We have wedgeplug valves in our FCC slurry and bottoms pumparound systems. There are a few valves that are having issues sealing and have had bonnet leaks in the past. We are evaluating repairing or replacing some of these valves.

I would like to focus on the bottoms pumparound system for this question. Our existing valves are wedgeplugs and do not have any means of flush connected (we do have heavy cycle oil flush on the slurry wedgeplugs). What other valves are acceptable in bottoms pumparound service? Would gate valves be acceptable? These valves in question are rarely operated and are only used for isolation purposes. Wedgeplug valves are quite expensive with long lead time. I'm told metal seated ball valves will be similar. Since there is less chance of catalyst carryover in the bottoms pumparound, I'm curious about the criticality of having wedgeplugs in this service. Our valves appear to have ~40 years of service. Additional process conditions are below:

Location: Bottoms PA downstream of steam generators going back to fractionator
Operating conditions: 60 psig @ 510°F
Design conditions: 91 psig @ 725°F

Thanks to you all in advance.