With 40 years' experience owning saltwater based boats I've observed that 316
stainless is the standard in high end marine use due to aesthetics not strength
or longevity. Grant, KZ1W already covered the machining/weld issues. In a
purely hardware, nuts/bolts usage there little reason to go with the 316 in our
applications.
Anywhere 304 is used and there is an interface where oxygen is excluded and
water is trapped, like under every bolt head/washer etc., there will be visible
rust. No way to stop it. Any location where there is no water entrapment/oxygen
exclusion but there are incidents of abrasion, contact with non stainless iron
based metals, bleach etc., in other words anything that breaks the thin
chromium oxide layer that makes stainless, stainless will also produce rust
spots.
On a tower out of sight who cares as long as it doesn’t reduce structural
strength. If it happens at ground level, a cable interface panel for instance
and it's an issue then those rusty areas can be repaired by re-passivating the
surfaces and thus restoring the chromium oxide layer. In aerospace lots of high
dollar, high temperature, toxic solutions/processes are called for. In our
usage lowly oxalic acid is your friend. Absolute cheapest solution, and readily
available, I even saw it on grocery store shelves in French Polynesia for
nearly the same price as in Seattle is, Bar Keepers Friend. It's like
Babbo/Comet and may other mildly abrasive household cleaners but has oxalic
acid as an added ingredient. The bartenders reference comes from its special
ability to clean stainless steel sinks etc. in the food service industry.
Wipe it on, scrub gently until the bad stuff goes away. In our application use
either a rag, plastic brush, or plastic scrubby pad, not steel/bronze pads as
their metal chemistry will mess with the process. Rinse it off with fresh
water but no other soaps etc. as a follow up. The oxalic acid does its magic
and the abraded/damaged spot with cease bleeding rust as the chemistry will
restore the microscopic thin chromium barrier.
One other negative about SS fasteners is their tendency to gall. Tighten a bone
dry, non-lubricated SS nut/bolt and all the sudden from one wrench turn to the
next they are literally welded together. I'm a big fan of a marine product
called TefGel however any good anti-seize lube, or any of the silicone based
dielectric greases that many if us to seal connectors etc., are great for this
application. A little dab will do yah and save you a lot of grief!
One other observation... in thinking about stainless steel, if we think of it
as "stain less" rather than stainless we will likely be less disappointed in
its aesthetic characteristics.
73.
Patrick, W7TMT
-----Original Message-----
From: TowerTalk <towertalk-bounces@contesting.com> On Behalf Of Grant Saviers
Sent: Thursday, June 3, 2021 19:41
To: towertalk@contesting.com
Subject: Re: [TowerTalk] 306 stainless steel
316 is not easy machining. The (better) marine industry now uses it in 316L
grade which has lower carbon. This prevents alloy redistribution from the heat
which causes welded joints to rapidly corrode. 316L is also the most corrosion
resistant 300 grade. Ask McMaster for certs on the u-bolts you are
considering, since the detailed specs say 316 (which is probably ok).
All stainless has crevice corrosion problems if there is no oxygen to reform
the oxide layer. Probably not an issue in u-bolts, but has been in sailboat
keel attaching bolts. Bronze alloys are better.
Hot dip galvanized u-bolts might have a 3 to 10 year marine environment life.
Probably good for the life of an antenna in no/low chloride environments. (why
different than a tower?) They look fine on my (low chlorides air) antennas
after 20 years. see
https://galvanizeit.org/knowledgebase/article/the-performance-of-hot-dip-galvanized-steel-in-water-environments
Grant KZ1W
On 6/3/2021 15:02, Richard Smith wrote:
> I Googled:
> "tensile strength of 304 and 316 stainless steel" and the result shows that
> the two alloys have very close tensile strengths and yield strengths.
>
> I bought a bunch 316 SS hardware, planning to use them at the PJ4K station on
> Bonaire, but with the travel restrictions haven't been able to go and try
> them yet. It may take some months or years to see a difference between 304 SS
> and 316 SS, but the Caribbean is a good test bed.
> 73, Rich, N6KT
> On Thursday, June 3, 2021, 09:55:03 AM PDT, jim.thom jim.thom@telus.net
> <jim.thom@telus.net> wrote:
>
> I'm going to buy some U bolts from mcmaster carr....and they come
> in 316 marine grade stainless, with mating 316 stainless nylocks.
> Other than corrosion resistance, I believe 316 SS is the same
> strength as 304 SS, but I am not sure about this. These are the
> insulated type U bolts, like VE6WZ uses on his 80+40m yagis.
>
> I have never seen 316 SS. Has anybody had experience with 316 SS ??
>
> Jim VE7RF
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