The mechanical properties of some operating pipelines are unknown or uncertain, yet pipe yield strength is a required input of design pressure calculations. ASME CRTD -Vol. 91 “Applications Guide for Determining the Yield Strength of In-Service Pipe by Hardness Evaluation: Final Report” [1] describes the means by which the lower bound yield strength of a pipeline segment can be determined based on nondestructive measurements of hardness in the field on randomly selected pipe joints. The procedure allows the lower bound limit of yield strength to be determined at a selected confidence level and with selected percentile limit of pipe that could have yield strengths lower than the calculated lower bound limit of yield strength.
Key steps in the process include:
• Preassessment to ensure that the pipeline segment includes pipe having consistent characteristics.
• Development of a qualified hardness testing procedure that replicates laboratory hardness test results.
• Qualification testing of the test technician.
• Adjustment of the data from randomly selected pipe joints to estimate the lower bound hardness of the pipeline segment.
• Determination of the lower bound yield strength for the pipeline segment based upon the calculated lower bound hardness.
This paper describes the key requirements of ASME CRTD - Vol. 91, the capabilities and limitations of the procedure for estimating yield strength from hardness, and the field application of the procedure.
