# Forum Home Renovation Metalwork & Welding  316 stainles wall eye + HD gal anka screws? reaction?

## DavoSyd

so attaching 5x4 shade sail to double brick wall, 
going big with the wall eye:  
and big with the bolts:  
will there be long-term corrosion concerns? or is 316 OK?? 
Dr Gal. seems to say no problems: https://www.galvanizeit.org/images/u...ized_Steel.pdf 
but there are some big words in his document, so hoping for something simple from our resident chemist/physicist Marc...

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## Marc

Ha ha, thank you for the compliment. Actually as you probably know galvo and SS do have some interaction that results in galvanic corrosion. It is minimal with austenitic SS like 316 that is the best you can get. 
There is a but though. And that is the ratio between the two metals.  
I built a pontoon and corresponding ramp in steel that I took for hot dip gal, and used all hardware, bolts, hinge, screws 316 SS in a salt water situation and have yet to see any trace of white zinc rust after 2 years.
I have a large anode, that is the steel structure coated in zinc, and small cathodes, the SS bolts and screws. The penetration of the galvanic current is low. 
In your situation the reverse is true and with a large cathode and small anodes, the galvanic corrosion will be able to penetrate the zinc much more rapidly. 
Ergo 
Buy stainless steel screws/bolts. 
There is a good explanation as to why in your link.

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## rebuildr86

id trust ramplugs in brick before those horrible things. then u can use stainless coach screws.
the galv on the heads of those things also wear out from the impact driving them in. https://www.bunnings.com.au/zenith-m...-pack_p2310667

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## Bedford

> so attaching 5x4 shade sail to double brick wall,

  Are they solid bricks?

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## Marc

The integrity of the wall is of course a separate consideration. you need a really good wall for that size sail. I trust you know that though. 
If you really _want_ to use galvanised screws, you need to isolate the current flow between the two metals, so in theory a plastic washer should work providing the sides of the screws don't touch the plate. In practice it would be nonsense of course. 
A plastic plug and 316 or 304 screws should be OK providing the system can take the pull of that sail. 
PS
Stainless steel fasteners contrary to popular belief are rather crappy and are not rated.

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## rebuildr86

yes stainless is soft as cheese. but i prefer that when there are 4 of them and there is no moment being put on them. (flush fix)

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## rebuildr86

id be worried bout the stainless bolt on the hook eye,  on that topic.

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## Marc

The worst with stainless bolts is galling. Especially with lock nuts. It can drive you crazy. In this case it should be ok but the SS screw will be easy to break so I would go one size larger.
As for that hook, all you need is a bit of anti seize grease with copper or nickel or some other poison.  :Smilie:

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## DavoSyd

> Are they solid bricks?

  yeah, solid bricks...

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## METRIX

Nothing wrong with Anka's use them all the time, I won't touch Dyna's anymore, but I never drive them in mechanically, always use a Socket set to ensure they bite good, they won't let go if your base material is good. 
HDG and Stainless either austenitic (3 series) or martensitic (4 series) do not particularly like each other, there is a heightened reaction of the base metal. 
Options would be buy some Stainless rod, cut it to length, sharpen one end and chemset them in, or as Rebuilder said ramplug and Stainless coachies.

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## DavoSyd

thanks all,  
I'll get on the ladder tonight and take some close ups of how the existing 316 wall eye & gal Anka set up is faring (after over 2 years in situ) ...  
I'm asking now about it cause I'm doing second shade sail and didn't realise before that what I was using could cause issues...

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## Marc

Davo, if you have time and like a good laugh, there is a discussion here that spans over a decade on this issue. Some of the posters know what they are talking about, most is nonsense or half true. The best article is the one you linked. I like the explosion post the best  :Rofl5:  https://www.finishing.com/197/66.shtml

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## Bros

> I built a pontoon and corresponding ramp in steel that I took for hot dip gal, and used all hardware, bolts, hinge, screws 316 SS in a salt water situation and have yet to see any trace of white zinc rust after 2 years.

  316 Deadly in salt water.

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## Marc

What do you mean deadly?

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## Bros

> What do you mean deadly?

  Unseen corrosion much worse than mild steel.

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## Marc

Oh ... I see, I thought you had some other explosive story, ha ha. 
Sure, the incorrect grade of SS can be a problem but certainly not worse than mild steel, come on!
There are different type of 316 for marine application and then there is duplex stainless steel. 
I have 12mm 316 wire rope stay cables in salt water doing just fine.

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## DavoSyd

here's the one that's been up since january 2015:   
there's no red rust, but there is that white kinda stuff? is there much of a reaction going on there?  
tops of bolts are fine - i used a socket wrench to install...

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## DavoSyd

> I have 12mm 316 wire rope stay cables in salt water doing just fine.

  all the 316 bits on my kayak are all still shiny, but i do wash them off after every trip...

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## Bros

> Oh ... I see, I thought you had some other explosive story, ha ha. 
> Sure, the incorrect grade of SS can be a problem but certainly not worse than mild steel, come on!

  Far from it as mild steel you can see the corrosion and when it gets scale on it it slows down the rate of corrosion with 316 SS it appears perfectly good but take the fasteners out and they are like swiss cheese whereas mild steel while rusty and slowly wasting away 316 SS disappears at an alarming rate.
When we built a boat we had some through hull fittings and at 6 mths and 18 mths we removed one of the bolts for inspection to see if our assembly prevented salt water leaking into the bolt, thankfully it was OK.
That's why I used the term deadly in reply to use is salt water as all could look right but in fact it is dangerous.
Crevice Corrosion.

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## Bros

> all the 316 bits on my kayak are all still shiny, but i do wash them off after every trip...

  They are not totally immersed for an extended time.

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## DavoSyd

> They are not totally immersed for an extended time.

  neither is my shade sail anchor?

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## pharmaboy2

Gee, Ive been around a fair few boats when out on a stand, and certainly ours had all 316 fittings below the waterline - actually above as well, apart from the odd marine grade aluminium trim. 
I see the logic, but I dont see any boat manufacturers replacing SS fasteners with steel on glass hulls. 
most of these conversations are esoteric and theoretical anyway.  The only case of proper fast Galvanic Ive experienced in the real world was carbon fibre to aluminium

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## Bros

> neither is my shade sail anchor?

  Agree but I was responding to a sentence in Marc reply where he quoted   

> 316 SS in a salt water situation

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## rebuildr86

every single one of my shade sail stainless turnbuckles froze up from galling. (zenith 316 from bunnungs) That was in perth about 10 ks from coast.
This caused an issue as the sails got old and stretched, resulting in the need to buy new ones. I once made the mistake of going galv, only to have the pressure points on the hook and eye wear out in 2 months and start rusting.
ur dammed no matter which way u go, but i can definately say a stainless steel screw into a plastic ramplug is the best solution I found. (here in wa) You completely ignore the recommended gauges and pick a screw that litteraly only just fits down the the first bit of the plug.
My experienced coleagues and I have never been able to make an anka screw tight in the clay face bricks we have in WA. 
Those bricks in davos post look like nice dense bricks so our situation over here is a bit different.

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## DavoSyd

treat SS turnbuckles with respect... 
if they are getting hot while you are turning them, they are going to gall! 
slow non-jerky action seems to work for me...

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## Marc

> Gee, I’ve been around a fair few boats when out on a stand, and certainly ours had all 316 fittings below the waterline - actually above as well, apart from the odd marine grade aluminium trim. 
> I see the logic, but I don’t see any boat manufacturers replacing SS fasteners with steel on glass hulls. 
> most of these conversations are esoteric and theoretical anyway.  The only case of proper fast Galvanic I’ve experienced in the real world was carbon fibre to aluminium

  Agree that many conversation involving SS are out there. Just look at that thread I linked.
That anchoring you have there Davo is in perfect shape from what I can see. If you are really worried, have a plastic washer under the fasteners. Anti galling compound works. Also tighten by hand.
Bros, a catastrophic failure due to pitting or crevice corrosion indicates the grade selected is the wrong for the environment.

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## DavoSyd

> That anchoring you have there Davo is in perfect shape from what I can see. If you are really worried, have a plastic washer under the fasteners.

  not so worried now after my trip through the various information that i found, i think it will continue to be relatively OK primarily because the water (thing that causes the galvanic reaction) is not present for very long. so if there is a sufficient 'ingredients' for corrosion, it is only there for a little while.  
i will continue to monitor the fittings regularly, but pay more attention to the bolts. i was most concerned about corrosion at the ferrules (nickel plated copper), but these seem OK too... i will go with with the same SS/gal anchoring on the new shade sail...

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## Jon

So many terms used in this thread that I have not heard since my 3unit Engineering Science in the HSC.  
I am sure I used to be able to identify Austenite, now I had to look up what it meant.  Use it or lose it, i lost it.

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## Bros

> Bros, a catastrophic failure due to pitting or crevice corrosion indicates the grade selected is the wrong for the environment.

  But you recommend 316 and I have seen 316 bolts disappear in a very short time with the bolt head looking perfect but the rest eaten away.
Now maybe these people know a bit more them you and I.  Article: Selection of 316, 304 and 303 types of stainless steels for seawater applications

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## pharmaboy2

Interested to know what the environment was that killed the 316, and what a short time is. 
i know that risers in boats are cast iron because no stainless survives because of the temperature of the saltwater.  The other thing that seems to be needed often is a sacroficial anode.  If the water is not hot, I can’t imagine anything outsurviving the 316, possibly duplex, which becomes a maintenance issue.  Using mild steel so you can see the corrosion is just a recipe for being unable to remove and inspect I would have thought. 
thats where things become really painful, when you can’t remove the bolt assembly.

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## Bros

I have seen it in two places. The first was in large rotating trash screens that are used where seawater is pumped from rivers. These screens were 6M diameter and 4 m wide rotating at about 10 rpm/hr. On the wheel were bolted segments of SS screens. These screens had boltholes which had 50mm 316 SS bolts to the main wheel pretty similar to this. https://www.ovivowater.co.uk/applica...t/drum-screen/
The problem was the bolts were not fully sealed nor open to the saltwater so this resulted in crevice corrosion and it occurred in about 2 yrs. The bolts looked incredible as the bolt head looked perfect but the shaft was eaten through. There were hundreds and hundreds of these bolts and the replacements I believe were Inconel, i still have a few that were left over.
The other place was in a wooden hull boat where the bolt wasn't sealed from the seawater and a small amount of stagnate salt water was up against the bolt shaft.
Stainless is fine provided it is exposed to the salt water or is totally sealed like a fastener with the head exposed and the shaft sealed up.
Piles on wharves are steel but they have a sophisticated cathodic protection system.

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## Marc

Seeing that there is such interest in stainless steel for marine applications, see below two articles that engage some of the basics of SS in marine environment. There are probably hundreds more and if you read a bit you will soon realise that the opinions differ. 
Let's note however that the discussion was not the use of SS in seawater but a rather much milder and less understood corrosion problem derived from the use of different metals making contact in the open, rain or shine.  Galvanic corrosion of a Bunnings sourced fitting has little to do with "marine". And anyone with some experience in using this cheap things knows that there is little to fear from galvanic corrosion but ... to put your mind at rest, use SS with SS and forget about it. 
But just to follow some of the thoughts above. The risers in marine engines, that is the part of the exhaust where exhaust gases and hot water from the heat exchanger meet and flow out to sea, called risers because they go up and then down to prevent the engine from flooding when at rest, are made of cast iron only because it is cheaper to do so, and they are made to be replaced like many other parts of an engine like marine manifolds,  they are not built for eternity. 
However if you really want you can buy SS risers. The problem is you would be wasting your money because they don't corrode but they crack from heat stress and not corrosion. 
One could build risers to last forever casting them in duplex SS but they would probably be unpopular due to cost. 
Stainless steel is an alloy designed for different applications and different chemicals. There is no "better" alloy, just the right one. There is a long list of 300 series SS each designed for a specific purpose. There is a list of 316 SS with various grades of molybdenum that are adequate for some applications and not for others. Even when we talk "marine", what does that even mean? Permanently under water in the ocean? or on the deck of a sailing boat with occasional splash? on a beach front house balcony? A sea pump shaft turning at 3000 rpm and 80 PSI?
And where? Sydney? Perth? Nice? Not the same !  :Smilie:   Corrosion Resistance in Marine Environments Selecting Stainless Steels for Seawater Pumps

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## Bros

If you are going to use SS in a totally submersed environment you need to do your homework thoroughly as getting 316SS from the local boat shop could end up in heartache. 
One of my friends bought an expensive fiberglass boat and asked me to have a look at it. When I did I noticed light rust streaks from the hinges. Thinking they used 304 screws i took a magnet down and half the hinge was magnetic the other half non magnetic and they were supposed to be marine 316SS hinges.
I had to install a light stand on a pontoon and i was to use 50 x 50 RHS. I did my research went to the metal merchant got the price and said I want a 6M length. They looked up the inventory and found a length in Darwin so they freighted it back and i got it at the quoted price.

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## Marc

Risk of galvanic corrosion between two dissimilar metals. Very low between all the different SS
Very high between SS and Zinc, but the table does not consider the very important factor of mass difference, yet we already discussed that.   http://www.anzor.com.au/blog/galvani...-metals-apart/ 
The rust probably came from the pin in the hinge, but only a guess. 
A lot of cheap rubbish made in China passing for quality. The old story.  
The other part about RHS I don't understand. Is that stainless RHS? And how did it stand up to corrosion?
i would make that out of duragal, take the lot to HDG and paint with 2 coats of Luxepoxy4

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## Bros

Sorry aluminium

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## Marc

Even better. 6000 series?

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## Bros

> Even better. 6000 series?

  Cant remember but it was not what the metal merchant wanted to sell me.

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