Hi all,

I had a discussion with a senior today and I don't agree with him, so please give me your opinion.

situation: a vertical pump pumping cooling water from the harbour into the piping system. Directly on the outlet nozzle there is currently a XJ with tie-rods. Then we have some pipe and after that a 90 degr. bend in the horizontal plane.

My senior says we have to remove the tie-rods and we have to restrict the bend in the direction of the pump nozzle. Imo this will create an "extra" external force (pressure*ID area) on the pump which the pump housing has to transfer to the foundation. This load has to be added to the other external nozzle loads. My senior however says that force will work on the inner of the pump and not on the nozzle directly and should not be used to check the max allowable nozzle loads.

I think we better keep the tie-rods and give the pipe some freedom in the direction of the pump-nozzle so the complete force resulting from the pressure is balanced in the system (pump - XJ with tie rods - bend).

Your opinions please.

HI Corne
I also work with same kind of system just now. I used untied bellow & put hold down support after the elbow. I consider pump body & hold down support will take of thrust force.
I cross check typical previous plant , Yes it was also made like that.
(Also I agree something we made before not necessarily to copy all the time.)
Let some expert to give comments.

Untied and the thrust goes into the pump casing etc. If the vendor says its ok then fine otherwise leave it tied

Thanks for the replies so far. And what do you think is the best solution?
I prefer the tied version as it doesn't give high forces on both the pump and a support.

The best pipe design is the one which has no compensator.

If you have to have compensator you need to know why. After you know why you can decide what type.

Tied compensator is for lateral movement. For large lateral have one with nipple (Universal). Untied can take all kind of movements but requires guides and anchor blocks (Pump plus one at the bend). If you have high pressure and substantial axial and lateral movements you can look using 3 hinge compensators in 3 pin system.

There is also a design where you do not have rods but hinges, either one set or two sets. These can take high compression stresses. There are also rod designs that can take compression. Compression comes into design when pump not running.

With untied you can easily run into a situation that the civils cannot make big enough support base for the block. I had this once with cooling water line. So you do not need only to talk to pump people you need to talk to civils if you use untied.

Corne,

I believe that your system has a minimal temperature making it a lot easier to analyze. For your case, the EJ is more likely used to isolate pump vibrations. Like John said, if you can leave the tie/control rods, leave it there... this won't hurt the pump.

If your boss insist on removing the tie/control rods because he doesn't like it, then, make sure you have a guide (up-down & lateral restraints)near the EJ which is between the fix support at the bend.


Goodluck!

If the EJ is to isolate vibration EJ manufacturer needs to know this.

Good point those guides are required. If not there EJ can easily pop. See EJMA code installation/design recommendations for more information.