2 replies to this topic

Dear all,
I am facing problem of vapor locking in mechanical seal oil system of multistage centrifugal pump.
Description of Pump: 8-stage horizontal centrifugal(2+1combination ),back to back arrangement of impellers,Pumps are used to increase pressure of fluid in crosscountry pipeline to pump it to next pumping station.Pumping fluid: LPG, Max RPM=3420,Max capacity of one pump=150 Mt/hr,max discharge pr=78 kg/cm2.Flow rate is controlled with help of variable frequency drive.
Operating data: (1.)suction pressure 20-23 kg/cm2,discharge pressure: 64-65 kg/cm2 @ 280MT/hr flow of LPG (2 pumps parallel)
(2.) suction pressure 20-23 kg/cm2,discharge pressure: 57-59 kg/cm2 @ 230MT/hr flow of LPG (2 pumps parallel)
(3.) suction pressure 20-23 kg/cm2,discharge pressure: 50-52 kg/cm2 @ 150MT/hr flow of LPG (1 pump running)
Pumping temperature=45-50 degC these are flow patterns; maintained as per downstream pipeline customer availability.
Mechanical seal description:
double seal, tandem arrangement at both dive and non drive end ,API plan 52 with API plan 11, For API plan 11 flushing line, one tapping is taken out after fourth stage of pump, and bifurcated to both ends seal's flushing point(through orifice),and this flushing LPG returns back to pump.For plan 52 there is seal oil tank with required piping,seal oil tank pressure is atmosphere pressure.Buffer fluid seal oil is mineral oil.Circulation of oil is maintaained with help of pumping ring and thermal siphon effect. Alarm are there for seal oil level in tank and seal oil tank pressure.
Problem: vapor locking occurs frequently after 2 or 3 days in seal oil circulation lines( coming out of seal and going to seal from seal oil tank).what are reasons for this.We check this by touching(cold or hot) seal oil circulation pipes and rising level in tank.Is seal box pressure becomes nearabout equal to vapor pressure of LPG at pumping temp.(45-50 degC). Vapor formation starts, and seal faces pops out.will increasing seal box pressure( by variation in orifice dia.) give any solution? Any suggestion/inputs are appriciated.

[ankur2061]

Rathore,

Have you send your query to the pump/mechanical seal vendor? Presumably the mechanical seal is provided by some reputed vendor (Flowserve, John Crane, Burgmann??). These are some of the most reputed manufacturers of seals & if your seal is supplied by any of them, they will definitely help you to trouble-shoot.

My sincere advice would be to contact the seal manufacturer to resolve your problem instead of resorting to hit-&-trial measures. You risk a lot in damaging the pump and also creating a hazardous situation (IT'S LPG ISN'T IT).

Regards,
Ankur.

[Qalander (Chem)]

Dear rathore

any update on 'ankur' advice.

Has the problem been resolved?