Advanced techniques for residual stress measurement and data processing in fatigue crack growth rate tests of FH36 and 9% Ni steel at cryogenic temperatures

Safety assessment of cryogenic temperature liquefied gas storage tanks is one of the crucial technologies for reducing CO2 emissions. Residual stresses (RS) in welded structures can significantly impact their structural integrity. Measuring RS in cryogenic environments and studying the impact on crack propagation is essential for safety assessments. Studies have proposed methods for measuring RS based on specimen deformations during crack propagation. However, some of the methods have limitations in measuring RS in cryogenic environments. Additionally, existing methods are only suitable for specific specimen types. This study introduces a method for measuring RS applicable to various specimen types and compares the RS induced stress intensity factor (SIF) measured through different methods. This study suggests that the RS induced SIF calculated from the deformation is not only due to the welding but also to the applied load during the test. By analysing the relationship between applied loads and the SIF induced by RS, this study eliminates the influence of the applied load and isolates the SIF caused exclusively by welding RS. The welding RS induced SIF at different temperatures is compared. The crack growth rate for FH36 and 9% Ni steel at different load ratios and temperatures is presented. The fatigue crack growth rate curve is corrected by considering the SIF induced by welding residual stresses.