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A 22-inch onshore natural gas transmission pipeline experienced an in-service rupture in January of 2018. The rupture was caused by an axial crack that occurred 150 Km (93 miles) downstream of the closest compression station. While the root cause analysis of the rupture was in progress, excavations of indications reported by a Hard Spot In-Line Inspection (ILI) were undertaken starting approximately 42 km (26 miles) downstream of the rupture. These excavations discovered predominantly circumferential crack colonies, with a number of through-wall cracks being leak. The root cause analysis concluded that both the axial and circumferential external surface cracks are consistent with hydrogen environment assisted cracking generated by the impressed-current cathodic protection system, operated near the pipe-to-soil recommended potential limit of −1200 mV as measured with respect to a saturated copper/copper sulfate reference electrode (CSE). Transportadora de Gas del Norte (TGN) implemented a series of preventive and corrective measures that included pressure testing, cathodic protection improvement, coating rehabilitation programs and In-Line Inspection programs among others. This paper presents the background and approach used in the root cause analysis, summarizes the methodology, results and findings, and discusses their implications in the management of the Pipeline Integrity of the pipeline system operated by TGN.

This paper describes the activities and stages completed as part of the Integrity Management Program for SCC in the natural gas system of Transportadora de Gas del Norte (TGN-Argentina) which started in 2000. This document focuses in a pipeline section of the system, which suffered an in-service failure in 2002 due to high pH SCC. This event triggered a series of activities, whose results are detailed in this paper. These activities involved soil analysis to determine the susceptibility to develop SCC along the system pipelines. For susceptible sections, the program included hydrostatic testing to levels of 100% and 110% of SMYS followed by replacement of degraded coating. The paper also details the experience in the use of new internal inspection tools with EMAT technology. The capability of the EMAT tool to detect and size SCC defects and the possibility of discriminating between SCC colonies that have been recoated and those that may still be active due to degraded coating is discussed. Finally, the severity of SCC cracks detected by in-line inspection is assessed using API 579 methodology, and the feasibility of using this assessment results to determine the critical SCC defect sizes for detection by ILI tools is analyzed.

A leak on a girth weld was detected on a 609.6 mm (24 in) diameter transmission gas pipeline while recoating works were being performed. Failure analysis determined that the leak was caused by a pre-existing defect in the girth weld. This pre-existing defect had not been evolving over time. Nonetheless, because of the stress particular condition to which the gas pipeline was subject during the recoating work, the defect destabilized and progressed to failure. In order to reduce the risk of occurrence of similar failures, a total of 27,000 girth welds were individually analyzed, corresponding to a length of 191 kilometers (118 miles) of the same gas pipeline section. The analysis included evaluation of internal inspection runs and girth welds gammagraphs available from the recoating work. Hence, not only was the data analyzed individually, but a comparison of the different sources of information to find a correlation was also performed. Features detected in the analysis were classified and prioritized base on comparison with the failed girth weld defect. Also correspondence with crack like indications was considered. Severity of anomalies was categorized on four levels. A set of the highest severe crack like anomalies with potential failure were selected for direct assessment. The complete process involved the assessment of 399 anomalies in total, revealing cracks on 79 girth welds. Metal reinforcements were installed as permanent repair on 27 girth welds according to repair criteria, and direct assessment findings were used to correlate internal inspection signals with features. This paper discusses the results of the analysis, the field findings, and the actions taken.

Gasoducto del Pacifico is a pipeline that carries natural gas from southern Argentina to Chile, through the Patagonian Andes. During previous years of operation only minor sign of soil movement were registered by the monitoring program, taking the form of ditch settlements. However, on September, 2005 a landslide took place producing a gas leak, at a segment that was previously characterized as a non-critical one. An initial office review of available information and site pictures would not yield a clear reason of land movement initiation given the terrain mild slope. Actions were taken aiming at three different time frames. Immediate remedial actions were taken such as ditch opening to free stresses and replacement of buckled pipeline. Integrity specialist flew to the site to conduct geological survey and a stress analysis was conducted at a lab, allowing to asses and manage present risk before transportation began. Mid-term solutions were implemented as the ditch remained open until the next summer season, when access to the site was guaranteed. Finally, two new river crossings were constructed to mitigate this natural hazard permanently. Lessons from this incident revealed design aspects that need to be reconsidered to assure mountain pipelines integrity.Copyright © 2013 by ASME