“My stainless went rusty. It can’t be stainless. What’s gone wrong? Who’s to blame? How can I repair it?”
Although the majority of cold roll steel tube work perfectly as intended by the designer and fabricator, you will find a significant amount of instances where someone, frequently the end-user, is disappointed with the performance in the material. What causes these disappointments often get caught in only a few basic categories. In virtually all cases, a little basic knowledge would have prevented or significantly improved the circumstance.
About the assumption that prevention surpasses cure, this post addresses these complaints.
The causes of disappointment can arise at any time from the long supply chain that often relates to a stainless steel project. This assists to describe why problems occur. Getting the appropriate knowledge to all parts of the availability chain is difficult and it takes only ignorance in a single small part to generate a problem at a later time. The primary issues are:
Significance of surface finish in determining corrosion resistance
Lack of knowledge here is really a major cause of problems. Most specifiers and designers understand the importance of choosing a grade of stainless-steel, as an example 1.4301 (304) or 1.4401 (316). But surface finish reaches least as vital. The topic is fully explored in The significance of Surface Finish in the appearance of Stainless-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 offer adequate corrosion resistance in several severe environments notably heavy urban and coastal ones.
A typical surface finish achieved with 240 grit alumina abrasives is implicated within the corrosion of stainless-steel in urban and coastal environments. Occasionally, surface roughness Ra values have already been measured at well above 1 micron which is known as inadequate in these environments.
The possible lack of any specified surface finish on architectural drawings could be the source of the very last problem.
If, at any stage of your supply chain, there is certainly question regarding the appropriate surface finish, specialist advice should be sought.
Importance of post-fabrication treatments
Besides some specialised processes, welds in steel section always bring about some extent of heat tint. Heat tint is largely an oxidised surface which has a reduced corrosion resistance when compared to the parent material. Therefore, the regular practice is to handle some form of post weld treatment to enhance the corrosion resistance.
Information on these procedures is 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 accomplish this can lead to unnecessary price of rectification later on.
Need for segregating carbon and stainless
Sometimes “rusting” of stainless steel ends up being nothing in the kind. This is the rusting of carbon steel which contains contaminated the surface of the stainless steel sooner or later in the production process. Possible resources for contamination from carbon steel include:
Lifting Gear, Ropes, Chains
Whenever you can, stainless-steel and carbon steel ought to be fabricated in separate regions of the workshop or better still in separate workshops. Where unachievable it is essential to clean down machines used for carbon steel before utilizing them for stainless. Steel surfaces ought to be protected with plastic coatings for as long as possible.
Need for site management
It really is quite entirely possible that everything to be done well in fabrication, only for the project being spoiled by inappropriate practices at your location. The issues outlined in 3. apply equally as much towards the site installation as any place else along the way.
Additionally, it must be remembered that precisely what is ideal for one building material is completely unacceptable for an additional. For stainless it requires to remembered that masonry and brick cleaners might have hydrochloric acid sometimes called muriatic acid. If these fluids need to be used by any means near duplex stainless steel tube, care needs to be taken to protect the steel surfaces. If splashes occur, they will be immediately washed with water. Failure dexopky10 do it can lead to serious attack of your stainless-steel contributing to expensive rectification costs
Need for choosing correct grade for your application
This aspect almost goes without saying. It is actually only this far down inside 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.