[TowerTalk] 306 stainless steel

Fri Jun 4 16:15:04 EDT 2021

Follow Up

I received several questions off list regarding the cleaning process. Since they were all essentially the same I'll respond here. My apologies if this isn't of interest to all.

On simple surface rust stains the cleaner will often wipe it right off with only brief contact. On other more difficult areas especially weldments where parts come together at a weld joint a different technique is needed. 

Mix the powdered cleaner with water to create a wet paste. Dab it on with a small brush into the problem area. Keep it wet. Do Not Let It Dry Out. Easiest way is to cover the area with a wet scrap of cloth or heavy duty paper towels that will follow the contour. Come back and check it at your convenience. If more contact/dwell time is desired dab at the paste to mix it up a bit more, add water if/as required and re-cover to keep it moist. Once you get to where you want to be it's important to rinse the area completely and use your brush to remove all the paste residue.

It is not a miracle cure but will go a long way in removing the rust and inhibiting its return in most situations.

73,
Patrick, W7TMT

-----Original Message-----
From: TowerTalk <towertalk-bounces at contesting.com> On Behalf Of W7TMT - Patrick
Sent: Thursday, June 3, 2021 20:47
To: Grant Saviers <grants2 at pacbell.net>; towertalk at contesting.com
Subject: Re: [TowerTalk] 306 stainless steel

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 at contesting.com> On Behalf Of Grant Saviers
Sent: Thursday, June 3, 2021 19:41
To: towertalk at 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 at telus.net <jim.thom at 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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