To ensure satisfactory corrosion resistance for the welded joint, slag, spatter and oxides must be removed. Welding oxide is rich in chromium, which means that the material underneath the oxide has been depleted of chromium, thereby reducing its resistance to pitting corrosion. Post-weld treatment is therefore very important if the weld is to be exposed to acidic or neutral; chloride containing solutions such as seawater and pulp bleach plant liquids.
In these cases, pickling should be carried out to remove this oxide and enable the formation of a new protective and passivating oxide layer. Note that failure to use sufficient shielding gas during pipe welding may result in oxidation of the root side. In such cases the root side has to be cleaned by mechanical or chemical means.
Annealing
Stress-relief annealing of a non-stabilized stainless steel at temperatures within the range 550-650°C involves a risk of chromium carbide precipitation and might reduce the resistance to wet corrosion. Stabilized material however can undergo stress-relief annealing within the temperature range 550-650°C without any problems.
The safest method is to carry out stress-relief annealing at temperatures in excess of 1,000°C. The temperature levels can be provided by the manufacturer.
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