Practical, not Pretty: Corrosion Allowances explained…

When you look at the image of the Kochi boilers what do you see? A far away land? An intense discussion between friends? Or just some rusty, old boilers? Believe it or not, this is what the inside of the majority of in-service air receivers look like… but don’t worry – Abbotts have this covered!

One of many things that we pride ourselves on here at Abbotts is our success with inspectors, and this is partly down to our sensible corrosion allowances.

Why does corrosion allowance matter? Well carbon steel rusts…or to use the scientific terminology, it ‘oxidises’. Despite the name, carbon steel consists primarily of iron. The iron undergoes a redox reaction with oxygen in the air to form iron oxide, a reddish-brown substance more commonly known as rust. Over time this gradual ‘flaking away’, exposing the next layer of iron to oxidation, results in a very gradual thinning (we’re talking years and years) of the metal. For carbon steel pressure vessels, design codes have your back and effectively supplement the minimum calculated material thickness with an allowance for corrosion… hence the term.

When it comes to this allowance, how much is too much? Design codes used in pressure vessel manufacture state a minimum corrosion allowance: each code is different. Some customers want more and add a further safety-margin on top. Some customers want less…if chemical coatings are used to protect the internal surface from oxidation for example: zinc-plating (galvanising) and epoxy-coatings, does this off-set the need for a corrosion allowance…no exposure = no oxidation, right? Now there’s a debate! The truth is, as long as the design code is considered, it is up to you. Some would argue the more steel the better, whereas others would say this produces over-engineered, heavy vessels, with costs driven up unnecessarily.

Regardless, Abbotts will always consider your requirements. We’re not fussy 😊, your vessel WILL be compliant… after all, the customer is always right!

To get in touch, ring us on +44 1636260438 or drop us an email at We’re always happy to talk.

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