Category: Surface Finish & Corrosion Resistance (page 2)
Surface Finishes, Treatments & Cleaning
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Should heat tint discolouration in the heat-affected zone of stainless steel welds be removed? In cases where the application involves an ‘aqueous’ corrosion hazard, the local reduction in sub-surface chromium can affect the corrosion resistance of the steel. The removal of weld heat tint from stainless steel fabrications using acid pickling or electrolytic methods not only improves the overall appearance but is vitally important for restoring the full corrosion resistance of the finished product. As a general rule, if you can see a discolouration on the surface due heat tint, this should be removed as part of good post weld cleaning practice for any stainless steel welded joints. (37)
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When it comes to comparing simple surface roughness Ra values, it is possible to make the wrong conclusions, particularly when comparing different types of surface. John Swain of Anopol explains how this can happen
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The corrosion resistance of stainless steels is derived from the alloying element chromium. A chromium-rich oxide film forms naturally on the surface of the steel. If damaged, the film will normally repair itself. In this condition the steel is in the passive state. If the film is destroyed the surface is in the active state.
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