Problem No. 17: Loose liner or overlay welding?

In urea plants, high pressure equipment typically has a carbon steel pressure-bearing wall, which is protected against carbamate corrosion by means of a protective layer, typically made from 311L UG or 25-22-2 stainless steel.

Typically a loose liner or overlay welding is selected to provide this protective layer. But what is the best choice, what are the advantages and disadvantages of loose liners and overlay welding and what are the actual experiences in the field? An important difference between the two options is that an overlay welding leads to a leak before break scenario, while a loose liner leads to a break before leak scenario. Loose liners therefore require a proper leak detection system.