The importance of accurate hardness measurements for the success of an ILI system addressing hard spots in pipelines

One of the most recent anomaly type that became of concern to pipeline operators are local variations of the pipe wall’s metallurgical hardness, typically referred to as “Hard Spots”. Not only weakening the pipeline’s stress resistivity but also increasing susceptibility to stress corrosion cracking (SCC), especially regulators and organizations in the United States and Canada have recognized the requirement for operators to become active on this topic. Comprehensive studies with a novel in-line inspection (ILI) tool utilizing Dual Magnetization Technology method for addressing Hard Spots have recently been conducted in co-operation with several pipeline operators. The studies included pull tests with artificial defects as well as real inspections and subsequent field validation programs. A stable procedure was found for accurate hardness measurements on artificial defects and for field verifications, which is of crucial importance for the success of the ILI method. The results available today confirm the capability of the ILI system not only to detect but also to accurately characterize hard spots in terms of length, width and hardness. This technical report will describe the basic measurement principle of the novel ILI system and outline the results achieved in full scale tests and actual in-line inspections. It will describe the method and process applied for field validations that are the basis for an accurate determination of the ILI system’s performance.