1997 Volume 15 Issue 1 Pages 135-140
Most of offshore structures for oil exploitation are composed of a deck and legs which are framed by welding many pipes. The prediction and control of the welding deformation is very important for the efficient and economical building of offshore structures. This is a basic study of the prediction and control, of which object is the offshore structure of jacket type.
Almost all studies on the welding deformations of pipes (cylindrical drums, cylindrical shells) have been performed in relation to the local deformation by the circumferential butt welding. In this study, the welding deformation when a pipe (brace) is welded on the wall of another pipe (chord), like the welding of T-joint or Y-joint, was investigated in the actual building process of a jacket. The local deformations of the braces by welding were measured near the joints. At the same time, the influential factors, such as brace sizes, groove shapes, welding sequences, heat inputs, etc., on the local deformations were investigated.
The correlations between the deformations and the factors were examined. As a result, it was made clear that the total heat input (the summation of heat inputs per unit length, of all welding passes) for each joint had influence on the local deformations most. The relations between the local deformations, namely, axial shrinkage, in-plane rotation, out-of-plane rotation, of the brace and the total heat input were formulated by the regression analysis. Also, the mechanisms of the increase and decrease of the deformations were discussed in detail, related to the total heat input, the welding sequence, etc. In the next report, the welding deformation of the whole structure will be simulated by the theoretical analysis, using the above relations for the local deformations.
