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

The Flanges calculator provides four alternative basic design options; ‘Lapped’, ‘Slip-On’, Socket & ‘Weld-Neck’, the principal dimensions for each are provided in the associated diagram. All of the minor dimensions are as provided in the ASME code and described in the ‘Help>Context’ menu.
By altering the dimensions of the Weld-Neck option, for example, you can create any one of the other three designs. However, it is simpler just to:
1) Select a design nearest to your own (from the options list)
2) Select a [bore] size nearest to your own (from the list)
3) Alter the flange dimensions and material allowable stresses to achieve your desired result.

First of all, I am afraid that we (at CalQlata) are not permitted to return the purchase price of a calculator once the security key has been issued. This is a rule imposed upon us by our contributors.
However, Flanges has been designed to do exactly what you are asking of it.

Despite being able to select standard flange sizes and designs (that provide you with all the appropriate dimensions), you can change any input value you wish for any flange design-type and you will get the results for your modified design.
Moreover, The input and output data for all dimensions are provided using ASME VIII’s symbols to give you the opportunity to verify your data with ASME’s

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.