Class 150 flange temperature limitations

[TD2K]

I'm currently working on a project with 18" class 150 HVGO suction piping from the vacuum tower to the pumps. Operating temperature can be from 530F up to 600F and class 150 flanges meets the design pressure and temperature requirement. We are reviewing whether class 150 flanges should be used or should be use class 300 flanges?

I'm aware of section 2.4.2 in B16.5 which talks about the tendency for class 150 carbon steel flanges over 400F to relax and develop leaks if exposed to severe thermal cycles and/or external loads and the need to check bolt tightness.

One of our engineers recalls seeing a section (he thought it was in B16.5) recommending/suggesting minimum class 300 flanges be used when operating temperatures were over 400F. While it's similar to section 2.4.2, he thought it specifically suggested class 300 flanges.

Does this ring a bell with anyone? I've gone through B16.5 and B31.3 and can't seem to find such a recommendation.

 

[unclesyd]

I don’t remember ever seeing a recommendation or requirement, code values, other than our internal specifications that calls out Class 300 C/S flanges over Class 150 C/S flanges. I didn't find any reference to my notes from classes on either 31.1, 31.3, 16.5 concerning this recommendation. None of our internal piping specs pushed the limits of a flange.

Our specification crossed over at 300°F mainly due to getting the gasket seating stresses for the higher temperature gaskets required.

We have some areas where the piping specs calls out all Class 300 C/S flanges due to the recognized problems with the 3" and 8" flanges if used with spiral wound gaskets.

S/S was all Class 300 above 150 PSIG and/or 300°F.

 

[1969grad]

You might check the ASME BPV code. Seems to me that they have an appendix on flange bolting.