Mechanical seal faces sticky problem. 2

[ouyaseals]

Dear Engineers:

Nowadays our clients'mechanical seal faces is sticky togethe. It can not work.

The type is similar with BT-Burgmann seal type.And the size is 45mm. The fluid is hot clean water, tem' is less than 100 centigrade degree.
Both of the faces are SSiC and polished within 1 lightband.

We think the problem is so smoothy face and heavy pressure.

Any new advice on this problem?

 

[bk19702]

Be more specific about the problem. What do the faces look like? What is the failure frequency? Symptoms?

Without knowing more about the problem, at least the rotating face should be matted in general when running hard faces together. There may be a specific procedure internal to Burgmann that calls for polishing both (it may be material specific). You should be able to run a good metal filled carbon vs. TC in this application for the most part.

 

[flexibox]

change 1 face to carbon and ensure that you have suficient Delta T so that the seal does not vapourize. you probably have hard faces because your system is dirty. I recommend API plan 23 with a magnetic filter. check if you have solids when you drain the pump and put a magnet to it to see if it is magnetic.

 

[ouyaseals]

Thanks for the advices from bk19702 and dear Flexibox firstly.

Inserted carbon vs.T.C is not acceptable, because this mechanical seal is just to replace Packing before. The working height is very short, less than 18mm in fact.

Also we checked to use Carbon vs. SiC as trial in two seals. But we are not satisfied with the WORKING LIFE of this change. Carbon face was worn so soon and broken so easily to leak.The fluid, yes, there were some very small grains.

How about H10 from Burgmann?
Any new advice?

Best regards,
Paul paultsu@gmail.com

 

[bk19702]

What's the pressure? Do you have a flush on the seal already? I'm confused as to the reason why the working height is impacting your material change. You should not have a problem running a metal filled carbon against TC in this service; you can run SiC if it makes you feel better. The bottom line is you will need to ensure you have enough of a vapor pressure margin inside the seal cavity to keep the water from flashing. At 100 deg C, you need at least 1.03 barg or more inside the seal cavity for vapor suppression. The 'stickiness' you describe tells me you just don't have an adequate fluid film at the seal interface. Water has excellent thermal conductivity characteristics, relatively speaking, but it is generally a poor lubricant for seal faces so you need to carefully review the entire application specifics. I've run seals with an uncooled recirculation flush (Plan 11, 13, 14, etc.) at these temperatures successfully; provided the vapor pressure margin inside the seal chamber is sufficient and the seal materials are designed for the temperature then that could be an option for you. The plan 23 would definitely help you as cooling the water down (below 71 deg C would be optimum) will prolong your seal life. Keep in mind that installing a plan 23 is not a plug and play system. You need to make sure your heat exchanger is properly mounted and you have provisions to vent the loop prior to startup. Vapor lock in a plan 23 loop is a killer for the seal. If you do decide to go with a plan 23, also keep in mind you'll need an alteration to your seal design to include a pumping ring for circulation.

 

[smart2006]

Dear bk19702, please explain the following:

"The bottom line is you will need to ensure you have enough of a vapor pressure margin inside the seal cavity to keep the water from flashing. At 100 deg C, you need at least 1.03 barg or more inside the seal cavity for vapor suppression. The 'stickiness' you describe tells me you just don't have an adequate fluid film at the seal interface. Water has excellent thermal conductivity characteristics, relatively speaking, but it is generally a poor lubricant for seal faces so you need to carefully review the entire application specifics."

 

[bk19702]

If the water is not cooled, there needs to be adequate vapor suppression inside the seal chamber so that an adequate fluid film will be present at the sealing interface. Based on the process information provided, there needs to be 1.03 barg inside the chamber to provide enough of a margin over the fluid vapor pressure (water @ 100 deg C). The alternative, if seal chamber pressure is not adequate, is to cool the process via a plan 21 or 23 as mentioned.