Air compressor tank cathodic protection

[Eddyde]

That seems overkill as I'm willing to bet exactly nobody does this, and there's probably compressors over 20 year old.... I know hydrostatic pressure test is required for stuff like compressed gas tanks and LPG cylinders, but I don't see it for air compressor tanks...

In New York City, one needs proper certification to operate an air compressor, I was a licensed air compressor operator for over 20 years. Also compressor tanks must be tested every 3 years by a certified testing company. If you don't have the proper license or test reports the city will issue fines. I know other municipalities in the US have similar requirements.
Overkill? Perhaps if you have a small portable compressor but if you have an 80 gallon tank at 175 PSI in your shop, you would be smart to have it tested every 5 years or so.

 

[taiwanluthiers]

In New York City, one needs proper certification to operate an air compressor, I was a licensed air compressor operator for over 20 years. Also compressor tanks must be tested every 3 years by a certified testing company. If you don't have the proper license or test reports the city will issue fines. I know other municipalities in the US have similar requirements.
Overkill? Perhaps if you have a small portable compressor but if you have an 80 gallon tank at 175 PSI in your shop, you would be smart to have it tested every 5 years or so.

What so if you got a job site compressor for nailing you have to have it certified and you must be licensed? That seems overkill. Or are there exceptions? Do they ask for license when you buy one from Harbor Freight?

 

[Eddyde]

What so if you got a job site compressor for nailing you have to have it certified and you must be licensed? That seems overkill. Or are there exceptions? Do they ask for license when you buy one from Harbor Freight?

Yes, small portable compressors are exempt, though I cannot recall the limitations. No, you don't need to show any license when buying a compressor, but you need to have the license to install and use it.

 

[Eddyde]

You also need a license to spray paint in NYC, I held that one as well.

 

[taiwanluthiers]

Yes, small portable compressors are exempt, though I cannot recall the limitations. No, you don't need to show any license when buying a compressor, but you need to have the license to install and use it.

So if you have a hobby shop with a 5HP fixed compressor, you have to be licensed? How would they enforce it?

But then again if you lived in NYC you likely can't afford to have a hobby shop anyways, rent is too expensive for that.

 

[Eddyde]

So if you have a hobby shop with a 5HP fixed compressor, you have to be licensed? How would they enforce it?

But then again if you lived in NYC you likely can't afford to have a hobby shop anyways, rent is too expensive for that.

I owned a custom cabinetmaking shop located in an industrial building. All such commercial establishments are subject to routine inspection by the fire department and other agencies. So no getting away with any shenanigans.
Sure in a home shop it is hard for the city to enforce the compressor ordinance. But if you had an accident and didn’t have the proper paperwork you’d bet your insurance wouldn’t pay and you might even be prosecuted if someone got seriously injured or killed.
One could easily have a hobby shop in NYC located in a garage or basement. Yeah renting a space would be expensive.

 

[RJSakowski]

Stainless Steel tank would be nice, but it actually rusts too if exposed to salts. Perhaps not necessarily as physically strong as some steels, but I bet these tanks are not anything complicated, just cheap to make.

It is my understanding that a Hot water tanks come with either a 5 or 10 year warranty. Same tank just more insurance and $$$!

So here is my question. Consider a hot water heater that is not being used and sets with water in it for 10 years, while the water is shut off. Has the rusting process stopped? I recently looked at a building that appeared to be abandon, but it had new hot water heaters put in during a partial remodeling process that occurred almost 30 years ago. On the outside they look like new, just very dusty.

I once had a hot water heating system. The radiators, some pipes and the pumps were just made from common steel or cast iron. However they did not rust out from the inside. I think this is because the water is not changed very often, the Oxygen in the water must be depleted after a while and so there is no more rusting. Is this reasonable?

Are those 30 year old hot water heaters any good?

Dave L.

We are still using an electric hot water heater after more than forty years and it was used when I installed it. I keep waiting for it ti fail so I can install a new water heater bit it's like the Energizer bunny. There is no sacrificial magnesium rod although we do have ferrous iron in our water which may contribute to preventing rust. If I draw a bucket of water and let it stand, the ferrous iron will oxidize and separate out as a thin layer of rust at the bottom.

Also more than forty years ago, I built my own air compressor using a portable 10 gallon air tank, a compressor, and a 1 hp motor. It is still functional and lives in my barn where I use it mostly for airing up tires. I made a platform to mount the compressor and motor and welded it to the top of the tank and there is a pinhole leak at one of the welds which is inaccessible for repair. The slow leak down of a charged tank is a relatively minor irritation so it remains unrepaired. Given the location of the leak, there is little chance of a serious rupture and the compressor remains in service.

In order to see the benefit of cathodic protection, the less active metal has to be on good electrical contact with the more active metal and both have to be immersed in a conductive liquid. It works for a water heater because the tank is full of water and it works for the marine appication for the same reason. Water collecting on the bottom of a compressor tank wouldn't meet the later requirement.

Zinc coating does work and is commonly used for potable water pipes. Pressure tanks for private wells also were galvanized so the process is well known. Hot water heaters used to be advertised as glass lined as a preventive for rusting out. Modern pressure tanks use a bladder which isolates the tank from the air ballast but this is more to prevent air from dissolving in the water, requiring a periodic recharge than for rust prevention.

 

[taiwanluthiers]

We are still using an electric hot water heater after more than forty years and it was used when I installed it. I keep waiting for it ti fail so I can install a new water heater bit it's like the Energizer bunny. There is no sacrificial magnesium rod although we do have ferrous iron in our water which may contribute to preventing rust. If I draw a bucket of water and let it stand, the ferrous iron will oxidize and separate out as a thin layer of rust at the bottom.

Also more than forty years ago, I built my own air compressor using a portable 10 gallon air tank, a compressor, and a 1 hp motor. It is still functional and lives in my barn where I use it mostly for airing up tires. I made a platform to mount the compressor and motor and welded it to the top of the tank and there is a pinhole leak at one of the welds which is inaccessible for repair. The slow leak down of a charged tank is a relatively minor irritation so it remains unrepaired. Given the location of the leak, there is little chance of a serious rupture and the compressor remains in service.

In order to see the benefit of cathodic protection, the less active metal has to be on good electrical contact with the more active metal and both have to be immersed in a conductive liquid. It works for a water heater because the tank is full of water and it works for the marine appication for the same reason. Water collecting on the bottom of a compressor tank wouldn't meet the later requirement.

Zinc coating does work and is commonly used for potable water pipes. Pressure tanks for private wells also were galvanized so the process is well known. Hot water heaters used to be advertised as glass lined as a preventive for rusting out. Modern pressure tanks use a bladder which isolates the tank from the air ballast but this is more to prevent air from dissolving in the water, requiring a periodic recharge than for rust prevention.

The compressor I have was bought used. It looks a bit old but is in a good condition, it's 5HP 3 phase motor and the pump puts out something like 20CFM. The tank appears to have a slow leak, but upon later investigation it wasn't the tank because if I put the drain valve in a certain position the tank holds pressure very well (which tells me it's actually the drain valve that is leaking). When I do drain it I see no hint of rust, so no idea if the tank is structurally sound. I mean I only turn it on when I need to use the air sander (which I prefer to electric ones, for some reason even a cheap air sander is much more comfortable to use and more powerful than an electric one), and any other time the tank is slowly bled of its air.

I really hope the tank don't explode but I've never heard of a compressor air tank explode in Taiwan, and these are used literally everywhere.

BTW I never seen an upright air compressor in Taiwan. All the belt driven ones I seen have the tank lying on its side. Upright would have saved a bunch of floor space.

 

[B2]

We are still using an electric hot water heater after more than forty years and it was used when I installed it.

Yes, I had a house built in the 50s which had an original electric water heater that just kept working then one of the two heating elements died about 1986 and I replace it. I should have replaced both heater electrodes but did not. When doing so I peeled back the tank insulation to discover the tank was made of copper (or brass) by the color. Very hard to believe. I was shocked, but it was not magnetic so not made of steel. So it was probably worth $ even back then. Then, in 1988, I took another job and was working 1000 miles away while by wife and family remained behind for a while. While gone the second heater element failed and there was limited warm water. My wife just called a plumper and he hauled the entire hot water heater a way and installed a cheaply made unit. He told her the copper one was bad, but I know better...! It was not leaking.

My experience with failed gas hot water heaters is that they always rust through near where the flame hits them at the bottom! Sure this is the hottest spot and the water inside may even boil. I guess I do not really know if the rusting is only from the inside or if some of it is coming from the outside. Most of the heater tanks are said to be "glass lined", what ever that really means. If this is the case, I suspect that the expansion during heating at the flame area may play havoc with the glass bond. The latest one that I installed said this and yet there is still a cathodic anode. Why? Ans.: The damaged areas are still exposed. https://meridian.allenpress.com/cor...athodic-Protection-In?redirectedFrom=fulltext

This is a very old technology, see the old US patent: 2267361.

2267361 - Google Search

Dave

 

[pontiac428]

Hmm, ferrous oxide means you are on well water in Wisconsin or Nevada, reducing conditions in the aquifer. As pumped, the high pH stabilizes the ferrous oxide as an oxide-hydroxide. As the water absorbs CO2 from the atmosphere, the hydroxide depletes and the blackish ferrous can oxidize to red ferric. As long as it isn't bound already to something tougher, like phosphate- ferrous oxide is bound very tightly to that, and will settle out as black dust.

The eastern Wisconsin aquifer also has a lot of uranium in it. It's probably all sequestered with the minerals and rust in your hot water heater. You can dissolve it and reclaim it with bleach and collect it with electrodeposition on an electrode.

I bet you didn't know you were so close to critical mass...