Use of Belzona inside pump casing 2

[packdad]

We have a horizontal centrifual pump in a raw (lake) water system. We are apparently considering the use of a Belzona product to coat the inside of the pump casing to protect it from erosion/corrosion. Since this is a critical-application pump, should I be concerned about the Belzona coating chipping or flaking off at some point and locking the impeller? Unfortunately, I don't have any more specific details at this point, and I have not talked to Belzona yet, although I intend to when I get the chance. I was just looking for any opinions or operating experience you folks might have. I've seen Belzona used on piping and valve seats before, but not pump casings.

 

[packdad]

And, no, I don't know how/if this work could potentially affect pump performance, although any experience with this would also be appreciated. Right now, I'm just thinking in worst-case terms.

 

[macmil]

I am involved with relining of, typically, worn hard iron cases of slurry pumps, and also sometimes water pumps, typically vertical turbine pumps, using epoxy, ceramic, urethane etc
This sounds as though you are doing it on a new or unworn pump case; any specific reason why ? i.e. sand or silt in the water ? Unless you are expecting significant wear right away, I would wait and see if there is a wear pattern, and restore the worn parts back to the original dimensions when required. You should consider several aspects; one is reducing the internal casing dimensions which may adversely affect the pump performance, and possibly could increase your wear rates; a second is that the surface preparation before application of the Belzona is critical, or you will experience your feared delamination with resulting possible problems. Another point, if it is a new installation, is the effect on warranty. It is a bit hard to be more specific as you have given no sizing information. There are I believe several different grades of Belzona; the supplier should be closely involved.
mac

 

[rmw]

What is the basic metallurgy you are starting with???

Maybe you have a mis applied pump, if the metallurgy is not hard enough for erosion protection.

Are you aware of any of the manufacturers of 28 Chrome Cast Iron pumps??? Now, talk about hard stuff!!! Could your pump manufacturer furnish a casing and impellers in that stuff??

It is typically used among others, in applicationl like coal pile run off ponds, and ash sluice systems, where the abrasive attack is worlds worse than most lake water would be.

rmw

 

[PUMPDESIGNER]

The coating will probably change pump performance, and usually this is noticeable.

In big generalities:
Head Capacity Characteristic - Smoother and slicker coating may cause curve geometry to flatten causing pump to run further out towards BEP and beyond BEP, resulting in additional power draw. Coating could also cause the curve geometry to become unstable in the form of droop.

Efficiency Characteristic - Pump usually becomes more efficient because the coatings are often slicker and smoother than original bare casting, this causes additional power draw at all points on the curve (not just at BEP and beyond BEP).

I could possibly think of more things, but that is a start.



PUMPDESIGNER

 

[jay165]

I would not use Belzona in this application. In addition to the previously mentioned reasons affecting pump performance, it will exfoliate over time with exposure to high water velocities. It is a fine coating system, but works best in stagnant or low velocity applications.

 

[bingopin]

Have used Belzona and other similar coatings many times in water pumps with mixed results. Regardless of what Belzona says, I consider it a temporary repair that will allow time to engineer and procure a metallurgy upgrade or some other modification.

 

[packdad]

Thanks for the input, everyone. I've been away from the office and on nights to boot, so I haven't had time to discuss this in detail with our system engineer. He would be able to say for certain why we want to coat our pump casing.

However, I think it is an attempt to address a drop in pump performance over time. Casing erosion is apparently suspect - the pump casing is carbon steel (216 WCB). As I've said, my concerns are flaking off of the coating and changes to pump performance. Most Belzona applications that we've done have been in low-flow areas or areas upstream of a strainer.

I tend to agree with those that think a new casing of a different material would be a better option. If the pump weren't so critical, then I might be more inclined to give the Belzona a try.

 

[corrosionman]

Packdad
If your Belzona is applied correctly then you can totally ignore any fear that it will come off. Preparation must be by shotblast cleaning prior to coating with a thin coat.There is a UK Company who offers an epoxy coating for pumps and because it is a very smoothe high gloss finish they claim it significantly improves the pump efficiency.
However the biggest advantage is that impellors are usually of brass or stainless. If so, you have a dissimilar metal situation and the pump body is quickly seriously damaged by corrosion. The Belzona is not really very tough or hard wearing but it prevents electrical action which causes the problem.There are many brush applied coatings which do the same job equally effectively. What you must check is materials of construction and potential for lake water to cause D.M.Corrosion. Put both meyals in a tub of the water and check the potential they develop as a quick guide. Cheers DW

 

[packdad]

The impeller is bronze, by the way.

 

[smckennz]

Hi Packdad
if Belzona was superior to the virgin pump materials then the supplier would apply it as an original coating. OK for filling holes and bedding but many users expectations are unrealistic. If its a clean, clear lake and you are using cast iron casing/bronze impeller its highly unlikely you will have a problem. Using a repair product to pre-emptively "improve" reliability does not seem a sound practice.
From time to time you will need to service your pump; bearings, packing/seal, clearances etc. If your application is truly critical, then installing a standby pump would appear prudent.

Cheers

Steve

 

[rmw]

If this pump is so critical, why don't you consider changing the metallurgy of the impeller and/or wear rings?

Seems like coating the steel pump casing, while running a bronze impeller is going at it from the wrong direction.

Even if the coating, (any coating) was successful, and gave zero problems, the impeller would be gone long before the casing even needed to be considered as a candidate for coating.

rmw

 

[poppeye]

Pacdad,
There are many other epoxy based compounds on the market that will out perform Belzona for your application. Belzona was approved by the U.S. Government in 1981 as a permanent repair for erroded casings on U.S. Naval Vessels. Repairs using Belzona were conducted onboard the U.S.S. Ajax, a repair ship. I assisted Navsea Technical personnel and the representatives from Belzona in these repairs. I was very impressed and so were the Government personnel. I retired from the Navy in 1993 and entered the Industrial Pump Repair market shortly afterwards. I was lucky enough to stumble on a product called Cronatron Welding Systems. They offer a products called Pollymet and Polly-ceram. At the time I was trying to tackle a problem Timken Co. was having with their 12" Hazleton pumps 5500gpm @73ft. The water carried with it carborundum that was erroding the discharge head just below the pump outlet flange. Cronotron offered the Polymet as a base coating with a hard ceramic coating of Polyceram as a top coat. The surface was shot blasted clean followed with a grinding wheel preparation. The area is cleaned with brake cleaner to remove any residue. The initial coating of up to 2" of Polymet was applied with the Polyceram at a thickness of 10mil. Pumps previous to this type of wear were lasting 8-10 months then patch welded. At 1.5 years this pump was removed for impeller upgrade. There was an area worn the size of a quarter at the previously repared area. This area was re-preped and coated with Polyceram. Since that time I have performed many repairs with these items with great sucess. These items are quite expensive when compared to Belzona, but well worth it. The most important thing is the base metal preporation to avoid separation of the coatings. Cronatron can be contacted at 1-800-458-3222.

Poppeye

 

[wxia]

One Belzona coating called Supermetalglide, works fine in raw water pumps and high lift pumps. It is NSF approved, tested by pump OEMs that effective in new pumps for efficiency improvment (Flowserve, Goulds, Aurora etc.)
Our experiences indicated that if the coating is applied properly, it should not delaminate easily, but protect the pump and maintain the pump efficiency, unless encountering severe abrasion.

 

[Berko]

Try talking to Weir Engineering Services for pump coatings, they have a lot of experience of coating pumps for corrosion, erosion + in many cases efficiency improving coatings.

As a division of Weir pumps, they now how to prepare the internals of the pump casings (i.e. machining rebates, surface prep, etc).

I hope this helps,

Berko

 

[Twincam]

Hi packdad,

I am using a product similar to Belzona on the pumps I work with and it has helped extend the expected life of the casings. The pumps are Sulzers and Allen Gwynnes, about 35 years old. The expected coating life is 10 years before recoating is required, but it will probably last 15. The medium is raw water for the electricity production industry. Performance is 750l/s @ 255.0 mWg, and 1000l/s @ 350 mWg.