Spring material in Deepwater use

[DubMac]

Does anyone have suggestions/comments on the 17-7 material below for use in a spring (clock style I think they call the type) for use in 10,000 ft seawater?


17-7 PH Stainless Steel Strip, Condition A per AMS 5528

 

[DubMac]

Should have added.....The material above will meet strength requirements; the issue is it's anti-corrosion properties in that environment, as opposed to say an Elgiloy.

 

[EdStainless]

You never use PH stainless in the A condition. You always age them.
I wouldn't use 17-7 in seawater. Maybe 13-8. This alloy has the best corrosion resistance in the H950 condition (highest strength).

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Plymouth Tube

 

[DubMac]

Thank you EdStainless

 

[DubMac]

Do you have an opinion on Elgiloy? I'm not sure what it even is. A proprietary name? I am being told it is the very best material all things considered for this service: tensile strength, corrosion properties...but apparently not that easily obtained in reliable quantities (whatever that means).

 

[SJones]

Any chance of elaborating upon the specific location and function of the spring

Steve Jones
Corrosion Management Consultant

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

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

 

[DubMac]

Sorry, on the pump forum, I regularly must beg for more information from posters; hard to work in the dark.

Location would be inside a tool rated for use in 10'000 ft ocean depth; temp is at 40 degF. The spring would be subjected to slightly filtered seawater (a screen only keeping out larger particles. It is configured just as a clock spring. Can't say much more without breaching confidentiality.
Totally understand if you are unwilling to comment further.

 

[EdStainless]

Elgiloy and MP-35N are age hardening, high Co alloys.
Elgiloy was developed by the Elgin watch company for use in springs. It is now owned by ELP.
It is a very special small lot material, but very strong and great corrosion resistance.

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Plymouth Tube

 

[DubMac]

That makes perfect sense on the Elgiloy,,,interesting. Thanks EdStainless!

 

[TVP]

DubMac,

What kind of life expectancy do you have for this spring? 17-7 even in the proper condition (CH900, TH1100, etc.) will not have good corrosion resistance in seawater, and will fail due to corrosion fatigue due to surface pitting or crevice corrosion. Elgiloy is certainly the best option for performance, but cost and availability is not so good.

 

[EdStainless]

If you went with 13-8PH or a5-7PH (about 2% Mo) and provided some galvanic protections (Zn anodes) it would not be unreasonable to expect a few years life at this depth. Shallower would be worse, but deep is cold and little oxygen so corrosion will be very slow.
You do need to design at lower stress values because you are in seawater to avoid the risk of CSCC.

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Plymouth Tube

 

[DubMac]

Thanks TVP and EdStainless,
This will not be for permanent installation; down at depth for usually a few days at a time, maybe 3 weeks tops on any one run. Then it would be brought up and could be cleaned if that would help. These will mostly be used for over 2000' water at minimum.

Availability of Elgiloy has been checked and nowhere near the supply dependability to consider.

It would however be preferable that, at these service intervals, the spring not need replacement more than once every two years.

The galvanic protection is interesting. Would you envision just attaching a strap to any one point on the spring, or is does galvanic action increase with increasing surface contact area?

It sounds like 17-7 is out and I will move forward with 13-8PH or a5-7PH selections; most likely balanced against price.

Thanks to "Da Botya's" help! I will come back to report what I find searching these new materials.

 

[TVP]

I agree with EdStainless, try 13-8 or 15-7 PH stainless steels. Regularly cleaning the surface after taking it out of service will improve its lifetime.