What is the difference between pitting and crevice corrosion?

The main difference between pitting and crevice corrosion is the geometry of the corrosion site. Pitting occurs across the open surface of a component, whereas crevice corrosion is associated with a crevice - one that forms around a fastener, washer or joint, in a sharp corner, or in an area where liquid flow is slowed, such as a dead spot.

The two are linked. If a corrosion pit is allowed to keep corroding, it effectively forms its own crevice, and the rate of corrosion accelerates as conditions within the pit become more aggressive.

How to detect pitting corrosion

Pitting is usually detectable through a thorough visual inspection, with pits able to grow deep enough to perforate a component. It can also initiate cracks in tensile-stressed components. Environments with higher chloride concentrations are prone to pitting, especially at higher temperatures.

When examining components, look for reddish-brown iron oxide deposits and any pits that have formed on the metal surface.

How to detect crevice corrosion

Crevices exist between joints and underneath dirt and deposits that accumulate on surfaces, so these are the areas to inspect.

Frequently asked questions

What is the key difference between pitting and crevice corrosion?

The key difference is geometry. Pitting occurs across an open surface, while crevice corrosion happens in a confined gap - around a fastener, washer or joint, in a sharp corner, or wherever liquid flow is restricted, such as a dead spot in a system.

Can pitting corrosion turn into crevice corrosion?

Yes. If a corrosion pit is allowed to keep growing, it effectively creates its own crevice. Conditions inside the pit then become more aggressive, which accelerates the corrosion rate further - so the two mechanisms are linked rather than entirely separate problems.

How do you detect pitting corrosion during an inspection?

Pitting is usually found through careful visual inspection, looking for reddish-brown iron oxide deposits and visible pits on the metal surface. Pits can grow deep enough to perforate a component or initiate cracking, and are more likely where chloride levels and temperature are higher.

Where should you look for crevice corrosion?

Crevice corrosion forms in confined gaps, so inspection should focus on joints, fastener contact points, and areas underneath dirt or deposits that have built up on a surface - anywhere the working fluid cannot freely reach and refresh the surface.

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