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Why Passivating Stainless Steel Bollards & Handrails is Important

Oct 19, 2020 | News

In our efforts to resolve all surface finishing issues for customers, we expanded our range some time ago to include Chemical and Electrolyte Cleaning products for Stainless Steel and they are proving to be very much in demand. However, it is without doubt the expertise that we provide with the products that is earning us new customers, trust and loyalty!

Not so long ago (although it was pre-COVID and so seems like an eternity!), we became aware of an issue that an urban council had with rust on their stainless steel roadside bollards. Interestingly, they were rusting at a different rate in different locations. The manufacturer was being asked to explain this, with the implication that it was somehow a manufacturing flaw.

However, Garry, our Technical Sales Manager, became involved and quickly understood what had happened. Initially, he went to the scene of contention to study it. He studied the location and the activity around the bollards. The bollards were located along a busy street and very close to the side of the road. It transpired that the bollards were most rusted beside a roundabout, a location which not only has a lot of traffic, but traffic which is braking frequently. A local aggregate quarry was also located nearby.

According to NCBI, brake wear can contribute significantly to emissions, which include iron oxides. Stainless steel, by definition, must have a chromium content of 10.5% which in the presence of oxygen reacts and forms a protective passive layer called the chromium oxide layer. This layer is just a few atoms thick and is not visible. This passive layer is self-healing to minor mechanical damage in the presence of oxygen.

The passive layer can experience contamination from environmental influences, such as liquids containing chloride such as sea water & road salts, sulphur dioxide, certain fluids and rust particles. However, when bollards are located at the edge of a busy road, they can also be contaminated from elements such as construction aggregate washings, which can contain iron oxide from aggregate abrasion on the trailer bed of the transporting vehicles. When vehicles brake, the iron oxides from their brake dust travels through the air, or are splashed in wet conditions, onto the stainless steel bollards. Upon contact with air moisture, these microscopically small particles can corrode on the non-rusting surface of the stainless steel. This is referred to as film rust and sometimes, descriptively referred to, as tea bag staining.
If this staining is cleaned within a short space of time, the corrosion resistance of the stainless steel is retained. However, if left untreated for a long period of time, then the iron oxide layer can build up and will form a barrier, preventing the chromium oxygen reaction from maintaining the passive layer. This would allow the stainless to become contaminated, which could then require a costly mechanical treatment to repair.
This location was a perfect storm for extraneous rust to flourish. Once everyone understood what had happened, thanks to Garry, the blame game was stopped in its tracks and we got to work removing the extraneous film rust through a quick chemical process and finally passivating the bollards. Another good day at the office, providing the expertise and products to support our customers!

For more information, please check our website or call us on 049 555 2340
Source https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4315878/

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