No abstract

Improvements in in-line inspection (ILI) technology have led to an increase in the probability of detection and ability to characterize geometric features such as wrinkles, the assessment of which was introduced into CSA Z662, “Oil & Gas Pipeline Systems”, in the 2015 version. The CSA wrinkle acceptance limits are based predominantly on fatigue assessment criteria; part of the assessment procedure is confirmation that wrinkles are free from associated cracking. In practice, this often restricts the assessment to wrinkles that have already been investigated in-field and where the absence of cracking has been confirmed by non-destructive examination (NDE). This paper describes the assessment of a series of wrinkles that exceeded the CSA height criteria, reported by ILI within field bends in an insulated liquid pipeline. Strain-based assessment, supported by in-field investigations, was used to investigate the likelihood of associated cracking. Utilizing the high resolution caliper ILI tool data, three-dimensional profiles of the wrinkles were generated. Previous work that compared “tool-measured” with “field-measured” profiles identified that caliper tool measurements can underestimate the true depth and profile of wrinkles, this effect is more pronounced for particularly sharp wrinkles. The wrinkle profiles were therefore adjusted based on the historical field-tool correlation. Strain profiles were then calculated using the guidance within ASME B31.8 Appendix R. It was identified that the majority of the wrinkles exceeded the 6% strain limit commonly applied to dents. One field bend containing multiple wrinkles was subsequently excavated in order to gather detailed profile information and to inspect for cracking. Upon excavation, the wrinkles were not visually apparent, but their presence was confirmed following removal of the insulating coating. Profile information was subsequently recorded using laser scanning technology. In addition, NDE confirmed the absence of cracking, despite the fact that the majority of wrinkles were associated with strain levels that exceeded the CSA limiting value, 6%. The laser scan data were then compared with the adjusted “tool-measured” profiles. It was observed that the adjusted measurements based on the ILI tool data were conservative, and in some cases excessively so. The caliper measurements were optimized by identifying a factor that could be systematically applied to the “tool-measured” wrinkle profiles, which provided consistency with the profiles measured by the laser scan, thereby improving the accuracy of the dimensions and strain estimation of the remaining (non-excavated) wrinkles. Finally, a S-N based fatigue assessment was performed using operational cyclic pressure data and estimates of the stress concentration factors associated with the wrinkles. The calculated fatigue lives exceeded the expected operational life of the pipeline.

The Cactus-San Fernando gas pipeline system was constructed between 1977–79 in 42 and 48-inch diameter pipe. The pipeline extends for a total length of 650 km in 10 piggable sections. This paper details the work conducted to allow the pipeline to be re-validated to its original design pressure. The overall aim of the project was to demonstrate the future integrity of the pipeline system. The scope of the study was extensive and required innovative project management techniques. It encompassed caliper inspections and high-resolution magnetic inspection, the provision of global positioning surveys (GPS), Pipeline Integrity Assessment including repair schedules, future corrosion prevention and reinspection strategy and pipeline rehabilitation including non-destructive examination (NDE), material testing and repairs. The whole process was reviewed and ratified by an approved Certifying Company who issued a Certificate of Mechanical Integrity, valid for a fixed period of 2 1/2 years.

Recent incidents outside Canada prompted the Canadian Energy Regulator (CER), the British Columbia Oil & Gas Commission (BCOGC) and the Alberta Energy Regulator (AER) to advise pipeline operators regarding the possibility of girth weld strain-induced failures in high strength pipe. In early 2020, the CER issued a Safety Advisory (SA) relating to the possibility of girth weld strain-induced failures in high strength (Grade X 70 or higher) steel line pipe. There was a concern that similar incidents could occur in Canada, given comparable conditions. Furthermore, the SA stated that.... “The CER expects that regulated companies can demonstrate that longitudinal strains resulting from loadings such as those described in Section 4.2.4 of CSA Z662-19 [essentially external loading over and above typical operating loads] have been accounted for in the design, construction and operation of pipelines where strain could potentially accumulate in under-matched girth welds”. With respect to the SA, the failure causes were consistently linked to combinations of: i) high strength pipe with a minimum tensile strength exceeding actual weld strength values, ii) girth weld HAZ softening as a result of the welding process, iii) loads applied to the pipeline causing additional longitudinal strain, and iv) pipes welded with a standard bevel and alignment of approximately 45° between the heat affected zone (HAZ) and the root bead. Emera New Brunswick (Emera) initiated an assessment of the 30 inch diameter, 145 km long, API 5L Grade X70 Brunswick Pipeline that evaluated: i) pipeline material, welding and construction records with respect to specified requirements, and ii) the propensity of the pipeline to external loading via the analysis of repeat inertial measurement unit (IMU) data and a geohazard review of locations exhibiting bending strain to understand the stability of the pipeline in relation to potential external loading. This paper describes the systematic approach taken to address the potential concerns, the key results and recommendations of the study and how Emera has incorporated those findings into processes within its management system and protection programs.