THE EFFECT OF STRAIN ON THE SUSCEPTIBILITY OF PIPELINE GIRTH WELDS TO SULFIDE STRESS CRACKING

摘要

For sour service conditions there are stringent weldment hardness requirements that must be satisfied in order to minimise the risk of sulfide stress corrosion cracking (SSC) in service. Currently in standards such as DNV OS-F101:2000 and BS4515:2000 the hardness threshold requirements remain unaltered for welds that are strained, for example, as can occur during pipe reeling and laying operations. Work has been carried out to investigate the SSC behaviour of samples, taken from a pipe girth weld, that were strained to conditions that simulated those of a typical pipe reeling operation and conventional hardness limits were shown to be unsafe. Samples were taken from a C-Mn steel girth welded pipe, manufactured to API 5L X65, and were subjected to tensile and compressive strain to simulate the pipe installation. Four point bend sulfide stress corrosion cracking tests of 30 days duration were performed on specimens manufactured from the strained and unstrained material in NACE TM0177 solution A. The results showed that the application of such prestrain to the specimens led to failure by SSC despite the HAZ hardness remaining below the allowable limits specified in the relevant codes (e.g. ISO15156, DNV OS-F101 and BS4515).