Hydrotest

[JSPCGY]

Dear All

We are in the process of hydrotesting piping system. Piping is already installed with pump in it.

Do we absolutely need to isolate the pump ?

Can you not leave the pump inside the piping loop ? Under what conditions, this can be done ?

what are the pros and cons of each ?

Thanks

 

[Artisi]

Guess it is Ok so long as the pump can stand the test presssure. Although you might need to prepare the pump for hydrotest - check with the pump manufacturer for recommendation.

 

[flexibox]

if you leave the pump in the system so that it is pressurised then you need to consider the seal. If you have a mechanical seal, you may have foreign matter that gets to the seal and you end up with a seal failure on start up. Foreign matter can be weld slag in pipework for example, dirt, etc. Also make sure that the seal can withstand the static pressure.
If you have gland packing then you may blow the packing gland or you cannot obtain static pressure because it will be the weakest link. If you take the pump out flush the pipe work then put the pump in line if you want to include in the system

trust this helps

 

[BigInch]

Its obvious there are no "pros". You'd be more accurate calling them risks.

"The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward X-CEO BP
"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.live.com

 

[zdas04]

Good way to put it BigInch. I've seen pumps that had lower rated suction that discharge (usually PD pumps) so a test on the discharge could break the suction.

David

 

[jistre]

Count me in the "it's just something I'd rather not do" chorus. There are so many things that could possibly go wrong that just become impossibilities if you take the pump out of the loop and blank/block the line.

Also, because of the wording of the question, I'm picturing a pump in a closed loop. However, if the pump is not part of a closed loop, then there's always the chance that equipment and piping somewhere upstream of the pump might be vulnerable to the test pressures required to test the discharge side of the pump.

I just prefer to blank pipe sections off between equipment attachment points and test those. After all, I'm just interested in the pipe, not the equipment at either end, which should have already gone through its testing at the shop if it's pressure retaining equipment.

 

[QualityTime]

You will get some leakage at the seals and this will throw off the pressure test

 

[BigInch]

revisit flexibox comments above.

"I am sure it can be done. I've seen it on the internet." BigInch's favorite client.

"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.live.com

 

[inginear3]

If this is a centifugal pump with a mechanical seal, this should not be done. I am assuming you will go to 1.5*design pressure or flange rating (for Cl.150 429#, Cl.300 1100#). The seal will open up at that high pressure and you will damage it and fail the hydrotest.

I'm not a seal expert but I believe seals are actually intended to "leak". We provide a flush (such as a API Plan 11) to reverse that leakage back into the stuffing box or we allow it to "leak" back to the suction side of the pump (such as a API Plan 13). Without fluid circulation and flush the faces will open up and you will most likely damage the spring(s).

It won't take long to install some "pancake" blinds in the pump flanges. Just be sure you don't move the pump when you install the blind plates. Verify alignment prior to startup. If you have spectacle blinds (which is the preferred way to install spools going to a pump) be sure you swing them to keep the stress off the pump.