Troubleshooting High Vibrations in API 610 Multistage Pump Operating with Saltwater

[babak.darmanzadehgmailcom]

We are experiencing severe vibrations and operational issues with two identical API 610 six-stage centrifugal pumps (6"x6) that were originally designed for crude oil service. We are now using these pumps in different locations to pump saltwater, and the performance has been significantly worse than expected.
Pump Details:
* API 610, 6-stage, 6"x6
* Original design: Crude oil (density 900 kg/m³, temperature 60°C, viscosity 13.2 cSt)
* Design head: 380m
* Design flow: 100 m³/h
* Speed: 2950 RPM
* Impeller: Six vanes
* Diffuser: Six vanes, enclosed type
* Casing: Diffusers separated from upper casing
* Bearings: Dual 7311BECBJ (non-drive end), 6213J (drive end)
* Material: Duplex stainless steel
* Minimum stable flow: 30 m³/h
* NPSHr at rated flow: 2.35 m
Current Operation (Saltwater):
* Fluid: Saltwater (100 g salt per liter)
* Current flow: Reduced to 13 m³/h to control vibrations and amperage
* Symptoms:
* High vibrations, particularly at the non-drive end
* Vibrations felt in the ground around the pump
* Pressure pulsations in suction and discharge (approx. 20%)
* High noise levels with a harmonic rhythm
My colleagues believe the pump's issues stem from it being designed for crude oil rather than saltwater. However, I'm confident that the pump's materials and design are suitable for saltwater. I'm looking for a clear plan of action to address these problems and prevent further damage. Could you provide guidance on where to start and any insights into the potential root causes?

 

[LittleInch]

Now you're making even less sense.

Discharge pressure 7 bar? What happened to 34 barg, never mind the 43bar it should be producing??

Still think you need to strip the shaking pump down and have a good look inside.

 

[babak.darmanzadehgmailcom]

Now you're making even less sense.

Discharge pressure 7 bar? What happened to 34 barg, never mind the 43bar it should be producing??

Still think you need to strip the shaking pump down and have a good look inside.

This information was read from the parallel pump, which works fine. It has a suction pressure of 0.4 bar and a discharge pressure of 7 bar (100 psi). It is a different pump with a 35 m head.
The shaking pump is off now because of bearing failure. But when both are on, the total flow reaches 16,500 barrels per day. They may not discharge on the same line. However, the difference in suction pressure is confusing to me. This is likely due to my lack of experience and knowledge in correlating the appropriate data.

 

[LittleInch]

The first thing to do here rather than just scratching around is to go and properly draw up the piping diagram of pipe sizes, connections, locations of pressure gauges, valves, changes in diameter to allow anyone else to try and figure out what is going on here.

Then knowing the location of pressure gauges in relation to the pumps and each other, plus any flow measurements, then record what happens in operation.

But again your data make no sense.

For a pump with an inlet pressure of 0.4 barg or even 1 barg and a diff head of 35m, it simply cannot produce a discharge pressure of 7 bar.

You need to go and collate all the available data on both pumps and pipework and valves before you can figure any of this out.

However one thing I can tell you and that is your bigger pump is just far too big.

 

[Artisi]

Is there a pump hydraulic performance curve available?
At first look I would say the pump is way oversized for the current application, possibly removing 1 impeller might get you to somewhere near the performance you want.

Why haven't you taken this problem up with the pump manufacturer/ supplier?

Time to repeat a couple of points from the above.
1.The pump is oversized
2. Why haven't you involved the pump manufacturer / supplier.

You should be employing an experienced pump engineer to look at your problem, currently you're thrashing around confusing the issue further with each post.

 

[georgeverghese]

150m of convoluted suction piping sounds like trouble to me.
10-15m of head on salt water tank = 1barg in the suction line at most. After you've replaced the damaged NDE bearing on this pump, connect a flex hose from this tank direct to this pump suction, and see if this thumping at the NDE side disappears and flow improves. A 4-6inch hose will do for 70m3/hr.

 

[JJPellin]

I guarantee there is a balance line. The seal system could not function otherwise. I don't believe you have made any statements about the vibration characteristics. What is the primary frequency? What is the maximum amplitude? Where is the vibration highest? In which direction?