Strong muscles, weak coating
Would the owner be happy with this? That is the question we ask ourselves about every product we come across. In this series we put the coating of a wide range of products, objects and structures under the microscope. This time: a pull-up bar in Houten.
From a distance: not much wrong
This pull-up bar hangs outdoors in Houten, in a C3 environment, and has done so for about two years now. From a distance it still looks fine. Slightly discoloured and a few cracks in the rubber, but otherwise it all seems not too bad.
On closer inspection: rust and discolouration
Up close, it turns out there is quite a lot going on. We found three defects. What do you think the cause is?
1. Discolouration of the coating (defect)
Observation: the black coating has turned grey and matt, especially on the side facing the sun.
Consequence: the discolouration has no functional consequences, but it is certainly not attractive.
The question: why is the discolouration already so extreme after two years?
Cause: discolouration is almost always caused by UV radiation. Many polyester powder coatings are highly resistant to sunlight, whereas epoxies are not.
That is why epoxies are mostly used for indoor applications, or outdoors as a primer. After all, epoxies offer very good corrosion protection. When they are used outdoors, they are always given a polyester topcoat. That way you get the corrosion protection of the epoxy and the UV resistance of the polyester. In this case, that was probably not done.
2. Completely rusted bolts and nuts (defect)
Observation: some bolts are almost completely affected by red rust. In a few places white rust can (still) be seen. Some other bolts are not affected at all.
Consequence: the rusted bolts are not a pretty sight. At first glance, however, the strength of the mounting is not yet at risk. That could well be the case within one or two years.
The question: why are some bolts rusting so quickly, while others are not?
Cause: two types of bolts were used: stainless steel (see the A2 marking) and galvanised. The galvanised bolts are probably of a quality intended for indoor use (electroplated).
3. Rust on the pull-up bar itself (defect)
Observation: red rust can be seen mainly on the welds and on some edges.
Consequence: the rust is not attractive, but will not cause any functional problems for the time being.
The question: why is there already such severe corrosion after only two years?
Cause: the welds were not fully covered by the coating. This is because they contain small holes that powder coating has difficulty getting into (Faraday cage effect). In addition, only one coat was applied. As a result, uncovered spots are not covered after all by a second coat.
The rust next to the bolt was probably caused by damage that occurred while the bolts were being tightened: the spanner hit the edge, locally damaging the powder coating. From this damage, the corrosion crept under the coating and pushed it off.
So whose fault is this?
The user decided to hang a product made for indoor use outdoors. The coating cannot withstand this. The UV radiation and moisture it is exposed to outdoors cause premature degradation.
The quality of a coating is matched to the application. The supplier cannot be blamed for the pull-up bar rusting outdoors. That is not what it was designed for.
How could this have been prevented?
This could only have been prevented if the user had read the manual. It states that the product may only be used in dry rooms.
- Use does not match the intended application. The product was made for indoor use. The pretreatment, the number of coats and the type of coating are matched to that.
- Making it suitable for outdoor use. If the supplier also wants to sell the product for outdoor use, improvements will be needed in the finishing of welds and edges, the pretreatment and the quality of the powder.
- Verifying the quality. To check whether the product then actually meets expectations, salt spray tests and accelerated weathering tests matched to the required service life can provide certainty.
- Recording it in a specification. If the surface treatment and/or the production of the parts are bought in, the requirements for these tests should be clearly set out in a paint specification that is shared with the supplier.
That is how you avoid discussions about quality and cost afterwards.
The art of specifying
What does your purchasing specification say about the coating? Coatings largely determine the service life of a product. Is that as clear to your supplier as it is to you?
We help companies to clarify these expectations, record them professionally and verify that they are met.
