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Re: [TowerTalk] 306 stainless steel

To: Grant Saviers <grants2@pacbell.net>, "towertalk@contesting.com" <towertalk@contesting.com>
Subject: Re: [TowerTalk] 306 stainless steel
From: W7TMT - Patrick <W7TMT@outlook.com>
Date: Fri, 4 Jun 2021 03:47:11 +0000
List-post: <mailto:towertalk@contesting.com>
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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