First let me say since the rubber tire was invented we never worried about the age of them. When they were worn out or cracked we replaced them.

So I have and older travel trailer with two bigger (taller tanks). Most likely from the trailer era (1980's). Most likely with some propane in them.
From memory we used to have new valves put in them and were good to go. Now what is the current shenanigans regarding older tanks.

Take them to a gravel pit. Light a couple road flares and leave burning against the tank. Go a good 100+ yards away and shoot.

It makes a decent fireball.

They won't fill them because Internal rust is one issue that 'may' compromise the integrity of the tank/vessel...Boom! Also the new(er) tanks with the new(er) valve design have an OPD (Overfill Protection Device), to prevent against a dangerous overfill...Boom!

They can be inspected, certified and put back in service, but good luck finding somewhere that does it, and will do it for less than the cost of a new tank. Best bet if you want to 'game' the system, is to turn it in for a new/certified one for the cost of the propane fill. The propane tank exchange services do certify tanks as part of their service/process. Not sure who does this by you (because you have a 'secret location'), but find one that completely fills the tank, as not all propane tank exchange services do. Near me AmeriGas does provide a complete fill, but Blue Rhino does NOT. Also, at some of the AmerGas locations near me you can pick out your tank, and if you look close, they do have new or nearly new/not abused tanks in their inventory. YMMV

Regarding disposal 'shenanigans, older tanks near me can be 'recycled' at the dump by first venting it, and then removing the valve. Again YMMV

Trade them in for new filled ones at the local convenience store for 20 bucks.

nhracecraft, I don’t know anywhere that exchanges 30lb tanks. All the propane exchanges around here are 20lb (5gal) tanks.

Those 30lb tanks have gotten expensive. Our local propane supply will recertify them when they fill them for $5. Each recertification is good for five years. If the outside has nice paint and isn’t rusty, they pretty much just slap the new sticker on it and fill it.

^^^I guess I missed the 'bigger/taller' description in the OP. Anyway, I'm shocked anyone would re-certify a tank for $5, and apparently do it w/o doing an internal inspection. I researched 're-certification' of my existing tanks a while back, which were in 'mint' condition, and couldn't find anyone that would or could do it.

Thanks guys. Not 20lb. A bit bigger. I will take to a legit propane outfit to see what they say. If nothing else I hope to be able to get something out of them exchange wise. Even if 201b. Well see.

Just out of curiosity, what amount of pressure are these tanks (and/or the 20 pounders) designed to handle? I would guess that the margin of safety would be twice what the working pressure of a "full" tank is supposed to be (or is it measured solely by weight?) Surely, some level of pressure safety might be assured with an air compressor? Not "certified," but at least giving the user a sense of security.

Just guessing they may be old 40# tanks?
Any tank UP TO 40# is required to have an OPD valve. If they are really that old, they will not have an OPD.

Take them to someone like Airgas and see what they say, but they may or may not help you out.

I had a propane tank from my gas grill that I couldn’t get filled at a gas station because it was expired. They recommended I take it to Amerigas, the major propane supplier in the region. The guy there just exchanged tanks with me, giving me a new tank and only charging me for the propane to fill it.

Are these the RV type that are oriented to sit flat on their sides? Some are hung underneath. These are not removed to get refilled, they are stationary to the RV.

These are different from the backyard BBQ tanks that sit vertically and are easily removed to take for filling.

Take the RV to a real genuine propane full service business. They can inspect them as well as the propane lines for damage or leaking, and verify the inline pressure to the device, such as the stove and water heater.
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These are vertical tanks mounted on a platform on the tongue of the trailer.

These are larger than you bbq 20lb tanks. And guessing they are close to 40 years old.

Give them or sell them to somone who does alot of casting. They work great for smelting alot of wheelweights at one time. Stand them off a distance and shackle to a tree. Shoot a hole in it above where you plan to cut. Fill with water, drain(maybe a couple times) then use angle grinder to cut bottom off. Works much better than cast iron.

Sometimes some people repurpose them into smokers for meat.
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i like bean cookers idea

I used to work at Airgas.Every propane cylinder will have a WC# number stamped on it. Water capacity.
71.7 = 30lb, 95.6= 40lb. Every fill plant will have a chart. If yours is different
there are charts on the interweb.
If I recall correctly, recertify is just a visual inspection, not too rusty and no deep dents GTG.
They COULD recert for five years. I believe the OPD valves became mandatory in 2007. Most welding
fill plants won't revalve, would send it somewhere.
As recommended above I would try Amerigas, Sububan,anyplace that just does propane. They may just swap you for a newer one.
They are used to getting old tanks.
Hope that helps.

Thanks Schmelby, it does.

There's a farm in the country where good propane tanks go after a long and productive life.

The farmers name is Hikock 45

The local Ace Hardware does refill, one of my bottles was too old, when I asked what he meant the kid explained the date stamped on the bottle etc. he swapped out a new one to me. He said they send in the older ones to somewhere to be inspected….

quote:

Originally posted by nhracecraft:
They won't fill them because Internal rust is one issue that 'may' compromise the integrity of the tank/vessel...Boom!

Rust was a problem with steel cylinders. All aluminum now, no rust. Haven't seen a steel tank in 25 years.