Selective seam weld corrosion (SSWC) is a narrow form of corrosion occurring at the pipe long seam and results from different corrosion resistance characteristics being present in the seam when compared to the pipe body. This form of corrosion can produce metal loss cross-sections (CS) that are very challenging to resolve with current non-destructive evaluation (NDE) methods routinely used in-the-ditch for typical metal loss evaluations. Since the shapes of natural SSWC are known (in many cases) to not conform with the conditions prescribed by laser profilometry manufacturers as valid for their...
Selective seam weld corrosion (SSWC) is a narrow form of corrosion occurring at the pipe long seam and results from different corrosion resistance characteristics being present in the seam when compared to the pipe body. This form of corrosion can produce metal loss cross-sections (CS) that are very challenging to resolve with current non-destructive evaluation (NDE) methods routinely used in-the-ditch for typical metal loss evaluations. Since the shapes of natural SSWC are known (in many cases) to not conform with the conditions prescribed by laser profilometry manufacturers as valid for their published performance specifications, an investigation into the actual NDE performance of various techniques is required to fill the industry gap. In addition, SSWC has been known to fail at burst pressures significantly lower than would be predicted by commonly used corrosion-based assessment models which are indicative of a plastic collapse failure mode. This observation implies that SSWC can fail in a crack-like manner, and as a result, NDE techniques that are commonly used for crack characterization should be considered as potentially viable NDE technologies when searching for the most accurate NDE technique for validating inline inspection (ILI)-based SSWC calls in the ditch.
This project conducted research with an intent to improve the in-ditch NDE measurements and subsequent assessments of SSWC. To do this, pipe joints containing natural SSWC samples were sourced from multiple PRCI operator members who consented to having the pipe destructively tested (post-NDE evaluation) to obtain a truth data set against which NDE techniques’ accuracies could be assessed. The SSWC characteristics observed with destructive testing were documented and formed a stand-alone data set for use both in this study and for future research. The study also evaluated previously issued industry guidance for identifying SSWC (and provides updated guidance) as well as determining the in-ditch performances for SSWC depth sizing for multiple NDE technologies. These performances were documented, and a best practice recommendation was put forward for determining SSWC groove depths for future NDE validation digs.
In addition to investigating NDE performances, this study also evaluated fitness-for-service (FFS) approaches for SSWC by analyzing multiple expected failure modes. The study considered the potential to categorize SSWC features by failure-mode based upon the SSWC cross-sectional feature shape (based upon metallurgical cross-section test data) and summarized findings for appropriate/conservative integrity management (IM) decision criteria by way of a decision flowchart that accounts for important variables such as SSWC geometry, pipe attributes, and pipe history. A limited set of burst tests were conducted within the study (three pipe spools were burst tested four times) to evaluate the flowchart outcomes. While initial results show promise, further research is required to fully understand SSWC burst behaviors and associated interaction rules in a more general sense.
The contents of this report are intended for anyone who performs in-line inspections, integrity assessments, or utilizes NDE inspection results for SSWC applications. This includes operators, NDE vendors, ILI vendors, and contractors performing ILI performance assessments or IM assessments.