Crevice corrosion is a localised form of corrosion that characteristically occurs in regions of confinement where a solution stagnates and chloride ions can build-up due to poor fluid flow. Crevice corrosion is a particularly important form of corrosion due to the difficulty in its detection and its ability to cause rapid loss of structural integrity, even in materials that are otherwise corrosion resistant [1]. The severity of crevice corrosion is extremely dependent on the crevice geometry; the tighter and deeper the crevice, the more severe the corrosion. Particularly vulnerable areas for attack include:

• Washers
• Gaskets
• Insulation
• Threads
• Lap joints
• Dis-bonded coatings/paint

The susceptibility of a material or component to crevice corrosion can be determined under laboratory conditions. At the Materials & Engineering Research Institute, recent developments in additive layer manufacturing (3D printing) have been exploited to provide rapid development of multiple crevice assemblies that can then be utilised in corrosion testing as described in ASTM G78 and ASTM G43.

The number of crevice sites can be used to determine the resistance of a material to the initiation of localised corrosion, whilst the depth of attack can be related to the rate of crevice propagation [2].

Figure 1 - Infinite Focus Microscopy of 420 Stainless Steel following 30 day exposure in 3.5% NaCl at room temperature.

Figure 2 - Infinite Focus Microscopy of 304 Stainless Steel following 30 day exposure in 3.5% NaCl at room temperature.

Figure 3 - Infinite Focus Microscopy of 316 Stainless Steel following 30 day exposure in 3.5% NaCl at room temperature.

[1] Kennell, G. F., Evitts, R. W., & L., H. K. (2008). A critical crevice solution and IR drop crevice corrosion model. Corrosion Science(50), 1716-1725.

[2] NACE International. (2018, March). Crevice Corrosion. Retrieved March 9, 2018, from NACE International: https://www.nace.org/Corrosion-Central/Corrosion-101/Crevice-Corrosion/