I've worked for both GLS firms for many years and have the following comments:
1) Ta plugs are used as repair material for 99% of applications. Occasionally you would have a request for a grounding plug, but typically in the liq. phase as mentioned above. Most likely this plug is related to a...
We manufacture glass lined batch reactors and this the technology we use to charge solids while maintaining a N2 purge of the vessel and eliminating operator exposure to dust/solid & fumes.
http://www.ddpsinc.com/powderpump
To solve the problem of inspection, have you looked at continuous lining monitoring? Both GLS companies you mentioned produce them. They are very "sensitive" (aka. a pain to set up) to process conditions, but it sounds like your process is a settler (my assumption) with very little process...