“My stainless-steel has gone rusty. It can’t be stainless. What’s gone wrong? Who’s to blame? How could i repair it?”
Although nearly all cold roll steel tube work perfectly as intended from the designer and fabricator, you will find a significant number of instances where someone, often the user, is disappointed through the performance from the material. The causes of these disappointments tend to get caught in only some basic categories. In the majority of cases, a little basic knowledge could have prevented or significantly improved the problem.
About the assumption that prevention surpasses cure, this post addresses these issues.
What causes disappointment can arise at any time within the long supply chain that often applies to a steel project. This can help to describe why problems occur. Obtaining the appropriate knowledge for all areas of the availability chain is actually difficult and it takes only ignorance in a small part to create a problem at a later time. The primary issues are:
Significance of surface finish in determining corrosion resistance
Lack of knowledge in this field is really a major reason behind problems. Most specifiers and designers understand the value of choosing a grade of stainless steel, by way of example 1.4301 (304) or 1.4401 (316). But surface finish reaches least as important. The niche is fully explored in The significance of Surface Finish in the style of Stainless.
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 several severe environments notably heavy urban and coastal ones.
A frequent surface finish achieved with 240 grit alumina abrasives has been implicated in the corrosion of stainless steel in urban and coastal environments. Occasionally, surface roughness Ra values happen to be measured at well above 1 micron which is known as inadequate over these environments.
Lacking any specified surface finish on architectural drawings is most likely the method to obtain the ultimate problem.
If, at any stage from the supply chain, there exists question in regards to the appropriate surface finish, specialist advice needs to be sought.
Importance of post-fabrication treatments
Besides some specialised processes, welds in steel section always result in some degree of heat tint. Heat tint is actually an oxidised surface that features a reduced corrosion resistance in comparison to the parent material. Therefore, the normal practice is to execute some kind of post weld treatment to improve the corrosion resistance.
Information on these procedures are available 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 achieve this can lead to unnecessary expense of rectification later on.
Need for segregating carbon and stainless-steel
Sometimes “rusting” of steel turns out to be nothing of your kind. This is basically the rusting of carbon steel which has contaminated the top of the stainless-steel sooner or later in the production 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 even better 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 must be protected with plastic coatings for as long as possible.
Incredible importance of site management
It is quite possible for everything to get done well in fabrication, only for the project to be spoiled by inappropriate practices on site. The difficulties outlined in 3. apply just as much towards the site installation as any place else at the same time.
Additionally, it should be remembered that what exactly is appropriate for one building material is entirely unacceptable for the next. For stainless-steel it requires to remembered that masonry and brick cleaners could have hydrochloric acid sometimes called muriatic acid. If these fluids need to be used in any way near 304 duplex pipe, care needs to be taken up protect the stainless surfaces. If splashes occur, they will be immediately washed off with water. Failure dexopky10 do it will lead to serious attack of the stainless causing expensive rectification costs
Importance of choosing correct grade for the application
This aspect almost goes without saying. It really is only this far down within the list because it usually is considered. However, if the “wrong” grade continues to be chosen the effects could be severe. Some guidelines on material selection are provided here.