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?

 

[georgeverghese]

You havent said anything about the shaft seal flush plan.

Calcium and magnesium salts may have caked up the pressure balancing line between discharge and suction that is meant to reduce the axial thrust loads on the bearings ?

 

[babak.darmanzadehgmailcom]

Plan 31+53/B

 

[Artisi]

Without knowing what the actual flow, head requirements for the new application it will be guess work what the problem is, however seeing as you have reduced the flow so much, I would say the pump is well oversized for the duty.
A lot more detail is required.

 

[babak.darmanzadehgmailcom]

Without knowing what the actual flow, head requirements for the new application it will be guess work what the problem is, however seeing as you have reduced the flow so much, I would say the pump is well oversized for the duty.
A lot more detail is required.

Would increasing gap B by trimming the impeller vanes be a viable solution to the oversized pump problem?

 

[pointsman]

Is this a long coupled pump, and if so was the shaft realligned after the pump was moved?

 

[babak.darmanzadehgmailcom]

Is this a long coupled pump, and if so was the shaft realligned after the pump was moved?

Yes its a long coupled. But we realligned shaft several times.

 

[LittleInch]

Well please describe the new operating conditions (suction pressure, discharge pressure, flow and temperature)

13 m3hr is well below its min stable flow so not a surprise there.

Your discharge pressure and power will be at least 10% above the original design so flow probably needs to be reduced to a max of 85% of previous for CO.

Also was this a Duplex STl Stl pump?

Was the pump moved and not aligned properly or did you just change the fluid in the same pipes?

This looks like three times the amount of salt of seawater so is this produced water? Any other gases dissolved in it.

Sounds like pressure surging caused by too low a flow or insufficient suction pressure or cavitation / gas in the inlet fluid.

 

[TenPenny]

When you say the flow is reduced to 13m3/h to reduce vibrations, does this mean you were trying it at a higher flow rate, or is this where you run it on salt water? The pump is designed for 100, and you're running at less than 15% of that. You can expect high vibrations and short bearing and shaft life if this is what you are doing.

The materials would be fine for salt water, that is not your problem.

 

[EdStainless]

Are you sure that both impellers and diffusers have 6 vanes?
That sounds like a nightmare for vane pass issues.
Have you generated new pump curves for the new density and viscosity?
New NPSH, new BEP, and such?

 

[Artisi]

Until such time the required flow and head for the new installation is known it's all guess work and wheel spinning.

All that can be assumed at this point is the pump and duty don't match.

 

[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?

Sorry for lack of information. I would like to add full detail here.
Pump Type: API 610 BB3, axially split, 6 stages with 6 impeller vanes and 8 diffuser vanes (similar to Baker Hughes MSN BB3)
Mechanical Seal: API 682 Plan 31
Operating Conditions:
* Suction Pressure: Fluctuates between 10-15 psi (0.7-0.9 bar)
* Discharge Pressure: Fluctuates between 460-500 psi (30-32 bar)
* Temperature: Ambient
* pH: ~6 (non-acidic)
* Total Dissolved Solids: 6 grams per 100 milliliters
* Salinity: 110 grams per liter (3 times seawater salinity)
Flow Rate: This value seems questionable and needs verification. The operators reported flow rate is 3000 barrels per day, but based on the datasheet, it is expected to be around 5000 or more barrels per day.

Fluid Properties (from Datasheet):
* Vapor Pressure: Max: 1236 kPa, Min: 360 kPa
* Relative Density: Max: 0.9, Min: 0.86
* Viscosity: Max: 13.2 mPa·s (cP), Min: 5.1 mPa·s (cP)
* Temperature: Max: 335 K
Pump Performance Data (from Datasheet):
* Flow Rate: Max: 120 m³/h, Rated: 100 m³/h, Min: 33 m³/h
* Discharge Pressure: Max: 4240 kPa, Rated: 3890 kPa, Min: 3550 kPa
* Suction Pressure: Max: 1480 kPa, Rated: 790 kPa, Min: 450 kPa
* Differential Head: Rated: 370 m
* NPSHa: 3.5 m
Driver Information:
* Electric Motor: 3300V, 50 Hz, 3-phase
* Nominal RPM: 2980
* Nameplate Power: 200 kW
Performance at Rated Conditions:
* Impeller Diameter: Max: 236 mm, Min: 210 mm
* Rated Power: 155 kW
* Efficiency: 60%
* Rated Flow (at 236 mm impeller diameter): 120 m³/h
* Minimum Flow (Stable): 33 m³/h
* Preferred Operating Region: 84 to 132 m³/h
* Allowable Operating Region: 33 to 140 m³/h
* Maximum Head (at rated impeller): 430 m
* Maximum Power (at rated impeller): 178 kW
* NPSHr (at rated flow): 2.35 m
* NPSH Margin (at rated flow): 1.15 m
Nozzle Sizes:
* Suction: 4"
* Discharge: 3"
* Drain: 3/4"
* Vent: 3/4"
Materials of Construction:
* Case: A890 Gr1B
* Diffuser: A890 Gr1B
* Impeller: A890 Gr1B
* Impeller Wear Ring: A890 Gr1B (hard faced)
* Case Wear Ring: A890 Gr1B (hard faced)
* Shaft: A276
Bearings:
* Radial: 1 x Deep Groove Ball Bearing 6213J
* Thrust: 2 x Angular Contact Ball Bearing 7311BECBJ
Coupling: Flexible with spacer, compatible with API 671
Weight:
* Pump: 2540 kg
* Driver: 1830 kg
* Base: 2010 kg
Performance Curves: Characteristic curves for hydrocarbon and water are provided.
Crude oil Performance:
* Number of Stages: 1
* Speed: 2980 RPM
* Density: 900 kg/m³
* Temperature: 62°C
* Viscosity: 13.2 mPa·s (cP)
* Flow: 100 m³/h
* Head: 370 m
* Power: 155 kW
* Efficiency: 59%
* NPSHr: 2.52 m
* BEP: 100 m³/h
Water Performance:
* Number of Stages: 1
* Speed: 2980 RPM
* Density: 999 kg/m³
* Temperature: 20°C
* Viscosity: 1 x 10⁻⁶ mm²/s
* Flow: 100 m³/h
* Head: 373.9 m
* Power: 158.1 kW
* Efficiency: 64%
* NPSHr: 2.25 m
Impeller Size:
* Maximum: 236 mm
* Minimum: 210 mm

 

[babak.darmanzadehgmailcom]

Until such time the required flow and head for the new installation is known it's all guess work and wheel spinning.

All that can be assumed at this point is the pump and duty don't match.

Sorry for lack of information. I tried to add more detail in a reply to my first post.

 

[babak.darmanzadehgmailcom]

Are you sure that both impellers and diffusers have 6 vanes?
That sounds like a nightmare for vane pass issues.
Have you generated new pump curves for the new density and viscosity?
New NPSH, new BEP, and such?

Sorry for lack of information. I tried to add more detail in a reply to my first post.

 

[babak.darmanzadehgmailcom]

When you say the flow is reduced to 13m3/h to reduce vibrations, does this mean you were trying it at a higher flow rate, or is this where you run it on salt water? The pump is designed for 100, and you're running at less than 15% of that. You can expect high vibrations and short bearing and shaft life if this is what you are doing.

The materials would be fine for salt water, that is not your problem.

I added more information. Hope it could hrlp for better understanding.

 

[babak.darmanzadehgmailcom]

Well please describe the new operating conditions (suction pressure, discharge pressure, flow and temperature)

13 m3hr is well below its min stable flow so not a surprise there.

Your discharge pressure and power will be at least 10% above the original design so flow probably needs to be reduced to a max of 85% of previous for CO.

Also was this a Duplex STl Stl pump?

Was the pump moved and not aligned properly or did you just change the fluid in the same pipes?

This looks like three times the amount of salt of seawater so is this produced water? Any other gases dissolved in it.

Sounds like pressure surging caused by too low a flow or insufficient suction pressure or cavitation / gas in the inlet fluid.

I Added more info. Next week I will provide vibration analysis too.

 

[georgeverghese]

Does this pump not have a min flow recycle loop, set to maintain flow at > 33m3/hr or so ? Is this pump on fixed speed drive or VSD ?

 

[babak.darmanzadehgmailcom]

Does this pump not have a min flow recycle loop, set to maintain flow at > 33m3/hr or so ? Is this pump on fixed speed drive or VSD ?

Fixed speed. No bypass line. It's highly possible the minimum flow is reached and operators told me flow of another pump with similar duty.

 

[georgeverghese]

So the flow through this troublesome is not 13-20m3/hr, but actually > 33m3/hr ? Does this pump have a pressure balancing line ? If not, how are high axial thrust loads addressed ?

 

[babak.darmanzadehgmailcom]

I didn't see a balance line on this pump. Is it possible that the impellers are arranged in a way that cancels out the axial thrust, preventing high loads on the bearings?