Material Selection for Submersible Centrifugal Seawater Pump 1

[Ygnis]

Hello

I've been assigned to recommend materials to be used for different parts of a submersible centrifugal seawater pump. I need to select commercially available materials for construction of the following parts of the pump:

1.) Pump Casing
2.) Impeller
3.) Shaft

The seawater pump will be used in the environment with the following conditions:

Total Dissolved Solids: 25,000 ppm
Operating Pressure: 10 bar gauge coastal seawater
Operating Temperature: 30 degrees Celsius
Location of Pump: 10 meters from coastline into the sea

Any reference to a website or pdf file will also be useful.

Regards,

 

[patprimmer]

What life do you expect?

How many will you make?

Will they be permanently installed or regularly transported and handle roughly maybe?

Regards
Pat
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[arunmrao]

In my opinion,they should be a Duplex SS grade with PREN of 32 minimum. Please refer to a link below from Grundfos for such applications.

http://in.grundfos.com/content/dam/... solutions/waterutility/pdf/sl-se-s-pumps.pdf

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[SJones]

http://resource.npl.co.uk/docs/scie...ials/publications/online_guides/pdf/pumps.pdf

http://www.copperinfo.co.uk/marine/

http://www.nickelinstitute.org/Know...seawater&pageIndex=0&sortBy=r&filter=keywords

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

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

 

[EdStainless]

http://www.nickelinstitute.org/en/T...neWaterDesalinationandOilfieldBrinePumps.aspx

How deep? what will the oxygen content be?
If no O2 then Ni-Resist will work, if there is any O2 then you need high alloy SS.
Duplex would be your best bet.

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[patprimmer]

I'm actually wondering if nylon might work.

Regards
Pat
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[arunmrao]

Pat,it is a mindset issue amongst us Metallurgists (me included),we fail to consider ceramics and plastics as alternate materials solutions and go about recommending high alloys for simple applications.



_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[patprimmer]

I know GF Nylon and GF polyester have both been used in pumps in underground mines where lots of mud and slurry are involved.

I know salt water won't be an issue.

Abrasion resistance might be.

Tooling costs may very well be an issue hence my original question.

Regards
Pat
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[EdStainless]

Nylon is to sensitive to water.
A number of thermosets have been used, Ryton is one that comes to mind.
Depends on the pump size. For large pumps metals work better.

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Plymouth Tube

 

[patprimmer]

35% GF nylon does not move all that much with water. Also if matching parts are all made from nylon it all swells in unison so clearances are not impacted upon all that much.

It is used extensively in pumps for fire fighting and for underground mining. Sure, they are relatively small but the OP makes no mention of size along with a lot of other data required to make a valid recomendation.

Polyester holds shape and clearances a bit better but is not normally tough enough for rough handling.

Ryton is PPS (polyphenylene sulphide) and is a thermoplastic, not a thermoset. It is hard and strong but quite expensive. It's main reason for selection is for its high temperature resistance which does not apply here.

Regards
Pat
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[stanweld]

With wave action, I would suspect sand intrusion which might prove detrimental to nylon. Amongst the other questions listed above, will the pump be operating intermittently or continuously and if there is scheduled downtime, how long will it be? operating conditions may limit the usefulness of stainless steels.

 

[Ygnis]

Hi everyone. I noticed that many companies are using stainless steel for their seawater pumps. And I noticed that duplex is most commonly used.

In response to the questions, I will try to answer the questions posted below:

Q: "Will they be permanently installed or regularly transported and handle roughly maybe?"

A: The pump will be permanently installed on-site. My question is that will the recommended material change if the pump is to be regularly transported?

Q: "How deep? what will the oxygen content be?"

A: The pump will be installed 100 meters below sea level. I haven't found out the oxygen content but I guess there will be small amounts of oxygen dissolved in seawater. I will let you know once i find out the oxygen content.

Q: "will the pump be operating intermittently or continuously and if there is scheduled downtime, how long will it be?"

A: The pump will be operating continuously although I don't know how long the down time will be. May I ask how does the downtime affect the material that will be used for the pump? i.e. will a pump with a longer downtime require a different material?

I would like to thank everyone for their responses.

 

[EdStainless]

The more that the unit is handled the more robust the design and materials of construction need to be.

The more variable the operating conditions (stand by, high flow/low flow, change in temp or oxygen) then the more corrosion resistant the materials must be.
I don't know how you will install a pump this deep when you are right at the coastline.

For deep set, fixed location seawater pumps there are a few choices.
Traditionally the stages (impellers and bowls) would be cast Nickle Aluminum Bronze, with shafts and bolting all Monel.
It is hard to beat this combination in seawater service.
Another traditional option would be to use cast Ni-Resist pump stages. These are used commonly in high salinity applications.
If you move to SS construction you need to asses some risks. You should be able to use alloys that would not be suitable for surface use since you will be colder and lower oxygen.

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Plymouth Tube

 

[Ygnis]

After doing some research and with the assistance from you guys, i was thinking of using super duplex stainless steel for pump casing, impeller and shaft.

For shaft and impeller, we were thinking of using some stainless steel of higher quality as the impeller and shaft will experience a higher water velocity (pump operating at 10barg). We are thinking of using super duplex stainless steel, AL-6XN, since the PREN is 45.4.

My team and i did consider Ni-Cu for pump casing but we were thinking it might not be very suitable as it will cause galvanic corrosion if we use NiCu for pump casing and AL-6XN for impeller and duplex.

So, do you think the materials selected will work out?

 

[Ygnis]

Sorry, I made a mistake, i don't think AL-6XN is super duplex. I'm thinking of super duplex stainless SAF2507 for pump casing, impeller and shaft.

 

[EdStainless]

You want the casing to offer mild galvanic protection to the impellers and shaft.
The key question is what alloy combination does the pump manufacturer offer?
Don't ask for the impossible.

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Plymouth Tube

 

[mshimko]

I echo ed's comment above, with my rewording: must ensure all materials are galvanically compatable, and if not IDENTICAL, then ensure the larger parts are slightly less noble compared to the smaller parts.

As to materials, my experience starts with CuNi and bronze as a low end option, moves up to monels, then C22, then inconel/titanium. It all depends on what you want afor service life and maintenance requirements.

 

[EdStainless]

to repeat myself:
Traditionally the stages (impellers and bowls) would be cast Nickle Aluminum Bronze, with shafts and bolting all Monel.
It is hard to beat this combination in seawater service.
I have seen NAB pumps run in seawater for decades.
In general teh Cu alloys will not suffer crevice corrosion and will have less bio-fouling. This is a combination that can be very tough on even high alloy SS units.

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