Instrument Erection Sketches & Erection Items

Hi all,

I am designing Instrument Erection Sketches for all types of Gauges & Transmitters (Some are Chemical Diaphragm Seal Type).

I am designing for 2 projects:
1. Oil & Gas Project (Refinery)
2. Nuclear Power Plant (Outside Cell)

- For oil & gas projects, we largely use pipe fittings. Tube fittings are used only just before the instrument manifolds.

- For Nuclear project, we use only Tube fittings are used.

My Questions are as follows:
1. Are there any standards for these erection sketches?
2. What is the significance of using pipe fittings largely in oil & gas proj
3. What is the significance of using tube fittings largely in nuclear proj

Awaiting your replies, as I may require more clarifications based on your replies for the above.

Many Thx in advance....