stress concentrations in machined piping reducer

[BSukolsky]

Hello, I am considering a pipe reducer machined from billet where the ID remains constant but the OD is reduced. I would like to calculate relative stress concentrations of different fillet/radii in this corner stemming from internal fluid pressure.

I am having a hard time finding the right formula, a point in the right direction would be appreciated.

 

[KevinNZ]

Are you designing to piping or pressure vessel code? Which one?

 

[SnTMan]

Constant ID. Odd reducer.

I'd look at standard charts of stress concentrations from engineering handbooks, etc. Maybe try Google...

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[LittleInch]

How big a reduction in OD are we talking about??

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[r6155]

See Roark´s stress and strain.

Regards

 

[BSukolsky]

Not designing per any code.

Material is plastic in sizes from ~4" through 36" nominal diameter. OD reduction is from DI-OD to IPS-OD (25.8" vs. 24.0" OD for example).

The closest charts I have found are round shafts with shoulder fillets but 1)these charts are for solid rod and not tubular piping and 2)stresses shown are axial or torsional, not stemming from internal pressurization.

 

[SnTMan]

Here

And here

Might be useful

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[mskds545]

BSukolsky,

If you only have internal pressure, it is relatively straightforward to calculate the free displacements of the ends of the two cylinders (that is, the displacement the joined ends would experience if they didn't restrain one another). Then determine the radial force and moment required to maintain compatibility, and add in the moment you get from centerline misalignment. F/A+M/Z will get you the membrane and bending stress. Roark's covers this geometry with the midwalls aligned in Table 13.4. You could use that and just add in the centerline misalignment. Roark's might cover centerline misalignment somewhere, but you can also use PD5500 equation C.18. You can probably find a suitable stress concentration factor for the fillet in Peterson's. Peterson's Chart 3.6 covers your situation exactly, but for a pretty limited set of thickness ratios. You could probably use that as a check on your calculation method.

-mskds545

 

[BSukolsky]

mskds545 this is perfect, thank you.

 

Never leave a machined geometric stress raiser 'sharp'; blend grinding it to smooth out the transition will give a significant reduction in SCF.

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