Sensitivity analysis of half bead and alternative gtaw techniques

Sensitivity Analysis of Half-Bead and Alternative GTAW Techniques
The alternative six-layer technique displays a tolerance to the variables of welding

BY P. J. ALBERRY

ABSTRACT. The ASME XI shielded metal arc half-bead technique and an alternative, mechanized, six-layer gas tungsten arc technique have been assessed using a computer model sensitivity analysis. These techniques have been developed for repair welding of heavy-section steel components in light water reactors without postweld heat treatment. The as-welded heat-affected zones are compared in terms of structure, grain size and hardness. The likely sensitivity of each technique to systematic and random variations in welding parameters is assessed. Introduction In 1979, EPRI initiated a research contract EPRI-RP 1236 entitled "Repair Welding of Heavy Section Steel Nozzles" for Babcock and Wilcox, Alliance, Ohio. This project was designed to define and validate an alternative to the ASME XI halfbead repair procedure for light water reactor nozzles. Both repair procedures are intended for use without postweld heat treatment. The half-bead procedure uses a layer-by-layer refinement and tempering technique and is carried out manually. Half of the first layer of weld metal is ground off manually to facilitate the refinement and tempering action of subsequent layers. The heavy dependence on time-consuming manual activities was considered to be a serious practical limitation in reactor environment due to the prolonged exposure to radioactivity. Consequently, with the use of a computer model, an alternative GTAW technique capable of mechanization was designed. The computer model work was carried out in three phases. The first phase was to establish the basic welding metallurgy for SA508 Class 2 heat-affected zones (Ref. 1). The second phase was to use the computer model to develop a viable gas

tungsten arc welding (GTAW) procedure (Ref. 2). The third phase, a computer model sensitivity analysis of the