pump casing leakage hole

[sunloco]

http://photo.163.com/photos/sunloco/67009346/

Please see the link about the pics of pump casing.
This is seconde casing of in-line pump that was damaged.we could find any problem for medium or structure failure.
in the casing near to casing wear ring there is obvious abrasion ,especially there was a hole coming out .but for impeller there is no any abrasion . buddies ,is there any analysis for this case ?

 

[JJPellin]

It looks like what the old-timers used to call "steel worms". I would categorize it as corrosion/erosion damage from abrasives in the product or velocity-dependant corrosion mechanisms. The damage tends to concentrate in high velocity areas and once damage appears, it progresses rapidly. It can attack any discontinuity in the parts. It tends to be worse in the stationary parts rather than the rotating. But a set-screw hole where an impeller wear ring is attached can be the starting point of similar damage on the impeller. We started seeing this in many pumps a few years ago when our crude slate changed. According to our metalurgist, our new crudes produce naphthenic acid corrosion at certain temperatures. But this corrosion mechanisms depends on velocity to remove the stable corrosion by-products so it shows up as localized grooves, swirl patterns and "worm tracks" in carbon steel, CA6NM (chrome steel) and other materials. What is the case material? What is the product being pumped?

 

[Artisi]

Are you sure there are no abrasives in the pumped liquor, the pics seem to indicate typical erosion as pointed out by JJPellin - from the pics I couldn't be sure and say there is corrosion much involved. A couple of close-up pics would be nice and might indicate a bit more info.
Also, what is the duty and is the pump operating near to its BEP - as recirculation could also be a contributing factor.


Naresuan University
Phitsanulok
Thailand

 

[PBroad]

I don't know if your fluid has any adsorbed air but there could be a "cavitation issue" see

http://www.mcnallyinstitute.com/01-html/1-3.html

 

[motorsdirect]

I agree with the last message...This looks like cavitation...which can be caused by air leaking into the system and having no way of excaping once it finds its way to the pump...a lot of pumps have breather holes in the castings to help, but these get blocked over time.

Jeff

http://www.motors-direct.co.uk

 

[JJPellin]

Cavitation damage tends to be very jagged and irregular. The individual cavitation bubbles collapse randomly over an area creating a rough deeply pitted surface. The damage shown in the picture has swirl marks and patterns to it that show no sign of cavitation. It is pure erosion or a corrosion/erosion mechanism. I am certain cavitation has no role in this damage.

 

[Artisi]

Agreed, what is shown is these pictures is typical erosion damage - not cavitation, and besides, air leakage into a pump system is not cavitation.

Naresuan University
Phitsanulok
Thailand

 

[arunmrao]

I suppose this is a cast casing. If true, then it is more related to a foundry defect. The mold has not been properly filled while pouring and there might have been an attempt to cover this flaw superficially,which now stands exposed.