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“My stainless steel has gone rusty. It can’t be stainless. What’s gone wrong? Who’s to blame? How can I fix it?”
Although the vast majority of stainless steel applications work perfectly as intended by the designer and fabricator, there are a significant number of instances where someone, often the end-user, is disappointed by the performance of the material. The causes of these disappointments tend to fall into only a few basic categories. In nearly all cases, a little basic knowledge would have prevented or significantly improved the situation.
On the assumption that prevention is better than cure, this short article addresses these issues.
The causes of disappointment can arise at any point in the long supply chain that often applies to a stainless steel project. This helps to explain why problems occur. Getting the appropriate knowledge to all parts of the supply chain is difficult and it only takes ignorance in one small part to create a problem later on. The main issues are:
Briefly, a bright polished surface gives maximum corrosion resistance.
A directional polish equivalent to the EN 10088-2 2K (Ra = 0.5 micron max), usually produced using silicon carbide (SiC) abrasives, will give adequate corrosion resistance in many severe environments notably heavy urban and coastal ones.
A common surface finish achieved with 240 grit alumina abrasives has been implicated in the corrosion of stainless steel in urban and coastal environments. In some cases, surface roughness Ra values have been measured at well above 1 micron which is known to be inadequate in these environments.
The lack of any specified surface finish on architectural drawings can be the source of the final problem.
If, at any stage of the supply chain, there is any doubt about the appropriate surface finish, specialist advice should be sought.
Good fabrication practice always includes post weld treatment. Failure to do so can give rise to unnecessary cost of rectification later on.
Lifting Gear, Ropes, Chains
Wherever possible, stainless steel and carbon steel should be fabricated in separate areas of the workshop or better still in separate workshops. Where not possible it is important to clean down machines used for carbon steel before using them for stainless steel. Stainless steel surfaces should be protected with plastic coatings for as long as possible.
In addition, it must be remembered that what is appropriate for one building material is totally unacceptable for another. For stainless steel it has to remembered that masonry and brick cleaners may contain hydrochloric acid sometimes called muriatic acid. If these fluids are to be used at all near stainless steel, care should be taken to protect the stainless steel surfaces. If splashes occur, they should be immediately washed off with water. Failure to do so will result in serious attack of the stainless steel resulting in expensive rectification costs
If these simple guidelines are followed the number of disappointed users will be reduced