Welds may be specified by fairly detailed codes which will set out the exact properties required for a specific application. Some general criteria are : Penetration: how far the weld penetrates into the joint, often expressed as a percentage. This is a combination of how the joint is prepared and set up, the process used and the current/voltage applied. It is possible to have both too little (weak joint) and too much (poor finish in the back side of the joint) penetration. Defects: including porosity caused by contamination of the weld due to inadequate preparation/cleaning or inadequate shielding, craters caused by reducing current too rapidly at the end of a run, cold starts (poor penetration at the start of a run) Undercutting: thinning of the parent metal at the edges of the weld usually caused by not enough filler metal relative to current. appearance: welds should have a reasonably smooth, uniform and consistent appearance Oxidation: welds need adequate shie...
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