Be Careful with RT-4 Vessels in Corrosive Service

I think it’s time we talk about “RT 4” vessels and heat exchangers. I see them everywhere in corrosive processes and highly consequential service and I really wish I didn’t. 

So what is “RT 4”?  Well “RT 4” simply means that “RT 1”, “RT 2”, or “RT 3” do not apply. It does not mean anything else specifically about what kind of weld inspection was applied to the vessel. 

How much radiography or other weld inspection is applied to a vessel marked “RT 4”? Some? None? I don’t know, but probably not a lot. I personally assume that no weld inspection was performed unless proven otherwise. This is where I have a problem with “RT 4” vessels and exchangers. I don’t feel comfortable placing vessels and heat exchangers in service without having some sort of assurance regarding the quality of the welds.   When I uncover the root cause of unplanned shutdowns too many times these “RT 4” vessels are to blame.

I consider the cost of maintenance and inspection in my designs and I do not believe any money is saved in the long run by operating “RT 4” vessels.