What Are My Options? Review of Non-Destructive Mechanical Tests for Steel Linepipe Yield Strength

Abstract Methods for non-destructive estimation of steel linepipe yield strength (YS) and ultimate tensile strength (UTS) are surveyed, recognizing that YS is important for grade estimation. Operators seek rapid, accurate, precise, reliable, and repeatable non-destructive testing methods to estimate pipe YS as part of the process to determine Maximum Allowable Operating Pressure (MAOP), burst pressure, and to perform other critical calculations. We provide a description of several methods to estimate steel linepipe YS. First, several methods of hardness testing are discussed, with the most focus being placed on two portable hardness measurement methods that have been tested extensively: ultrasonic contact impedance (UCI) and portable Rockwell testing. These two instruments work well in the field and complement one another. For example, if operating/vibrating pipe degrades UCI accuracy, portable Rockwell hardness testing can be used instead. Several additional aspects of these and other hardness tests are discussed, such as surface preparation, wall thickness requirements, indentation size, and the necessity of orienting the hardness tester normal to the surface. Note that hardness testing is not often used to estimate YS directly, but rather to establish a lower bound estimate for YS. Second, several commercial devices have been developed to provide a direct estimate of YS, and three of them are extensively reviewed in this work, including Instrumented Indentation Testing (IIT), Hardness, Strength, and Ductility (HSD), and Profilometry-based Indentation Plastometry (PIP). Some literature data are not comparable due to different sample groups and testing conditions. Therefore, the authors tested these three instruments on a uniform set of pipes and provide a brief “at-a-glance” comparison of IIT, HSD, and PIP. The results indicate that the root mean squared error (RMSE) for the three instruments for YS ranges from 4–5 ksi for YS and 3–6 ksi for UTS. Additionally, the mean absolute percentage error (MAPE) for the three instruments ranged from 6–7% for YS and 3–5% for UTS. IIT performed the best for YS estimation, and HSD performed the best for UTS estimation, but the differences among all three instrument results were small. An additional approach for estimating strength based on composition and microstructure alone (PRCI’s Checkmate) is also discussed. For each method the discussion includes the mechanism (working principle), logistics, dimensional considerations, potential pitfalls, and example models of test instruments. By offering a thorough overview, we aim to assist operators in identifying the most suitable non-destructive test for their specific requirements.