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  • 1.  Best material for sea environment ?

    Posted 12-19-2023 00:44

    Hello 

    I am looking for best metal material like s.st. HASLA or titanium to function under sea level for long time ? moreover, the material must be with good machine ability. 

    does shot peen process might enlarge the life cycle under water? ( the part is very long rod 8-12 meter, Dia. of 80mm with very accurate screw thread. 

    Thank you 



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    Eli Yudkevich
    consultant engineer
    self employ
    kfar saba
    972 523663911
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  • 2.  RE: Best material for sea environment ?

    Posted 01-04-2024 14:26

    Your question might have gotten lost in the holiday shuffle. Perhaps someone can answer it in the new year....

    "I am looking for best metal material like s.st. HASLA or titanium to function under sea level for long time? Moreover, the material must be with good machine ability. 

    does shot peen process might enlarge the life cycle under water? ( the part is very long rod 8-12 meter, Dia. of 80mm with very accurate screw thread."



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    Carrie Hawk
    ASM International
    Community Engagement Specialist

    440-338-5497
    carrieh@asminternational.org
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  • 3.  RE: Best material for sea environment ?

    Posted 01-05-2024 08:28
    There are several highly alloyed stainless steels that might do the job: superaustenitic stainless steels with 6% (or more) molybdenum or superduplex stainless steels with 4% molybdenum. None of the standard precipitation hardening stainless steels are truly resistant to seawater. 
    Titanium (CP) is highly resistant to corrosion in seawater. Common aerospace alloys (Ti 6-4, etc.) are less resistant. Some of the beta titanium alloys are even more resistant to corrosion. You should consider whether the lower elastic modulus of titanium (15 million psi vs 29 million psi for steels) will be an issue. Also, titanium and its alloys are more troubled by galling. 
    Since it sounds like this may be a "one-of-a-kind" part, the cost of the material may be a minor issue. I'd look at whether a corrosion nickel alloy (such as C-22, N06022) or its hardenable equivalents would be more desirable from a reliability and availability standpoint. Also consider whether K-500 (UNS N05500) is what you want.
    The intended lifetime of this part is an issue -- days vs. years may drive your decision in different directions. The costs and consequences of failure must be considered. 
    Shot peening is great for improving fatigue resistance, but will not help corrosion resistance. Is the shot peening to be done before or after threading? The first might not be effective, while the last might interfere with the accuracy of the thread. Consider rolled (vs. cut) threads.
    Cathodic protection will provide substantial corrosion protection, but in seawater will produce calcareous deposits that may interfere with screw operation.
    Finally, consider biofouling. It will be difficult to prevent, and may also interfere with screw operation.

    --
    John Grubb



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  • 4.  RE: Best material for sea environment ?

    Posted 01-05-2024 09:03
    Thank you, your explanation is very useful. 





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  • 5.  RE: Best material for sea environment ?

    Posted 01-06-2024 02:33

    You could look at Super Duplex SS that has exemplary service in Oil & Gas subsea

    Geoff



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    Geoffrey Warburton
    GW Consulting
    United Kingdom
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