Hydrotest pressure (90% SMYS Criteria) for API5L X65 PSL2 20" OD 8.5mm THK pipe.

[Arshad Ahamed]

Hi all,

We have used 20" 8.5mm THK API 5L X65 PSL2 Pipe for Skin Effect Heat Traced Pipeline (pipeline beyond refinery walls, and ASTM A106 Gr.B XS 20" piping inside the refinery). The design pressure of the pipeline is 45kg/cm2.

Inside the refinery, the hydrotest was done at a pressure of 67.5 kg/cm2 (1.5 times the design), while outside (corridor piping), the hydotest was done at a pressure of 131 kg/cm2. I was told that the 90% SMYS Criteria was adopted here.

Could someone clarify this and tell me exactly how the calculations come into effect? At what pressure will the specified hoop stress corresponding to 90% SMYS be generated.

P.S : I'm in my 7th month in this industry , so kindly bombard all your ideas and thoughts here. I'm looking at a huge learning opportunity!

Thanks and Regards.

 

[LittleInch]

What I suspect here is that someone has located the code break between B 31.3 and B 31.4 or B31.8 at a point on the pipeline like the fenceline instead of somewhere sensible like the pig trap.

Or to be fair maybe you're referring to plant pipework and pipeline and the code break is in a sensible point.

The pressure test difference arises from the different hydrotest requirement between piping and pipeline.

You need to find out where the code break is and what each code says about hydrotest pressure.

The pressure to generate 90% SMYS you calculate from the design code.

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

 

[weldstan]

in addition to LittleInch comments, the 90% SMYS hydrotest would imply a design of 72% of the SMYS or a hoop stress of 48.6 ksi in the X65 pipe to obtain minimum thickness. If your refinery was essentially in the middle of nowhere this woud be permited under B31.8. If not a lesser design stress would be required; however, one could still hydro at 90% of the SMYS.













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[Arshad Ahamed]

Eqn. 6 of Clause 10.2.6.5 of API 5L Spec lays forth the Hydrotest Pressure eqn. as P = (2*S*t)/O.D,
where S is the specified minimum yield strength (65 ksi for X65 PSL2), t is the thickness (8.5mm here) and O.D is 500 mm.

The Yield Pressure was found as 152.41 kg/cm2. and the Hydrotest Pressure corresponding to 95% SMYS is 144.79 kg/cm2.
We have done the pressure test at 140 kg/cm2 and that has attracted some flack from the other departments - mainly maintenance and inspection, for having unnecessarily pushed the testing bar too high, when the norm mentions that the minimum hydrotest pressure should be 1.5 times the design pressure (45 kg/cm2 design in our case) and should not exceed the pressure that would result in a hoop stress corresponding to 95% SMYS at the lowest point of the pipeline.

The major concern raised was that the pipe "may" have already yielded while performing the hydrotest close to the yield point.

What are your thoughts on this one?

 

[mk3223]

Arshad, you may verify what's the Code requirement of the hydro tested pereeusre for the pipeline, i.e. 90% or 95% of SMYS.
In the original OP stated that the pipe was tested at 90% SMYS, or 131 kg/cm2. but in the last reply, it was changed to about 92%, or 140 kg/cm2. It looks like that the pipe was conducted the test with a wrong pressure.
May consider an investigation of the detail procedure used in the test, and have a pipeline inspection for any potential overstrain condition of the pipeline if the test pressure higher than the Code requirement.

 

[LittleInch]

Worth a pipeline system in particular you need to state clearly where the pressures are:
High point?
Low point?
Start of pipeline?

Without elevation data it isn't possible to say if the line was overstressed or not.

If you have a plot of pressure versus volume of water pumped into the pipeline by the pressure pump you should be able to see if this is a straight line (all elastic stain) or whether it starts to curve over which is indicative of some yielding.

Lots more information required here.

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