Dissimilar Metal Corrosion – what’s the impact?

by Owe Forsberg, Vice President IDCON, Inc. – helping mills to become world class maintenance organizations.

Here’s a real-life root cause analysis (RCA) for you to think about.

A trailer was repaired after the side was scraped. The bolts that held the cross members to the aluminum frame on the side were replaced.  The trailer passed the DOT inspection. One day it was loaded with 22 tons of materials from the external warehouse to the plant to be processed, packed, and shipped as final product to the customer. At the entrance of the plant there was a slight dip, when the trailer hit the dip – it folded.

What caused this trailer to fold?

A Root Cause Problem Elimination (RCPE) of the failure was initiated. The conclusion was that dissimilar metal corrosion (galvanic corrosion) occurred between the aluminum frame and the carbon steel cross members. The root cause was due to lack of isolators for the bolts, preventing the bolt to become a conductor between the aluminum and the carbon steel.  Looking at noble chart for metals you will find that the aluminum will be the sacrificial anode vs. the carbon steel. Also, the salt on winter roads may have accelerated the corrosion rate of the aluminum frame.

The root cause can be extended to the lack of work process using the correct repair procedure, lack of training, and access to the correct technical information.