Tensile Testing and Analysis of Notched Low Alloy Steel Specimens

Abstract

Notched axisymmetric specimens of two high strength low alloy steels used frequently in the subsea industry have been tensile tested to failure in air and in a 3.5% NaCl artificial seawater solution with cathodic protection (CP). The aim of the testing was to provide input to an initial assessment of elastic-plastic static load-capacity analysis of low alloy steels with material and quality control requirements according to ISO 13628-7 (ISO-7). The tensile testing in seawater with CP was performed in order to investigate whether hydrogen as formed by the CP system may have an effect on the ductility and strength that needs to be taken into account in the static load-capacity analysis and hence in design. Local and global static load-capacity criteria from ASME VIII Div. 3 (Div.3), ISO-7, NORSOK U-001 (U-001) and API 6X (6X) have been considered for the notched specimens. Recommendations regarding elastic-plastic static load-capacity analysis of subsea equipment are given. The specimens tested in seawater with CP were found to have a reduced ductility and strength compared to the corresponding specimens tested in air. Further testing in seawater with CP is recommended before it can be concluded whether the environmental effect of the hydrogen needs to be included in the static load-capacity analysis of high strength low alloy steels.