Pump failures

[soken2006]

I have an Acid system in our steel pickling line. 4 pumps in parallel pumping 18% acid to a '6 storey tower' Each floor of the tower have 4 sets of spray headers. So many pumps failed, and replacing these pumps cost a lot of money and management is giving us a lot of pressure. We hooked up the motor and take the horsepower reading and observe changes. The Hp required for all 4 pumps showing they are running on the 'left' side, or low flow side of the curve. A while later, one pump starting to fail, Hp dropped by 10. I didn't hear any cavitation noise while the pumps are running, even though it is cavitation, shouldn't it deteriorate before Hp dropped in a sudden? Also, is there another explaination for sudden drop of Hp of a centrifugal pump, which means pumping less flow, other than suction blockage? Thanks.

 

[Artisi]

To fully understand what is happening you will need to establish the flow rate, inlet and discharge pressure, SG of the liquor being pumped, pump speed and power input. If you have this information and a pump curve you can then start to analyse the problem - otherwise it's all guess work.

A description of the "damage" to the pumps or better still some photo's will greatly help.

Phitsanulok
Thailand

 

[stanweld]

What are the materials of pump construction? It would appear that the materials selected/provided may have been inadequate for the service.

 

[soken2006]

Gents:


Thanks for your advise. I don't know how to load pictures onto this chat room unfortunately. I do have some pictures of failed impellers. The impellers are made of Fibre glass. The acid is 18% HCL and SG is 1.15.

To Artisi:


I worked on this with my Piping Engineer, learning it from the pump curve, without flowmeters, individual discharge and inlet pressure gauges (have one common discharge pressure gauge), there is nothing we can do. I am curious to know why did the Hp dropped in all of a sudden, but there were no excessive noise or vibration that can be detected. That's what puzzles me.


Thanks

 

[JJPellin]

Have you seen the inside of a failed pump to see what may be happening? We purchased a set of fiberglass pumps for a sour water service. These pumps failed suddenly and catastrophically. We found that the particular fiber glass formulation was not compatible with our service. The material would swell and soften and eventually, the metal hub imbedded in the fiberglass impeller would tear loose and the impeller would stop spinning. That could definitely cause a sudden drop in amp draw without necessarily making a lot of noise. We changed to a different grade of fiberglass and got some improvement. Eventually, we changed to stainless steel pumps and got away from fiberglass entirely.

 

[soken2006]

Thank you very much for your replies. This is what we plan to do, it just puzzles me to what happen to the pumps when no significant noises were detected by Amp draw dropped significantly. Thanks.

 

[Artisi]

soken2006
" it just puzzles me to what happen to the pumps when no significant noises were detected by Amp draw dropped significantly"


See the comment below from JJPellin - does this mean anything to you.

"he metal hub imbedded in the fiberglass impeller would tear loose and the impeller would stop spinning."


Phitsanulok
Thailand

 

[pumpking]

Glass fibre reinforced pumps have limited success in these kind of applications, simply due to the glass fibres being chemically attacked or suffering in some way.

We manufacture pumps in Polypropylene and PFA for such applications and have many years success, however, these are virgin material with no mechanical fillers, which tend to be the weak point of non-metallic pumps.

If you have continued failures, it will be worth investigating the virgin Polypropylene line as they will tend to be a lot cheaper than St Steel, but more importantly, more reliable in the long term.

visit

http://www.cdrpumps.co.uk

and click on applications to see similar applications.

Hope this helps in some way ?

 

[lilliput1]

What is the operating condition on the pump suction? Is the pump inlet below or above the level of the fluid in the suction tank? What is the absolute pressure on the fluid level. What is the pump rated minimum NPSH? What is the specific gravity of the fluid. What is the pressure drop in the suction piping. Does the suction piping slope down going to the pump or does it rise up? What is the suction piping highest elevation compared to the fluid level in the tank? Have you done an available NPSH calculation?