Assume HDS means High speed diesel?

TO avoid flashing the LPG into an interface tank and having to deal with some violent two phase flow / large volumes of vapour, you will need to send the interface to a pressurized vessel able to handle LPG at your pumping temperature and keep it liquid.

What you do with the interface after that is up to you, but I would slowly lower pressure and let the LPG flash off and then use the LPG gas for something useful then pump the HSD into the HSD tank.

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I've read of companies using pipeline pigs / pig receivers in these operations in order to reduce the volume of contaminated fluid that needs to be handled at the delivery point. There may be information on the net or from your colleagues in other companies which run these multiproduct pipelines on what type of pig to use.

In reality pigs pass fluid at a rate of about 1%. Following a series of tests which showed little to no impact on the interface size of using pigs or spheres many multi product pipeline companies don't use any physical separation but minimise IF by keeping flow and pressure constant and swapping over products faster in the inlet manifold.

That plus the coast of the pigging and the added risk from the operation male it non preferred.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.