Hydrotest pressure exceeded
Hydrotest pressure exceeded
(OP)
Hi Gents,
This is the case: 2" Pipeline SCH 80 API 5L Gr B. The system is rated at #600. The length of this pipeline is about 800 meters.
This system was undergoing a hydrotest as a part of the construction process. The test pressure was set at 2175 psi (company standard fro test pressure on gas pipelines at that rating).
Due to sudden ambient temperature increase, the pressure went above 3000 psi (3000 psi is the maximum reading of the gauge, so probably pressure could have gone higher).
Unfortunately the pressure test was unattended at that moment and test operator did not realize about this.
The fact is that the entire pipeline was exposed to a pressure much higher than the hydrotest pressure (over 3000 psi) and we are not sure if the pipes suffered damage due to the over pressure. There are no external evidences of damages like deformations or pipe movements. There wasn't any leak either.
Should we be concern about the mechanical integrity of this pipeline now after it has been exposed to this extreme pressure? Should we conduct any particular test to determine if it actually suffered some damages?
Thank you very much in advance for your replies.
Kind regards,
This is the case: 2" Pipeline SCH 80 API 5L Gr B. The system is rated at #600. The length of this pipeline is about 800 meters.
This system was undergoing a hydrotest as a part of the construction process. The test pressure was set at 2175 psi (company standard fro test pressure on gas pipelines at that rating).
Due to sudden ambient temperature increase, the pressure went above 3000 psi (3000 psi is the maximum reading of the gauge, so probably pressure could have gone higher).
Unfortunately the pressure test was unattended at that moment and test operator did not realize about this.
The fact is that the entire pipeline was exposed to a pressure much higher than the hydrotest pressure (over 3000 psi) and we are not sure if the pipes suffered damage due to the over pressure. There are no external evidences of damages like deformations or pipe movements. There wasn't any leak either.
Should we be concern about the mechanical integrity of this pipeline now after it has been exposed to this extreme pressure? Should we conduct any particular test to determine if it actually suffered some damages?
Thank you very much in advance for your replies.
Kind regards,





RE: Hydrotest pressure exceeded
RE: Hydrotest pressure exceeded
Therefore I suspect you've been lucky and you've not actually reached the yield stress of the pipe. If you have some idea of the temperature increase you can estimate the pressure rise - see this FAQ http://www.eng-tips.com/faqs.cfm?fid=1339
I would just test it to the original pressure again. If you did yield it somewhere then that piece might be a bit thinner and would now be work hardened, but so long as it withstands your normal hydrotest then you should be Ok. Watch the pressure versus volume in graph very carefully and take lots of measurements. If the slope starts to tail off as you get to the test pressure then you are yielding somewhere and that point will be a weak spot or could fail in later years much sooner than otherwise.
Be very clear if there was only this pipe and no other connections or fittings.
I wouldn't use any of the flange bolts again....
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Hydrotest pressure exceeded
And throw those studs away; nuts will be OK to reuse.
RE: Hydrotest pressure exceeded
I hate Windowz 8!!!!
RE: Hydrotest pressure exceeded
RE: Hydrotest pressure exceeded
If they did happen to meet minimum test time, what would you say about that?
I hate Windowz 8!!!!
RE: Hydrotest pressure exceeded
I take the point about the fact that it might have passed the hydro, but would prefer to do it properly and make sure there was no excessive yielding anywhere. In this case going beyond the code minimum sounds like a good plan to me.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Hydrotest pressure exceeded
I hate Windowz 8!!!!
RE: Hydrotest pressure exceeded
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Hydrotest pressure exceeded
I hate Windowz 8!!!!
RE: Hydrotest pressure exceeded
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Hydrotest pressure exceeded
I hate Windowz 8!!!!
RE: Hydrotest pressure exceeded
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Hydrotest pressure exceeded
I am gladly surprised about the quantity of answers and I do apologise for not replying back before. I went out on shift leave just few days after I posted this thread.
I just followed your advisements and conducted the Hydrotest again at the right test pressure, of course this time we ensured constant surveillance during the test. We have replaced the bolts/studs and the gaskets used during the previous hydrotest.
I was actually proposing the usage of a P-T chart recorder so that we will not miss any detail. However, this suggestion was not taken since the test period is short. I could not find any code or regulation to support me on this but I think it should be a must for the hydrotest. What would have happen in this case if test operators arrive before than me to the gauge location? they would probably have rapidly reduced the pressure so when I reach the place I wouldn't have noted anything. They would probably remain silent. Anyway, I would like to know your thoughts on this regard.
I went through the calculation path posted by LittleInch based on combined gas laws (Boyles, Charles and Gay -Lussac).
Since we don’t know exactly the temperature at the time of the hydro test, let’s just make assumptions:
Hydro test time = 10:00am – 12:30pm , 8th May 2014
Scenario 1 (conservative side)
Steel Temp at 10:00am = 35 C
Steel Temp at 12:30pm = 55 C
Initial pressure = 2175 psi at 10:30 am
Temperature difference = 20 C
20 x 63.84 = 1276 psi
New pressure = 2175 + 1276 = 3451 psi.
Scenario 2 (ultraconservative case)
Steel Temp at 10:00am = 25C
Steel Temp at 12:30pm = 60C
Initial pressure = 2175
Temperature difference = 35 C
35 x 63.84 = 2234 psi
New pressure = 2175 + 1276 = 4409 psi.
MAX pressure to get to the SMYS = 6410 psi
The two scenario shows that at given temperature differences, the pressure does not exceed the SMYS.
In order to exceed the SMYS, a temperature difference of 66.40 C is needed. (this is not realistic and attainable in ambient condition)
LittleInch, is this the calculation path followed by you?
Thank you very much all for your replies and once again my apologise for not answering this before.
Kind regards,
Cesar
RE: Hydrotest pressure exceeded
RE: Hydrotest pressure exceeded
All the codes normally say is that a record of temp, pressure needs to be taken with start / finish as the minimum, but every 30 to 45 mins is recommended. Chart recorders are normally just seen as good practice or used to prove to an inspector what happened.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way