Methods of Removing Post-Weld Heat Tint
The appearance of heat-tint after welding is common as the surface layer of the metal becomes rich in chromium during the welding process. Removing heat tint is a legal requirement when the metal is used for a drinking-water application but it is good practice to also remove any heat-tint to ensure the metal continues to perform to its optimum potential.
Removing heat-tint from stainless steel fabrications can be achieved using a variety of methods including brush-on gels and pastes, immersion acid or spray pickling and the electrolytic method. All of these methods utilise nitric acid which leaves the stainless steel surface in a passive condition; the process is called passivation. Although nitric acid treatments are effective at removing heat-tint, they cannot be solely relied upon to remove enough meal from the surface. To solve this problem, a combination of finishing treatments can be used including mechanical treatments such as grinding and abrading before passivation takes place.
Following the manufacturer's instructions to the letter is incredibly important when using strong acids as an excessive contact time with the metal will lead to pitting damage. When a superior surface finish is required, such as for aesthetic reasons or for optimising corrosion resistance, a final electro-polishing process will provide the desired result. All finishing techniques will improve the overall appearance of the finished product.
It is just as important to consider the inside weld-face of any fabrication. Although not visible, these areas will be in direct contact with the service environment and must therefore be of superlative quality. Even if weld-backing gas systems have been used, heat-tint removal on inside faces after welding is perhaps even more important than those on the outside.
BS Stainless LTD supply a comprehensive selection of welding wire and our team are extensively trained in order to give our customers clear, expert advice on any aspect of welding.
For more information on the BS Stainless range of stainless steel sheet, duplexes, welding wire, Aluzinc and stainless steel strip coil, please contact our dedicated team on 01772 337555 or email at firstname.lastname@example.org.