Distortions in Large Stiffened Ship Panels Caused by Welding: An Experimental Study

Abstract

Severe distortions are observed in fabrication of large stiffened ship panels using lower thickness plates ranging from 3 mm to 10 mm. It requires expensive postwelding fairing operations. It is naturally preferable to control the distortion during fabrication than to apply fairing operations. Welding sequence plays an important role in controlling distortion. The aspect of weld sequencing has been studied only on a small and extremely simple form of test models. Possible welding sequences were worked out, based on principles of heat balancing or heat accumulation and subsequent behavior of such panels. Based on this, large stiffened panels were fabricated using low carbon steel of shipbuilding quality considering four different welding sequences. Initial and final distortions of these panels were measured using high precision coordinate measuring machine. In this investigation, experiments and measurements played a very important role, as numerical simulation of such large panels would have been prohibitively expensive or not feasible. This study established the pattern of welding sequence that needs to be followed for minimizing welding distortion in the fabrication of large stiffened panels. Gainful conclusions were drawn to give directions to welding designers to work out the appropriate sequence of welding to minimize the weld-induced panel distortions. 1. Introduction Ship structural components are built by assembling various stiffened steel plates. Large steel plates are stiffened by welding stiffeners using fusion welding process which is a common welding method used in the shipbuilding industry. Severe thermal gradients in the welded components occur because of intense localized heating in the heat-affected zone (HAZ), followed by uneven cooling. As a result, residual stresses and distortions occur in the welded components. These distortions are introduce in the block assembly process in shipbuilding. These unwanted distortions result in additional production cost because necessary rectification process and extra manpower are required. These also cause delays in shipbuilding.