×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Unusual pump casing erosion situation

Unusual pump casing erosion situation

Unusual pump casing erosion situation

(OP)
Here's an unusual situation...

1. Centrifugal pump in slurry service. Hardened alloy material.
2. Short outage to briefly do maintenance elsewhere---nothing done with this pump.
3. When pump starts up, the pressure drops dramatically. within days.
4. Removal of casing shows concentric rings all around suction, almost to edge of casing. Impeller, however, looks essentially undamaged. Some machine marks still visible.
5. New casings show same erosion, not quite as fast, but much faster than ever before. Same materials of construction used over last two years without issue.
6. Slurry does not seem to have changed.

Any thoughts on why this could be???

RE: Unusual pump casing erosion situation

Some photographs would be a great help.
 

Naresuan University
Phitsanulok
Thailand

RE: Unusual pump casing erosion situation

Hello Artisi and p92,
Photos would be best.
Just post 'em up somewhere and give us the link.
Put 'em up high res if possible so that we can download them and zoom.  

PUMPDESIGNER

RE: Unusual pump casing erosion situation

(OP)
Mmmmm...well, technically, I'm not supposed to send any photos (even harmless ones like this) without a signed form for each company I send it to. I can only imagine how many forms I'd have to sign for a Web posting...  =)

What would you be looking for in particular? There doesn't seem to be any pittting in the circular grooves on the inside of the casing. The grooves are concentric. There are more of them than can be easily counted. The materials people say that it looks like erosion is the primary issue, not corrosion. I just don't know what the reason behind the erosion would be, other than the slurry's being different or there being recirculation somehow.

Is there a possibility that quality control issues with the casing can cause recirculation?
 

RE: Unusual pump casing erosion situation

What model and size of pump are we talking about - is it open or closed impeller, what are the materials of construction, what is the slurry.

WHAT HAS CHANGED RECENTLY, if you used to get 2 years life from casing.

No connection between quality control and recirculation, recirculation is a function of pump hydraulics.
Have you check material of casing against spec - is it as hard as it is supposed to be.


 

Naresuan University
Phitsanulok
Thailand

RE: Unusual pump casing erosion situation

(OP)
4" suction, 3" discharge, 10.25" open impeller. Ferralium 255 material of construction. Chemical slurry, so it's not like a rock slurry or something.

The "what has changed recently?" is the part that has gotten me confused. It doesn't look like anything has changed. We took a short outage, not touching those pumps at all during the outage, and the readings I've looked at (pressure, temperature, level, etc.) look the same after the event as compared to before.

One thing that has changed is that, normally, there is a recirculation line that bleeds off the main line so pressure doesn't get too high. Right now, it is plugged---but it plugged after our issues started, not before.

There's no connection at all between quality control and recirculation? I've heard of people trying to weld repair their casing and getting unusual circulation patterns, so I thought quality control might be coming into play here.

I've material-checked the metal, but not the hardness yet. I didn't check the hardness because the first casing that had damage was one we had run on for several months, so it seemed unlikely that it was softer. However...

We have Pump 1 and Pump 2 as in-line spares. Pump 1 first had the casing issues, but it's always been Pump 2 since then, for the next three casings. (Normally, we would run on Pump 1 all the time, but it has developed a habitual leaking problem, so we run on it only intermittently.) I dismissed hardness as an issue at first. But now I think that maybe Pump 1 was an anomaly and Pump 2 may follow more of a pattern (like being not as hard as before).

Any more thoughts? Thanks for the feedback so far...
 

RE: Unusual pump casing erosion situation

The only wild card thought I have at the moment is some hard solids in the slurry. If the open impeller front clearance is a bit wide - you may have solids jamming between the impeller and the casing - this is the only thing I can see that will give you concentric grooves worn into the casing.

Naresuan University
Phitsanulok
Thailand

RE: Unusual pump casing erosion situation

I think that the suction vortex has the most predictable flow pattern, allowing the slurry to "phonograph" your suction inlet.  You may or may not see the same wear pattern within the casing because of the more complex flow pattern due to pressure differentials within the casing.

Suction diffuser?

RE: Unusual pump casing erosion situation

(OP)
Hi Ethan317,

I may not have stated the situation as clearly as I thought. The suction nozzle actually looks pretty clean. It's once you get inside the casing that you see the "phonographing." It goes as far as the outside diameter of the impeller.

You think a suction diffuser would still be the way to go in this case, or would that not help this particular situation?

RE: Unusual pump casing erosion situation

p92,

The suction diffuser would probably not help in that case. I threw it out there for fun.  I'm curious about that recirc line that's plugged.  Let's not confuse internal casing recirculation with an auxiliary recirculation piping plan.

Ethan

RE: Unusual pump casing erosion situation

p92,

It looks like there might be a pattern hidden in your posts:  does the wear show up more on pumps that are started/stopped more frequently?  I could imagine a situation where the slurry segregates slightly during flow stoppages, and the resulting "clumps" of material could do a lot of damage until the flow is up and humming along again.

Ben T.

RE: Unusual pump casing erosion situation

(OP)
The pump actually runs continuously. When we switch over to the in-line spare to make repairs to a pump that is having issues, we flush out the troubled pump ahead of time.

We thought we might have had a clump when the first pump had its issues, but having it for four other pumps after that is less plausible.

p92

RE: Unusual pump casing erosion situation

Hi

Im an After Sales Expert for all kind of Power Plant and Industry Pumps, Valves, Stainers and so on. To check the real damage reason some photos would be helpful. Please, enclose also the techical datas of the pump together the photos like (Medium incl. PH value, Volume, High, Suction and Discharge pressure, Temperature).

With the help of this information it should be possible to have a better look to the problem.

Bye and greetings from Germany
Jochen

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close