Fracture Toughness Testing of Seamless Pressure Vessels Steels in Gaseous H2 and Sour Environments

Abstract High pressure gaseous hydrogen has detrimental effects on the fracture toughness of Low Alloy High Strength (LAHS) steels and its effects needs to be evaluated. On one side, ASME Code, Sec VIII, Div 3 art. KD-10 indicates ASTM-E1681 as the fracture toughness testing procedure for material evaluation in gaseous hydrogen applications. Due to the comparative simplicity of testing self-loaded Wedge Opening Load (WOL) specimens from ASTM-E1681 in constant displacement, this type of test has become a “standard” for the industry. On the other side, fracture toughness evaluation of materials for OCTG applications in sour service is usually performed following Method D of NACE TM0177. This is also a test procedure that employs self-loaded double cantilever beam (DCB) specimens. In the present study a LAHS steel for seamless pressure vessels applications was tested in H2 gas at 550 bar and in sour environment (NACE Solution A with 1 bar of H2S and SR39.3 (pH 3.5) with 0.07 bar of H2S and N2 balance to reach 1 bar total pressure). The results allow the comparison of both testing techniques and the relative severity of gaseous H2 against usual environments for sour performance evaluation.