TRV arrangements around meters, control valves and loading arms

[Michael_C]

I'm considering a bulk petrochemical storage facility with road tanker loading facilities. For TRV arrangements, we direct product back through thermal relief bypasses across block valves, with product being directed back to tank. There is a scenario where the product being loaded into road tankers has passed through a meter, a control valve (controlled by the batch controller) and then through the loading arm into road tanker. The meter and control valve are fitted flange-to-flange, and then into the loading arm. My questions:
(1) Is thermal relief required across the control valve and meter arrangement to prevent thermal pressure buildup in the loading arm?
(2) Is it permissible to relieve from downstream to upstream of such a meter - are the legal / compliance restrictions on this?

Your views would be appreciated (please reference codes and standards as far as possible). Thanks all.

 

[LittleInch]

Thermal relief is a relatively small amount but you need to be able to quantify the amount, if any, which returns tot he tank after it has been metered.

An unscrupulous operator could divert lots of product back to the tank. So you might get pulled up if the system is audited by a customer or some third party organisation which "certifies" your system as being secure in terms of metering if you can't show a means of quantifying the thermal release or to notice if e.g. the relief valve starts passing.

Depends on the volume and start / finish temperatures are for the locked in section, but some liquid fuels do expand quite a bit and the ROT is about 3 bar per degree C rise.

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