“My stainless steel has gone rusty. It can’t be stainless. What’s gone wrong? Who’s to blame? How do i fix it?”
Although most duplex stainless steel pipe work perfectly as intended with the designer and fabricator, there are a significant amount of instances where someone, often the end-user, is disappointed with the performance of your material. The sources of these disappointments tend to fall under only a few basic categories. In nearly all cases, a little basic knowledge would have prevented or significantly improved the problem.
Around the assumption that prevention is preferable to cure, this post addresses these complaints.
What causes disappointment can arise at any point inside the long supply chain that usually is applicable to a steel project. This helps to explain why problems occur. Obtaining the appropriate knowledge for all parts of the supply chain is hard and it only takes ignorance in one small part to generate a problem afterwards. The principle issues are:
Incredible importance of surface finish in determining corrosion resistance
Lack of know-how in this area is a major cause of problems. Most specifiers and designers understand the significance of choosing a grade of stainless steel, as an example 1.4301 (304) or 1.4401 (316). But surface finish are at least as essential. The niche is fully explored in The significance of Surface Finish in the appearance of Steel.
Briefly, a bright polished surface gives maximum corrosion resistance.
A directional polish equivalent to the EN 10088-2 2K (Ra = .5 micron max), usually produced using silicon carbide (SiC) abrasives, will provide adequate corrosion resistance in several severe environments notably heavy urban and coastal ones.
A frequent surface finish achieved with 240 grit alumina abrasives has become 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 proven to be inadequate over these environments.
The absence of any specified surface finish on architectural drawings could possibly be the way to obtain the ultimate problem.
If, at any stage from the supply chain, there exists question regarding the appropriate surface finish, specialist advice needs to be sought.
Need for post-fabrication treatments
In addition to some specialised processes, welds in cold formed steel always cause some extent of warmth tint. Heat tint is actually an oxidised surface that features a reduced corrosion resistance compared to the parent material. Therefore, the normal practice is to carry out some form of post weld treatment to improve the corrosion resistance.
Information on 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 so can give rise to unnecessary cost of rectification afterwards.
Need for segregating carbon and stainless-steel
Sometimes “rusting” of steel happens to be nothing in the kind. This is the rusting of carbon steel which has contaminated the surface of the steel sooner or later in the development process. Possible causes of contamination from carbon steel include:
Lifting Gear, Ropes, Chains
Wherever possible, stainless steel and carbon steel ought to be fabricated in separate areas of the workshop or better still in separate workshops. Where extremely hard it is very important clean down machines utilized for carbon steel before using them for steel. Stainless-steel surfaces ought to be protected with plastic coatings provided that possible.
Importance of site management
It is actually quite entirely possible that everything to become done well in fabrication, only for the project to become spoiled by inappropriate practices on-site. The issues outlined in 3. apply just as much towards the site installation as somewhere else during this process.
Additionally, it needs to be remembered that what exactly is appropriate for one building material is completely unacceptable for the next. For stainless-steel it must remembered that masonry and brick cleaners might have hydrochloric acid sometimes called muriatic acid. If these fluids should be used in any way near 304 duplex pipe, care must be taken to protect the stainless steel surfaces. If splashes occur, they should be immediately washed off with water. Failure dexopky10 do this can lead to serious attack of the stainless resulting in expensive rectification costs
Incredible importance of choosing correct grade to the application
This aspect almost goes without saying. It can be only this far down within the list mainly because it usually is considered. However if the “wrong” grade continues to be chosen the effects may be severe. Some guidelines on material selection receive here.