Flange over pressure 1

[KevinNZ]

While the piping codes (B31.1, 31.3) allows piping pressure to exceed design pressure for short periods the flange codes do not. Is this correct or does the piping codes allow over pressure for flanges because flanges are part of the piping?

Seems clear in B31.1 that you can not exceed the flange rating.
"..variations in pressure and temperature
inevitably occur, and therefore the piping system,
except as limited by component standards.."
Table 126.1-1 lists flange code B16.5 as a component standard.

B16.5 says "Pressure–temperature ratings are maximum allowable
working gage pressures.."

Interesting flanges and piping are hydrotested at the same (over) pressure.

 

[The Obturator]

In case of Pressure-relief Valve or Rupture Disc, ASME B16.34 2.5.1. (2017) allows 10% overpressure over flange limit for 'limited duration'.

*** Per ISO-4126, the generic term 'Safety Valve' is used regardless of application or design ***

*** 'Pressure-relief Valve' is the equivalent ASME/API term ***

 

[LittleInch]

B31.1 and B 31.3 are different codes and are written differently.

The key difference is that B 31.3 allows for the pressure temperature of the listed component (say flanges to B 16.5) to be exceeded.

Phrase is contained in section 302.2.1 "Where the owner approves, provisions of this code may be used to extend the pressure temperature ratings of a component beyond the ratings contained in the listed standard"

B 31.1 does NOT contain a similar section and As I read it doesn't allow for this and in 102.2.4 states the internal pressure and temperature allowed should include for occasional loads and transients.

Now quite how you get a piping system to exist without flanges or components is beyond me, but maybe if it was all welded pipe.

Hydrotest is always different to working gage pressures...

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