Double containment for piping

[meister]

I have an existing single wall piping system and I would like to convert to double containment for toxic gas service. I am familiar and have installed double walled piping systems, but in this case I would like to keep the existing single walled system due to cost and down production time. The straight pipe is easy enough to add a second clamshell barrier, but how to do this around the flanges and valves while still being able to service these systems when required. Any thoughts???? Thanks!!