Better steel welding for lower shipyard costs
Welding is the preferred process for joining of metal plates. However, thin welded steel plates used in the effort to produce lighter ships are subjected to increased distortion, restricting their use and increasing costs per ship due to failure when used. Experimental measurements combined with finite element modelling were used by EU-funded researchers working on the ‘Predicting and managing weld induced distortion in thin-walled, steel structures’ (Distortion) project in order to identify the relationship between welding process parameters and pre-existing materials stresses to minimise distortion. Extensive experimental investigation of fabricated high-strength alloy steel plates produced by butt welding was conducted. Studies included measurements of transformation temperatures, or temperatures at which a transformation in phase occurs during heating or cooling, given that low transformation temperature (LTT) may improve fatigue strength. The relationship was evaluated with residual stress measurement using the neutron diffraction technique. In addition, kinetics of the relationship between transformation temperature and microstructure of fabricated welds provided useful information for the finite element model. Researchers implemented the numerical approach in a thermo-elastic-plastic analysis of the welded plates to predict distortion in thin-walled structures. The efficient algorithm facilitated selection of material for the LTT weld wire to obtain desired stress of the final weld. Numerous simulations and experimental analyses of thin-walled welded steel structures led to proposals for process and materials optimisations leading to reduced distortion in such structures of critical importance to the shipping industry. Continuation of the project findings promises to lead to new understanding of the many parameters affecting distortion in thin welded steel plates with the potential to significantly reduce the labour costs of shipyards related to the reworking of components.
