Hydrotest Pressure Exceeded 1

[grosenbalm]

For a 2220# piping system, the hydrotest pressure (3330# - 1.5 x MAWP) was exceeded. The piping system (pipe, flanges, gasket, and bolts) were hydrotested at 6500#. Since this is a test for leaks only and not a test for integrity, i.e. x-ray, are the pipe and flanges still usable or do they need to be replaced? Gaskets and bolts will be replaced. Does the ASME Code reference any of this?

 

[unclesyd]

Can you comeback with some physical parameters of your system?

Things like pipe size and sch with flange class along with materials.

Did you have any leaks at the flanges?

 

[dcasto]

what was the % SMYS, did you keep a chart that could be reviewed to see if the material went plastic? (a sudden drop in pressure while increaseing it.

 

[grosenbalm]

unclesyd,

The pipe is 6" sch 120 A-106 GR B
Flanges are 6" RTJWN 900# sch 120 A-105
There was leaking between flanges during the hydrotest, which was abruptly stopped after this was noticed.

 

[grosenbalm]

dcasto,
The minimum yield strength for the flanges is 50,719 psi.
The minimum yield strength for the pipe is 53,800 psi.
Yield strength was not exceeded during the hydrotest, thus there was no plastic deformation. We believe the pipe and flanges to still be usable but wanted to confirm.

 

[dcasto]

At Grd B the calculated SYMS is 5938, however, grade B is really a rare material and most pipe comes out at x42. If the pipe is x-42, then the SYMS is 7125. Y might want to verify the yield dtrenght as a document you can add to your records.

A lot of pipeliners use to take the lines to yield. They'd start the test and as they got close to the yield strenght pressure they woul slow up the pump and watch the pressure on the line. At some pressure a joint or two would go plastic and the pressure would drop. At that point they would hold the pressure and call that the test pressure.

If you have the chart that does show a drop due to plastic deformation and you can show the pipe has slightly m ore more than 35,000 yield strenght, then its good to go.

 

[JohnBreen]

Does the ASME Code reference any of this?

No.

The ASME B&PV Code and the ASME B31 Codes for Pressure Piping address ONLY new construction. Anything that happens beyond the erection of the system is not covered. Ergo, a damaged piping system is not addressed by these Codes.

Regards, John.

 

[JohnBreen]

and..........

Yield strength was not exceeded during the hydrotest, thus there was no plastic deformation.

Oh really? So, you happened to have strain gages on the entire piping system at the time of the accident?

One interesting thing about hydrostatic testing is that the local areas that DO yield during a NORMAL hydrostatic pressure excursion will pass the load on to adjacent elastic regions. Usually this results in a beneficial residual stress. This of course is the basic idea behind auto frettage of high pressure piping systems.

JB

 

[unclesyd]

As above I don't think that there was a permanent deformation of the pipe and suspect that the flanges rolled/cupped or there was some yield in the bolts.
I show that it would take 7100 psig to start permanent deformation of the pipe.

I would dimensionally check the flange faces for cupping and as you state use new gaskets and fasteners.

I'm curious as to what you are at the limit on the allowables for the Class 900 piping system.

 

[dcasto]

JohnBreen, What if you built a new line and only 1 joint out of 30 miles had below specified yeild strenght? or just 1 foot of it?

 

[msharptx]

I am writing on behalf of grosenbalm (original post-er)

JohnBreen, how do you know it will take 7100 psig to start permanent deformation of ?

Is there a specified %SMYS not to be exceeded in ASME B31.3?

Thanks all.

 

[DSB123]

msharptx,
You ask how JohnBreen knows it will take 7100psig to start deformation. On reading the thread I cannot see anywhere that JohnBreen quotes or suggests such a value. Miss-quoting people is not a thing to be condoned. Care should be taken to correctly quote the right people.

Just a point of clarity.

 

[vpl]

I'm pretty sure that msharptx meant unclesyd. Getting a name wrong is really not that big of a deal, IMO.

Patricia Lougheed

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

Want to post an image? Look at the FAQ's in forum559

 

[eliebl]

Please check B31.3 as it contains the statement that the test pressure shall not exceed the yield strength at test temperature. They also reference paragraph 302.3.2(e) for allowables for flanges.

EJL

 

[DSB123]

vpl,
It's just as easy to get the reference to quotes right as it is to get them wrong. For me it's important to be precise when quoting but it sounds as though maybe it is not in your industry!!

 

[grosenbalm]

Back to the question at hand:

unclesyd,

How do you know it will take 7100 psig to start permanent deformation?

Is there a specified %SMYS not to be exceeded?

 

[unclesyd]

The numbers come from applying Barlow's Formula.

I used a similar calculator to this one. The one that I used gives a more conservative value. My calculator uses 58% of the tensile value as the yield value.
You can use 58% to 62% of the tensile. The min value of the tensile strength for SA106 Gr B is 60000.

http://www.engineersedge.com/calculators/pipe_bust_calc.htm

 

[msharptx]

unclesyd,

Thanks, and sorry if I appear to be going in circles here.

We were able to get MTR's on the pipe, which show a yield strength of 50,400 psi (76,200 psi tensile). Using Barlow's Formula, I get an 'Internal Pressure of Minimum Yield' value of 8,550 psi for the 6.625" OD, 0.562" thick pipe. Since we hydrotested the pipe to 6,500 psi only, am I correct to assume that the pipe is okay?

Thanks again.

 

[unclesyd]

Yes, you are OK for every piece of pipe that the MTR covers.

As I posted before, physically check the flange faces for any deformation,cupping. I think in your case that the bolts stretched just enough to act as relief valve. I would be surprised if the bolts yielded.

 

[dcasto]

msharptx you are ok. If you are missing an MTR or are worried, like I said before you can have the pipe tested for yield strenght and add to your MTR's