An Insight Into What it Takes to Validate Inline Inspection Tools for Reliable Hard Spot Identification and Measurement

Abstract A hard spot is a localised area of increased hardness, defined in 49 CFR Part 192 as “an area on steel pipe material with a hardness greater than or equal to Rockwell 35 HRC (Brinell 327 HB or Vickers 345 HV10)”. Hard spots result in localised areas of increased residual magnetic field following magnetisation by an inline inspection tool run. These magnetic fields can be measured using a low or no field approach and used to detect and classify hard spots and to predict the hardness. There are significant challenges in moving from pull test or dig data to creating a validated specification for hard spot inspection. The essential variables for hard spot inspection — sources of variation which must be controlled within defined limits for a successful result — are more numerous than for comparable inline inspection technologies. This is due to the two-step magnetization and measurement process and the range of factors related to the pipeline conditions, the hard spots themselves, and the inspection tool which could affect the magnitude of the residual field. The relative scarcity of hard spot examples and the difficulty in manufacturing hard spots to predictable tolerances means that the data required to validate across the range of all essential variables is not readily available. This paper describes how Baker Hughes, in collaboration with industry partners, are using a multi modal approach to combine FEA, pull test and dig data to cover the essential variables required for inline inspection of hard spots and establish a validated POD, POI and POS specification.