Add Corrosion Allowance in Steam Service

Zero corrosion allowance for steam service? When did this design become normal?

Many times I see steam service equipment designed with a 0.25” (6 mm) nominal thickness and zero corrosion allowance. This occurs because steam service is often included in the lowest Risk Category in plants. Low Risk Category equipment will inherently have a zero corrosion allowance requirement. I’ve reviewed enough internal inspection reports for equipment in steam service to conclude that steam can be corrosive, especially in bottom head components.

Not including a corrosion allowance in the original design calculations often leads to dangerously thin components when real-world conditions eat through the zero corrosion assumption. Please reconsider designing with zero corrosion allowance for equipment in steam service.

Unsure about assumptions made in your steam service equipment? Metalmark Engineering can review inspection history, perform in-service thickness readings on your equipment, and provide accurate T-min calculations to ensure your steam service equipment is safe for years to come. 

Thanks to the U.S. Chemical Safety and Hazard Investigation Board for providing pictures of their investigation.