Centrifugal cast iron pump wear rings - switch to brass 2

[Rputvin]

The company I work for has a line of Chinese pumps that we buy as parts and assemble in the US to use in our equipment. They are the generic end-suction, close coupled, cast iron cases and impellers, simple type 21 seals, being put into water/glycol loops in industrial applications, 1hp to about 40hp NEMA frame, that just about everyone makes their own little flavor of.

There are occasions where equipment is shipped and ends up sitting for long durations - sometimes up to years as projects are delayed or whatever reason. We ship with corrosion inhibitor glycol in the pump cases as water is used as test fluid at our shop and can't be 100% drained, to prevent the pumps from freezing and cracking in shipping/storage. Going through a drying step instead is not something we can implement.

The main issue that pops up from these instances is that the impeller will rust in place and the pump needs to be broken free before it will run - usually a wrench on the motor shaft is all that's needed, but it generates a service call every time. We're considering using brass wear rings as they'll be somewhat immune to the rust issue at the nose of the impeller where it seizes up, but I'm mildly concerned we're introducing a new variable into what is otherwise a bulletproof design that will last the life of the system (10-20 years) as long as the motor is kept healthy and the pump isn't abused running outside its happy zone.

I'd love to hear some feedback and help with the decision on whether we want to use these in limited capacity when we know a prolonged storage is in the pump's future, or if it would be wise to move our entire product line over to brass to help protect against variables we can't control. Or if this is a bad idea wholesale and we should just deal with the infrequent issue of stuck impellers.

 

[EdStainless]

Brass pumps will be expensive and in the end work exactly the same.
I can think of a couple of possible steps.
Find pumps that come with drain plugs so that they can be emptied and then spray the inside with a corrosion inhibitor.
OR you could put a step in the startup instructions to use a wrench and rotate the pump before energizing.

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P.E. Metallurgy, consulting work welcomed

 

[TugboatEng]

I need to clarify a sentence.

We ship with corrosion inhibitor glycol

Do you mean corrosion inhibited glycol? Glycol is NOT a corrosion inhibitor.

Using a film forming inhibitor in your test fluid can allow the pump to air dry without major corrosion.

Bronze wear rings on both the pump casing and impeller can help with sticking but introduce another problem. Bronze pump components are very sensitive wear, especially if the pump is operated on the right side of the pump curve. Cast iron is tougher under cavitation conditions.

Bronze wear rings won't prevent corrosion in the seal cavity which can also cause the pump to get stuck.

 

[Rputvin]

Brass pumps will be expensive and in the end work exactly the same

To clarify, this is just the wear ring for the impeller that would switch to brass. It's about a $15-30 cost increase per unit. It's not insignificant in terms of % of cost, but it's still a fraction of what a domestic supplier would charge for the same China-sourced part.

Our pump cases have drains, and we use a shopvac to assist the draining. Even when dried as best as we can we've had freeze damage, and rusting over years of storage is still an issue. Since moving to a glycol fill we're no longer damaging pumps.

Our paperwork has instructions that address this issue. It would require them to read the manual.

Do you mean corrosion inhibited glycol? Glycol is NOT a corrosion inhibitor

Yes, we're using NuCalgon TyIon B20 as the corrosion inhibitor, mixed with bulk 'heat transfer fluid' KostChill propylene glycol.

We have used all manner of inhibitors and other methods to prevent corrosion. Most of them work great in the short term, but this issue persists. To be honest I'm not 100% sure the failure is corrosion seizing the nose of the impeller into the wear ring, but that's the only tight interface that would impede rotation, and what we see when we run corrosion tests in house, but none of our tests have been on the scale of years of prolonged idle/storage. Our seal components are stainless for the spring and sleeve and whatnot or buna/viton/ceramic/silicon depending on the specific seal material, so there's not much in the seal pocket that will contribute to this issue.

Brass/bronze being softer than cast iron is part of my concern. We can't control operating conditions, so there are pumps that see less than ideal conditions for years on end - I don't want to generate more overall service calls from worn wear rings in an effort to mitigate a minor inconvenience with a few stuck pumps per year.

 

[Artisi]

pumps in long term storage require ongoing attention, the unit needs to be rotated on a regular basis - also the mech. seals don't appreciate long-term sitting there stationary, and you have the problem of the motor bearings Brinelling. The unit should be rotated on a regular basis, this could be done by hand and should form part of storage procedure.
regarding the "rust" problem, is it financially viable to fit bronze wear rings to the impeller and in the case?

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.)

 

[Rputvin]

Artisi - If I could control the storage in any way this would not be an issue. Customer buys a custom piece of equipment for Project X and needs it in 10 weeks. The unit is shipped, and two years later we're informed the project is finally underway, the unit was installed very recently and now it won't turn on, it's leaking, parts are missing, you get the idea.

It is financially viable to install a brass/bronze wear ring (I need to investigate exactly what alloy is available from our supplier), but you've mentioned other potential issues that need consideration and whether or not the added cost of the wear ring will actually provide a benefit and not just wear out faster on other builds that would otherwise be fine with iron rings.

 

[Artisi]

Rputvin, your supply should include information on long term storage plus a limit on warranty of maybe 12 months from shipment or start of operation within a set period of initial supply.
Wear rings corroded together means storage wasn't within your instructions for storage and will void warranty.
I realise customer service is number 1 so compromise is all important - but




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.)

 

[Rputvin]

your supply should include information on long term storage plus a limit on warranty of maybe 12 months from shipment or start of operation within a set period of initial supply

I'm not sure why you assume we don't already have this in place, but I appreciate the advice.

Regardless of who is paying for it - it needs to get fixed. The intent is to remove the service call entirely as service call volume for "trivial" items is becoming an issue and hiring more service guys hasn't been working out too well for the last few years.

 

[3DDave]

Perhaps - prior to final assembly, spray/dip/otherwise coat the separate housing and impeller with a water repellent coating. Wd-40 springs to mind, but I'm sure there are many others. Then test with plain water; the coating will allow the majority of the moisture to drain.

If still unsure, add in some sodium polyacrylate, like a teaspoon / 1 gram per 30 cu-inches, before sealing the pump. Sodium polyacrylate is used as a food additive. It may clog small-pore filters and tiny orifices, but is otherwise less stiff than Jello. This should capture any remaining loose water; it's worth testing.

I would also use some low strength locking compound to seal the plugs to prevent water ingress in storage.

Consider raising the price on the pumps to exclude cheap and uncaring customers/provide more cushion for those who think a higher price means they can be more abusive.