There are companies that have great understanding of successful technical practices for stainless steel metal fabrication. To ensure the highest quality they always stick to the industry regulations, for the benefit of both, end users and industry members. These companies have stringent standards of education, training and competence, professional and personal conduct and committing themselves to continuing competency development. Using services of these companies, you can be sure that your stainless steel metal fabrication will be performed by technically competent specialist and you will be provided by the best ending results.
Surface damage, contamination and defects that happen during fabrication process are all harmful to the oxide film that protects stainless steel in service. Some of common defects and damage include:
Scratches and mechanical damage – Gouges and starches from crevices on the steel surface, providing great place for corrosion. Scratches may contain carbon steel or other contaminants and will also raise customer concern in situations where appearance is essential. Prevention is the best way to avoid this to happen, otherwise, mechanical cleaning would be the most effective solution.
Surface contaminants – Common contaminants include common salt and carbon steel. Grime and dust arising during fabrication may contain these contaminants. Paint, crayon, oil, fingerprints, grease may also contain products that can provide crevices for localized corrosion and they should be removed. The most often fabrication problem is embedded iron and loose iron particles, which rust very quickly and intimate corrosion.
Welding – The high temperature of welding can introduce steel surface and other defects. Stray, slag, spatter and undercut must be minimized as they are potential site of corrosion. General cleanliness and removal of potential carbon contaminants is essential in obtaining good weld quality.
Heat tint and scale – Scale and heat tint happen when stainless steel is heated to high temperatures during welding. Deleterious oxides of chromium may develop and they lower the corrosion resistance of the steel.
Distortion – Stainless steel has low thermal conductivity coupled with relatively high coefficient of thermal expansion. So, stainless steel expands very quickly with the input of heat that happens during welding and as a result of this there can be distortion. This can be minimized by using lowest amperage with good weld quality.
Removal of surface contamination
There are three methods of repairing the stainless steel surface:
Mechanical cleaning – Wire brushing should be done only with stainless steel bristles, but it's important they not been used on any other surface. Clean flapper wheels and clean abrasive disks are commonly used to remove heat tint and other imperfections.
Chemical and electrochemical cleaning – Heat tint, embedded iron and other contaminants can be removed by acid pickling, usually by electropolishing or with a nitric hyrofluoric acid mixture. These processes are leaving a clean, defect-free steel surface.
Passivation – This process involves treating stainless steel with dilute nitric acid solutions or pastes. They remove contaminants and allows for a passive film to be shaped on a fresh surface, following machining, grinding, etc.