Corrosion / Errosion within Seal Flush Pump?
Corrosion / Errosion within Seal Flush Pump?
(OP)
Hello everyone! I'm a young, relatively new engineer and have encountered a problem with one of our seal flush pumps. It is a single stage, horizontal centrifugal pump operating @ 285 gpm and 185 psi. It receives suction off of a potable water tank and is used to flush the mechanical seals of several other larger pumps. We tore the pump apart noticing increased amount of noise and saw extreme corrosion and pitting within the volute case, impeller, and stuffing box, as well as within the suction pipeline. My question is, could this also be a case of cavitation even though there is more than enough NPSHa comming off the potable water tank? All the parts are carbon steel.





RE: Corrosion / Errosion within Seal Flush Pump?
Posting a picture of one or more of the parts would help.
RE: Corrosion / Errosion within Seal Flush Pump?
Immediately from your post, the flowrate and pressure sound high, meaning that what may be happening is the pump is hanging on the end of the curve. Alternatively, it could be that the circulating pump is not generating sufficient pressure and the seal faces are weeping product into the flush liquid - normal recomendation is to have seal flush liquid 1.5 bar above stuffing box pressure to avoid faces lifting off - seal and pump manufacturers can advise more specific figures for these !!
It may be worth looking into how the pumps operate, are they working at constant flow, or do they move up and down the curve during operation ? If they do move, you may want to investigate and ensure you are not putting any 'hammer' back to the pump - the effect of this again is to lift process end seal faces allowing product into the fluch system.
Hope this will be a starting point for you - alternatively, buy a mag-drive from www.cdrpumps.co.uk ????????????
RE: Corrosion / Errosion within Seal Flush Pump?
RE: Corrosion / Errosion within Seal Flush Pump?
Check the water for fine solids and also check pH.
RE: Corrosion / Errosion within Seal Flush Pump?
RE: Corrosion / Errosion within Seal Flush Pump?
I recommend to check all possible reasons as follow:
Pitting corrosion could be option, you should check pump materials for suitable seleccion and realize if there is any corrosion agent, ph and temperature in your pumping fluid. From Ductil Iron to SuperDuplex materials are avilable for Corrosive hanling fluids.
If it is erosion could be option, you should check tip velocity, max RPM, % in solids by weigh , D50 and Casig/Impeller hardness to determine if your type of pump could handle this fluid.
In another hand, it is an standard rule that if NPSHa > NPShr then there is no cavitation (that is not always true).
Cavitation for recirculation at discharge or for high velocity are present some times.
RE: Corrosion / Errosion within Seal Flush Pump?
RE: Corrosion / Errosion within Seal Flush Pump?
RE: Corrosion / Errosion within Seal Flush Pump?
Try API S6 materials.