PREMATURE CORROSION OF WELL-HEAD FLEXIBLE HOSES: A CASE STUDY

摘要

As a result of the premature failure of a number of 321 stainless steel flexible hoses on well-heads in coal seam gas fields, several of the hoses were analyzed to determine the root cause of the failures. The failures occurred as a result of pitting and associated cracking of the hoses. The cracking occurred circumferentially through along the corrugations of the inner hose. The investigations indicated that the failures were the result of Sulfide Stress Cracking (SSC) that occurred due to hydrogen sulfide generated by Sulfur Reducing Bacteria (SRB). It was established that the hoses were in the work hardened condition, which made them susceptible to SSC. A review of the specifications and well test data found that this failure mechanism was considered to be low risk as there was insufficient hydrogen sulfide within the product flow. Although SRB were known to be present, the risk of SSC due to hydrogen sulfide generation by microbial action had not been identified. This risk is also not well identified in standards and guidelines used by the oil and gas industry in general. This problem may be mitigated by either specifying the hoses to be supplied in the solution-annealed condition, or using an appropriate highly alloyed material that retains resistance to SSC when in the work hardened condition.