Reference to your post stefano santoro (Coastal)

API 520 & 521 do provide you the basis for safgurding a pressurised system. Relieving a pipeline of proposed size and wasting so much gas is not a good idea, it costs and much more cost to environment. I have following suggestion to make:

1. Carry out hydraulics and determine pressure drop across the pipeline
2. Create valve assemblies
3. Divide the pipeline in sections with the required pipe rating use higher rating for subsequent sections until a large pressure difference comes.
4. Make positive isolation and rated ESD.
5. Do the above for all sections.
6. You will not need to go to a over-pressure situation at all, thus no relief.
7. Economics dictates the utility of above.

Alternatively.

1. You can have PCVs (Class VI leakage) at appropriate location which will piss when pressure rises before the relief pressure is achieved - meanwhile action may be taken.

Alternatively.

1. Install few loop lines to discharge gas to reduce pressure.