Corrosion protection

Corrosion is rarely a surprise. It is the predictable outcome of a metal, an electrolyte and time — and almost every industrial corrosion failure can be traced back to one of three decisions taken long before the damage appeared: the environment was misjudged, the surface was inadequately prepared, or the coating was asked to do something it was never tested for.

This hub covers what drives corrosion on industrial assets, and what genuinely slows it down.

Corrosion is an electrochemical process, not a material defect

Steel corrodes because it is thermodynamically unstable in the presence of water and oxygen. Left alone, it returns to the oxide it was refined from. Nothing in that process is a manufacturing fault or a quality problem — it is the default state, and protection means interrupting it, not preventing it.

Interrupting it requires breaking one link in the chain: remove the electrolyte, isolate the metal from it, or supply electrons from somewhere else. Barrier coatings do the second. Galvanising and sacrificial anodes do the third. Design that drains rather than traps does the first, and costs nothing at the drawing stage.

What determines how fast it happens

Three factors dominate, and only one of them is usually specified with any care.

Time of wetness. How long liquid water sits against the metal, not how much rain falls. This is why corrosion under insulation is so aggressive, and why a sheltered surface that never dries can corrode faster than an exposed one that dries in an hour.

Contamination. Chlorides and sulphates dissolved in that water raise its conductivity and, on stainless steel, drive a different failure mode altogether. Soluble salts left on a surface before coating are invisible and are the single most common cause of premature blistering.

Temperature. Higher temperature accelerates the reaction — but only while liquid water is present. Above the point where the surface stays dry, corrosion effectively stops, which is why equipment that cycles is worse off than equipment that runs continuously hot.

Specification is where most of the outcome is decided

A coating system is selected against an environment. Get the environment wrong and everything downstream is wrong with it — the system will be under-specified for the service, or over-specified for the budget.

ISO 12944 exists to make that classification explicit rather than intuitive, and it is the starting point for most protective coating specifications. What it does not do is tell you the condition of the substrate, the level of soluble salts, or how long the surface will sit between preparation and first coat. Those belong to the specification too, and they are the items most often left out.

What this hub covers

Corrosivity classification and how to apply it. Corrosion under insulation, where the mechanism is ordinary and the detection is the problem. Galvanic couples in mixed-metal assemblies. Flash rust and the window between blasting and coating. And the point where the honest answer is that a coating is not the right tool.