Steel Grade Selection for Corrosive Oil and Gas Pipeline Environments
Most oil and gas resources contain H2S and/or CO2. Among them, some oil and gas wells contain only H2S or only CO2, while more oil and gas wells contain H2S and CO2. For the corrosion and protection problems containing only H2S, for more than 50 years, a lot of research has been done, the corrosion mechanism is relatively clear, at present, corrosion control methods and protection measures are relatively mature , and NACE MR0175/ISO15156 is formed internationally. Standards and specifications, China is capable of manufacturing API 5CT pipes and casings of API standards, and has developed the petroleum industry standard SY/T0599.
Research for Octg Pipe Materials
In the past 20 years, much research has been carried out on the CO2 corrosion mechanism and protection measures under high temperature and high pressure conditions. However, for the study of corrosion mechanism and regularity of H2S and CO2 at the same time, due to the complex interaction between H2S and CO2, a perfect theoretical system has not yet been formed. Many theoretical and technical issues have not yet been further studied.
Development of Octg Pipe Steel Grades in China
Since the beginning of this century, some oil and gas fields have been developed in the harsh environment of the world. Foreign countries have increased research and development of corrosion-resistant oil well pipes that are resistant to CO2 and CO2, H2S, Cl- coexistence (and, of course, H2O). For anti-CO2 corrosion, the API Spec 5CT specification lists two steel grades, L80-9Cr and L80-13Cr, and each manufacturer has established its own non-API steel grade series. Such as JFE of Japan, Live Gold, National Tianguan Group, Baosteel, etc. The coexistence of CO2 and H2S, or the partial pressure of H2S is not critical, but Cl- is high, 13Cr steel (including super 13Cr steel) cannot meet the requirements, should use 22Cr duplex stainless steel (ASF2205) or 25Cr super duplex stainless steel, including High Ni, Cr stainless steel and Ni and FeNi-based alloys such as G3, 825 and 028 containing more than 20% Cr and containing Ni30% or more are used.
The IC content of Tarim and Chuanxi underground wells is extremely high. Special attention should be paid to the NKK material selection guide when selecting oil housings. NKK selection guide shows that 22Cr duplex stainless steel and 25Cr super duplex stainless steel not only have better uniform corrosion resistance than 13Cr and super 13Cr oil casings, but also have superior pitting resistance and some SSCC resistance. JFE models JFE-UHP-15Cr-125 and JFE-UHP-17Cr-110-125 have higher strength and CO2 corrosion resistance than Super 13Cr, but They are not a substitute for duplex stainless steel under high IC conditions.
