15-5 vs. 316 SS 1

[Beth]

We have been asked by a client to substitute 15-5 Precipitation Hardened steel for 316 SS in a machined (encapsulated) part for underwater connector applications. They have also asked that the part be heat treated to H900. Does anyone have experience with this metal? What is its corrosion resistance, before and after heat treating? Compared to 316 SS? We are concerned about our warranty and the viability of the materials substitution. Any websites you know that may be helpful would also be appreciated. Thanks

Handle - Beth

 

[rembrandt]

Beth,all precipitation hardened Stainless type alloys are suspect in salt water service, especially in the temper range given by you, (H900) they fail by stress corrosion cracking when stressed at 35, 50 and 75% of their respective yield strengths and exposed at depth. This alloy failed when exposed at depth due to the stresses imposed by it being squeezed between insulators such that it was slightly bowed. Cracks originated at unreamed drilled holes
in the specimens.
(for a good reference book I suggest you try and source the 'SEAWATER CORROSION HANDBOOK', it is sometimes referred to as 'SCHUMACHER', and published by Noyes Data Corporation,
Park Ridge, New Jersey.) Hope this helps.

 

[chrisyd]

Beth? Beth Wright from the isle of wight?

 

[mcguire]

Beth
It's been a long time since you posed the question, but the best material solution would be a duplex stainless, such as 2205. It has high strength ( 50% higher than 316) and greater resistance to scc and pitting corrosion. See site

http://www.stainlesscenter.com

for data

 

[WalterHarris]

Beth,

Have used successfully the 17-4 and 15-5 precipitation hardened alloys at H1100 (17-4) condition in seawater applications. The real question is; What is the specific application? None of the stainless materials including 316 really perform well in long term submergence in deep water (low oxygen). It experiences pitting. But if your going to be in and out of the water periodically or based in the splash zone or in an environment that is highly oxygenated then they work great (remember to insist on true, quality passivation). I've seen even the best materials corrode terribly when not passivated. 17-4 and 15-5 have many similar characteristics. The same type of material is very often used in seawater for boat shafting. Check out Aquamet(trade name) shafting. But... the corrosion resistance of the 17-4 is about the same as 316 only if it's heat treated to the right condition. Check out the ASM metals handbooks. It's been a long time since I used it but I do remember the H1100 being near minimum condition for good corrosion resistance. I'm not sure which side of H1100 H900 is, I think it's better, higher strength. I believe the harder it was the better the resistance. My experience is with heavily used ROV components and bottom mounted underwater equipment including periodic high level stress for lifting. Have used many stainless steel underwater connectors backshells etc. The best materials for long term deep submergence (low oxygen levels) including cost and everything is probably mild steel. Corrosion rates are so predictable and even that they can be accurately predicted. Have actually put down machinery for 15 to 20 years and pulled up mostly just to look at it. Was still working well. Another good material for longer term submergence is titanium. High strength and corrosion resistance.