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RE: [PSUBS-MAILIST] stainless vs aluminum



What I need to be aware of is that I will need any aluminum structural components to be approx 50% larger than what would be an equivilent steel member.  Also the steel has more of an elastic range before failure than does aluminum.
 
 
Here is a good overview of steel vs aluminum:
 
http://www.kastenmarine.com/alumVSsteel.htm
 
Brian
 
 
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org]On Behalf Of Ken Martindale
Sent: Friday, May 07, 2010 3:05 PM
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] stainless vs aluminum

It’s my understanding that Stainless Steel after machining needs to be passivated. This process removes any free iron on the surface and replaces it with chromium or nickel oxide.

 

The process consists of soaking in an acid bath of primarily nitric acid with some chromic acid. I have used this on a number of objects used in the sea with positive results.

 

Jim what acid did you use in an your passivation process??

 

Ken Martindale

 

From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of ShellyDalg@aol.com
Sent: Friday, May 07, 2010 4:08 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] stainless vs aluminum

 

In a message dated 5/7/2010 6:45:34 A.M. Pacific Daylight Time, jimrudholm@gmail.com writes:

The first overnight outside and they had a thin rust film. The cure
was to soak the parts in acid to remove embedded iron from steel tools
including drills.

This brings up a good point. When working with stainless, pieces get embedded from tools. This is evident when using a wire wheel.......gotta use a stainless wire wheel. It'll get crusty real quick. Heat control and restoring a "worked part" back to clean solid SS is the only way to minimize corrosion. For small parts like brackets it's best to use 316L-SS so the cost is kept low. Larger pieces in 304 are OK but you must watch the seams, welds, and breaks ( folds ) for any corrosion and clean it right up before it gets to be a problem.

Using ZINC sacrificial anodes helps a lot too. They will cut your corrosion way down.

Frank D.