Frequently Asked Questions
In order to maintain optimum corrosion resistance, the oxide scale and the Cr-depleted layer formed during welding must be removed. This may be done by a variety of mechanical and chemical means but the best corrosion resistance is achieved by acid pickling, preferably preceded by grinding.
The most commonly used bath for removing oxide scale is an aqueous solution of nitric acid 10-15% with 0.5-3% hydrofluoric acid. Alternatively, pickling paste may be used. As these acids are highly toxic, appropriate safety precautions must be followed.
Grinding and pickling give the best improvement in terms of critical pitting temperature because this method removes oxides, the underlying chromium-depleted layer and other susceptible areas such as those associated with surface slag inclusions. A grit size of 360 or finer is recommended for grinding. Wire brushing by hand, with a stainless steel brush, or sand blasting may also be used but are less effective because they generally do not remove the chromium-depleted layer.
For more information on corrosion resistance of stainless steel welds and post-weld cleaning, please contact us.