“My stainless steel went rusty. It can’t be stainless. What’s gone wrong? Who’s to blame? How could i correct it?”
Although most cold roll steel tube work perfectly as intended through the designer and fabricator, there are a significant variety of instances where someone, often the user, is disappointed by the performance from the material. The sources of these disappointments usually get caught in only some basic categories. In virtually all cases, just a little basic knowledge will have prevented or significantly improved the circumstance.
Around the assumption that prevention is superior to cure, this short article addresses these problems.
The cause of disappointment can arise at any point in the long supply chain that usually relates to a stainless steel project. This helps to spell out why problems occur. Receiving the appropriate knowledge for all areas of the availability chain is tough and it takes only ignorance in one small part to produce a problem afterwards. The main issues are:
Incredible importance of surface finish in determining corrosion resistance
Lack of know-how here is actually a major reason for problems. Most specifiers and designers understand the significance of choosing a grade of stainless-steel, by way of example 1.4301 (304) or 1.4401 (316). But surface finish is in least as crucial. The subject is fully explored in The significance of Surface Finish in the appearance of Stainless.
Briefly, a bright polished surface gives maximum corrosion resistance.
A directional polish comparable to the EN 10088-2 2K (Ra = .5 micron max), usually produced using silicon carbide (SiC) abrasives, will provide adequate corrosion resistance in many severe environments notably heavy urban and coastal ones.
A standard surface finish achieved with 240 grit alumina abrasives is implicated in the corrosion of stainless-steel in urban and coastal environments. Sometimes, surface roughness Ra values have already 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 source of the final problem.
If, at any stage of the supply chain, there is any doubt in regards to the appropriate surface finish, specialist advice needs to be sought.
Need for post-fabrication treatments
Aside from some specialised processes, welds in cold formed steel always result in some extent of heat tint. Heat tint is largely an oxidised surface that has a reduced corrosion resistance when compared to parent material. Therefore, the regular practice is to undertake some sort of post weld treatment to boost the corrosion resistance.
Information of these procedures can be found 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 produce unnecessary cost of rectification down the road.
Significance of segregating carbon and stainless
Sometimes “rusting” of stainless turns out to be nothing in the kind. This is the rusting of carbon steel that has contaminated the top of the stainless at some stage in the development process. Possible causes of contamination from carbon steel include:
Lifting Gear, Ropes, Chains
Wherever possible, stainless-steel and carbon steel must be fabricated in separate regions of the workshop or better still in separate workshops. Where extremely hard it is essential to clean down machines useful for carbon steel before using them for stainless. Stainless steel surfaces should be protected with plastic coatings so long as possible.
Importance of site management
It is quite easy for everything to be done well in fabrication, only for the whole project to become spoiled by inappropriate practices on location. The difficulties outlined in 3. apply equally as much for the site installation as elsewhere along the way.
In addition, it must be remembered that exactly what is suitable for one building material is very unacceptable for an additional. For stainless it needs to remembered that masonry and brick cleaners may contain hydrochloric acid sometimes called muriatic acid. If these fluids are to be used in any way near duplex steel tube, care should be come to protect the stainless-steel surfaces. If splashes occur, they must be immediately washed with water. Failure dexopky10 achieve this can lead to serious attack from the stainless leading to expensive rectification costs
Incredible importance 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 has been chosen the results might be severe. Some guidelines on material selection are provided here.