Tack welds should not be thinner than specified for the root weld and should be subject to the same quality requirements for welding as are also applicable for the root weld. The length of the tack weld should not be less than four times the thickness of the thicker of the parts to be joined. For workpiece thicknesses over 50 mm or for high-tensile materials consideration should be given to increasing the length and thickness of tack welds. This may also include a two-pass weld. Attention should also be paid to the use of lower-tensile filler metals when welding higher-alloy steels.
For joints that are supposed to be welded using automated or fully-mechanised processes, it is necessary to include the conditions for fabricating the tack welds in the welding procedure.
If a tack weld is to be included in a welded joint, then the shape and quality of the tack should be suitable for incorporation into the final weld. It should be fabricated by qualified welders. The tack welds should be free from cracks and prior to final welding should be cleaned thoroughly. Tack welds that exhibit cracks should be grooved out. However, crater cracks may also be removed by grinding. All tack welds that are not to be included in the final weld should be removed.
Any necessary aids that are temporarily attached for the construction or assembly of parts with fillet welds should be designed so that are can easily be removed again. The surface of the component must carefully be ground smooth again if the aid is removed by cutting or chiselling. It is possible to demonstrate by means of a dye penetrant test that the metal is not cracked in the area of the temporary weld.