Does Burst Pressure = 4 X Working Pressure? 2

[tmech77]

I have a stainless steel compression fitting that has a working pressure of 6000 psig. The manufacturer' rep does not know what the relationship is between working pressure and burst pressure. I do not have time for him to research it. Does anyone know what the burst pressure would be? I heard from someone that it is either 3.75 or 4.00 times the working pressure. I would like to know what the real value is and where the information can be found. I have to document it for our customer. Thanks for your help.

 

[desertfox]

Hi

I can't find much on the way of compression fittings although the relationship between burst and working pressure depends on the safety factor for the product, the link below shows burst to working pressure as 6:1 for tube.
Fitting appear to be rated for the maximum allowable working pressure of the tube but I cannot find the safety factor.

https://www.hydraulic-supply.com/pdf/HSCCatalog/TubingPipe.pdf

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[tmech77]

DesertFox I looked thru the attachment you sent and it looks like the fittings are using a 4x safety factor. Thanks for all the info.

 

[tbuelna]

What does your customer's PO or design spec require? Obviously the burst pressure should be well above the working pressure, but by what factor is between you and your customer. Fluid systems are often required to demonstrate a proof pressure capability by test that is some factor (1.5 or 2.0 times?) above working pressure. Burst pressure is much higher than proof and usually only required to be verified by analysis. The factor used for burst pressure will vary based on the particular application.

 

[tmech77]

I believe the spec that pertains is one that I found shortly after I initiated this question to the web site. I believe ASTM F 1387 Section 8 defines the test to certify that a fittings burst pressure will be at least equal to 4 times the working pressure.

 

[desertfox]

hi tmech77

You're welcome

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[moltenmetal]

Compression fitting joints are usually rated to the limitation of the tubing they're installed on, with a few exceptions- female adapters for instance, where their wall thickness of the female NPT part limits the fitting directly. You need to consult the fitting mfg's literature to understand what they're offering. For the compression fitting end itself, a properly assembled joint should be strong enough to allow the tubing itself to rupture before the fitting slides off the end of the tube or fails in any other way.

Tubing is rated like pipe: safe allowable stress is set to 1/3.5 of the ultimate tensile stress or 2/3 of the yield, whichever is lower for the material.

 

[racookpe1978]

And, even IF you test 10 samples to "burst pressure" none will fail at anything close to the same pressure.

As with any mechanical thing made of slightly different crystals at slightly different times under slightly different conditions, each will be machined slightly different and will ultimately fail at different pressures.

At best, you'd get a range of pressures with a fairly large standard deviation between the individual failre points. So, expect only a theoretical value.

 

[boo1]

ASTM F1387-99, TABLE 3 Specimen Geometry and Testing Requirements, and Table S1.1 Supplementary Tests specifies the number of specimens required for testing.