PR186-223601-R01 Evaluation of Selective Seam Weld Corrosion Susceptibility
Authors: McMahan Tara , Amend Bill , Evans Ken , Bubenik Tom , Rosenfeld Michael 
Published: August 2024

Selective seam weld corrosion (SSWC) in autogenous welds is characterized by accelerated corrosion of or near the bondline which results in a groove-like feature that often coincides with shallower corrosion that can extend beyond the limits of the longitudinal seam. Historically, SSWC has been referred to as "grooving corrosion", "knife-line attack", or "trench-like corrosion". In 2021, the Pipeline Research Council International, Inc. (PRCI) funded a project, PRCI Project EC-2-12, to evaluate SSWC as a threat to gas and liquid pipeline systems. The project included a literature review of key parameters influencing the likelihood of SSWC within a particular type of pipe over others, benchmarking of the key parameters using industry experience and data, and the development of a susceptibility process for the threat of SSWC within gas and liquid pipeline segments.

From the literature review, a summary of hypothesized influencing parameters was compiled and those considered to more strongly and consistently indicative of susceptibility were identified as key parameters (e.g., longitudinal seam weld type, chemical composition of the plate material, and evidence of a post-weld heat treatment, etc.). The key parameters were then benchmarked against pipeline industry data from confidential as well as public sources. Industry data were collected for line pipe known to be susceptible to the threat of SSWC (i.e., SSWC has been identified within it through direct examination and/or metallurgical analysis). Additionally, mill test reports for line pipe manufactured prior to 1990 and historical line pipe manufacturing specifications that could indicate typical manufacturing practices of the time were collected and compiled.

As a result of the benchmarking effort, some key parameters were confirmed, and others were dismissed if industry data indicated it was unlikely they could be relied upon to determine susceptibility to the threat of SSWC individually or in concert with other parameters. Key parameters confirmed as reliable through industry benchmarking and considered readily accessible to most pipeline operators informed the development of a SSWC susceptibility determination process. The process is comprised of 'swim' lanes that consider threat history, line pipe susceptibility, and environmental influences.

The project also included an investigation into the Barnacle probe technique as a potential field deployable methodology to determine susceptibility to SSWC. Currently, it is the most common method to test for SSWC susceptibility in the field and is an electrochemical cell that attaches to the exterior of a pipe directly over the bondline after the surface has been properly cleaned. The linear polarization resistance (LPR) technique is used within the Barnacle cell to measure the polarization resistance of the bondline compared to the polarization resistance of the surrounding base metal. The ratio of the polarization resistances, which is a measure of the relative corrosion rates at the bondline and surrounding metal, provides an indication of how susceptible the bondline is to SSWC. The Barnacle probe technique was applied to materials with varying degrees of anticipated susceptibility. The results of the technique were benchmarked using accelerated dissolution tests to measure actual grooving ratios for the same range of materials.