Hello!

I have a question about internal pressure. In Asme B31.8 or another code, internal pressure is design pressure or operating pressure? Also, what should i type to Caesar input for pressure? Maksimum operating pressure, operating pressure or design pressure?

About "another code" I second Mr. Dave Diehl opinion in the last post of
http://forums.coade.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=74610

About B31.8, a good reference may be a conference paper with title
MOP, MAOP, DP and MAWP- UNDERSTANDING THE DIFFERENCES TO AVOID UNNECESSARY COSTS by John Aumuller and Vincent Carucci, just google the title and you may find it. There isn't an ultimate answer to your questions, but at least the article would bring some light in your decisions. You may carefully review B31.8 2018 edn as well.

You (sometimes/often) have multiple tiers of pressure and temperature combinations that a pipe must be designed for.

In terms of pipe spec building in B31.3, "design pressure" and "design temperature" are the coincidental pressure and temperature that results in the largest minimum required thickness.

For example, you could have a design point of 1000 psig at 100 deg F and you can have a design point of 100 psig at 1000 deg F. Depending on the material, one of these will override the other and be "design temperature" and "design pressure" in the eyes of B31.3.

However, that does not mean as stress analysts that we only analyze to the so-called "design pressure" and "design temperature."

The analyst is required to analyze for the worst case stress condition, which means, as far as stress analysis goes, they're all design points. Someone will have to decide which combinations are realistic, and not overly conservative.

The piping code does not make this decision.