For pump nozzle protection, you have 2 goals:
1) To prevent over-distortion of the casing
2) To protect the impeller and rod

Ideally, your pump manufacturer selection will include verbiage to enhance the nozzle loads for your pump.

With that said, you should have an earnest discussion with the end user / operator to explain that if the pump lines are to be evacuated, the springs should locked after cool-down, if the pump can't handle the cold spring, or if you don't check to see if it can. That's not our call.

Two notes of caution:

1. With such a heavy liquid that you calculate dynamic effects at bends. Normally we ignore these because we're flowing too slowly with too light a liquid to account for the extra 0.1% of load this will cause. I don't know this for your application, and you shouldn't assume, either, and it sounds like this additional load can be the final straw.

2. Normally pump manufacturers should use the hydrotest case to validate their pin. You should consider using the greater of WW+HP and W+PX+TX where PX and TX is the greatest pressure/temperature they will choose to release the pins.

If they don't tell you, then you should provide the numbers you choose and insist they get put onto the P&IDs.