Can anyone please advise if installing a pressure transmitter directly in the roof of a refurbished API 650 tank is permissible? If it is, where can I find some installation details of this arrangement ?
I suggest that you refer to the requirements for mounting the specific piece of equip. I'm sure their website will give diagrams. I would expect that most times the unit would be mounted on a flanged or threaded roof nozzle. API has standard details for roof nozzles also.
You can mount instrumentation in a tank roof in a threaded or flanged nozzle. Normally a pressure transmitter would be located on the shell to measure liquid level, rather than on the roof.