PRESSURE VESSELS & CODES

Hello there guys,

I need you all to help me out, don't hold back pls. Treat my questions for the Rookie that I am.

I was practicing the design of a Slug Catcher in PV-Elite. I tried both ASME 1 and PD 5500.

INPUTS:

Design temp 80 deg C, Design pressure 137 bar, Liquid density 741.4kg/m3, Shell I.D. 3.55m, Shell T/T length 5.25m, Hemispherical head, Orientation Vertical, Corrosion all. 3mm.

RESULTS

A) ASME: Shell thickness 190mm, Weight 297,493.7kg

B) PD 5500: Shell Thickness 130mm, Weight 186,180.8kg

QUESTIONS:

1. Why do I have such wide differnces in my results. (Im aware the two codes employ different materials (hence differences in thickness) and also different factors of safety (correct me if I'm wrong pls.) but when do I decide which codeto use?

2. In real life situations, who decides what code to use for a design? The Principal/client, The Vendor/Manufacturer, The Designer (due to data availed to him by the process condition???

3. Where can I access PD 5500 (I have access to ASME though).

4. What are the indices that determine values for external pressures to when designing vessels. For example I've seen 0.2 bar for diesel storage vessel, -1 bar for Slug catcher, 1 bar for an open-top vessel.

I can't thank you enough for reading through all these. I shall be even more grateful if you respond to SOS.

Cheers,

Jibril