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Q&A forum: Flanges Calculator
(pipeline and piping)

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I have just downloaded the flange calculator.
For some reason the long and radial flange stresses keep being calculated as zero.
I would not expect this and can not see and error.
why is this?

CalQlata Note: The above query was concerning a Slip-On Flange

There is no such thing as zero stress in any material at any time. Simply supporting or handling a material will induce stresses and all materials contain residual stresses from their manufacturing process. Therefore, SH, SR and ST can never be zero (theoretically).
However, design codes, standards and specifications are written for commercial industries to ensure safety factors are sufficient but also practical.
CalQlata's Flanges calculator is based upon ASME VIII, the world's foremost design code for pipeline and piping flanges, which applies its safety factors to the material from which the flange or pressure vessel is manufactured and its welding procedures (ASME IX), it does not apply safety factors to its calculations.

Therefore, the calculations in ASME VIII are simple but accurate for the loads considered (internal pressure and bolting tension) and does not complicate matters by combining the dominant primary stresses; tangential (ST), hub (SH) and radial (SR) because they are not coincident. It also assumes that the clearances and tolerances applied to the manufacture of loose flanges are such that no locking or interference occurs at design temperature between the pipe and flange. Each of these stresses is treated as a Principle stress and therefore considered to be a design condition in the flange at each relevant location.

Slip-On flanges have no hub so SH is set to zero. This is not strictly true as the fillet weld at the back of the flange is effectively a hub in which stresses would be induced during bolting. But the moments in the fillet weld are so much smaller than would occur in a normal hub that its stresses are not considered to be a design factor.
The internal pressure in a Slip-On flange applies only to the pipe not the ring, so SR is set to zero. This is not strictly true as the pipe and ring are welded together, but the radial stresses from internal pressure at the welds will be significantly less than the pipe so this stress can be ignored.
Tangential stresses are the highest in a Slip-On flange by a significant margin, this therefore becomes the design condition.

ASME VIII therefore takes the commercial view that if the ring of a Slip-On flange is capable of supporting the tangential stresses from bolting (almost always the highest stresses), hub and radial stresses can be ignored.
I must say I agree with them, especially given the fact that their material safety factors are reasonable.

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