Q & A > Question Details

In a CDU/VDU unit a Desalter is provided downstream of the crude charge pump. What should be the design pressure of this vessel?
Should it be crude charge pump-shutoff pressure or should it have a maximum operating pressure of vessel + 2 kg/cm2g, similar to the design pressure of the other pressure vessel?

It may be noted that this vessel is protected with a PSV. The conservative approach is to design this vessel for pump shut-off however this will lead downstream piping and equipment to be higher class which has cost impact.

Please suggest what is the practical approach and why?

21/02/2020 A: Jake Gotham, InSite Technical Services, jake.gotham@insitetechnical.com
The default position should be to design the vessel and pipework for the shut-in head of the pump plus the maximum suction pressure. Depending on your regulatory environment and the design codes that apply in your jurisdiction, you may be able to risk assess an alternative solution.

Before you take credit for the PSV, you should establish whether it is sized for this scenario, and whether the system downstream of the PSV can handle the large volume of liquid that would accumulate.
21/02/2020 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
Cost implications of higher pressure are minimal. You really don’t want to be worrying about the potential for blocked in pressure relief of your crude charge. That also has cost and safety implications too. Design the vessel for blocked in conditions and be done with it.