TECHNICAL BASIS FOR MASTER CURVE FOR FATIGUE CRACK GROWTH OF FERRITIC STEELS IN HIGH-PRESSURE GASEOUS HYDROGEN IN ASME SECTION VIII-3 CODE

The design of pressure vessels for high-pressure gaseous hydrogen service per ASME Boiler and Pressure Vessel Code Section VIII Division 3 requires measurement of fatigue crack growth rates in situ in gaseous hydrogen at the design pressure. These measurements are challenging and only afew laboratories in the world are equipped to make these measurements, especially in gaseous hydrogen at pressure in excess of 100 MPa. However, sufficient data is now available to show that common pressure vessel steels (e.g., SA-372 and SA-723) show similar fatigue crack growth rates when the maximum applied stress intensity factor is significantly less than the elastic plastic fracture toughness. Indeed, the measured rates are sufficiently consistent that a master curve for fatigue crack growth in gaseous hydrogen can be established for steels with tensile strength less than 915 MPa. In this overview, published reports of fatigue crack growth rate data in gaseous hydrogen are reviewed. These data are used to formulate a two-part master curve for fatigue crack growth in high-pressure (106 MPa) gaseous hydrogen, following the classic power-law formulation for fatigue crack growth and a term that accountsfor the loading ratio (R). The bounds on applicability of the master curve are discussed, including the relationship between hydrogen-assisted fracture and tensile strength of these steels. These data have been used in developing ASME VIII-3 Code Case 2938. Additionally, a phenomenological term for pressure can be added to the master curve and it is shown that the same master curve