Mechanical Seal Failure on Feed Water Pump

[andrenov]

Dear Floor,

In our operational area here, we have numbers of pumps serving the boiler. The capacity is quite big. Currently we are facing leaks which oftenly occured in our pumps. Just for the information, we are using the treated water, which is periodically observed and monitored.

What I need some advice from all of you is what does actually happen in my pump? Did I miss something in the quality of the feed water?

Or, should the modifications be made on the seal flush design?


Kindly need your advice,

Thanks

&2-nov

 

[dgsbsme]

Are there expansion joints on the suction &/or discharge?

It could be thermal expansion of the piping attached, causing pump casing deflections leading to seal wear.

 

[Pumpsonly]

First of all you should post this thread in the mechanical seal engineering or pump engineering forums.
Secondly , What advice are you expecting when you gave no information about your pumps and operating condition.

 

[1gibson]

Perhaps you could change your piping plan from a plan _____ to a plan _____, that might be more appropriate for your seal type of ______ at service temperatures of ______.


But most likely there is an alignment or deflection issue.

 

[racookpe1978]

Yes, talk to the pump and seal dudes.

That's their area of expertise, from which the first thing they will ask is the questions above. 8<)

 

[andrenov]

Actually, I have submitted also this question to that group and uniquely I just have the responds from all of you guys.

The feedwater pump is horizontal multisatage pumps with a horizontally split casing. A constant speed 4160 HP electric motor drives tat pump. The suction piping of the pump includes a tee type strainer (3/16" dia. removal) which provides additional pump protection from the solids enter the system.

The operating fluid is boiler feed water , with SG 1.0, vaporating presure 7.5 PSIA, 180 Deg F, 1.0 CP viscocity.

The chamber pressure is 100 - 300 PSIG, suction pressure is 50-250 PSIG and discharge pressure is 2960 PSIG.

We are using API Seal Flush Plan no. 11, with injection rate 4 GPM. Currently we are using cartridge type of mechanical seal.

There is 18" to 10" reducer from the incoming header to the suction piping, and there is 12" to 8" reducer from the discharge piping to the outcoming header.

And we are often facing the mechanical seal leak problem.

Kindly need your advice, please.

Thanks

 

[JJPellin]

I would not normally consider an API Plan 11 as suitable for 180 °F boiler feed water. We would always install an API Plan 23 in this service (circulation from the seal to a seal cooler and back to the seal, closed loop). A decent Plan 23 should drop the water temperature on the return line to the seal below 130 °F.

I often ask students in classes I conduct what the hardest stream to seal with a mechanical seal is. They rarely get the right answer: water. There are very few streams harder to seal than hot water.

You did not mention what seal type you are using. We would install a multi-spring pusher seal with EPR o-rings and a close clearance gland bushing (disaster bushing). We would pipe the Plan 23 very precisely with 3/4" tubing sloped with large radius bends from the seal to the cooler and cooler to the seal. We would often install a magnetic separator in the return line to catch pipe scale. We would install a local thermometer in the return line and instruct the operators to take action if the return temperature increased above 150 °F.

We would set up preventive maintenance tasks to clean the magnetic separator every six months and back-flush the cooler once a month. We would ask the operators to blow down the water side of the cooler weekly to remove any sediment. We have a very specific start-up procedure for this arrangement to be certain that it is properly vented and purged.

It is still possible that you have other pump issues that are contributing to the failures. But, I would start with the seal and seal piping plan first.


Johnny Pellin

 

[JJPellin]

I was not able to find any related thread in either the mechanical seal or pump forums. If you had posted it there, you would have probably gotten more responses from experts in the field.

Johnny Pellin

 

[Pumpsonly]

andrenov,

A check on your profile,you had only started 2 threads and none related to this.

Any way JJPellin has given a very good answer.

 

[CaracasEC]

At 80 deg C and up, water lubricity lessened. Plan 11 has an orifice installed have you checked this during your last overhauling? I agree with JJpellin using plan 23 as this reduce temperature, improve lubricity and improves vapor pressure margin. Please take note that the basic purpose of the seal system is to provide clean, cool fluid at the faces of the seals with the correct amount of pressure and flow.

 

[andrenov]

Dear Floor,

I just have submitted the related attachments,

they are :
1. mechanical seal drawing
2. sectional drawing of mechanical seal + material data sheet



Kindly need your advices please,

Regards

.: &2-nov :.

 

[andrenov]

The mechanical seal drawing...

FYI,