What Are the Causes of Intergranular Corrosion?

Steel is more resistant to corrosion than most metals, but under the right circumstances, corrosion can wreak havoc on steel pipes, structures, and more. One common kind of corrosion, intergranular corrosion, eats away at steel from the inside out, making it hard to spot and particularly insidious.

If you’re wondering, “What’s intergranular corrosion?” “What are the causes of intergranular corrosion?” and “How do I prevent it?”, read on—we’ll go over what you need to know about intergranular corrosion below.

What’s Intergranular Corrosion?

Intergranular corrosion, also known as intercrystalline corrosion and interdendritic corrosion, is a form of corrosion that attacks the grain boundaries (instead of the surface) of a material. Intergranular corrosion is difficult to spot—in most cases, you can only obtain a positive identification by doing a microstructure examination under a microscope.

Why Does It Happen?

So, what are the causes of intergranular corrosion? Intergranular corrosion is a result of local differences in composition. Grain boundary depletion, namely chromium carbide precipitation, is a common reason for this difference. When the corrosion-resistant elements in a grain vanish, the area where the element is lost turns into an anode. This causes corrosion and grain loss along the affected grain boundary.

In the case of chromium carbide precipitation, the most common cause of intergranular corrosion, precipitation occurs when you sensitize metal in temperatures between 1020-1560°F during heat treatment or welding.

How Can I Prevent It?

Fortunately, like most kinds of corrosion, intergranular corrosion is preventable. You can prevent intergranular corrosion by:

• Using low carbon grade stainless steels
• Using steel surface treatments (like hot dipping or zinc phosphate priming)
• Using steels alloyed with titanium or niobium

Corrosion can wreak havoc on structures. But you don’t have to let corrosion win. Dreiym Engineering can help you prevent corrosion by designing cathodic protection systems and testing existing systems for cathodic protection interference. Contact us today to learn about our services and how we can help keep corrosion at bay.