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Frequent Failure of Reciprocating Pump Crankshaft

06/18/2021 7:50 AM

One reciprocating pump installed in DHDT plant to supply water (Presence of H2S) in reactor. Pump pressure and flow is 180Kg/cm2g and 34M3/hr respectively. Pump was commissioned in 2019 and but crankshaft got fail 3 times .Refer the attached pic. It seems to be fatigue but whether is it supposed to happen during such short span of operation (approx. 3-4 months). Please suggest what may be probable causes ?

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#1

Re: Frequent Failure of Reciprocating Pump Crankshaft

06/18/2021 9:35 AM

Maybe due to biogenic sulfide corrosion, where H2S is converted to sulfuric acid by bacteria.

https://en.wikipedia.org/wiki/Biogenic_sulfide_corrosion#:~:text=Biogenic%20sulfide%20corrosion.%20Biogenic%20sulfide%20corrosion%20is%20a,the%20presence%20of%20moisture%20to%20form%20sulfuric%20acid.

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#6
In reply to #1

Re: Frequent Failure of Reciprocating Pump Crankshaft

06/20/2021 11:32 PM

How sulfide corrosion may take place ?

Crankshaft is not suppose to contact with sour water.

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#9
In reply to #6

Re: Frequent Failure of Reciprocating Pump Crankshaft

06/29/2021 7:50 AM

Every seal has some leakage.

There are no perfect seals.

There may be small leaks around the shaft seal that evaporate rapidly due to internal heat and are not found in a liquid form when examined,but the corrosion and breakdown of the oil may still occur.

When it cools down, or fails and is examined,you find no liquid,so one thinks there is no leakage.

Have an expert replace the shaft seal(s). The seals are very easily damaged by inexperienced personnel.

Please give feedback on the results.

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#2

Re: Frequent Failure of Reciprocating Pump Crankshaft

06/18/2021 10:49 AM

Reciprocating pumps depending on design sometimes create repeating pressure shocks equivalent to hydraulic "hammers" that reflect back and overload bearing surfaces etc. Is output "elastic" enough to absorb these? If not you may have to add some device specific to counteract that. S.M.

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#3

Re: Frequent Failure of Reciprocating Pump Crankshaft

06/18/2021 2:05 PM

You should look down stream,... with what said before, that could be a form of water hammer.

off the top,.. it may help to put in some type of capacity’s or accumulation tank that has some type of an air bladder, or even where you can pressurize it with air to absorbs and dampen the shock from the possible water hammer effects.

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#4

Re: Frequent Failure of Reciprocating Pump Crankshaft

06/18/2021 2:44 PM

..."Crankshaft failure can be attributed to the following causes: overload conditions, insufficient lubrication, cavitation, bearing failure to name a few. If these conditions are experienced, the crank shaft should be inspected."...

You need to have a forensic examination by a qualified person that can determine the exact cause or causes, of this frequent failure....I'm thinking lack of proper lubrication, for some unknown reason, and/or overloading of pump...I would check the pump specs to see if you are running the pump well within the margin of safety...Pushing a pump close to its rated limits everyday, is not a good idea....In this environment I would be looking for lubricating oil contamination causing lubrication failure...I also would look at the design of the pump to see if it the best choice for this application....also would check with manufacturer for similar failures in the field....

https://chemacinc.com/2019/05/06/high-pressure-plunger-pumps-crankshaft-wear-and-tear/

https://www.pumpsandsystems.com/triplex-pumps

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#5

Re: Frequent Failure of Reciprocating Pump Crankshaft

06/20/2021 5:22 AM

With the conditions stated,be certain that your lubricant is the type specified by the manufacturer of the pump for the type fluid you are using.

H2S is very corrosive and may cause problems with oil chemistry if not properly formulated for this purpose.

There could be a combination of factors here,and as SE stated,have a reliable lab perform an analysis on it.

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#7

Re: Frequent Failure of Reciprocating Pump Crankshaft

06/21/2021 5:16 AM

Please describe the outcome of the pump manufacturer's site visit.

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#8

Re: Frequent Failure of Reciprocating Pump Crankshaft

06/29/2021 6:45 AM

perhaps the working temperature effect was already mentioned above but

you could look for smth. alike a "random search"

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#10

Re: Frequent Failure of Reciprocating Pump Crankshaft

07/02/2021 4:30 PM

i was initially thinking of possibility of the poor material choice of the pump manufacturer - so it ?? might degrade under "long term" "stress relieving" ??
(the src. of the idea is the carbide drill failure at overheating and alike)

the car engines work for decades ...

... so , if your breakup evt. is thermal related it might be more likely for some local "stresses"

i'm not a mech. eng. - so ...

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