Home › Welding Knowledge › Post Fabrication Clean-up of Duplex Stainless Steels #2

Post Fabrication Clean-up of Duplex Stainless Steels #2

Weld Spatter, Heat Tint, Flux, Slag, Arc Strikes

All these defects may occur during welding. They can act as crevices and initiate crevice corrosion in chloride-containing environments and should be avoided or removed after welding. Weld spatter can be avoided during fabrication by using an anti-spatter compound. Heavy weld discolouration or heat tint should be avoided by inert gas shielding and by purging the back side of welds with an inert gas. Often, however, heat tint cannot be totally avoided and must be removed during postweld clean-up. Flux and slag inclusions as well as arc strikes should also be removed before putting equipment in service. Weld spatter, weld heat tint, flux, slag, arc strikes, and weld undercuts can all be removed by mechanical cleaning such as fine abrasive grinding, or with a stainless steel wire wheel or brush. It is important that a fine grinding wheel is used, as coarse grinding marks can themselves cause corrosion in service by allowing deposits to stick and crevices to form.

The one distinctive feature of duplex stainless steel is that the weld heat tint tends to be thin, adherent, and more resistant to chemical removal than for austenitic stainless steels of comparable corrosion resistance. Weld heat tint can be removed chemically by pickling; for example, pickle 2205 with a 20% nitric-5% hydrofluoric acid solution. This solution dissolves the chromium oxide and also attacks the stainless steel so that the chromium-depleted layer is removed. Similar in their effect, but easier to handle for large pieces, pickling pastes can be used in place of the acid solution. However, it should be recognized that the pickle paste will produce a hazardous solution when rinsed, and appropriate safety, handling, and disposal procedures are the responsibility of the user. Depending on the corrosion resistance of the duplex stainless steel, a less or more aggressive acid can be required to remove the heat tint.

Research has shown that the best corrosion resistance after welding is obtained by using chemical cleaning after mechanical cleaning.

Other articles you might like;

Filed: Welding Knowledge
tags: , , , , , , , , , ,