ASME B16.5 Ceiling Pressure 1

[kpl012]

I inherited a system that has class 300 lb. CRES316L pipe flanges. The issue is the steam system design pressure is 420 psi, 470F. I have tried the annex D calc in B16.5 but come up short 401 psi. The calc uses a ceiling pressure also. Can anyone tell me the purpose of the ceiling pressure and is there a way to justify leaving them in place ?

 

[Duwe6]

What part of Class 300 / 300# flange are you having trouble with. If you actually need a Design MAWP of 420 psi of at a MAWT of 470°F, everything you 'touch'* has to be replaced with something [Class 600] that is rated for it. Otherwise, derate that system.

*Touch = disturb. Meaning any repairs or modifications have to include replacing of all the underrated flanges in the scope-of-work, including boundary flanges. You can justify leaving alone the flanges that are currently performing well, if nobody touches them.

Or do nothing, with some back-up documentation. Something that 'works' is to write up your deficient system [assuming a derate is not feasable] as being deficient per Code, but adequate. There isn't any 'magical' difference between 401 psi and 420 psi [4½% low]. This memo needs to be in the form of a Non-Conformance Report - NCR; or Management of Change - MOC. There need to be signatures from Engineering and/or Inspection, the Unit operating these flanges, and from Management. The document needs to give the justification for leaving the underrated flanges in-service; usually includes the phrase "continued Good Service". If Management or Plant decline to sign, start replacing flanges.

 

[kpl012]

Thank you for your reply. Any thoughts on the ceiling pressure for ASME B16.5 ?

 

[Duwe6]

Not a clue - sorry. Guess I haven't bumped into it yet

 

[LittleInch]

From B16.5 section A-3

The rules for establishing pressure–temperature ratings
include consideration of ceiling pressures pc that
effectively set limits on the selected stress. The ceiling
pressure–temperature values set an upper bound for
high-strength materials and are imposed to limit deflection.
Ceiling pressure values are listed in Tables A-1 and
A-2. Ratings in excess of these ceiling values are not
permitted under this Standard.

The ceiling pressure for #300 at your temp is approx. 680 psi so shouldn't be an issue. As noted above this is to limit pressure and avoid "silly" ratings using high strength material.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[kpl012]

ASME B16.5 APP A 2009 and subsequent use a 70% for groups 2 & 3 for selected stress below creep at specified yield at temp. T., which is always the lowest of the 2 other criteria. Is this the sole called safety factor?

 

[kpl012]

What is the difference bewteen coded and non-coded flanges ?

 

[GenB]

Duwe6. NCR to correct a mistrake will be resolved with meeting Code or an acceptable resolution.
KplO12. Check if your material is dual 316/316l and you may be able to use a higher Stress. Or use its higher stress to temp per Sect II.D tables.

 

[kpl012]

SECT II-D of the BPVC has stress tables. Can anyone tell me if there is a safety factor built into the values and if so what it is and which edition I may be able to find it in ?