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HOW TO REPAIR CONTAMINATED STEEL SURFACES

15-06-2016
by 
in 

Prevention is better than cure when it comes to errors in steel fabrication because it’s not always a simple, easy or cheap job to repair contaminated steel surfaces.

In order to maintain their optimum corrosion-resistance, steel surfaces must be clean and have an adequate supply of oxygen. 

This is because steel does have some ability to self-heal if it gets damaged because the chromium in the steel reacts with oxygen in the air or water to form a protective, passive coating, but it generally becomes necessary over time to physically repair the chromium-oxide surface when the contamination becomes severe.

Obviously, prevention is best and contamination should be avoided at all times during the storage, handling and fabrication stages and of course, during the service life of the steel product itself. 

Common causes of contamination include surface damage, defects, scratches, mechanical damage, accumulation of dust and grime, oil, grease, fingerprints, paint, residual adhesives, grinding dust, weld spatter and embedded or loose iron particles. It’s therefore essential that steel fabricators are fastidious about cleanliness and that they take every step to avoid contamination in their workplace.

If stainless steel surfaces are damaged or contaminated, there are three ways of cleaning these:

Mechanical cleaning

Wire brushes with stainless steel bristles, abrasive discs and flapper wheels can be used to repair minor imperfections as long as they are completely clean and haven’t been used on any other surface. Deeper and more intense mechanical grinding or blasting will be required to get rid of any severe staining and pitting and restore the surface completely.

Chemical and electrochemical cleaning

Contaminated steel surfaces can be cleaned with mild domestic cleaning creams or polishes that contain calcium carbonate or citric acid to remove any mild staining or surface ‘blooms’.   It’s also possible to use acid pickling or electropolishing to remove embedded iron and other contaminants. This can be done with a saturated solution of oxalic acid applied with a soft cloth or cotton wool, phosphoric acid cleaners or dilute nitric-hydrofluoric acid – but it is imperative that these aren’t left on the surface for too long otherwise pitting may occur.

Passivation.

When staining is more severe, the contaminated surfaces can be treated with nitric acid solutions or pastes. This process removes free iron, but not iron-oxide contaminants, and results in the passive chromium-rich oxide film being re-formed on the surface. 
Again, this is a delicate process and due care must be taken.

A reputable steel fabricator will take every precaution to prevent surface contamination in their workshops because mistakes can be difficult and costly to resolve. 

One such company is WA Steel, a Perth-based company specialising in sheet metal fabrication with almost 30 years of industry experience.

A reputable steel fabricator will take every precaution to prevent surface contamination in their workshops because mistakes can be difficult and costly to resolve. 

One such company is WA Steel, a Perth-based company specialising in sheet metal fabrication with almost 30 years of industry experience.

WA Steel
Ph: 08 9377 3778
www.wasteel.com.au

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