As I mentioned in my first blog post, these blog posts will be short and to the point with the intent of providing useful information to remember without using much of your valuable time. The first corrosion issue we will be discussing is Corrosion Under Insulation (commonly referred to as CUI). So you have a system that has very little corrosion potential and then you get the call that you have a leak- what happened..? Being an external corrosion mechanism, CUI can get you regardless of the any other corrosion issues. CUI is a very damaging corrosion mechanism caused by moisture under insulation or fireproofing.
The following are few important CUI facts that you should understand:
1. Corrosion (pitting & localized loss + cracking in stainless steel) is possible at the following temperatures for carbon and stainless steels:
Carbon and low alloy Steels: 10°F (–12°C) and 350°F (175°C)
Austenitic and duplex Stainless Steels: 140ºF (60°C) and 400ºF (205°C)
2. Corrosion rates increase with increasing metal temperature.
3. Cyclic systems with varying process temperatures or intermittent service can increase corrosion.
4. Insulating materials that hold moisture or wick can increase corrosion.
5. Airborne contaminants can accelerate corrosion.
a. Chlorides from cooling tower drift or marine environments
b. SO2 from nearby stack emissions
c. Salt water environments on Offshore platforms
What should I do/Actions to Consider?
i. Verify that your current CUI program is considering the proper temperature ranges for carbon and stainless steels in your plant.
ii. Do you have any Cyclic Systems in your plant? Verify with your process conditions with your process specialist to insure your covering all operating conditions for your equipment.
iii. Verify that your CUI program is taking into account other factors that cannot be identified from the office. Do you have insulated systems near cooling towers, stacks or vents? Do you have steam tracing leaks? Do you have damaged insulation?
All comments and questions are appreciated!
