Pipework vibrating around pumps

[WilliamTz]

Hello

I have a fierce problem with a pipework header off a set of 5 pumps with respect to vibrations being transmitted form the pumps...see attached picture...water pressure 6 bar 140 degC.
A few weeks ago the coupling between the motor and pump shafts was worn and needed rubbers replaced around the bolts (sorry about the vague details). The pump caused really bad vibrations in the entire pipework above the pump on the suction and discharge headers and shock the pipes the steel structure supporting them....it was literally swaying......we shut down all pumps immediately and restarted one at the time and figure out the one that was causing problems. Got the coupling fixed and no issue since..until yesterday..another pump is now causing problems...don't know the details yet but the pipework started to shake again yesterday until the pump causing it was switched off... Surely the pumps are entitled to wear and fail without causing the system to vibrate and shake.
The pumps have bellows in and out of them but I do think the pipework going from low level to high level on the discharge side about 4.5m is a little too long....so they need additional supports at high level.......also some of the shoes under the pipes sitting on supports are just sitting there and others are spot welded into place...
Any thoughts on my issues?

R

 

[LittleInch]

Well spot welding supports is not normally a good sign - it means someone has had issues before with pipe movement, stress or vibration and has taken an easy way out, but this then invalidates all the analysis undertaken on the system during design.

It does look a little flexible design, but given the temperature it needs to be to allow the expansion at 140C.

The fact it only vibrates if there is something wrong with the pump sounds ok to me. To try and design your pipework such that it doesn't move when your pump is going crazy would result in a stiff system which may not be able to expand and reduce stress.

Fix the pumps.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[mk3223]

As seen in the photo, my questions are:
- if the pumps are properly aligned, anchored, and grout on the foundation
- if the suction & discharge pipes are proper supported to protect pump in-/out-let nozzles
- if the check valve provided on each pump discharge before the common manifold.
- why multiple block valves on each pump discharge line?

 

[Artisi]

Look like Grundfos packages, pump, motor, baseplate, coupling, designed for the pump to be bolted directly onto the baseplate with allowance for shims under the motor for final alignment - - - so why is the one pump that can be seen clearly have a big stack of shims under the pump?

You say that the pumps are fitted with bellow couplers on inlet and discharge, are these restrained from axial thrust into the pump flanges?
The axial thrust generated is the area of the bellows X the discharge pressure, at 6 bar this is an enormous thrust onto the pump, resulting in major misalignment and coupling failure.
Fix the pump installation and remove the problem.


It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)