amount of sodium bicarbonate equals the difference in the concentrations of sodium and chloride as shown below. The mass balance for bicarbonate will therefore be as follows: (5.6) C0, Bicarb equals the initial amount of sodium bicarbonate. By combining the equations for the equilibrium constants with the required electro-neutrality and the mass balance for bicarbonate one gets the following expression for the concentration of the hydrogen cation: (5.7) This equation is solved by using the Newtons method. The pH in a condensed water system saturated with iron carbonate can also be calculated. Based on a similar deduction as above, the equation becomes: (5.8) Where (5.9) Gases are not ideal at high pressures. To compensate for this, the partial pressure of a gas is multiplied by a fugacity constant. The real CO2 pressure can then be expressed as: (5.10) The CO2 partial pressure is found by one of the following expressions (5.11) The fugacity coefficient is given as (5.12) 45 Prediction of Corrosion Rate and Its Affecting Factors Discussions of Results 6. Corrosion Rate Results and Discussions Using Equations in sub-chapter 5.2, the charts of corrosion rate with several parameters on basis of given temperature, pH, CO2 partial pressure and shear stress have been generated with several assumptions as describe below: * The model is valid for temperature 5 150 C, pH 3.5 6.5, * CO2 partial pressure 0.1 10 bar and shear stress 1 150 Pa. * The model is not applicable when the H2S partial pressure is higher than 0.5 bar, * or when the ratio between the partial pressure of CO2 and H2S is less than 20. * The model can lead to underproduction of the corrosion rate when the total content of organic acids exceeds 100 ppm and the CO2 partial pressure is less than 0.5 bar. 6.1 Effect of Temperature Corrosion rates as a function of temperature with specific amount of CO2 (in % mole) are shown in 6.1 to 6.12. The corrosion rates starts instantaneously still at low temperature due to continuous dissolution of Fe2+ ion in the solution. As the temperature increases corrosion rate increases due to the formation of porous iron carbonate films, results in the initiation of cracks and spallation of the oxide layers formed on the metal surface. The chloride ion easily ingress through the surface and significantly increases the corrosion at the temperature range of 40-80oC. Further increase in temperature the corrosion rate decreases significantly due to the formation of denser, adherent and homogeneous layer of iron carbonate, which is, protects the metal to further corrosion. As the partial pressure of CO2 in the solution increases the formation of weak carbonic acid (H2CO3) favors, which increases the corrosion rate. However at higher temperature the bicarbonate ions (HCO3-) formed on the surface gives more carbonate ions (CO32-) results in formation of more insoluble iron carbonate which increases the solution pH and corrosion rate decreases significantly as shown in 6.1-6.12 at 120oC. In many literatures, it has been reported that Fe2CO3 precipitation is temperature dependent and for its precipitation super saturation with the Fe2+ ion is required which is 5-10 times higher than the thermodynamically calculated values of solubility. (16) 6.2 Effect of pH The effect of various pH on Corrosion rates are shown in 6.1, 6.4, 6.7. Lower Corrosion rates are obtained at the higher pH, the corrosion rate does not change much with pH higher than 6.5, even if some ferrous carbonate precipitation occurs, reflecting the fact that a relatively porous, detached and unprotective layer is formed. There are other indirect effects of pH, and by almost all accounts, higher pH leads to a reduction of the corrosion rate, making the pH stabilization (meaning: pH increase) technique an attractive way of managing CO2 corrosion. 6.2,5,8,10,11,12 are described Corrosion rate at pH 4-4.4 at specific temperature (90-120oC) with various mole of CO2, CO2 partial pressure and shear stresses have constant corrosion rates compare to other corrosion rates with different pHs at similar temperature. The reason of this phenomenon is the acceleration of increasing formation of weak carbonic acid (H2CO3) during temperature 90-120oC which causes increasing corrosion rate has equal acceleration with the formation of iron carbonate which is formed on the surface of steel and create the passivity behavior. 6.3 Effect of Partial Pressure An increase in partial CO2 pressure (PCO2) typically leads to an increase in the corrosion rate. The commonly accepted theory is that with PCO2 the concentration of H2CO3 increases and accelerates the cathodic reaction, and ultimately the corrosion rate ( 6.2,3,4,5,6,8,9). However, when other conditions are favorable for formation of ferrous carbonate layers, increased PCO2 can have a beneficial effect. At a constant pH, higher PCO2 leads to an increase in CO32- concentration and a higher supersaturation, which accelerates precipitation and protective layer formation. With CO2 = 30% mole 6.4 Effect of Partial Pressure The effect of wall shear stress may have two different effects on the corrosion rate: * The general corrosion rate may increase with 10-30% as shown in Fig 6.10-12 * Local mesa attack may occur at high values of wall shear stress which can give corrosion rates which is 10-100 times higher than expected if the corrosion attach was general corrosion. Prediction of Corrosion Rate and Its Affecting Factors An Experimental Approach to Investigate Long Term Corrosion 7. An Experimental approach to Investigate Long Term Corrosion 7.1 Introduction of LPR method The LPR technique has become a well-established method of determining the instantaneous corrosion rate measurement of steel in cement structures. The technique is rapid and non-intrusive, requiring only localized damage to the cement cover to enable an electrical connection to be made to the steel or directly from steel to steel. Due to the widespread corrosion of steel in cement structures there has been a concerted demand for the development of non-destructive techniques to enable accurate assessment of the condition of steel. LPR monitoring has been developed to address this need. The technique is rapid and non-intrusive, requiring only a connection to the steel. The data provides a valuable insight into the instantaneous corrosion rate of the steel, giving more detailed information than a simple potential survey. The LPR data enables a more detailed assessment of the structural condition and is a major tool in deciding upon the optimum remedial strategy to be adopted. It is thus imperative that the LPR measurements obtained are accurate. In LPR measurements the steel is perturbed by a small amount from its equilibrium potential. This can be accomplished potentiostatically by changing the potential of the steel by a fixed amount, E, and monitoring the current decay, I, after a fixed time. Alternatively it can be done galvanostatically by applying a small fixed current, I, to the steel and monitoring the potential change, E, after a fixed time period. In each case the conditions are selected such that the change in potential, E, falls within the linear Stern-Geary range of 10-30 mV. The polarization resistance, Rp, of the steel is then calculated from the equation. (7.1) From which the corrosion rate, Icorr, can then be calculated (7.2) where, B is the Stern-Geary constant. A value of 25 mV has been adopted for active steel and 50 mV for passive steel. In order to determine the corrosion current density, icorr, the surface area, A, of steel that has been polarized needs to be accurately known: (7.3) The present residual strength and, by extrapolation, the remaining service life of the structure can be estimated. In a conventional LPR test the perturbation is applied from an auxiliary electrode on the cement surface. The surface area of steel assumed to be polarized is that lying directly beneath the auxiliary electrode. However, there is considerable evidence to suggest that the current flowing from the auxiliary electrode is unconfined and can spread laterally over an unknown, larger area of steel This can lead to inaccurate knowledge of the surface area of steel polarized and result in an error in the calculation of the corrosion current density, which, in turn, will produce an inaccurate estimate of the condition of the structure being investigated. In order to overcome the problem of confining the current to a predetermined area, the use of a second auxiliary guard ring electrode surrounding the inner auxiliary electrode has been developed. The principle of this device is that the outer guard ring electrode maintains a confinement current during the LPR measurement. This confinement current prevents the perturbation current from the main inner auxiliary electrode spreading beyond a known area. In order to select an appropriate level for the confinement current two sensor electrodes are placed between the inner and outer auxiliary electrodes. The potential difference between these sensor electrodes is monitored and a confinement current selected to maintain this potential difference throughout the LPR measurement. The performance of the guard ring has been shown to be an improvement upon that of a single unconfined auxiliary electrode, giving a more accurate value for the corrosion rate of the steel being monitored. At present the established method of guard ring LPR measurements uses galvanostatic control. This method relies upon the potential response, E, to the selected perturbation, I, falling within the linear region of the Stern-Geary plot. The use of a potentiostatic device would enable the potential shift itself to be selected, ensuring the measurement falls within this linear region and hence, would not risk the inaccuracies incurred by applying too large a galvanostatic perturbation. 7.2 Experimental Procedure Using the concept and principle of LPR, an experiment for monitoring and measurement corrosion of Surface casing can be developed. Casing steel is isolated with cement and flooded with water at certain level of high and CO2 is injected into water at certain level. The experiment can be done with several variables such as Temperature, CO2 composition in the water and salt contain ( 7.3). After certain period, corrosion on surface casing shall be monitored and measured using LPR tool. The both electrodes (reference and working electrode) can be placed inside of the casing or the reference electrode can be also placed on the cement surface as well. The result which is given by digital control system has to be calculated using equation 7-1-3 and compared by corrosion current table to determine condition of the steel. The following broad criteria for corrosion have been developed from field and laboratory investigations with the sensor controlled guard ring device given in Table 7.1 Table 7.1 Corrosion current vs. condition of the steel (18) Corrosion current (Icorr) Condition of the steel Icorr 0.1 A/cm2 Passive condition Icorr 0.1 0.5 A/cm2 Low to moderate corrosion (17.1 m/year) Icorr 0.5 1.0 A/cm2 Moderate to high corrosion (34 m/year) Icorr 1.0 A/cm2 High corrosion rate (345 m/year) The device without sensor control has the following recommended interpretation Icorr 0.2 A/cm2 No corrosion expected Icorr 0.2 1.0 A/cm2 Corrosion possible in 10 -15 years Icorr 1.0 10 A/cm2 Corrosion expected in 2-10 years Icorr 10 A/cm2 Corrosion expected in 2 years or less 45 Prediction of Corrosion Rate and Its Affecting Factors Conclusions 8. Conclusions 1. The Norsok M-506 model was used for this study allowed clear calculations of trends for the general corrosion rate for the carbon steel. The temperature range 5-1500C was particularly covered. The parameters of main importance were (in order of importance): the pH, the fugacity of CO2, temperature and the mean wall shear stress with several assumptions as describe below: * The model is valid for temperature 5 150 C, pH 3.5 6.5, * CO2 partial pressure 0.1 10 bar and shear stress 1 150 Pa. * The model is not applicable when the H2S partial pressure is higher than 0.5 bar, * or when the ratio between the partial pressure of CO2 and H2S is less than 20. * The model can lead to underproduction of the corrosion rate when the total content of organic acids exceeds 100 ppm and the CO2 partial pressure is less than 0.5 bar. 2. As the temperature increases corrosion rate increases due to the formation of porous iron carbonate films, results in the initiation of cracks and spallation of the oxide layers formed on the metal surface. 3. An increase in partial CO2 pressure (PCO2) typically leads to an increase in the corrosion rate. 4. The wall shear stress may have two different effects on the corrosion rate: * The general corrosion rate may increase with 10-30% dependent on the wall shear stress and fugacity of CO2. * Mesa attacks may occur at high values of shear stress. 5. Casing Steel which is isolated with cement will start to corrode when the cement loss alkalinity during its life time and cracking. 6. Linear Polarization Resistance method can be used to monitor and determine corrosion on surface casing Prediction of Corrosion Rate and Its Affecting Factors References References: 1. Samant, A.; Corrosion Problems in Oil Industry Need More Attention, Technical paper from Oil and Natural Gas Corporation Limited, February 2003 2. Keranl, M., Harrop, D.; The Impact of Corrosion on the Oil and Gas Industry, SPE, Production and Facilities, August 1996 3. Tomasz Szary.; The Finite Element Method Analysis for Assessing the Remaining Strength of Corroded Oil Field Casing and Tubing, Dissertation paper from Freiberg University, September 2006. 4. Mok Chek Min.; An Introduction to Corrosion, CMM NDT Services, 2008 5. https://octane.nmt.edu/waterquality/corrosion/corrosion.htm 6. https://www.materialsinspectionassociates.com/CO2.php 7. https://corrosion.ksc.nasa.gov/faticor.htm 8. Scoppio, L.; Assessment of Corrosion and Environmental Cracking of Metallic Materials in HPHTCs/K Formate Brines. 3rd Annual ChemiMetallurgyTM Technical Symposium, November 2007 9. https://www.imoa.info/moly_uses/moly_grade_alloy_steels_irons/oil_country_tubular_goods.html 10. J.A. Straatmann, A.P. Grobner. Molybdenum containing steels for Gas and Oil Industry Applications. Climax Molybdenum Company, 1978. 11. Dishimaru et al. in JFE Technical Report No.2, (Mar 2004) 12. Hashizume, Shuji. Materials selection in Oil and Gas Production. Tenaris NKKTubes, January 2008 13. https://www.sumitomo-tubulars.com/materials/index.htm 14. Technical Memorandum Gemite Products Inc, Corrosion of Steel in Concrete due to Carbonation. 22 April 2005 15. George V.Chilingar, Ryan Mourhatch, Ghazi Al-Qahtani. The Fundamentals of Corrosion and Scaling. Gulf Publishing Company. 2008 16. A. Turnbull, D. Coleman, A. J. Griffiths, P. E. Francis and L. Orkney, Effectiveness of Corrosion Inhibitors in Retarding the Rate of Propagation of Localized Corrosion, Corrosion, Vol. 59, No. 3, 2003, pp. 250-257. 17. https://www.cosasco.com/ 18. Ha-Won Song, Velu Saraswathy, Corrosion Monitoring of Reinforced Concrete Structures A Review, International Journal of Electrochemical science, 2007. Appendix A.1 Input parameters A.1.1 Basic input parameters The basic input parameters for the CO2 corrosion model for carbon steel are given in Table A.1.1. The allowed units and ranges are also given Table A.1.1 Basic Input Parameters Parameter Units Range Comments Temperature C 5 to 150 F 68 to 302 Total mass flow kmole/h 10-3 to 106 Only relevant when CO2 is given in kmole/h. CO2 fugacity in the gas phase bar 0,1 to 10 The CO2 partial pressure shall be psi 1,45 to 145 the total pressure. mole% variable The allowed ranges of mole% and kmole/h CO2 are dependent on the kmole/h variable total pressure. Wall shear stress Pa Can be calculated by use of other input parameters pH 3,5 to 6,5 Can be calculated by use of other input parameters A.1.2 Input parameters for wall shear stress calculations Wall shear stress is one of the parameters needed for calculation of corrosion rate. In the model, the mean wall shear stress in straight pipe sections is used. Obstacles and other geometrical changes in the flow will give rise to higher shear stresses than calculated by this program. Further, different flow regimes and geometrical obstacles may generate shear stress fluctuations where the shear stress peaks may be considerably higher than the average shear stress. High shear stress may cause mesa attacks, with corrosion rates significantly higher than what is estimated by this computer program. It is not the objective of this computer program to cover all such eventualities, and the user of the program shall evaluate the flow effect in each system/part of a system based on expertise and available experience and documentation. The mean wall shear on the wall at medium to high superficial velocities of one or both of the liquid and gas velocities where the friction factor, f, can be expressed as: Mixture density, velocity and viscosity is expressed as: To calculate the wall shear stress, the input parameters given in Table A.1.2, are as a minimum required Table A.1.2 Input parameters for simplified calculation of wall shear stress Parameter Units Range Comments Temperature C 5 to 150 F 41 to 302 Total pressure bar 1 to 1000 psi 14,5 to 14500 Superficial liquid velocity/ m/s 0 to 20 Requirement: turbulent flow, i.e. Liquid flow Sm/d (depends on internal pipe diameter) Re 2300 Superficial gas velocity/ m/s 0 to 40 Requirement: turbulent flow, i.e. Gas flow MSm/d (depends on internal pipe diameter) Re 2300 Watercut, % 0 to 100 Internal pipe diameter mm All diameters Requirement: turbulent flow, i.e. Re 2300 For more accurate wall shear stress calculations, the input parameters given in Table A.1.3 should also be used. Table A.1.3 Input parameters for accurate calculation of wall shear stress Parameter Units Range Default value Roughness m 0 to 100 50 Compressibility 0,8 to 1 0,9 Specific gravity of gas relative to air 0,5 to 1 0,8 Water density, w kg/m 995 to 1050 1024 Oil density, o kg/m 600 to 1100 850 Gas density, w kg/m 1 to 1700 calculated Water viscosity, w cp 0,17 to 1,1 calculated N s/m 0,00017 to 0,0011 Oil viscosity, o cp 0,2 to 200 1,1 N s/m 0,0002 to 0,2 Gas viscosity, G cp 0,02 to 0,06 0,03 N s/m 0,00002 to 0,00006 Watercut at inversion point, c 0,3 to 0,9 0,5 Maximum relative liquid viscosity, relmax 1 to 100 7,06 A.2 Interface of Model A.3 Comparison corrosion rate using another experiment (Parametric Study of CO2/H2S Corrosion of Carbon Steel Used for Pipeline Application, G. S. DAS A. S. KHANNA, Corrosion Science Engineering Indian Institute of Technology Bombay, 2004)