Maximum pipeline hydrotest pressure 3

[RGME]

I have a question related to the maximum hydrotest pressure for a natural gas pipeline.

API 5L X52 pipe material, 24” OD with 0.375” wall thickness will be shop hydrotested per API requirements to a hoop stress that is a minimum of 90% SMYS. This value turns out to be an internal pressure of 1462.5 psig.

When this piping is used for a natural gas pipeline, what should the maximum field hydrotest pressure be? I already know that the minimum pressure required by the design codes is 1000 psig, based on Maximum Operating Pressure.

Thanks for your help!

 

[BenjieL]

We hydrotest all our lines 1.5x. So, if your operating pressure is 1000, then the calculated 1426 is within the prescribed hydrotesting pressure limits.

 

[BenjieL]

CORRECTION: Calculated pressure of "1426" should read
"1462."

 

[TD2K]

B31.3 is hydrotested at 1.5x design, I thought B31.8 depending on the design class used could/was less than this?

 

[RGME]

Thanks for your responses so far, but what I'm really looking for is a guideline for setting the maximum[/b] field hydrotest pressure. I already know the minimum pressure. Does anyone have a feel for what the upper limit should be? Given that the steel pipe in question (API 5L X52) is hydrotested by pipe fabricators to 90% of the yield stress, I would think that any field test pressures would need to fall below this. Any ideas for setting that upper limit?

 

[CRG]

Maximum test pressure should be based on the limiting system component. Are there valves, flanges, equipment, etc. attached to the line? Use the limiting system component and the relevant piping code to calculate maximum pressure.

 

[denniskb]

You should be able to test well above the 90% SMYS level.

First the actual yield stress of the pipe is likely to be higher than the SMYS.

Second the stress is not uniform through the pipe wall.

You should be able to test to around 105% of SMYS at the lowest point of the pipeline.

The best option is a volume controlled test where the pressure is increased until the pressure change vs volume added has fallen to half of the slope evident during early pressuring. The pipe is basically pressurised until it shows clear signs of the onset of yielding.

You do need nerves of steel for this though and very good test equipment. I would strongly suggest an experienced and quality endorsed hydrotesting contractor for this.

The payoff is that you can get the maximum benefit from every mm of pipe wall put in the ground with a higher MAOP.

There are additional benefits in that the first yielding will be at locations with residual stresses from installation and welding and these will be stress relieved and left with the internal surfaces in compression. Dennis Kirk Engineering

http://www.ozemail.com.au/~denniskb

 

[hatata]

If the pipeline is designed in accordance to B31.8, The test pressure shall be in accordance to the location class , the permissible test fluid and the maximum allowable operating pressure (refere to ASME B 31.8).
as an example:
location class 1 division 2, test fluid is water, the min test pressure is 1.1 max. operating pressure and the max. is 1.1 design pressure.

Also you have to consider that the test pressure at any point of the test section shall at least be equal to the test pressure required in the B31.8 (ref. table 841.322 and A847.2), as applicable, or to the pressure creating a hoop stress of 90% SMYS of the line pipe material, based on the minimum wall thickness, whichever is higher, or unless otherwise specified by the design office.
During the hydrostatic pressure test the combined stress shall not exceed 100% SMYS of line pipe material based on minimum wall thickness. The combined stress shall be calculated in accordance with B31.8 (ref. A842.223).