Flexible joint?

[MarkoPezcha]

Hello everybody,

I have a doubt about one system piping. I have reciprocating pump FMC M0818 working at 1080 psi and 46.5 GPM and in the discharge line it has install flanges class #600. According FMC this pump has a maximun vibration of 0.4"/sec. So my question is Do I need a kind of felixible expasion joint to reduce the vibration in the outlet piping? I have been looking for it but i couldn't find it. Please any help will be great!.

Thnkas

 

[normet]

Marko,

There is something wrong with the quoted vibration when considering fatigue damage potential. The value quoted is a velocity. What you need is the displacement, which you may have to get from an acceleration. ie, F=ma. The acceleration will depend not only on the pump, but the stiffness of the base onto which it is set. Once you have the force on the outlet piping you can determine a stress and using the considerations in B31.3 you can determine if you are in a fatigue prone regime. When in doubt, be cautious and either dampen the vibration, or install a flexible connector.

 

[DLite30]

Inches per second (ips) are the most commonly used terms for machinery vibration levels. 0.4 ips is an a fairly typical vibration limit for reciprocating equipment, in fact I ususally see 0.5 to 0.65 as limits. Note that this is FMC's maximum vibration level, so realistically you'll probably see lower levels than that from the machine.

Now if you have any air in your system, you may end up with flow-induced vibration, so make sure everything is bleed out well, and the pump cann't find a source of air/gas/whatever at its suction.

All your piping should be hard piped...there's reason for a flex joint, and really a flex joint could potentially cause vibration issues, by introducing additional flexibility and lowering piping natural frequencies. You want to keep the piping stiff, and well supported.

 

[micalbrch]

I assume that this pump has a pulsation dampener and is installed on vibration pads?

The easiest thing you can do is to install a short (2-3' long) hydraulic hose on the discharge side.

 

[MarkoPezcha]

Dear normet,

0.4"/sec was the only information that FMC gave me.

Dear DLiteE30,

This is a water pump for with some saliny concentration. Maybe we don't need any flexible joint with this vibration as you said.

Dear Micalbrch,

Yes, we have installed a pulsation dampener in the discharge before the supposed flexibe joint. Is hydraulic hose usual in this piping system? Can I use this?

The outlet pressure in the pump is 1090 psi, we are using a pipe sch 160 and flanges calss #600.

We thought use a dresser joint but maybe this is not appropiate for this aplication, and I didn't find class 600. We are not sure.

Thanks

 

[micalbrch]

I have seen triplex pumps for water (around 1500 psi) working with a hydraulic hose between pump and steel pipeline. Ask FMC what experience they have with this.

 

[chief]

Reciprocating pumps are nearly always subject to vibration problems. Consider charging the accumulator,with a nitrogen charge to 500psi. Also a suction precharged damper
to about 20psi would help.

Offshore Engineering&Design

 

[chief]

Addendum, install a flexible hose at the suction inlet, this will absorb any potential spikes in the suction pressure. Ensure you have a positive pressure on the suction supply side.

Offshore Engineering&Design