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The purpose of this study was to investigate the reason of G105 coated drill-pipes suffering from washout after drilling for 70000–80000 m.

The microstructure, micromorphology and corrosion products near the washout were analyzed by metallurgical microscopy, SEM and EDS.

Results showed the metallographic microstructure of the material was typical tempered sorbite. No fatigue crack was observed. Drill-pipe washout was caused mainly by the inclusion of MnS in steel because of the excess S and by damaged coating, both of which induced pit nucleation and promoted the pitting corrosion process. The corrosion hole extended from the interior to the exterior, which resulted in the fracturing of the external drill-pipe surface under pressure.

This paper can give practical help to the selection of drill pipe materials in the future.

Important reserves of oil and gas, which are left to be discovered and produced, are mainly concentrated in challenging locations and under severe conditions such as high pressure (HP)/high temperature (HT). The presence of aggressive environments including H₂S, CO₂ and chlorides plus HP/HT causes a series of corrosion problems, which cost the oil industry billions of dollars a year. Thus, there is an increasing challenge for tubes (i.e. oil country tubular goods, for short, OCTG) used in producing oil and gas. The purpose of this study is to summarize different kinds of corrosion problems and their mitigation, to more efficiently protect OCTG from corrosion.

To effectively select proper mitigation methods, the mechanism of corrosion must be understood, which can be classified into four categories: sweet corrosion, sour corrosion, galvanic corrosion and microbiologically induced corrosion. Also, the effects of environmental and material factors on the corrosion rate are presented. Subsequently, current technology of mitigating these corrosion problems has been discussed, including the development of materials, application of chemical inhibitors and application of protective layers.

It is stressed that limits exist for each individual mitigation method; therefore, a careful balance between economic life of OCTG and safety in operation is required.

The main purpose of this essay is to give a brief review and detailed introduction and analysis about those technologies.