# 316 verses 304 for strength?



## SanDiegoChip (Jun 12, 2007)

Hi,
We have had a dodger built and a bimini built. Both we want to last a long time. We nevree thought to ask what the SS 1" frame is on either of them. 
Now we are building mounts on top of the bimini for our three solar panels and have purchased 316 from a local supplier, "Industrial Metals" and I am fairly sure it was 316 SS 1" tubing. It was a real hassle to purchase it as they did not know they even had it. Any way we then found out Keystone Brothers had 1" SS tubing so we bought a 24 foot length and cut it in half to trans port it. We then finished off the solar panel mounts with it. Now we have found out it is 304 SS.

So I know the 316 will resist rust better but is it any stronger?

Is there any way to tell what the difference is by looking at them as we do not know which part we made with 304?
I am thinking the dodger and bimini are made of 304 as the price was the best of the bids.

The bottom line is the 304 will develop rust easier and sooner. If it is as strong as 316 then this could be a non issue at least for now.

In fact it seems that 304 is stronger and that is really what we are looking for in this application.

See this text below"

_"316: For severe environments. Of course, there are many industrial processes that require a higher level of resistance to corrosion than Type 304 can offer. For these applications, Type 316 is the answer. 
Type 316 is also austenitic, non-magnetic, and thermally nonhardenable stainless steel like Type 304. The carbon content is held to 0.08% maximum, while the nickel content is increased slightly. What distinguishes Type 316 from Type 304 is the addition of molybdenum up to a maximum of 3%. 
Molybdenum increases the corrosion resistance of this chromium-nickel alloy to withstand attack by many industrial chemicals and solvents, and, in particular, inhibits pitting caused by chlorides. As such, molybdenum is one of the single most useful alloying additives in the fight against corrosion. 
By virtue of the molybdenum addition, Type 316 can withstand corrosive attack by sodium and calcium brines, hypochlorite solutions, phosphoric acid; and the sulfite liquors and sulfurous acids used in the paper pulp industry. This alloy, therefore, is specified for industrial equipment that handles the corrosive process chemicals used to produce inks, rayons, photographic chemicals, paper, textiles, bleaches, and rubber. Type 316 is also used extensively for surgical implants within the hostile environment of the body. 
Type 316 is the main stainless used in the marine environment, with the exception of fasteners and other items where *strength and wear resistance are needed, then Type 304 *(18-8) is typically used. "_
Taken from:
Bosun Supplies Inc
Stainless Steel Information Knowledge alloys 316 304

So it seems we are fine with what we have had built and what we are building or is this 304 a serious error?
Here is part of the project. We are installing cross supports etc now.







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One of two 135 watt panels going up. Also a 85 watt is going up there.
Thanks,
Chip


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## tommays (Sep 9, 2008)

I think you will be fine and if you treat it with something like spotless stainless which will passivate the surface there should not be any surface staining issues 

As far as strength if the 304 VS 316 was and issue then the design was cutting things a bit close


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## jrd22 (Nov 14, 2000)

304 is actually a bit stronger than 316 so you don't need to worry about it. They are both plenty strong for your application.


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## tommays (Sep 9, 2008)

316 seems to be the material of choice as it was the only thing offered to me this year when I bought the new stuff


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## boatpoker (Jul 21, 2008)

316 is harder than 304 therefore more brittle. 304 is a bit more susceptible to corrosion but either one is sufficiently strong for your appliaction .....
unless it was made in China, then all bets are off


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