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Posts: 1,810
Reply with quote  #1 
I have a customer with lots of pumps with a large percentage of them below ground in pump rooms, often damp due to lack of consistent sump pump operation.  In one particular room, the pumps are all grounded to the motors (I'm told not in the other rooms, but I've not verified this yet).  One of these pumps was recently replaced and the ground wire was left off the pump.  The inlet on this pump was apparently eat up with pin-holes, but not the outlet, and not the impeller.

Could this be from a lack of grounding?  I know there are rubber expansion joints on the discharge, but I'm not sure about the inlets.  I also can't recall if the joints are "bridged" by the bolts I see across some expansion joints (metal bellows joints mostly).  

I've not seen any of the damage personally, and I'm not clear on the story here, so just wondering what you guys have seen.

"The trend is your friend"

Sr. Member
Posts: 163
Reply with quote  #2 

About 15 years ago at our facility, the piping in one of our safety systems was found to be severely degraded due to MIC (Microbiological Influenced Corrosion).
I was not involved directly but from what I remember, it was not easy to locate the areas of corrosion with standard UT probes - I believe because of the small pin-hole type of defect?

Much of it was attributed to the fact that the system was not operated often (only during Safety PM tests) resulting in stagnant water along with the type of stainless steel used.

Since I don't recall all the pertinent details, I found this article describing MIC

I don't know if this even pertains to your client's particular situation or if the grounding cables have anything to do with it.

Just thought I would pass it along.

Jim P

Dave Reynolds

Posts: 53
Reply with quote  #3 
Have seen pin holes in vertical column pump with SS impeller, ductile iron "bell" on pump inlet. In my case it was cavitation causing the holes. If the water is swirling on top and visible to the naked eye, could be quite turbulent down below

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