Experiences and Modeling of Hydrogen Cracking in a Thick-Walled Pressure Vessel
ARMY ARMAMENT RESEARCH DEVELOPMENT AND ENGINEERING CENTER WATERVLIET NY BENET LABS
Pagination or Media Count:
Hydrogen cracking associated with armament structures has become more prevalent in recent times. Recent work by Troiano et al. has clearly shown that the utilization of specific barrier coatings, such as nickel, can impede the absorption of hydrogen and retard hydrogen-induced cracking. In this work, a thick-walled, autofrettaged pressure vessel was manufactured from ASTM A723 Grade 2 steel and heat treated to a yield strength of 1170 MPa. An outside diameter keyway was then machined. The keyway was exposed to concentrated sulfuric acid, leading to apparent cracking within 20 hours of exposure. An investigation of the affected keyway in the pressure vessel indicated that localized hardened areas were present. The base material possessed hardness values of Rc 37 to 39, while the keyway possessed localized hardened zones up to Rc 44. These zones extended to a depth of approximately 4-mm. The different hardness layers suggest that the environmental cracking incubated and propagated in two separate stages. Cracking in the hardened skin layer on the surface incubated quickly and propagated to approximately the 4-mm depth and arrested itself once it encountered the more ductile base material. Previously published crack growth dadt test data, and new data verify that this process of incubation and propagation occurred in a matter of seconds in the hardened skin layer. The cracking then resumed in the softer base material after approximately 300 hours of incubation time. Additional dadt testing of this condition has been performed over a range of yield strengths and verifies that incubation times and crack propagation rates are similar to those observed in this pressure vessel.
- Properties of Metals and Alloys
- Containers and Packaging