TWI Frequently asked questions
It is essential to refer to any application standard before deciding whether or not cut edges need to be dressed. For instance, BS 5400 for bridges and BS 5500 for pressure vessels, both contain detailedrequirements for the treatment of gas cut edges.
Gas cutting, if carried our correctly, will leave a smooth straight edge. It may have a glazed surface from the non-metallic substances in the steel which may prevent paint systems from adhering and a light grit blast or grindingcan remove this effect. Poorly operated or maintained gas cutting plant may leave a rough or hard cut surface, possibly with grooves. This may (but should not!) be acceptable for simple non-structural applications, but for structuraluse the edge will require dressing to ensure that any cracks which may have occurred will be removed. Usually, gas cut edges which are to be incorporated in a welded joint can be left as cut because the edge is melted into the weldmetal as long as the cut is even. The product standard or code may give gas cut edge requirements including allowable hardness and possibly grinding depths for removing the heat affected zone. As for welding, gas cutting should becarried out in accordance with an approved cutting procedure.
It is important to remember that in cases where the steel requires preheat for welding it may also require preheat for gas cutting to avoid cracks on the cut edge. The cut edges of ferritic alloy steels may also need to be groundback by some 1.5 to 2mm to ensure that any undesirable metallurgical structures, not sufficiently modified by the welding process, are removed. If not ground back it may be necessary to demonstrate that no degradation has takenplace.
Copyright by TWI, 2003
