Welding deformations and residual stresses are major factors which affect the collapse strength of externally pressurized vessels. Deflections in spherical shell welded along the equator have been already investigated by some of the authors.
In many cases of actual structures, a penetrator is welded circumferentially to a spherical shell. In these cases, the spherical shell near the weld line and the penetrator tend to sink inward.
In the 1 St report, the deformations of spherical shell caused by the welding of penetrator were investigated. Experiments were carried out in order to clarify the characteristics of welding deformations under the effects of shell and penetrator dimensions and welding procedures.
In the 2 nd report, one-dimensional thermal elasto-plastic analysis using Rayleigh-Ritz method was carried out to solve this problem theoretically. It was clarified by the analysis that the parameter λ and λα, which correlate the rigidity of shell and penetrator, and the parameter (Q/h) β, which correlates welding thermal cycle, are governing the welding deflections.
In this report, a method of reducing the welding deformations in spherical shell structures is discussed. Some deflection control methods are considered based on the results obtained by the previous reports. It is proved by experiments that the “thermal-shrinkage-fit method” is effective to produce initial reverse deflection and the “restraint load method” is more effective to reduce welding deflections. The Welding deformations in spherical shells can be prevented almost perfectly by controlling the restraint load together with adopting the initial reverse deflection, and the effectiveness of this proposed method is confirmed by experiments.
