Hydrotest pressurization rates...
Hydrotest pressurization rates...
(OP)
A co-worker and I were discussing a specification for hydrotests of piping and pressure vessels. While there is a lot of information on temperature limitations during a hydro (to avoid brittle fracture, etc), I can't find anything that provides guidance on pressurization rates. For example, if you have a piping system with a hydro pressure of 1800 psig, should you ramp up at 100 psig/minute?..50?..200?
My thoughts are unless you could shock the system by going to full pressure in microseconds such that you have some sort of kinematic effect...there is no need for a limit.
On the practical side, I know that hydro contractors bring in these big pd pumps and sometimes can overshoot the desired pressure because it may only take one pump stroke after the line is inventoried with water. So you may want them to slow down...but is that even practical.
API 570 give guidance on going to the max hydro pressure for x time and then dropping to the design pressure for inspection...but nothing on rate.
What about the depressure rate?
Your thoughts on the topic would be appreciated...
jrjones
My thoughts are unless you could shock the system by going to full pressure in microseconds such that you have some sort of kinematic effect...there is no need for a limit.
On the practical side, I know that hydro contractors bring in these big pd pumps and sometimes can overshoot the desired pressure because it may only take one pump stroke after the line is inventoried with water. So you may want them to slow down...but is that even practical.
API 570 give guidance on going to the max hydro pressure for x time and then dropping to the design pressure for inspection...but nothing on rate.
What about the depressure rate?
Your thoughts on the topic would be appreciated...
jrjones





RE: Hydrotest pressurization rates...
On vessels that we build, there is enough volume that this is not a problem.
RE: Hydrotest pressurization rates...
RE: Hydrotest pressurization rates...
Aside from the pump issues, what would people suggest for pressure up and pressure down rates.
jrjones
RE: Hydrotest pressurization rates...
It may be just crap, but it feels safe and I've never had a line fail while following it (no way to know if any of them would have failed if I'd gone up quicker).
DCASTO's comment is important. When I have to do hydro's, I'll fill a line with a centrifugal pump, never a PD pump, until I get water out all the vents then 25-30 psi higher. Then let it sit overnight and turn the pumps back on while venting the last of the air out. Finally, use a very small pd pump to get pressure. Filling with a PD pump feels pretty reckless to me.
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
The harder I work, the luckier I seem
RE: Hydrotest pressurization rates...
http://virtualpipeline.spaces.msn.com
"We can't solve problems by using the same kind of thinking we used when we created them." -Albert Einstein
RE: Hydrotest pressurization rates...
While the 10 psig/minute that zdas04 seems too slow, what is being proposed in the specification I am reviewing is upwards of 150-200 psig/minute. This "seems" fast, but I really don't have a basis. I have seen hydros done at >600 psig/min. I agree this seems crazy, and it is a reason for the specification, but I still have no sound basis to pick a rate (and justify it to the spec writer). I do agree with the tight control once the pressure>MAWP.
Just for clarification, inventorying and venting the line is not an issue...just the pressurization and depressurization.
Thanks for the continued discussion...jrjones
RE: Hydrotest pressurization rates...
David
RE: Hydrotest pressurization rates...
I am really interested in this discussion because I have literally witnessed 500+ hydros (on piping, vessels, tanks, pump casings, valves, etc). I am usually called after the line is holding pressure, but sometimes I have been there, knowing that I specified a ramp of 100 psig/minute max and seen the pressure go from 0 to 800 in 10 seconds. I have seen this more that I would care to mention (again...the reason for the specification) but it does make me question whether those rates are okay...I have never seen a pipe fail hydro other than through flanges or valve packing, etc. So maybe rates > 200psig are okay??
RE: Hydrotest pressurization rates...
See this thread: thread378-193569: Hydrotest Pressure Exceeded