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Discussion Starter #1
I'm rebedding everything on the deck of my Catalina 22 and will need a whole slew of new fasteners. A quick forum search doesn't reveal a ton of information on the different types of SS.

Looks like there's a ton of different grades (wikipedia says 150 different types). From what I've read 18/18 and 304 are the same thing. Wikipedia also says that 316 is commonly found on marine applications because of its anti-corrosive properties.

Obviously the different numbers stand for different alloy percentages. Any thoughts from some of the more experienced folks out there? I have to imagine that buying my fasteners at Lowes or Home Depot would be a heck of a lot cheaper than ordering from WM or Jamestown Distributors. But the reduced cost would likely be reflected in a lower quality SS (18/18 instead of 316).
 

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For what it's worth, I am a buyer of stainless steel food service items.

I have never seen an internationally recognized and accepted specification for stainless steel grades expressed as xx/xx (that's the chrome content/nickel content). In my opinion, the nomenclature was dreamed up by marketing types to confuse folks.

Stainless steel designations such as Type 304 or Type 316 are globally recognized specifications, published by organizations such as AISI (American Iron and Steel Institute).

The best quality steel in the world can be trashed by substandard processing techniques. Conversely, you can't make a silk purse from a sow's ear.

If you plan on keeping this boat and presuming you don't want to repeat this process every few years, I suggest you put the reliability of the vendor at or near the top of your criteria for choosing what and where to buy.

Good luck!
Paul

PS AISI Type 304 is commonly referred to as 18/8 or 18/10 in our industry. It has 18 - 20% chrome and 8 - 11% nickel. AISI Type 316 has 16 - 18% chrome and 10 - 14% nickel.
 

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Stainless Steel Types

I was also trying to find out about the differences between Type 302/304 and Type 316 as far as rigging applications go. From what I gather, 302/304 is the commercial grade and 316 has enhanced corrosion protection.

Is the cable used in rigging typically 316? Or could just as well be 302/304?

The reason I ask is they have very different breaking strengths, for example 5/32 302/304 breaking strength is about 2800 lbs and 316 is 3300 lbs.

Thanks,

Warren
 

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Discussion Starter #7
Warren,

I'd double check your breaking strengths... Everything else I can find remarks that 304 is stronger than 316, but at the cost of being more corrosive.

I'm not sure about Home Depot, but I called Lowe's and the sales person I talked to said that ALL fo their stainless supply comes from Hillman. Attached is a document from Hillman about the quality of their steel. I got it from one of my local hardware stores.

Depending on how you read into it, I would take this to mean that you don't get much of a guarantee when you buy stainless from a big box store.... At least not when its going to be used for a marine application.
 

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Discussion Starter #9
As I research further, it looks like both West Marine and Jamestown Distributors stock either 316 or 18/8 stainless. They do not specifically offer 304 as an option, just products in the 18/8 family.

West Marine's fasteners are supplied by Fasco
Jamestown Distributor's fasteners are supplied by Eastern Fastener Corp
Lowe's fasteners are supplied by Hillman

All 3 retailers say their stock comes from the 18/8 family. Because the only guarantee is of 18/8 quality (and not 304), for fittings requiring high strength (i.e. chainplates, pulpits, stanchions, sheet tracks) it really makes me wonder if I might as well save some money and head to the local hardware store.
 

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Basically, good marine grade stainless steels are the non-magnetic Austenitic grades—304 and 316 being the most common. While 304 is stronger than 316, it is far better to go with 316L, since 304 is far more vulnerable to crevice corrosion and chloride ion stress cracking. :)

BTW, carrying a magnet with you is a good way to quickly check if the stainless is non-marine grade Martenistic stainless steel, which is magnetic or not. If the magnet sticks, it ain't marine grade stainless. If it doesn't stick, it doesn't guarantee it is marine grade, but it is far more likely. ;)
 

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18-18 stainless and others

I sell metals including stainless. I also have a certificate from the MEI in ferrous metallurgy. That said, 304 and 316 are AISI Grades not specifications. A typical specification for stainless is ASTM A240 for stainless sheet and plate. ASTM A312 for stainless pipe, ASTM A213 for stainless tubing. For fasteners there is ASTM A193 (bolting) Grade B8 (304) Grade B8M (316), ASTM A194 (nuts) Grade 8 (304) Grade 8M (316). There are many other grades of stainless available and other specification that cover other types of products. It is correct that 18-8 indicates the mean of Cr and Ni in 18-8 stainless but other grades do meet 18-8 in addition to 304 and it is preferable to not specify 304 if you simply need 18-8. It is also true that 316 is more widely used in marine applications due to increased corrosion resistance over 304 in saltwater. There are other grades of stainless that have even more resistance and have been developed for resistance in salt water such as UNS N08367. I suggest you contact a reputable fastner manufacturer or supplier, let them know your particular application and they can steer you in the right direction. By the way, try to stay with the common grades like 304 or 316 and stay away from X5 18-18 which is not as readily obainable.
 

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I work now and again with stainless, and always try to use 316 for the boats. The sheet material is reasonably easy to guillotine, or waterjet cut and bend, but beware if you want to drill it using a hand drill with normal metal drill bits!
It can be harder than you expect in more ways than one !

I'm currently making a custom shaped cut and bent 1.5mm thick plate to cover and protect the hull-deck joint and the bow of a British Super Seal 26.
I have had to carefully mark the positions of the holes for the fairleads and forestay mounting plate on the CAD drawing so that I can cut them with our company's waterjet.

I don't think 304 is good choice for exposure to seawater.
 

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Stainless strength

The "breaking strengths" previously quoted are probably for the wire cable product and not necessarly attributable to the grade ie: 304 or 316. The wire cable strengths, I believe, are a function of the diameter of the individual wires that make up the cable and the overall diameter of the cable. In most material specifications (ie, plate, tube, pipe, fasteners) the minimum yield strength for 304 AND 316 is 30,000 psi while the min tensile strength is 75,000 psi for both grades. The yield is the point at which plastic deformation occurs, when the material stretches without breaking beyond the ability to return to the original size and the tensile strength is the point at which the material actually breaks. Of course, these are minimums and the actual results will be different with the product type, thickness, and many other variables. A generalized statement that 316 is stronger is not necessarily correct.

As for corrosion resistance, the primary cause of corrosion failure is precipitation of carbides into the grain boundaries of the material and the carbides being attacked by the acid, salt water, etc in which it is used. That is why austenitic stainless is solution annealed-that is heated to above transformation stage (around 1950 deg F. or so then quenched, or rapidly cooled) to put the carbides into solution and keep them there so there is less in the boundaries to corrode. It is said that 316 is somewhat more corrosion resistant under some conditions.

Overall, it is best to talk to an expert in the exact product you need.
 
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