L51775 Susceptibility of Modern ERW Pipe to Selective Weld Seam Corrosion in Wet Environments

Grooving corrosion is a phenomenon by which the weld seam of electric resistance welded (ERW) pipe is preferentially attacked in wet natural gas environments containing CO,. The attack initiates as an aligned string of pits which grow and intersect, forming a round-bottomed groove of damage centered on the weld seam. The susceptibility of ERW pipe to this damage mechanism is known to be related to the chemical composition (particularly the sulfur content) of the pipe, the welding process employed, and the use of a post weld heat treatment. Of particular concern to the natural gas pipeline industry is the fact that at the resent time there are no effective means for predicting the susceptibility of a specific lot of ERW pipe to grooving corrosion, prior to placing the pipeline in service. The objective of this program, therefore, is to begin the development of an accelerated laboratory test technique which may be useful as a screening test to establish the susceptibility of an ERW weld to grooving corrosion. A stepped potential, potentiostatic electrochemical test method was used to evaluate the susceptibility of ERW welds from five different pipe samples to grooving corrosion in environments representative of natural gas production. Three of the welds were believed to be susceptible to grooving corrosion and the remaining two were believed to be non-susceptible. Testing was performed under a variety of conditions (environment chemistry, temperature, and levels of polarization) in an attempt to identify conditions which enabled the correct differentiation between the susceptible and non-susceptible specimens.