Did you know boiler corrosion causes half of all forced outages and almost all tube failures of boilers, making it crucial to prevent? Any facility that uses steam boilers can suffer disruptions from corrosion damage. So how to prevent boiler corrosion?

In a steam boiler system, the primary routes for corrosion are due to the presence of oxygen in the feed, boiler, and condensate waters, with the risk of acidic type corrosion due to reduced pH in the condensate water. These types of corrosion are localized and aggressive and can quickly degrade metal pipework and lead to failure. Preventative maintenance really is the best way to counter this.

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The Science of Corrosion

Iron + Water=Ferrous Hydroxide + Hydrogen

It’s basic chemistry, but if dissolved oxygen is present, it combines with the ferrous hydroxide to form an insoluble compound, ferric hydroxide, which is rust.

There Are Different Types of Corrosion

Caustic Corrosion

This is where a concentrated caustic substance dissolves the boiler’s protective magnetite layer, commonly caused by the boiler water pH being too high, steam blanketing (poor circulation), or local ‘film boiling.’ Incidentally, checking boiler water pH should be a part of your logbook and maintenance for the boiler.

Acidic Corrosion

This results from the mishandling of chemicals during acid cleaning or the boiler pH being run too low.

Pitting Corrosion

One of the most destructive types of boiler corrosion, as it can be hard to predict before a leak forms. Pitting is a localized form of corrosion. Oxygen in the feedwater is a common cause of boiler tube pitting. If your boiler is pitting, you should investigate the proper operation of your deaerator or feedwater tank and chemical treatment. If you have a hot water system, oxygen pitting can occur if the system has a leak and brings in fresh water.

Crevice Corrosion

This is a localized form of corrosion, usually resulting from a crack in the boiler that does not get good circulation to wash away caustic corrosion.

Galvanic Corrosion

This is the degradation of one metal near a joint. It usually occurs when two electrochemically dissimilar metals are in electrical contact in an electrolytic environment.

Looking at the Effects to Prevent Boiler Corrosion

These include:

Lost efficiency
A shorter system life span
Higher costs – Corrosion can lead to increased repair costs from needing to replace damaged parts. In many cases, pitted tubes or other components require replacing instead of repairs.
Pitting or even holes – The pits will not repair themselves or change in their severity. Instead, they worsen as the chemical reaction that caused them to erode continues until the metal has a breach or failure.

How to Treat Corrosion

So you’ve discovered you have corrosion, now what? The optimum treatment program should incorporate a chemical oxygen scavenger to remove the oxygen with the ability to form a passive magnetite layer on internal metal surfaces, which in turn provides enhanced protection against corrosion. A volatile amine treatment should also be selected, which carries over with the steam and breaks down the condensate system, essentially by raising the pH of the condensate water. Scale and Alkalinity control treatments are also used to maintain clean heat transfer surfaces, prevent boiler corrosion, and help with corrosion protection.