Solving the Complexity of Hard Spots by Understanding Their Origin

Abstract The level of industry knowledge concerning hard spots has increased exponentially over the years. It is now well understood that hard spots are localized changes in microstructure that can take many physical forms, depending on a combination of variables such as steel chemistry and steel manufacturing processes. They can have a range of microstructures, different morphologies in terms of shape, and different hardness profiles, all of which influences the assessment of hard spots using nondestructive methods like in-line inspection (ILI). The first incarnations of ILI for assessment of hard spots were developed using pull tests with artificially produced hard spots. This was because, until recently, there was limited access to real anomalies that had been removed from service. Despite the fact that more hard spots have been removed from service and can be used for development, the need for artificial hard spots for pull testing and development of ILI performance specifications still exists. Recreating hard spots that accurately represent the anomalies that are present in vintage pipe (pre-1970s) remains a challenge. The increased level of knowledge about the different types of hard spots that now exists has provided a basis for creating representative anomalies. ROSEN developed a laboratory approach to create artificial anomalies that can be used in combination with the continually expanding set of field validation data to improve the assessment capabilities of ILI in terms of POD, POI, and sizing. This paper presents the work done in developing artificial hard spots for use in pull testing and laboratory research and the detailed investigation of different ILI measurement techniques (high and low magnetization in combination with eddy currents and geometry channels) to optimize the detection, identification, surface discrimination (internal/external), and sizing of different types of hard spots.