Mechanical seal build up on multi stage split case boiler feed pump 1

[Mech5656]

Hello All,

We have a multi stage split case boiler feed pump that is failing again and again on mechanical seals. Evidently, there is solid build up of process fluid in the seal camber and around seals. Here are few pictures. Here are pump rated conditions: 550 GPM, 3560 RPM, 3115 Feet Rated head. Can you comment on the root cause and what can be the solution?

 

[TugboatEng]

You left out the most important detail, temperature. It appears there is leakage around the cartridge indicating a failure of the o-ring/gasket. What elastomers if any are you specifying for your seal?

 

[Mech5656]

TugboatEng:

Yes, thank you for catching that. Operating temperature is average 250F. The O-rings on mechanical seals are made from Viton material. Seals rotating and stationary faces are: Tungsten carbide VS Carbon.

 

[TugboatEng]

I'm not a fan of Viton for hot water service. It's performance depends largely on the cure type and ranges from fair to excellent.

https://rainierrubber.com/wp-content/uploads/2014/01/Viton-Selection-Guide.pdf

You may find better performance and lower cost using EPDM rubber for the elastomers portions.

Of course, we haven't seen the seal faces or stationary elements yet. I'm only commenting in this direction because there appears to be leakage around the cartridge.

 

[Mech5656]

TugboatENG:

Sorry but viton can be used and we have used for higher temperature than 250F. Even the link you shared shows that it can last 3000 hrs at 450F. I will share photos of seal faces when they are available. Thank you!

 

[TugboatEng]

I said the performance of Viton ranges from fair to excellent in hot water depending on the type of cure used. Do we know the type of cure used for the Viton in this seal? It appears you are only getting fair performance. Most manufacturers don't advertise the type of cure used so it's difficult to know how your seal is going to perform in hot water. Can you show photos of the o-rings/bellows? Are they showing signs of compression set or hydrolysis?

 

[pierreick]

Hi,
What about the quality of the water, seems to me salt deposit?
Pierre

 

[Mech5656]

TugboatEng/Pierreick,

Thank you for replying to this post. After disassembling the pump, we noticed a lot more damages inside the pump like broken impeller, broken impeller rings and throttle sleeve. The shaft was bent by 0.034" (TIR)when checked on V-blocks. I am thinking there was severe pump shaft misalignment that caused the seals to be failed. Thanks again.

 

[nuuvox000]

In that case, make sure you have a dirt/air separator installed in the system.

 

[EdStainless]

I used to work in oil field equipment, and we had a lot of elastomer seals.
We qualified compounds by putting test articles into small pressure vessels with mixed oil and water and then heating for a couple of months.
Depending on the compound we used different temperatures.
After exposure we measured swell, hardness, elongation, strength, and notch sensitivity.
Once we qualified a compound the supplier could not change the formulation, not even the brand of an additive.
We had horror stories about someone swapping one fumed SiO2 for another and the resulting elastomer disintegrating in test.

If this is a boiler feedwater pump what is crystalizing? This should be pure water.
Tes, fix you alignment first. And make sure that the seals are aligned also.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[TugboatEng]

Boiler feed water has descalers and oxygen scavengers. My boiler experience used phosphates as a descaler. That could certainly leave a residue over time if the leak is slow enough that it doesn't wash away the build-up. There are other products that also contribute to dissolved solids but I am not familiar with them.

 

[JJPellin]

It looks like some of this leakage was coming from the point where the gland gasket (oring) crosses the casing gasket (Garlock or similar). This is a difficult spot to seal. Proper procedures for cutting the casing gasket at the face of the stuffing box is critical. Make sure you have procedures that require leaving the casing gasket long at the stuffing box until the upper case is torqued down. Cut off that tab of gasket material with a razor blade after the upper casing is installed.

Johnny Pellin

 

[Daren Samy]

Mr Mech5656! You have rightly pointed misalignment of pump shaft leading to pump internal damages. But my questions are ?
1. Are their no temperature detectors (RTDs) for bearing oil temperatures ?
2. Is their no call up card for vibration measurement of pump and motor on regular frequency ?
3. Is their no leakage detection line in case of leakage of mechanical seal or lube oil seepage from lybrith seal ?
4. Were clearances (axial float, casing wear clearances etc) were maintained as per design?

If all things are normal , then you should check for two things.
1. Any FME that has ingressed from suction side ?
2. Check the process fluid conditions

Moreover, is there any flushing plan for mechanical seal exist on pump?