“My stainless steel has gone rusty. It can’t be stainless. What’s gone wrong? Who’s to blame? How can I correct it?”
Although nearly all cold formed steel section work perfectly as intended from the designer and fabricator, you can find a significant number of instances where someone, usually the end-user, is disappointed through the performance from the material. The cause of these disappointments have a tendency to belong to only a few basic categories. In virtually all cases, a little bit basic knowledge could have prevented or significantly improved the circumstance.
About the assumption that prevention is better than cure, this information addresses these problems.
The sources of disappointment can arise at any point from the long supply chain that often is applicable to a stainless steel project. This helps to explain why problems occur. Getting the appropriate knowledge to any or all areas of the availability chain is hard and it takes only ignorance in a small part to generate a problem at a later time. The key issues are:
Importance of surface finish in determining corrosion resistance
Lack of know-how in this region can be a major cause of problems. Most specifiers and designers understand the necessity of deciding on a grade of stainless, for instance 1.4301 (304) or 1.4401 (316). But surface finish reaches least as crucial. The niche is fully explored in The necessity of Surface Finish in the appearance of Steel.
Briefly, a bright polished surface gives maximum corrosion resistance.
A directional polish similar to the EN 10088-2 2K (Ra = .5 micron max), usually produced using silicon carbide (SiC) abrasives, will offer adequate corrosion resistance in numerous severe environments notably heavy urban and coastal ones.
A frequent surface finish achieved with 240 grit alumina abrasives is implicated from the corrosion of stainless steel in urban and coastal environments. In some instances, surface roughness Ra values have been measured at well above 1 micron which is known as inadequate over these environments.
The possible lack of any specified surface finish on architectural drawings is most likely the method to obtain the ultimate problem.
If, at any stage in the supply chain, there is question about the appropriate surface finish, specialist advice must be sought.
Need for post-fabrication treatments
In addition to some specialised processes, welds in special steel section always lead to some degree of heat tint. Heat tint is largely an oxidised surface that features a reduced corrosion resistance in comparison to the parent material. Therefore, the conventional practice is to carry out some sort of post weld treatment to boost the corrosion resistance.
Information of these procedures can be obtained at:
Post Weld Cleaning and Finishing of Stainless Steels
Welding and Post Fabrication Cleaning for Construction and Architectural Applications
Good fabrication practice always includes post weld treatment. Failure to do this can lead to unnecessary price of rectification down the road.
Incredible importance of segregating carbon and stainless-steel
Sometimes “rusting” of stainless ends up being nothing of the kind. This is the rusting of carbon steel which contains contaminated the top of the stainless steel in the course of the production process. Possible sources of contamination from carbon steel include:
Lifting Gear, Ropes, Chains
Whenever you can, stainless steel and carbon steel must be fabricated in separate regions of the workshop or better still in separate workshops. Where not possible it is essential to clean down machines employed for carbon steel before using them for stainless steel. Stainless surfaces must be protected with plastic coatings as long as possible.
Significance of site management
It really is quite possible for everything to be done well in fabrication, only for the entire project to get spoiled by inappropriate practices on site. The difficulties outlined in 3. apply just as much to the site installation as anywhere else during this process.
Moreover, it must be remembered that precisely what is ideal for one building material is entirely unacceptable for one more. For stainless it must remembered that masonry and brick cleaners might have hydrochloric acid sometimes called muriatic acid. If these fluids are to be used by any means near 304 duplex pipe, care must be come to protect the stainless surfaces. If splashes occur, they will be immediately washed with water. Failure dexopky10 do this can result in serious attack from the steel resulting in expensive rectification costs
Significance of choosing correct grade to the application
This aspect almost goes without saying. It is actually only this far down in the list because it usually is considered. However, if the “wrong” grade continues to be chosen the consequences might be severe. Some guidelines on material selection are given here.