Seizure of wear rings 1

[replica]

Hi all,
I had experienced on seizure of the wear ring. Is the seizure of between impeller wear ring and casing wear ring always related to galling? or is there any other caused of the seizure? Any comments?

 

[JJPellin]

If I was not familiar with your last post on shaft wear, I would not be able to provide a meaningful answer to this new question. You might want to give some background information for those who did not read everything in the previous post.

Wear rings can seize up for a number of reasons. Galling based on material hardness requires two problems. First, the wear rings need to be able to touch. This requires clearance within the bearings or bushings or sufficient shaft deflection. The second requirement is to have materials that will gall. Typically, wear rings are designed with a hardness difference between the two rings to prevent galling. As an alternative, you can simply make the rings so hard that they cannot gall even if there is no hardness differential.

Another possibility would be differential thermal expansion. We once had a set of pumps that were experiencing severe corrosion from Naphthenic Acid. A good material to resist Naphthenic Acid corrosion is 317 SS. Someone decide to install 317 SS wear rings into a CA6NM (13% Chrome) casing. The 317 SS has a much higher thermal expansion rate than the chrome. Since the relatively thin wear rings could not expand outward because of the massive casing, they expanded inward, rubbing hard on the impeller and causing the pump to seize up. But, I know from your other post that your service is low temperature, so this is unlikely.

Since your pumps have 19 stages, I am leaning toward shaft deflection. A pump with this many stages poses a particular challenge when it comes to thrust loads. Typically, the thrust loads are carried entirely by the motor. And, with 19 stages, the total thrust can be very high. So, the design is modified to reduce the down thrust at normal or low flow conditions. This creates a new problem. If you reduce the down thrust at normal or low flow, you create the possibility of up-thrust at high flow. If a pump of this design is allowed to run into a slack like and drop off the right side of the curve, the thrust can reverse. A relatively thin shaft can easily buckle under compression when these conditions exist. If the shaft buckles, it can drive the rotating parts hard into the stationary parts, resulting in high wear or complete seizure.

Are these pumps ever run into an empty line or allowed to run off the right side of the curve while the line is flooded and pressurized?


Johnny Pellin

 

[Artisi]

For anyone wanting to comment on this post, it would be prudent to review the OP's previous post on "worn pump shaft" as it is possible the two have a common connection.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[replica]

JJPellin

Thank you for a great post and sharing your experience. Our casing and impeller wear ring are made of the same materials, ie SS304 but with different hardness.Casing wear ring and impeller wear ring have vickers hardness of 330Hv and 270 Hv respectively. The hardness different is 60 Hv (57HB) which is higher than 50HB recommended in API 610. I know that SS304 has very low galling resistance and prone to galling but the hardness difference is acceptable. Our pump has a worn out shaft that may cause imbalance and shaft deflection. The wear rings touched each other and seized. My question is, is this seizure because of galling? or can it stuck due to other reason, such as normal rubbing? As far as i know the evidence of galling is that it has to be a sort of adhesion wear whereby the materials from the two mating parts have to transfer from one's surface onto the other surface in the from of lump. If there is no material transfer than it is not galling even though the component seized. Our wear rings seized but when I analyse on the mating surface, I could not find any evidence that the material from casing wear ring had transferred on to the surface of impeller wear ring and vice versa. The seized wear rings can just be easily removed which I believe is not so if galling had occurred.

Are these pumps ever run into an empty line or allowed to run off the right side of the curve while the line is flooded and pressurized?

I am sorry that I cannot answer this question because I have no record on this.

 

[replica]

Artisi

Thank you for clarification.

 

[Artisi]

You probably realise that I like to deal with the practical aspect of failures - - why did it happen?
To me the theory of hardness / material differences is meaningless is solving your problem. The problem being is that the impeller has clashed with the casing - - WHY, solve that and the problem of galling goes away.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[samafa]

Hi Replica,

It may occured by temperature of fluid.. have you checked the clearance between both of wear rings? in some running clearance, we should cosider to give "galling clearance" as because thermal expansion in rings, i'm affraid that the clearance are too small enough to prevent the temperature..

This is just another side of view, mean while I can't see the appearance of those rings after seizure.

 

[replica]

Artisi

I agree with you ... I can see that your approach is more on solving the problem. In fact this is the aim of everyone. However in order to solve the problem I need to know exactly the cause of seizure. For example if the cause of rings seizure is due to galling, than I need to change the rings materials. But if the seizure is due to rubbing of impeller wear ring with casing wear ring than I do not need to change the materials and focus on how to solve worn out shaft.

samafa

The seizure of the wear rings is due to shaft deflection that cause the impeller wear ring to rub the casing wear ring. I think it is nothing to do with the clearance between the wear ring. Please refer to my previous post on worn shaft. The thing that I want to know is seizure always a manifestation of galling or can be due to something else..meaning that if you encountered the seize part..it is not always due to galling.

JJPellin

What I can understand from you post that seizure of the wear ring is not always due to galling. Am I right? or I got your statement wrong.

 

[Artisi]

What are you trying to ascertain, what is the mechanical action and reason for impeller / casing clashing or what is the metallurgical actions leading to galling?

Two completely different animals, although in your case I think connected.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[JJPellin]

I agree that galling is not required for an impeller to seize up. If there is a hard rub, heat will be generated. If the wear rings heat up and grow, the thermal growth can take up the available clearance. With no remaining clearance, the wear rings will seize. So, to Artisi’s point, avoid the rub and you avoid the seizure. Simply changing materials to try and reduce the galling potential won’t solve the main problem.

With that said, there are materials that can rub hard and not seize up. Some advanced non-metallic materials can rub hard or even run dry without seizing up. If that is what you want, consider some advance polymer based material for your wear rings. These might not prevent the failure entirely. But, they might buy you time. In some cases, they might buy you a lot of time. In crude oil, it might be very difficult to find a non-metallic wear ring material that is compatible with the process and able to withstand the abrasives present.


Johnny Pellin

 

[samafa]

Replica,


Mostly galling in wear rings come form friction between each other (after years I handled for repair/overhaul), rarely I see it comes form material itself when the pump had running ofcourse after we select the proper material. (if you had experienced with shaft deflection, that the first point to be noted)

You now, like stainless steel that easily to galling, per API 610 one ring need to be harder than other this point is "set" to accomodate galling reaction as because sliding-rub. Typically, hardened materials are more resistant to galling. So, if you want to prevent the galls, please make choose a dissimilar material; herdening or coat the material.

I think my comments enough for you to draw the summary.



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Suck, squeeze, bang blow..

 

[replica]

Artisi

Thank you very much for your comments. I will the shaft deflection issue.

JJPellin

Again, thank you very much for your comments and clarification.

samafa

Thank you very much for your comments. But I think I have to be careful on choosing the right wear ring materials because we are pumping sour crude oil and the material need to comply with NACE 0175. However as Artis stated, avoid the rubbing, then you will avoid galling.