We love Stainless Steel, and it is in fact growing rapidly throughout the world. Unfortunately, this material gets a bad rap when it comes to the ‘how-to’ for cleaning. It is quite interesting when we walk and check in on site and we notice that the cleaning is done one way on the lifts, the entrance Stainless Steel façade is neglected or tried to be clean another way and the safety bollards out the front still look near new, just with a few scratches and scuff marks on them. Not to mention, we have all seen the sides of the escalators in the shopping centres, oil from the machine pit mixed with Stainless Steel oil is just not a great look.
Fortunately, in this article we are going to talk about the factors that contribute to corrosion, tarnish and rust, specific conditions that accelerate the Stainless-Steel rusting process and understand what can further happen when it is not dealt with correctly and what to do about it. To begin with the end in mind, the answer comes down to the correct maintenance of your Stainless Steel.
Let’s begin to understand what corrosion is.
In simple terms “Corrosion is the tendency of a meta to return back to its mineral sate, the state it was originally in before refinement by man. It is a thermodynamic process that cannot be stopper, only slowed” Stainless Steel Surfaces A Guide to Alloys, Finishes, Fabrication and Maintenance in Architecture and Art By: L. William Zahner
There are also many different types of corrosion as well – rust, tea staining and tarnishing being a by-product. There are:
Uniform corrosion
Galvanic corrosion
Pitting corrosion
Intergranular corrosion
Weld corrosion
Erosion corrosion
Crevice corrosion
Line corrosion
Corrosion fatigue
High temperature corrosion
Stress corrosion cracking
Fretting corrosion
It’s interesting to note the different types of corrosion that can occur that can potentially lead to irreversible damage. The good news is that in commercial areas, there is only a hand full of potential corrosions that can happen and is usually a mix between human and atmospheric conditions. In other words, it is at time due to either chloride ions interacting with the surface, contamination from steel, human interaction, chemical interaction, or a combination of these factors. In which we can drill down and get to the bottom of this.
Let’s now explore some typical common conditions that we encounter frequently.
1- Uniform Corrosion
Tea staining is a form of uniform corrosion. Corrosion that occurs across the face of the surface of stainless steel. It’s a typical brownish colour that sits on the surface and begins to worsen over time when not removed. Tea staining is a result of the stainless-steel surface exposed to chloride salts (salty air) in humid environments.
The main issue typically faced is that it is left on the surface for a while, whilst the surface doesn’t change condition much or may get darker, the salt deposits begin to attack the crevices on the Stainless Steel and will begin to pit, which creates microscopic holes. Which can be isolated or actually tunnel under the surface.
This tea staining can be found on Stainless Steel lift doors, Stainless Steel bollards and hand rails, Stainless Steel pillars and facades, Stainless Steel architectural pieces or artworks and Stainless Steel kitchens after an acid wash on the tiles has been completed.
2- Transfer, Crevice and Line Corrosion
Transfer, crevice and line corrosion on Stainless Steel happens due to interactions with other metals that are corroding and have contact or in close proximity to the Stainless Steel and also rusted Stainless Steel corroding a complete rust-free Stainless Steel. There are multiple factors that this can occur in. in typical commercial area’s that we notice this, is in the following:
Corrosion from fixed bolts and washers
Corrosion from mechanically cut pieces of Stainless Steel with the edges not adequately cleaned.
Corrosion from a rusted steel structure that is in close proximity to other steel, Stainless Steel, and alloys.
The main issue when it comes to transfer corrosion is not typically the Stainless-Steel piece itself, but from an external source that a) has been introduced to it, such as a bolt and washer. Or b) by mechanically creating the environment for corrosion. Such as via laser cutting or welding.
This transfer corrosion can be found on laser cut Stainless Steel, perforated Stainless Steel, external mailboxes, other places that have to be mounted with nuts and bolts, kitchen equipment that has to be welded together and within the fabrication processes.
3- Erosion Corrosion
Erosion corrosion as defined in the Stainless-Steel Surfaces: a guide to alloys, finishes, fabrication and maintenance in architecture and art, Zahner - John Wiley & Sons, Inc. – 2019 as “subject to the conditions that would elicit cavitation”. This elicit cavitation can be caused through scratching the surface with materials stronger that stainless steel or by force or scraping a trolley alongside a lift panel. The issue here is that when the surface of the stainless steel is damaged, it can lead to pitting and rusting as defined in Uniform Corrosion which can lead to erosion corrosion.
But what we have noticed is that now there are different types of stainless-steel finishes being utilised. These finishes can be coloured stainless steel, mirror coloured stainless steel, stainless steel that have PVD coatings etc. when these surfaces are damaged, it is typically not fixable and have to be repaired. So, a caution on where you want to use these types of finishes.
Linear and standard finishes on Stainless Steel that you have seen in lifts, handrails and bollards are repairable, but you will run into the issue of the contractor unable to 100% match the existing finish. This is because not finish is the same, even if it the same batch of Stainless Steel used.
On the other hand, non-directional angel hair, mirror finish and glass beads are simpler to repair compared to linear and standard directional number #4 finishes. This is because the finishes can be simply recreated and not too much concern to match the existing finish, because the whole piece is not uniformly finished.
Where to from here?
Now that we have covered the main stainless steel rusting occurrences in our buildings and assets, now what can we do about them? Some items may be a bit difficult to deal with and others may be a simpler fixed.
Conduct a visual audit on all your stainless steel. You will be on the lookout for dullness, rusting, tea stains and other stains that does not look like pure new finished stainless steel. This can include the use of stainless-steel oil which is a factor in increasing the chances of rust. Some particular areas includes:
Stainless steel Lift doors and lift sills or tracks
The underside of stainless-steel handrails
Stainless steel Bollards
Steel and stainless steel structures typically on roof tops where air conditioning units are
Nuts, bolts and fasteners on steel and stainless-steel structures
Stainless steel and steel boxes
Cooling towers
Drainage systems and down pipes
Stainless steel facades and stainless-steel pillars
Stainless steel signage
Make a note of the asset, it’s damage and local within the building. Collate this information into a table
NOTE: if you have rust on particular structures of your building or that undergo heavy loads contact the maintenance company or a structural engineer for remediation. If not remediated structurally this can become a major issue.
3. Contact a specialist like Steel Renew to assist with the rust issues as a whole for the building for surface remediation and on going maintenance so you no longer have to dealt with corrosion on your assets.