US source for 316 stainless screws, etc? Especially metric

[s/v Jedi]

Originally Posted by markxengineerin

That's right, it's hard to find information on what I'm curious about, which is a measure of resistance to crevice corrosion in a marine environment (under salt water or exposed to the spray), 316 vs. 17-4 in a condition that's most suitable for something like a shackle, chain plate, or bolt. I don't know if such a metric as "resistance to crevice corrosion" exists, but it would be nice if it did, given the number of failures it causes on just about every boat. If you know more, please share.

Not an expert but I know it’s better to avoid it completely by selecting bronze rather than a steel allow.

[dlj]

Originally Posted by markxengineerin

That's right, it's hard to find information on what I'm curious about, which is a measure of resistance to crevice corrosion in a marine environment (under salt water or exposed to the spray), 316 vs. 17-4 in a condition that's most suitable for something like a shackle, chain plate, or bolt. I don't know if such a metric as "resistance to crevice corrosion" exists, but it would be nice if it did, given the number of failures it causes on just about every boat. If you know more, please share.

I'm uncertain what more you want me to share. If you use 17-4 PH in the marine environment you need to use the correct heat treatments. Reread what I've written above and ask me specific questions.

dj

[team karst]

I will go with nibral. If yellow metal is desired. Aquamet if white metal Gets pretty exotic/expensive after that. Duplex SS, titanium, nickel alloys.

Someone might have a crevice corrosion metric, but i have never seen.

[dlj]

Originally Posted by s/v Jedi

Not an expert but I know it’s better to avoid it completely by selecting bronze rather than a steel allow.

Bronze is a good alloy. There are many other alloys far superior to bronze. If you design for bronze - the correct bronze alloy - they work. There are hundreds of bronzes. Many would not give you satisfactory results.

dj

[team karst]

I tried to straighten nibral props u/w under duress once. They totally defeated me.

[team karst]

I have done quite a bit of salt fog testing, but not for crevice corrosion. It may take stress application as well.

[dlj]

Originally Posted by team karst

I will go with nibral. If yellow metal is desired. Aquamet if white metal Gets pretty exotic/expensive after that. Duplex SS, titanium, nickel alloys.

Someone might have a crevice corrosion metric, but i have never seen.

Nibral and Aquamet are both trade names, they use those names to hide the specific alloy being used.

The difficulty with metallurgy is the devil in in the details. The details are what actually matter.

There are no alloys being manufactured today that are "just marine grade" alloys. It would be cost prohibitive. All alloys used are specific grades produced to known standards. Trade names are used to protect "intellectual property" of the company applying them.

Aquamet for example, uses several commercially available alloys depending upon which name they have applied. Their trade name may also include specific processing parameters that they apply to the alloy specified.

Trades names don't really "enlighten" these conversations, in my opinion anyway.

dj

[markxengineerin]

Specific questions:

Is there a metric for crevice corrosion or maybe a standardized industry test where the failure is crevice corrosion, as it often is for 316 used on boats?
How does 316 (chosen for it's pure popularity and availability) compare to 17-4 H1100 or similar (chosen because it came up in this thread)?

Nothing against bronze, but I have yet to choose it for a homemade component due to the huge number of options available. I would be more likely to if someone like dj said something like "check this one out for use on highly loaded sailboat components" and it was easy to find from somewhere like McMaster.

[dlj]

Originally Posted by markxengineerin

Specific questions:

Is there a metric for crevice corrosion or maybe a standardized industry test where the failure is crevice corrosion, as it often is for 316 used on boats?
How does 316 (chosen for it's pure popularity and availability) compare to 17-4 H1100 or similar (chosen because it came up in this thread)?

Nothing against bronze, but I have yet to choose it for a homemade component due to the huge number of options available. I would be more likely to if someone like dj said something like "check this one out for use on highly loaded sailboat components" and it was easy to find from somewhere like McMaster.

So the difficulty with your first question, is that "crevice corrosion" is a rather vague term.

The definition from NACE (National Association of Corrosion Engineers) - now part of AMPP - the Association for Materials Protection and Performance:


crevice corrosion—localized corrosion of a metal or alloy surface at, or immediately adjacent to, an area that is shielded from full exposure to the environment because of close proximity of the metal or alloy to the surface of another material or an adjacent surface of the same metal or alloy.

So the difficulty for having a test for this are all the test set-up requirements to meet that definition. It's a well known corrosion phenomena, and has been well documented as occurring for many years.

Corrosion tests need to be repeatable and predictive. There are actually 5 fundamental areas where corrosion testing is done:

1) To study the fundamental mechanisms of corrosion.
2) To select the most suitable material for withstanding a specific environment
3) to determine the environment where a given material can be employed satisfactorily
4) to develop new alloys
5) to use as control for assuring uniformity of a product.

So you may think that either 2 or 3 above would be possible, but if you look at the definition, there are a ton of hidden difficulties in establishing a repeatable, predictable test.

The second part of your first question is fairly easy - 17-4 PH in the H1100 condition does not show the same crevice corrosion degradation as 316 does in the specific marine environment that we are interested in here. And yes, there is test data, I'd have to dig it up. I don't have the time right now.

Your second question to answer comprehensively would be a course in bronze metallurgy that would be well beyond the scope of this kind of discussion. But in very simple terms, you have cast bronzes and wrought bronzes. There are both bronzes and brasses (both cast and wrought) that can work well in the marine environment.

In order for anyone to answer your question "check this one out for use on highly loaded sailboat components" one would have to have all the engineering data regarding loading, application, etc. That's why people hire professionals to do that exact evaluation.

Apologies if this has not really answered your questions. It's about the best I can do given the medium and time available.

dj

[CarlF]

Another vote for Bolt Depot. Every size including metric in 316. Prices very reasonable. Top quality. Ship same day.

Used them a couple of dozen times without a screw up

[markxengineerin]

Thanks, that is helpful. Within any specialty of engineering, it seems the more you know, the more difficult it becomes to simplify things into a single test procedure or simple recommendation, yet this is what the non-experts want for ease of use.

I suppose with the bronze/brass options, if corrosion is truly a non-issue (is it universally the case?) the next concern for me is the fatigue strength. McMaster lists the yield strength of 464 "naval bronze" as 20ksi, similar for many others, pretty low in comparison to other options of stainless steels, titanium, etc, and not yet accounting for fatigue. Manganese and Aluminum Bronze look better, getting up near 100ksi, but seem harder to source in convenient sizes for diy type work. If I want to design "sleek" components, it's nice to have high strength to make the parts look proportional to today's boats and not something from the wooden ships of yore. Last question and sorry for the thread hi-jack, but do any considerations come to mind for marine parts made from Manganese vs. Aluminum bronzes?

[dlj]

Originally Posted by markxengineerin

Thanks, that is helpful. Within any specialty of engineering, it seems the more you know, the more difficult it becomes to simplify things into a single test procedure or simple recommendation, yet this is what the non-experts want for ease of use.

It's also sometimes a problem of common language. Often, the problems being face in the real world are really complex problems - corrosion is an area that is particularly difficult.

Originally Posted by markxengineerin

I suppose with the bronze/brass options, if corrosion is truly a non-issue (is it universally the case?) the next concern for me is the fatigue strength.

Most assuredly NOT a universal case... Fatigue strength, testing, what it means, etc is another area of pretty great complexity. Testing for both corrosion and fatigue require that the testing be shown to have application to the problem in real life.
The testing done in the lab has to be predictive of service. That's a huge area of work....

Originally Posted by markxengineerin

McMaster lists the yield strength of 464 "naval bronze" as 20ksi, similar for many others, pretty low in comparison to other options of stainless steels, titanium, etc, and not yet accounting for fatigue.

Fatigue strength is rarely given as it depends upon surface finish, loading patterns and more. I've done a lot of fatigue testing....

Originally Posted by markxengineerin

Manganese and Aluminum Bronze look better, getting up near 100ksi, but seem harder to source in convenient sizes for diy type work.
If I want to design "sleek" components, it's nice to have high strength to make the parts look proportional to today's boats and not something from the wooden ships of yore.

The marine environment is a tough one. You have a lot of unpredicatable conditions; corrosion, unexpected loading patterns or loads, more. Sometimes the simple mass of a component does things that you are not able to predict...

Originally Posted by markxengineerin

Last question and sorry for the thread hi-jack, but do any considerations come to mind for marine parts made from Manganese vs. Aluminum bronzes?

Both can be great alloy families for marine application. I'd suggest you read up on the CDA - the Copper Development Association's web site. Here's a link to their section on Copper Alloys for Marine Environments.

https://copper.org/applications/marine/

There are links to publications that may help you wade through this. At the risk of hyjacking the thread from the OP looking for stainless fasteners, give that link a look over. Perhaps you may wish to start a new thread at some point.

dj

[wyb2]

Originally Posted by s/v Jedi

I bet you never bought 316 fasteners on Amazon, let alone ones that turned out to be 304. Show me one case…. Which should be easy with the rampant shady business going on according to you.

Also, how do you tell if the 316 fasteners at Home Depot, Lowe’s, FastenAll, Bolt Depot, Ace etc. are actually 316 and not 304?

I did buy some Chinese washers, 316 and they were marked A4 which is the EU mark for 316.

The answer to how do you tell is most of the time you don’t. You trust that they have their supply chain and inventory mostly under control. With Amazon, I think many people have experienced reasons to not want to rely on that trust.

Here is a recent example of a very simple issue I (and I assume others) have with Amazon.

Literally the first search result. What material do we think this webbing is?

[mikk60]

Ace is the place in New England