Findings From an Investigation of Hydrotest Protocols

Experience has shown that in-service failures can occur in Electric Resistance Welded (ERW) line pipe shortly after a hydrotest as a part of line rehabilitation or in retesting to return to service. This can occur due to near-critical features that grew but remained in the line, or due to a pressure-reversal due to stable defect growth during the pressure test. The objective of this study was to improve hydrotesting protocols by developing and optimizing procedures for conducting hydrotests of pipe with ERW or Flash Welded (FW) seam defects, and validating the practical utility of the proposed procedures. This work has enhanced and adapted both failure and growth models to predict the behavior of defect shapes based on collapse and fracture theories, to assess idealized cold welds, hook cracks, and selective-seam weld corrosion (SSWC), and parametrically quantify differences and similarities in their response to increasing pressure. Based on insight from these analyses, this work has established a pressure-time sequence that incorporates the spike concept to expose near-critical defects to pressures that will cause them to fail and it has evaluated the sensitivity as a function of defect size with respect to time-dependent growth. In turn, insights from the outcomes of these analyses were used to identify potential hydrotest protocols.