acid rain and catchment thread

[Kenney]

So far, so good. We just pressure washed the tank and treated small kind rust with Ospho, then primed it. Haven’t noticed any new rust.

[terracore]

"Could be that it's always been acidic. Does anyone have pre-eruption readings that they've done?"

Regular, clean rain is naturally acidic due to interacting with carbon dioxide in the air and not interacting with minerals in the ground that neutralizes that.

According to the EPA web site: normal, clean rain has a pH of 5.0-5.5, "acid rain" is 4.0 (10x the acid)

[Rob Tucker]

I was talking to a Dept. of Ag offical the other day who told me that in past events the volcanic acid rain was corroding fencing and other metals to the point they had a program to share costs with farmers for replacing fencing.

Then I drove to Kona the other day and saw an unusual amount of fresh rust on the galvanized guard rails along the road. Sections further away from the national park were fine.

[terracore]

I talked to a guy who worked for the park installing fencing and he commented that the iron in the steel fence posts interacts with the galvanized fencing like an anode and cathode (I don't remember which one was which) and the acid rain acts as an electrolyte, the combination creates a weak electrolysis which causes the galvanizing material to come off the fence. He recommended using only galvanized T-posts where there is acid rain to greatly slow the process down. I imagine the guardrail anchors are also galvanized, but they are probably much deeper than a T-post and could be reaching something in the ground similar to an "earth battery" that completes the anode / cathode / electrolyte process when there is acid rain.

ETA: CLARITY

[Midnight Rambler]

Yes, the issue is that when you use two metals that have different electric potentials in contact with each other, electrons flow from one to the other like a battery causing rapid corrosion. This happened with the fencing at Kulani because they used galvanized steel fencing with stainless steel T-posts and wire. They're both rust-resistant, right? Not when you put them together...

https://en.wikipedia.org/wiki/Galvanic_corrosion

[Rob Tucker]

No, that's not what I'm talking about at all. My farm has been getting condensate from the plume for a few weeks now. Either a drizzle or driving rain. The roof on my stable was a dull galv. gray. Now it is orange. That's from acid rain. I don't know how far ranging the plume condensate is traveling but as I said I saw indications of it on Hwy. 11 in the national park.

[terracore]

On our property it seems to be happening in reverse. The galvanized fencing is fine, the steel T-posts are melting. These were ones installed by a previous owner. I installed galvanized t-posts and crappy home depot galvanized fencing, the T-posts are fine and the fence is melting. The level 3 or whatever its called galvanized fencing we got from Dels and Mirandas is doing fine.

[terracore]

Rob if I understand this correctly the change in the patina signifies the corrosion itself will eventually develop a temporary barrier similar to weathering steel, however eventually that itself will eventually corrode:

Corrosion behavior of hot-dip galvanized steel in simulated acid rain environment

Abstract
Corrosion behavior and failure mechanism of hot-dip galvanized steel (HDG) were investigated in an indoor simulated acid rain environment. The surfacial and cross-sectional morphologies of corroded HDG were observed by SEM; the elemental composition of the corrosion product was analyzed by EDX; the phase constituent of corrosion products was characterized by XRD; the corrosion rates of HDG were tested by mass-loss method. The results showed that the corrosion rate firstly decreases sharply, and declines slowly, and then rises slightly with time; corrosive media locally attack the galvanized layer generating pitts and corrosion products (ZnO ZnCl2 xH2O), then the later accumulated on the HDG surface. It follows that the corrosion products may act as a barrier, soon after it totally covers the surface of the HDG plate, to inhibit the penetration of corrosive media in the simulated acid environment. Initially corrosion rate decreases rapidly because the corrosion reactions proceed and corrosion products occur. The corrosion products become so dense that the corrosion rate further slows. Finally corrosive media penetrates galvanized layer, and corrodes the substrate, the corrosion rate becomes larger slightly. Throughout the process, the HDG layer provides certain protection to itself and the substrate.

Corrosion behavior of hot-dip galvanized steel in simulated acid rain environment.

Available from: https://www.researchgate.net/publication...nvironment [accessed Jun 24 2018].

[Rob Tucker]

terracore, Thanks for the info.

I got all my galv. T posts and fencing from Del's. Haven't examined the fencing closely yet but hopefully a $12k investment is hanging in there. I have one of my farm buildings on my place and the painted/kynar roof is fine. It is the older stable with a cheap metal roof that is astonishingly orange.

When and if things dry up I may treat it with Ospho and paint the roof.

This has got to be happening somewhere else too.

[randomq]

I went to clean the remaining Pele's hair from my gutters, and noticed that on the last half-inch of my relatively new HPM P7 roofing, the tops of the dips are bubbling up, as if there is rust under the paint. No scratches and just the factory edge on the roofing, so I am a little bummed about it. Not sure if this is acid rain related, or the factory edges need some touching up...