There are guides around, maybe best to contact the Notified Body that you will use. Suggest you gain an understanding of the PED - the text, Annexes, Guidelines, etc, can be found online within the following link:
. ASME has a guide for stakeholders detailing the extra considerations to take account of for PED compliance.
Basically you will need to determine the PED Category based on the contents, pressure, and volume, and that will lead into which Conformity Assessment Module(s) to use, and the extent of Notified Body involvement.
You still need to use a vessel code for design, such as ASME VIII (or better still EN 13445 which gives direct conformity to the PED).
