B31.1 allowable miter in steam pipe 1

[billbon]

When building steam piping in accordance with the B31.1 Power Piping Code I would like to know what the allowable miter, if any, could be in the middle of an aprox. 30 ft. run of 12" Sch 40 CS pipe. We have an elevation change that requires a 5 degree offset. The run of pipe would have a 5 degree angle then an aprox. 10 ft. length of pipe, another 5 degree angle then the piping continues on to make the elevation change. Will a single bevel, open root, full penetration welded mitered joint, with a 2.5 degree angle on each pipe be an acceptable and an allowable solution. Or would a 5 degree bend be more acceptable than a miter? If so , why? The opp. pressure is 75 psi. max. The system will have a lower opp. pressure of 35 psi. during the off season. I see there are formulas for design in the code book but I'm not sure how to complete these design calcs. or if they're even necessary. Please advise. Thanks billbon

 

[ytse]

B31.1 does not allow miter in steam pipe.
Para 104.3.3 (A.3)stated that miters may be used only if "The contained fluid is nonflammable, nontoxic, and incompressible, except for gaseous vents to atmosphere"
Since steam is a ompressible fluid, if follows that miter is NOT permitted.

 

[Cuemaster64]

Further question then. Would it be permissable to apply a flange at each end and slightly offset the the flange at the butt weld to achieve the desired offset effectively creating a slope in the line? Just curious.

 

[ytse]

When you offset the flange that the butt weld. That would become a mitered joint.

 

[KevinNZ]

Small mitres can be regarded as butt welds, There is a rule for calculating what angle this applies.

 

[KevinNZ]

Mitres can be used for steam service under 104.3.3 (C).

We apply C.1 based on many years using mitres for steam line up to 60". We have a low number of load cycles.

 

[NEMHolland]

can any one tell me what is the methodology of sellection the design pressure & Temperature for power plant piping (not the boiler piping ). i.e. feed water piping, condensate piping, extraction pipes from the steam turbine and drain pipes .
Regards