These passages have the potential for trapping corrosive fluids either from post-weld cleaning or the ultimate environment in which the assembly will perform. Welds, therefore should preferably be located on or close to the lap joint edges if the potential for corrosion exists. If the lap joint involves materials of dissimilar thickness the thinner member, if possible, should be located on the side nearest the weld torch or beam impingement. In this manner penetration requirements are reduced and accordingly costs are lessened. In welding lap joints weld parameters should be developed to prevent the melt in of the upper sheet from occurring too far in advance of the necessary conducted heat into the lower sheet.
Edge joints are similar to flange joints.
A common example is found in assemblies which recess a cover inside a container so that the edge of the container extends beyond the recessed cover. Care should be taken in fabrication and tolerance control to assure the cover and container are in close contact with minimum edge extension so that minimum weld melts are produced to avoid excessive weld melt roll over often resulting in the necessity of removing the excess in a subsequent finishing operation. This can be a costly operation. Corners of these assemblies are frequently poorly matched due to radii tolerances resulting in lack of fusion and melt back in these areas. This condition is especially critical if parts are to be machine welded.