Piping wall thickness calculation during hydrotest condition

[Sean_Wei]

Hi，Forums

Piping wall thickness calculation according ASME B31.3 is using the design pressure of pipeline，while the hydrotest pressure is at least 1.5×design pressure.

The question is why B31.3 doesn't require to do the calculation check under hydrostatic test pressure？

 

[Trestala]

The purpose of hydrostatic test is to verify the strength of your piping if it can handle the design pressure safely by using a pressure above it.

 

[goutam_freelance]

Refer the thread
https://www.eng-tips.com/threads/hydrotest-clarification.528306/

 

[GD2]

Hi，Forums

Piping wall thickness calculation according ASME B31.3 is using the design pressure of pipeline，while the hydrotest pressure is at least 1.5×design pressure.

The question is why B31.3 doesn't require to do the calculation check under hydrostatic test pressure？

It is all about stress. You need to convert the test pressure to stress. Use Barlow's equation. Make sure that stress does not exceed YS. Typically, companies keep it limited to 0.9YS at test temperature.
It's a bit of mind puzzling in the beginning. You need to learn the relationship between pressure and stress - tow different parameters but inter-related.

 

[LittleInch]

Asme b31.3 is for piping. The assumption is that the piping is essentially flat, so no elevation applies.

B31.3 is essentially stress at max 2/3 SMYS or 1/3 UTS whichever is lower.

Many steels fall into the UTS category.

But if not design pressure gives max 2/3 SMYS. Hydro at ambient temperature gives max stress at SMYS. So why worry. It's a test.

 

[Snickster]

The allowable stress as mentioned is set at approximately on 0.6 times or 2/3 of the yield stress. If you hydrotest at 1.5 times allowable you are testing at:

1.5 time 0.6 times the yield strength = 0.9 times the yield strength.

 

[KevinNZ]

Most hydro leak tests do put much stress in to the pipe. Starting with the design pressure you work out a minimum thickness, then add MA and CA then select the next standard thickness. The design and test pressure is then working on pipe wall that is thicker than the minimum and the stresses are low compared to yield.

Also the pipe has been hydro tested at factory. The site test is testing the circumferential welds which have stress 1/2 the hoop stress

 

[Sean_Wei]

Thanks，Everyone.

I completely understood，Everyone is so professional