A techno-economic evaluation of friction stir welding of DH36 steel

Friction stir welding of steel presents an array of advantages across many industrial sectors such as shipbuilding when compared to conventional fusion welding techniques. However, there seems to be very limited techno-economic assessment studies on its potential introduction in industry, and particularly in shipbuilding. A microstructure and property evaluation of friction stir welded low alloy steel grade DH36 plate, commonly used in ship and marine applications has been undertaken. In this comprehensive study, steel plates were butt welded together at increasing traverse speeds in order to improve the technical competitiveness of the process. Samples were examined microscopically and by traverse tensile testing, Charpy impact testing and micro-hardness testing in various regions of the weld. The study has examined a wide range of traverse speeds; from this, initial process parameter data have been established that are able to produce commercially attractive excellent quality welds through a substantial increase in the conventionally recognised welding traverse speed. In parallel, a comparative economic evaluation between friction stir welding and submerged arc welding has revealed a number of areas where the former is superior. However, the cost of the friction stir welding tool for steel has been exposed as the dominant obstacle for the wider commerical acceptance of the process on steel

Extending the life of a ship by extending her length: Technical and economic assessment of lengthening of inland vessels

The objective of MoVe IT! (Modernisation of vessels for inland waterway freight transport) project is to investigate cost-effective options for modernisation of the European inland fleet. One of the project tasks was to examine the feasibility of lengthening of existing small vessels (LOA < 86m) from both the technical and the economic point of view. With respect to that, the gradual lengthening (in several predefined steps) of two typical inland vessels of CEMT class II and III was examined. For each step, the ship structure scantlings were verified against the rules of classification societies, the manoeuvring features were simulated and the power necessary for attaining certain speed was calculated. Finally, the economic and environmental impacts of lengthening were assessed. The results of the analysis confirmed that lengthening can be viable, in particular for larger vessels (in this case, class III) where the payback periods were found to be relatively short. In addition, the lengthening proved to have a positive effect from the environmental point of view. The analysis also demonstrated that there are conditions related to waterway characteristics and economic environment under which the lengthening would not pay off, even though it would be technically feasible

Fatigue performance of friction stir welded marine grade steel

An extensive study on the fatigue performance of friction stir welded DH36 steel was carried out. The main focus of this experimental testing programme was fatigue testing accompanied by tensile tests, geometry measurements, hardness and residual stress measurements, and fracture surface examination. The S-N curve for friction stir butt welded joints was generated and compared with the International Institute of Welding recommendations for conventional fusion butt welds. Friction stir welds of marine grade steel exceeded the relevant rules for fusion welding. This newly developed S-N curve is being proposed for use in the relevant fatigue assessment guidelines for friction stir welding of low alloy steel. Fracture surfaces were examined to investigate the fatigue failure mechanism, which was found to be affected by the processing features generated by the friction stir welding tool

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