Tube bending and pressure rating reduction?

[knowlittle]

Question: Does bending reduce pressure rating of 304/316 stainless steel tubing? Is there a way to estimate the extent of pressure rating reduction?
Case: 90 degree bending of 1/4" OD 1/8" ID 0.035" wall thickness, using a hand held bending tool (clamping die dia. 0.9")

Thanks.

 

[moltenmetal]

No. Supported/guided bends done in tubing benders do not reduce the pressure rating of the tubing at all.

 

[racookpe1978]

As long as the tube is not crimped, pinched or kinked.

Workmanship is the key to maintaining roundness and maintaining the tube connections clean, square, and aligned.

 

[moltenmetal]

See the Swagelok Tube Fitter's Manual, p. 3-19. Note that this is for annealed material which is what you're typically bending. I don't know the result for 1/4 hard tubing which is sometimes used in high pressure applications.

 

[knowlittle]

Thank you for the replies. I now have a pretty good idea about bent tube strength. Thanks a lot.

 

[EdStainless]

Even if you were mandrel bending there would not be a reduction in rating, even though there is a reduction in wall thickness. With Stainless Steels they work harden enough that the small amount of thinning is accompanied by enough increase in strength to off set it.

Typically (for systems other than hydraulics with high pressure pulsation) tubing is rated based on some fraction of its burst strength. Usually 1/4 is used.

For high fatigue applications everything gets more complicated.

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P.E. Metallurgy, Plymouth Tube