An Investigation On LPC Rare Earth To Improve ZG25CrNiMo Performance Of Resisting H₂S Corrosion

Blowout preventer(BOP) is a key component of controlling device for oil and gas well drilling, playing a very important role to control of wellhead pressure and prevent blowoutsor accident when repairing well and other operations. ZG25CrNiMo is widely used for BOP cast. Oil and gas fields are relatively high content of hydrogen sulfide in China, and hydrogen sulfide corrosion of oil and gas fields equipments is more serious, which makes the corrosion resistance of the ZG25CrNiMo certain requirements. LPC rare earth is a new styel of rare earth,which is a product after abstracting cerium and neodymium from rare earth of rich cerium.A small range of applications seriously hinders the development of Chinese rare earth industry. Numerous studies show that rare earth can improve the corrosion resistance of steel. This research through laboratory investigation analyses the impacts of LPC rare earth on ZG25CrNiMo's organization, inclusion and corrosion resistance in wet hydrogen sulfide environment, and draws the main conclusions as following:(1) LPC rare earth plays the roles of oxygen and desulfurization, cleaning molten steel, improving the appearance of inclusions, grain refinement, micro-alloying effect in ZG25CrNiMo and improves over-all performance of ZG25CrNiMo. LPC rare earth plays the same role in steel as rare earth of rich cerium and others,so it can replace rare earth of rich cerium adding ZG25CrNiMo to improve the mechanical properties.(2) A solution in the NACE standard by different soaking time, casting ZG25CrNiMo's corrosion rate is 0.505g / (m2·h) and heat treatment condition is 0.310g / (m2·h), according to the 10 standard of metal corrosion resistance,belonging to 7 and 6 .(3) Average corrosion rate of casting ZG25CrNiMo, in which LPC rare earth content is 0.058%, 0.118% and 0.159%, is 0.374g / (m2·h), 0.345g / (m2·h) and 0.246g / (m2·h),and the average corrosion rate (after heat treatment) is 0.241g / (m2·h), 0.210g / (m2·h) and 0.109g / (m2·h).Whether as cast condition or heat treated, ZG25CrNiMo's corrosion resistance are six,which belongs to still corrosion.Compared with ZG25CrNiMo of non-LPC rare earth, corrosion resistance of ZG25CrNiMo containing LPC rare earth is greatly improved.(4) Compared with non- LPC rare earth ZG25CrNiMo, LPC rare earth can improve performance of ZG25CrNiMo's resisting stress corrosion in wet hydrogen sulfide environment, however, the performance of resisting stress corrosion is not so higher as LPC rare earth content .