Pump shaft material

[Focal]

Hello, I have a vertical turbine pump in water service with a 416 SS bowl shaft. It's corroded on all the exposed areas so I'm rethinking material. I'd like to go forward with a 2205 duplex but I'm concerned about the material strength being sufficient. Is there a rule of thumb or quick way of determining whether it's adequate or do I need to do some calculations? My aversion to this is I'd be making a lot of assumptions. The difference in shear modulus is ~8%.

 

[EdStainless]

416 will have lower pitting resistance and fatigue resistance because it is a free machining grade. Do you have any idea of its strength or hardness? Find either and we can work from that.
The two best options are either 2205 or Aquamet 22 (Nitronic 50).
I would be surprised if these are not strong enough.
But I need to ask what material are the impellers?
We always made sure that there was a hierarchy in corrosion resistance.
bolts>shaft>impellers>bowls

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P.E. Metallurgy, consulting work welcomed

 

[Artisi]

Suggest you calculate or have the shaft power requirement calculated and then start looking at material requirements. In many cases the material /diameter of the shaft can be well in excess of requirement.


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.)

 

[TugboatEng]

Is this a repurposed barge/cargo pump? 416 is a common trim for oil pumps and valves.

 

[TenPenny]

As a guideline, Goulds publishes these hp limits for vertical turbine shafts
I am only showing here 1" dia at 3550 rpm, but obviously these are proportional, and it gives you an idea of the relative strengths
HP Limitations, 1" shaft, 3550rpm:
416ss -- 142 hp
316ss -- 68 hp
Nitronic 50 -- 130 hp
Monel 400 or 17-4PH -- 191 hp
Duplex 2205 -- 126 hp
SuperDuplex 2507 -- 162 hp
Inconel 625 -- 142 hp

 

[EdStainless]

We used to run 1.188" shafts, cold drawn 625 (185ksi min Yield, 200ksi min UTS) and run them 675 HP at 3550rpm. We used 1.312" for 750hp.
For lower strength we ran K-500 Monel (95ksi Yield, 125ksi UTS) and run them 375hp at 3550rpm.

The issue is that 316, Nit50, M400, K-500, 17-4 and 625 are available in various strengths. Even for very high strength material we insisted on tensile elongations of at least 15%, we preferred at least 24% elong for low notch sensitivity and good damage tolerance.

The OD of the stages matters and how things are connected (impellers and couplings) is also important.

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P.E. Metallurgy, consulting work welcomed

 

[songshun]

316 is good material at this part

 

[EdStainless]

Annealed 2205 would be my choice if it has enough strength. It is corrosion resistant and tough.
As a second choice you can buy 1" cold worked Nitronic 50 shafting (it is used on boats).
It will be tougher and more corrosion resistant than 316.

416 is a lousy shaft material. It has poor corrosion resistance and because it is free machining it also has poor fatigue resistance.

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P.E. Metallurgy, consulting work welcomed

 

[Focal]

Wow, thanks for all the comments guys. We had a vertical turbine pump in a salt water solution with 416 shaft and it corroded through too. We replaced it with 2205 but it was an approved choice by the OEM. This pump is a different shaft size and I don't know the weight of the impellers. I know the 300's stainless steels were a concern with material strength with the salt water application and figured it would be the same case here. I'd like to go with 2205, but how can I establish confidence in it meeting the application? Are there factors I can run with the list you provided TenPenny? The shaft is running at 200 HP, 1780 rpm, and is 2.18 OD. From the diameter and lower speeds it instinctively seems to be adequate, but I really don't know.

Artisi, I haven't done these calcs. Wouldn't I need to know impeller weights, specific location, use the SG of the fluid, and all of that?

EdStainless, thanks for your comments. Haven't heard of Nitronic 50 before and will look into it. I'm leaning toward 2205, just want to rule out any doubt...

 

[EdStainless]

I believe that one mfg sells under the name Aquamet 22 (I think)

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P.E. Metallurgy, consulting work welcomed

 

[Artisi]

Focal: for the power calculation you need flow, head, or the pump curve plus SG. The impeller/s weight and any down thrust will figure in the elongation capabilities of the shaft material but is quite often ignore unless there very high thrust or a very long shaft.

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.)

 

[JS_]

It's standard practice, where I'm currently working to use Nitronic 50 for pump shafting.

Sulfuric Acid service

Average HP range of pumping equipment is around 400hp 1800 rpm usually with 2.188 OD shafting.

I've seen 600hp on some pumps with 2.188 shafting, but not recommended.

Best practice is to double check for your application.

 

[SJones]

Any idea of the "salt water solution" temperatures?

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.