Overview of a Comprehensive Study to Understand Longitudinal ERW Seam Failures

Abstract

In response to the National Transportation Safety Board (NTSB) Recommendation P-09-1, the Department of Transportation (DOT) Pipeline and Hazardous Material Safety Administration (PHMSA) initiated a comprehensive study to identify actions that could be implemented by pipeline operators to eliminate longitudinal seam failures in electric resistance weld (ERW) pipe. This study was contracted with Battelle, working with Kiefner and Associates (KAI) and Det Norske Veritas (DNV) as subcontractors. The purpose of this paper is to provide an overview of the project with focus on the study objectives, results, and on-going work. Phase I of the project consisted of four major tasks aimed at understanding the current state of the issues. Task 1 analyzed the databases gathered and qualified in five interim reports that dealt with 1) the failure history of vintage ERW seams, including flash-weld (FW) pipe and selective seam-weld corrosion (SSWC); documented in two subtask 1.4 reports, 2) the effectiveness of in-line inspection (ILI) and hydrotesting, and experience with predictive modeling, documented in subtask reports 1.2 and 1.3 and 3) literature concerning SSWC documented in subtask 1.5 report. Task 2 addressed experimental studies designed to better characterize the failure of ERW/FW seams and quantify the resistance of such seams (Subtask 2.1–2.3 and 2.6 reports) and their response to pressure (Subtask 2.4 and 2.5 reports). Task 3 considered aspects related to SSWC with four separate reports from subtask 3.1–3.4. Task 4 focused on integration of the other tasks, trending, and analysis. Phase II has been initiated and consists of five tasks with the following objectives relevant to the ERW and FW process: 1) develop and optimize viable hydrotest protocols for ERW/FW seam defects 2) improve the sensors, interpretive algorithms, and tool platforms in regard to ILI and In-the-Ditch-Methods (ITDM) to better ensure structural integrity with optimized detection and sizing, 3) bridge gaps in defect characterization in regard to types, sizes, shapes, and idealizations. The goal of this subtask is to increase pipeline safety through improvements in the tools needed to implement both ILI and hydrotesting, 4) validate existing models and, where gaps preclude validation, refine or develop models needed to assess and quantify defect severity for cold welds, hook cracks, and selective seam weld corrosion (SSWC) (the primary threats) for failure subject to loadings that develop both during hydrotests and in service, and 5) develop a digitally based framework to support integrity management of seam welds with enough flexibility to benefit from the experience embedded in the stopgap protocol. To date, this study has led to seventeen (17) reports. These publically available reports are located on the PHMSA website: http://primis.phmsa.dot.gov/matrix/PrjHome.rdm?prj=390. Based on the work completed during Phase I, gaps identified in the context of the NTSB Recommendation P-09-1 were supported by the historic records. Additionally, recent improvements in related technologies and integrity management practices point to the practical utility and viability of PHMSA’s current approach to manage the integrity of the U.S. pipeline.