Implementation of a New Tool for Pipelines Integrity Evaluation: A Correlation Between Local Strains and Hardness

Due to external interference, pipelines used for onshore as well as offshore operations can present dent and gouge defects. As such defects can seriously impair facilities’ integrity and performance, it is necessary to evaluate the strains in the vicinity of these defects. The development of non-destructive approaches to assess defects severity remains an issue in the pipeline industry. In the present study, micro-hardness - strain relationships are established for three steel grades of pipeline materials: API X52 modern, API X52 vintage and API X63 vintage. The micro-hardness – strain correlations of the three pipe materials are analyzed in order to verify if they can be described by a master curve. For that purpose, Notched Tensile (NT) tests are performed in Longitudinal (L) and Transverse (T) directions for each grade in order to reach high strain values (up to 70%). The relationship proposed by Tabor was improved with the introduction of three new parameters that allow considering actual material behavior.