Anti Rotation Pin comes out of In Board Stationary Face.

[shyamshins]

Dear All,

I am facing problem with Agitator seal. Everytime seal fails the anti rotation pin shears off from In board stationary face.
Portion of In board stationary face also comes out from face. I/B face combination is SIC VS SIC. This has repeated 4 to 5 times.
This is double cartridge seal.
Process details:
Product : ISO BUTYL BENZENE
RPM : 300
Temp : 180Deg.celcius
Operating Press.: 41 Kg/cm2.

What could be the reason of Anti Rotation pin coming out from Inboard stationary face?
Pls. find attached seal drawing.

 

[flexibox]

first of all when you say operating pressure do you mean the vessel pressure or barrier fluid pressure? i will assume the vessel pressure, if that is the case then you need to pressurise the seal at approx 45 -47 Kg/cm2. why are you using silicon vs silicon carbide? sounds like the seal face torque is very high and this is why you are having problems with the pins. are the faces both lapped flat and polished? you may need to do two things; 1)matt lap one face and polish the other to minimise face torque. 2)change one face to Carbon. when does the seal fail? On start up or after operation? If after operation then are you maintaining a positive pressure on the seal? if not you may experience reverse pressure. if this is the case then that can also explain the high face load and pin damage because in reverse pressure the face loads are very high. check you barrier pressure is ALWAYS above the vessel pressure.

trust that this helps

 

[shyamshins]

Sir,
1) Yes Operating pressure in reactor is 41 Kg/cm2 & that of barrier fluid is 44 Kg/cm2.
2) Operators operate this reactor by filling reactor with 100% product i.e. reactor is completely filled with product instead they should fill reactor with 70% product & then pressurize it with nitrogen to 41 Kg/cm2. I have conveyed the same.
3) This plant has 3 reactor & they keep changing over reactor from one to another. When reactor is in standstill condition the product that comes in contact with I/B faces gets crystallized and damages carbon face which is the reason why I/B faces were changed from CAR VS SIC to SIC VS SIC.
4) Seal fails suddenly during rotation.
5) Previously we have provided carbon vs Sic face still pin was coming out from stationary SIC face.
6) Other 2nos. of reactor having same seal design doesnot have anti rotation seal coming out from stationary face.
7) How can I know that reverse pressure is acting on seal ? & that too in Reator?
8) Barrier pressure is always maintained at 44 Kg/cm2.

 

[flexibox]

first of all barrier pressure must always be on before pressurising the vessel at all times. if you had reverse pressure you will most likely see product contamination in the barrier fluid. i dont see why the product crystalizes if its in the vessel, perhaps the product crytalizes or polymerises with heat generated by the faces. send some photos.

i think you may need a seal upgrade to engineer out your problems.

 

[RHurst]

From the drawing it appears that the inboard stationary face is retained, so it should not move axially even during reverse pressurization.

I would work with the seal manufacturer to understand if the housing and stationary face design are accurate. Additionally, the pin should be a pretty tight fit into the back of the face. If you are utilizing Sic v Sic like you mentioned, you may modify the housing to have the pin pressed into the housing instead of the face. This will allow you to put a tighter fit on the pin so that it stays put. Then have your seal manufacturer add a slot on the back of the stationary face to engage the pin.

Hope that helps.