Hi maxx. Sounds like you have an interesting job on your hands! Hopefully you have someone to talk to about these kinds of questions but if not I'll see if I can offer a bit of advise.
In the United States, we would use ASME Piping Code B31.3 for this. In other countries, they have their own codes. The codes have more than just pressure boundary calculations provided. They also provide requirements for the design on everything from flanged joints, mitre bends, constructed T's and similar piping fittings to requirements for inspection, testing, welding and many higher level considerations. The code also provides stress allowable factors for piping depending on material of construction. So rather than say, yes an 8" schedule 10 pipe is good for 8 barg, I'd say take a look at the code that exists in your country and make sure your entire piping system complies with it. It's not simply a matter of selecting a pipe that has sufficient wall thickness for the pressure.