WELD PREPARATION: Joint Tolerance & Cleaning

Joint Tolerance

The allowable tolerance of joint dimensions depends upon whether the welding is to be done manually or by mechanised means. Manual welding applications can tolerate greater irregularities in joint fit up than mechanised welding. The particulartolerance of a given application can be determined only by actual testing, and this tolerance should be specified for future work.

Cleaning

Cleanliness of both the weld joint areas and the filler metal is an important consideration when welding with the gas tungsten arc process. Oil, marking crayon,grease, shop dirt, paint,  & rust or corrosion deposits all must be removed from the joint edges and metal surfaces, to a distance beyond the heat affected area. Their presence during welding might  lead toarc instability and contaminated welds containing pores, cracks and inclusions. Cleaning may be accomplished by mechanical means, by the use of vapour or liquid cleaners, or by a combination of these. Organic solvents like carbon tetrachloride should not be used as any trace of it coming under the arc may lead to the formation of phosgene, a toxic gas. Acetone may be used.