A total of 108 seamless, forged pressure vessels, fabricated from ASTM A372 type IV (UNS K14508) and type V low aIIoy steel, are currently in 4,200 psi (29 MPa) gaseous hydrogen (GH2) service at the Kennedy Space Center’s (KSC) Space Shuttle Launch Complex 39 (LC-39). The vessels were originally used in 6,000 psi (41 MPa) GH2 service during the Apollo program. NASA recently received a letter of warning from the manufacturer of the vessels stating tbat the subject vessels should be now be removed from GH2 service due to the fact that the ultimate tensile strength (UTS) of many of the vessels exceeds the maximum limit of 126 ksi (869 MPa) now imposed on A372 steel intended for GH2 service, and
therefore are susceptible to hydrogen environment embrittlement. Due to the expense associated with vessel replacement, it was decided to determine by testing and analysis whether or not the vessels needed to be removed from GH2 service. Slow strain rate testing was performed under hydrogen charging conditions to determine the value of the threshold fracture toughness for sustained loading crack growth...
Keywords: hydrogen embrittlement, pressure vessel, gaseous hydrogen, slow strain rate, fracture mechanics, hydrogen charging