The underwater wet welding method for repairing of submerged structural members has been intensively developed during the last years. It is an economical and especially more time-independent procedure. The shortened repair duration is a major advantage in regions with rough sea climate as the North Sea area. During research projects the weldability and fatigue performance of pipe-patch connections have been tested. These joints are in use for repairing of collision indents. The shape of the actual used repair patch was optimized to the requirements of underwater wet welding at high tensile strength steels as BS4360 Gr 50D. Steel materials in this grade show problems in regard to high hydrogen susceptibility, and therefore cold cracking. The fatigue behavior of the patch-welded pipe structural member has been investigated. First test series were carried out using as-welded joints. In a second part of the project, post-weld-treated connections were tested. The weld seams on these joints were partially ground or hammer peened. The test results have been evaluated by means of the hot-spot concept and then faced with actual code requirements. Extensive strain gage measurements and finite-element calculations have been carried out to provide the stress state in the structural details.