Steel corrosion protection: can/should Fishoilene be sealed with any coating?

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Greendrake

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#2914771 16-May-2022 22:19

elpenguino:

How high is the water table? Any tendency for a particular PH of the soil in the area?

Water will be there for sure, not sure about PH though. I think if bare steel gets exposed the foot will be gone in a few years no matter what PH. If the coating stays intact, the foot will live indefinitely.

elpenguino:

What's the cost difference between making the large feet vs concrete with embedded anchor?

You would be surprised where a concrete truck can deliver to, although you haven't specified why access is difficult.

Cost is roughly about the same. But I have already bought all the steel and am now welding the feet, so no turn back. Part of the motivation was to learn welding — my first experience.

Good to know re concrete truck. One benefit of not using concrete is that should I ever decide to move/disasseble the sail, I would just dig the feet out. Not so easy with 1.5 tonnes of concrete per pile.

elpenguino

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#2914773 16-May-2022 22:23

Greendrake:

elpenguino:

How high is the water table? Any tendency for a particular PH of the soil in the area?

Water will be there for sure, not sure about PH though. I think if bare steel gets exposed the foot will be gone in a few years no matter what PH. If the coating stays intact, the foot will live indefinitely.

Yes and that's where hot dip ensures complete coverage. If you have thin or areas of missed application of coating your protection will be much poorer.

Happy welding !

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Jase2985

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#2914798 17-May-2022 05:57

would something like por-15 work? its used as a car under body sealer

Rust

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#2914799 17-May-2022 06:34

As you are committed to using steel, some things to keep in mind:

Corrosion will be accelerated at the wood/steel interface due to acids present in wood and chemicals from the treatment process. There are barrier products available, bituminous tape for example, which may offer some protection.

Stainless steel fasteners are absolutely the best choice. Galvanized 2nd choice. There is no third choice. Don't mistake the shiny zinc coated fasteners for galvanized ones (which are dull), they are not the same and will rot away in short order.

If you are still planning on using a consumer rust preventative then keep in mind that surface prep is paramount. Wiping down with a rag is not sufficient. The surface must be completely free of all oils and contaminants. Media blasting is preferred to remove mill-scale and other contaminants.

Do not under estimate just how harsh an environment soil is. There is chemistry happening in the forms of acidity, ion exchange and galvanic action. Fishoilene or similar will dissolve away very quickly. Consumer grade spray-on zinc products such as Zinc-it are useless. They are just a thin coating precariously sitting on top that will be scratched just by looking at them.

There are better zinc-based products available, also there are bituminous coatings designed to be used in footings that are quite good. Go to a specialist paint supplier and talk to them.

The reasons hot-dip galvanizing is so good are that the coating is thick and strong enough not to be scratched, and it is applied using electrolysis and is ionically bonded to the steel. Other coatings just sit on top with no bonding just waiting to be scratched off.

Bung

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#2914813 17-May-2022 07:48

(I am not an engineer) Looking at this I wondered what foundations a pole barn would need. A barn must have at least similar wind loads. The common plans call for 600mm holes 1000mm deep with 150mm poles, about 0.3 m3 of concrete per pole. Did your engineer think of a number and double it out of habit?

Ge0rge

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#2914821 17-May-2022 08:23

It purely depends on the wind forces in the area - I have a steel framed shed built recently, the uprights are bolted to the concrete foundations. Under each upright is 1m x 1m x 1.2m deep of reinforced concrete - it makes for well over 8m³ of concrete for preventing uplift, and that doesn't include the concrete for the floor itself.

It had to be rated to 180kph winds to satisfy council.

kotuku4

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#2915253 17-May-2022 18:17

I would galv and then epoxy coat.
Another option galv or epoxy and apply Denso system, primer, petrolatum tape wrap and PVC outer layer. We use this on burried joints on watermains, all metal to metal joints bolted with galv bolts. Usually steel or ductile iron epoxy coated fittings. Galv fixings in ground corrode unacceptably if not Denso wrapped.
The only material that can be compacted to 2.4t/m3 like concrete are well graded gravels think road pavement basecourse, soils will be lower density.

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kotuku4

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#2915266 17-May-2022 18:58

Most galvanized poles I've seen have a black epoxy or mastic coating for in-ground. Eg power, light poles, shade sail and carport poles. In either compacted backfill or concrete.

neb

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#2915325 17-May-2022 20:24

Fishoilene still exists? That stuff was used by Irish monks to waterproof coracles in the 11th century, I didn't know it was still used today given that there are much better synthetics available.

I think you're looking at this the wrong way round, I'd be looking more for what you can bolt the thing to that's suitable for in-ground use. So concrete in some heavy-duty hot-dip galvanised post-and-bearer brackets and bolt the piles to that.

Edited to add: And with that off-the-shelf configuration you can choose something that meets the council requirements out of the box without having to convince them that the custom setup you'd otherwise be using is OK too.

Greendrake

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#2915339 17-May-2022 21:32

Bung:

Did your engineer think of a number and double it out of habit?

He calculated that each of the 12 piles needs to be held down by 0.6 m3 of concrete at the very minimum.

The soil is pretty heavy, mostly clay, so roughly the same density as concrete.

Here is the foot design: 5 mm steel plate, base 700x700, height 500, pipe 155 inside:

MikeAqua

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#2915399 18-May-2022 08:57

Galv gets its protection from the layer of zinc oxide that forms on the surface. If you coat the galv, you prevent that coating forming starving the zinc of oxygen. I'd let it oxidise, before painting. There are primers that bind to oxidised galv.

Predrill all holes and check for proper fit/alignment before getting the steel hot dipped. Also chamfer the holes so the gal adheres properly. Consider how the structures will be supported during galvanising, and whether they might deform while being dipped.

I wouldn't use stainless fastenings if they are to be buried. They are less reactive than the galvanised steel. Therefore, in a wet environment, the galv will effectively become an anode that corrodes sacrificially to protect the stainless fastenings. You can observe this effects on boats trailers, which although galvanised

No problem to use stainless above ground, but personally, I would use an isolating resin like tef-gel or duralac between the fastenings and the galv.

Mike

pipe60

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#2915416 18-May-2022 09:09

Have you looked at simpler designs, here is the one I am doing 18 panels on 4 posts,Galv steel with concrete,can be rammed if required

Greendrake

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#2915716 18-May-2022 17:16

pipe60:

Have you looked at simpler designs, here is the one I am doing 18 panels on 4 posts,Galv steel with concrete,can be rammed if required

I can't do that angle (will waste lots of efficiency in winter — the main time of the year when I need the power).

At my angle (69°) the structure will be much more prone to be blown away killing somebody, so I've got to be serious about how it is held down to the ground.

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