| Abstract Scope |
The Delayed Hydrogen Crack Test (DHCT) was developed within Ohio State Welding Engineering to classify susceptibility to hydrogen assisted cracking (HAC) in dissimilar metal welds (DMWs) which see cathodic protection in subsea oil and gas operations. To date, over 220 tests have been completed with a 90% testing success rate. The test exposes welds to a uniaxial tensile load while simultaneously embrittling the material with hydrogen through a cathodic reaction within a test cell. Instead of seawater, which is the hydrogen source in service, the tests use dilute sulfuric acid. This raises the hydrogen concentration to the most extreme situation possible. The welds are run to failure or 1100 hours – whichever occurs first. Conservatively, a DMW that can withstand 1100 hours without cracking is deemed hydrogen resistant. To date only one interface has shown this behavior, with the rest ranging in susceptibility. Most welds tested are comprised of a nickel-based weld metal on low alloy steels. Fracture of these welds almost always follows the fusion boundary or HAZ where the most susceptible microstructures to HAC exist. Numerous conclusions have been made regarding DMW resistance. These include the effects of base metal composition, carbon contents, yield strength matching condition of the interface and welding process on cracking behavior. The DHCT has recently received a standardization: AMPP TM21453 2023.
This work aims to discuss the database in its entirety and speak regarding the various results seen during testing. Details of successful test setup and monitoring will be shared as well as the ongoing work to further advance and develop the state-of-the-art testing methodology. With recent emphasis rising on the hydrogen economy by various industries, DHCT will remain an important tool in classifying hydrogen resistance in welds. |