The task was to get information on the HAC for an underwater repair weld which will be done under hyperbaric conditions in a gaseous atmosphere. Tests on the real site are too expensive. Therefore, the aim was to use 1bar conditions to study the HAC for the repair weld.
Three main influence factors are governing the HAC: Microstructure, hydrogen content, and local strain. The physical and metallurgical effects of fusion welding on those three fields are numerous. For an engineering approach it will be necessary to concentrate on the main effects, which are supported by measurements and simulations.
The three influences factors should be at the test conditions as close as possible to the real conditions. Microstructure of the HAZ was easy to adapt, because high cooling rates are present under hyperbaric conditions. Hydrogen was introduced into the weld metal to a content measured during hyperbaric tests. Diffusion in the solid metal is not influenced by the surrounding pressure. The critical factor was the stress/strain condition.
A self restraining test was used (Instrumented Restraint Cracking test) to receive adequate strain in the weld zone. The intensity of restraint was correlated to a mockup of the real site, where measurements of its stiffness were done regarding critical conditions. The fillet weld, which will be used for this welding task, showed more risk to HAC than butt welds. This behaviour was correlated to its high restraint in more than one direction. A combined restraint in two directions was realized in a new type of IRC system.
Testing of the HAC showed three main influences of welding conditions: Hydrogen content, gap width and heating cycle. The results from the IRC tests with combined restraint showed good correlation to the welding tests, which were done on a mockup.