Boggles the mind doesn't it? It's not like it's news to anyone that the insides of tanks rust.
So why don't they galvanise them? Or use stainless? Or paint them?
Project for someone...flip the lines make it a vaccum pump and suck stone chip into the tank....I'll buy two!
I'll try to address these questions in part.
First off why not galvanize? in order for this to work the galvanizing process would have to be done after the tank was completely assembled. this is doable as pressure tanks for water wells used to be galvanized, operative words here used to be now almost all have neoprene bladders in them at least the smaller ones under 150 gallons. I do remember some very old air storage tanks that were galvanized but those dated back to the 1950s or 60s the galvanic coating usually hot dip zinc will eventually flake off inside of the tanks this can be caused by a number of things the changing of pressure up and down over a long period of time which causes the metal to expand and contract so the tank is going to fail eventually anyway either from rust forming in the areas where the galvanize had flaked off or from metal fatigue.
How about Stainless? good question and some of the more expensive compressors do actually have stainless tanks but they are rare and as I said expensive. Again not all stainless is created equal many grades will corrode or rust as we like to call it almost as readily as mild steel under certain conditions.
Painting can be an option providing a moisture cured urethane paint is used but it must be of a grade that will always remain flexible otherwise it will crack and rust will form under it.
How about other metals such as Aluminum? My US Divers 81 cubic foot scuba tanks were made of aluminum I used them for many years so long in fact that they had been hydrotested several times to retain certification. Some of the small pancake compressors do have aluminum tanks on them. so that has been done.
How about higher strength metals that are corrosion resistant such as core 10? No real reason not to except again the matter of cost and processing.
We could use boiler grade steel such as ASTN 516 that stuff should last for ever in such a mild environment as a air compressor tank. except for that nagging little word again "cost"
The way I look at it most compressor tanks are probably well enough engineered to have a service life well beyond most consumer grade compressors. But for the same reason your car needs an oil change regularly your wife's clothes dryer needs to have the lint trap cleaned and so on, compressor tanks require the water to be drained at regular intervals.
Not long ago I fabricated 3 replacement air tanks for a 1930 something truck. The originals had finally given up the ghost after 90 years. The reason I fabricated them instead of the guy just going out and buying them was their odd size placement and number of ports on them.
When he asked me if I would be interested in making them for him I said sure no problem. Well there is no such thing as tubing of any kind that had the exact same outer diameter at any thickness. So I was going to get some sheet steel rolled, well none of the metal works places anywhere within 600 miles of me had the capability or the willingness as in many cases to roll 3 cylinders each of which a different diameter some could roll the correct diameter and the thickness I wanted but their machines could not roll the length, the ones that had machines which could roll the length could not roll as small of diameter as I needed,
So I made my own plate roll
and my onw hydraulic power unit to power it
