Skelp Weld Crack Failure Investigation of 24” Helical Welded Pipeline
Authors: Al-Asfour Ali , Dubey Ashutosh , AlShuaib Khaled , Alsarraf Abdulmohsen , Jarragh Amer 
Published: December 2024

Abstract
Kuwait Oil Company (KOC) has been in operations since 1934 as a major upstream Oil & Gas Company with the main objective of exploring, producing & exporting Crude oil and Hydrocarbon Gases to customers across the globe. It operates several gas and liquid pipelines from 3″ to 60″ in diameter (More than 700 number of pipelines with a total length of more than 8,300 Km). The pipelines are buried, travel through different terrains, soil environment, subjected to different operating parameters and services. Maintaining the integrity and reliability of these pipelines to ensure safe operations is a challenge for the company.
Inspection & Corrosion Team (I&CT) bears the responsibility to maintain the integrity of this huge pipeline network in the Company. The team maintains the pipelines data, prepares the inspection plans, schedule In-Line Inspection (ILI) of the pipelines, conducting inspections, issuing recommendations and oversees repairs/replacement activities in the pipelines.
One of the challenge the Team recently faced was involving a 24″ High Pressure Gas Pipeline exporting high pressure gas from a Booster Station to a Refinery. The pipeline was constructed in 2014 and commissioned in 2017 in two sections. As the pipeline is a strategic in nature and has two sections i.e. Pipeline A from Booster Station to ISC (intermediate sludge catcher) and Pipeline B from ISC to the Refinery. Both were inspected in the year 2019 by conventional Magnetic Flux Leakage In-Line Inspection (ILI). Based on the inspection findings, the recommendations were provided for Pipeline A for replacing pipeline sections which were found affected by internal corrosion.
During replacement activities in pipeline A, linear type indications (suspected cracks) were observed in the bevel edge of the pipeline while conducting dye penetrant (DP) test. Furthermore, crack like features were observed in one of the skelp-weld of the pipeline as well during DP Testing. To confirm the extent of these indications, 48 nos. skelp welds (out of total 434), randomly were subjected to radiographic testing (RT). It is to the surprise, 47 out of 48 were found with crack like features. This raised a serious concern and threat to the overall integrity and future usage of the pipeline. Any leak in the pipeline being such strategic in nature can not only affect the operation/customer but possess a serious threat to the safety and environment.
A detailed investigation was undertaken by I&CT in collaboration with a third-party investigation agency to find the exact morphology & nature of these crack-like features and primary causes behind these features. The affected samples were taken from the pipeline and detailed testing & investigation including scanning electron microscopy (SEM), Energy-Dispersive X-Ray (EDAX), micro-hardness and various other NDTs were conducted on them. Based on the findings, it was found that the samples were severely affected by Hydrogen Induced Cracking (HIC) and Stress Oriented Hydrogen Induced Cracking (SOHIC). However, the skelp welds suffered from transverse crack caused by Sulfide Stress Cracking (SSC) mechanism.
This paper covers in details the initial inspection findings in the pipeline, detailed investigation methodology, type of testing performed, major findings, evaluation of the results and primary causes for the origin of these cracks in the pipeline. The investigation provides a further direction for recommendations to tackle the integrity concerns in the pipeline and furthermore devising the inspection plan & methodology for the Pipeline B.