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“My stainless has gone rusty. It can’t be stainless. What’s gone wrong? Who’s to blame? How can I repair it?”
Although most duplex stainless steel pipe work perfectly as intended with the designer and fabricator, you will find a significant number of instances where someone, most of the user, is disappointed by the performance of your material. The sources of these disappointments tend to fall into only some basic categories. In virtually all cases, a bit basic knowledge would have prevented or significantly improved the problem.
Around the assumption that prevention surpasses cure, this information addresses these issues.
The sources of disappointment can arise at any time from the long supply chain that often relates to a stainless steel project. This helps to describe why problems occur. Getting the appropriate knowledge to any or all areas of the supply chain is difficult and it takes only ignorance in one small part to generate a problem down the road. The main issues are:
Incredible importance of surface finish in determining corrosion resistance
Lack of awareness in this region is a major source of problems. Most specifiers and designers understand the necessity of choosing a grade of stainless steel, for example 1.4301 (304) or 1.4401 (316). But surface finish are at least as important. The topic is fully explored in The necessity of Surface Finish in the appearance of Stainless-steel.
Briefly, a bright polished surface gives maximum corrosion resistance.
A directional polish equal to the EN 10088-2 2K (Ra = .5 micron max), usually produced using silicon carbide (SiC) abrasives, will offer adequate corrosion resistance in many severe environments notably heavy urban and coastal ones.
A standard surface finish achieved with 240 grit alumina abrasives has been implicated inside the corrosion of steel in urban and coastal environments. In some instances, surface roughness Ra values are already measured at well above 1 micron which is known as inadequate within these environments.
Lacking any specified surface finish on architectural drawings can be the way to obtain the last problem.
If, at any stage of the supply chain, there exists question regarding the appropriate surface finish, specialist advice ought to be sought.
Need for post-fabrication treatments
Besides some specialised processes, welds in steel section always cause some extent of warmth tint. Heat tint is basically an oxidised surface which has a reduced corrosion resistance compared to the parent material. Therefore, the normal practice is to execute some kind of post weld treatment to further improve the corrosion resistance.
Information on 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 cost of rectification afterwards.
Importance of segregating carbon and stainless steel
Sometimes “rusting” of stainless-steel ends up being nothing of your kind. This is the rusting of carbon steel that has contaminated the surface of the stainless in the course of the development process. Possible causes of contamination from carbon steel include:
Lifting Gear, Ropes, Chains
Wherever possible, stainless and carbon steel must be fabricated in separate areas of the workshop or better still in separate workshops. Where unachievable it is essential to clean down machines employed for carbon steel before making use of them for stainless. Stainless-steel surfaces should be protected with plastic coatings as long as possible.
Incredible importance of site management
It can be quite entirely possible that everything to get done well in fabrication, only for the project to become spoiled by inappropriate practices at your location. The difficulties outlined in 3. apply equally as much towards the site installation as somewhere else in the process.
Moreover, it needs to be remembered that exactly what is right for one building material is entirely unacceptable for another. For steel it needs to remembered that masonry and brick cleaners might have hydrochloric acid sometimes called muriatic acid. If these fluids need to be used in any way near duplex stainless steel tube, care ought to be come to protect the stainless steel surfaces. If splashes occur, they should be immediately washed off with water. Failure dexopky10 achieve this can lead to serious attack in the stainless-steel resulting in expensive rectification costs
Need for choosing correct grade for the application
This aspect almost goes without saying. It is only this far down from the list mainly because it usually is considered. However if the “wrong” grade has become chosen the consequences may be severe. Some guidelines on material selection receive here.