Materials that require preheat for welding (see §10) shall be preheated in the same manner for thermal cutting or gouging.Surfaces for welding shall be clean and free from paint, oil, dirt, scale, oxides, and other foreign material detrimental to the integrity of the weld.Grinding wheels and wire brushes used on austenitic or other higher nickel shall not have been previously used on carbon or low alloy steels, copper alloys, aluminium or zinc coatings (paint or galvanizing). Only austenitic stainless steel wire brushes shall be used on austenitic or other higher nickel alloys. Grinding wheels and wire brushes shall be used only for a single type of material. Grinding discs containing sulphur (iron sulphate) or other harmful components shall not be used on stainless steels, 9% nickel steel or non-ferrous materials. All bevel above of 20mm of thickness shall be checked with VT plus MT o PT after grinding and machining.