Mechanical Seal Face Distortion
Mechanical Seal Face Distortion
(OP)
All,
I am experiencing repeated mechanical seal failures on double suction, radially split, between bearings pump. The operating conditions are listed below.
Fluid – Hydrocarbon
Operating Temperature – 485F
Suction Pressure – 30psig
Discharge Pessure – 200psi
Barrier Fluid – Royal Purple 22
Seal Pot Pressure – 100psig
The seal design was recently changed to a dual pressurized face to back rotating bellows seal. A set of seals were installed and shortly after the pump was started the thrust side seal began to leak barrier fluid in to the process. The coupling side seal never leaked. The seals were pulled and disassembled to find the thrust side seal had two wear spots that were 180o apart from one another (saddle distortion) on the inboard or primary stationary face. The seals were repaired and re-installed in the pump. Just as before, shortly after the pump was started the thrust side seal began to leak barrier fluid in to the process. The coupling side seal did not leak. Just as before, the same saddle distortion was found on inboard stationary face.
The face distortion issues have been addressed by using a stationary bellows as opposed to a rotating bellows in order to isolate the face from the gland. Any thoughts as to why the inboard or primary stationary faces experienced face distortion? Also any thoughts as to why just the thrust side seals experienced the face distortion? Any help is greatly appreciated.
I am experiencing repeated mechanical seal failures on double suction, radially split, between bearings pump. The operating conditions are listed below.
Fluid – Hydrocarbon
Operating Temperature – 485F
Suction Pressure – 30psig
Discharge Pessure – 200psi
Barrier Fluid – Royal Purple 22
Seal Pot Pressure – 100psig
The seal design was recently changed to a dual pressurized face to back rotating bellows seal. A set of seals were installed and shortly after the pump was started the thrust side seal began to leak barrier fluid in to the process. The coupling side seal never leaked. The seals were pulled and disassembled to find the thrust side seal had two wear spots that were 180o apart from one another (saddle distortion) on the inboard or primary stationary face. The seals were repaired and re-installed in the pump. Just as before, shortly after the pump was started the thrust side seal began to leak barrier fluid in to the process. The coupling side seal did not leak. Just as before, the same saddle distortion was found on inboard stationary face.
The face distortion issues have been addressed by using a stationary bellows as opposed to a rotating bellows in order to isolate the face from the gland. Any thoughts as to why the inboard or primary stationary faces experienced face distortion? Also any thoughts as to why just the thrust side seals experienced the face distortion? Any help is greatly appreciated.





RE: Mechanical Seal Face Distortion
RE: Mechanical Seal Face Distortion
As far as the difference between thrust end and radial end problems, I would have other questions. How is the pressure between the seals maintained? With double suction impellers, the seal chamber pressures should be the same (suction). But, is the barrier fluid pressure controlled to the same setting on both seals?
Johnny Pellin
RE: Mechanical Seal Face Distortion
* The inner faces do see ID pressure. The stationary face is retained with a retaining ring that is held in place with a snap ring.
* The faces were distorted under the optical flat after the fact.
* There are cooling coils on the seal pots. Each seal pot has a separate connection to the cooling water header.
* Each seal pot runs within 10 degrees of one another
* The face materials are silicon carbide vs. silicon carbide.
* The stationary face is a L-type with flexible graphite.
* Pressure between the seals is maintained with a N2 blanket applied to the seal pot (API plan 53A). The barrier setting is the same for each seal pot.
The frustrating part in all this is that the same seals were installed in the sister pump a year and a half ago and are running with no issue. This lead me to suspect something was wrong with this particular pump. The machinist swept the box face and it measured a variance of .001" perpindicularity. My thought was that when the pump was at operating temperature there was some case distortion being transmitted to the seal gland and inturn to the seal face. Specifically the case distortion is occuring on the thrust side of the pump.
Since the install of the stationary bellows design the seals are running fine. I just want to better understand why the faces were distorting in the first place.
RE: Mechanical Seal Face Distortion
Johnny Pellin
RE: Mechanical Seal Face Distortion
Johnny Pellin
RE: Mechanical Seal Face Distortion
I think its in the seal assembly somewhere together with initial lapping finish.
good to see problem solved
RE: Mechanical Seal Face Distortion