Repairing cracks in major structural steel members on offshore platforms could become a much easier and less expensive task in the near future, according to Stolt Comex Seaway. The firm, along with six partners in five European countries, is developing a means of deploying and operating friction stitch welding technology from an ROV.
Friction stitch welding is a means of repairing cracks in thick wall steels. The process involves drilling a series of holes in the crack, each hole being filled by rotating a consumable steel bar, so forming a friction weld. The sequence of filling overlapping holes is shown in the process diagram.
Hydraulic manipulators currently used offshore on remotely operated vehicles are unable to provide the one-millimeter precision required to apply the robotic welding system. A submersible electric robot arm, with controller, is therefore being developed to provide the degree of accuracy required in any water depth.
Friction stitch welding technology was originally developed by the Welding Institute in Cambridge, England, with sponsorship from SCS and a group of companies in the oil, nuclear, and construction industries. The project started in June 1997 with funding from the European Community Brite Euram 3 program, which will support research and development of the different packages of work being undertaken by each of the project partners.
Copyright 1998 Oil & Gas Journal. All Rights Reserved.
![This sequence of drawings shows how friction stitch welding manipulated by ROVs can be used to seal cracks in platform members. [20,277 bytes]](http://images.pennwellnet.com/ogj/images/off2/1298friction1.jpg){kind=link}