Corrosion Failure Causes of Super 13Cr Completion Tubing Strings

Combining with the corrosion test in laboratory,the influence of inner surface state,acidizing corrosion inhibitor etc. on the corrosion of super 13Cr completion tubing strings was analyzed by inner surface corrosion detection,and the corrosion failure causes for the super deep,super high temperature and high pressure gas well were discussed. The results showed that uniform corrosion was very slight on the inner surface of super 13Cr completion tubing strings,and pitting became more serious with the increase of well depth and temperature,the maximum pitting depth was up to 645 μm at about 6 000 m depth. The acidizing corrosion inhibitor did not display a good matching ability with the super 13Cr completion tubing strings,and there existed metal Cu scale adsorbing on the inner surface,which was not covered densely and thus led to serious pitting of super 13Cr completion tubing strings. The oxide scale on the inner surface of super 13Cr completion tubing strings was not removed completely,and there were some surface defects which promoted the occurrence of pitting and the crack nucleation and expansion of stress corrosion cracking (SSC). Therefore,it affected severely the structural integrity of completion tubing strings and resulted in the corrosion failure eventually.