Barrel life expectancy

What is the life expectancy for a barrel in a mass rocket stove heater? It would seem that the top of the barrel would get very hot and burn through fairly quickly.

When it does burn through, does it give you plenty of warning with small holes getting bigger gradually/slowly, or will it happen quickly?

Thanks.

Mike Kelly : First the good news, there are a lot of Rocket Mass Heaters that make use of Barrels That were made the same way 20 years ago, that you are now being
told to re-use,and re-purpose today! And these 20 years old R.M.H.s are still on their 1st barrel. Under different circumstances, I would like to be able to put up a reward
for someone who could show me a barrel that had failed among these veterans.

However Twenty years ago it was still possible to find barrels that were of much heavier gages than the then (and Now ) current crop! Except for a certain class of 55
gallon oil drum made especially for world war 2. the heaviest barrels were made in the 30s to be stacked on pallets and survive Travel as palleted units in international
travel in the holds of ships! All Barrels have been growing thinner and thinner with every passing Decade.

Some more good news, If you compare the average wall thickness of a 55 gal drum designed to hold Flammable petroleum products, be a palletized unit, transported by
any of the common carriers, they are still made of a heavier gage of a ductile steel than that of the average heat exchanger in a Fossil Fuel-fired Forced-air Furnace, is it
more good news or bad news that the heat exchangers found in these commercial units are rarely guaranteed for more than 20 years, any replacement would be prorated
like a used tire is- and anyway, how often have you heard of heat exchangers being replaced? Furnaces Yes, Heat Exchangers No! And that is after all, what we are re-using
these barrels for- as heat exchangers !

To day it is possible to find quite light 55 gal drums made for other proposes that holding Flammable petroleum products, and exempt from the requirement for stronger
construction, A favorite among D.I.Y. Rocket Mass Heater Builders is a 55gal drum that is made with one of the ends open, to be closed with a full sized lid and held in place
with a clamping band, these barrels are used and prized for the ease of vacuuming out the fly ash that settles out in the transitional area! This gives you a chance about
every 6 months or more often to inspect your barrel for potential trouble areas! This is my personal preference, and I collect these barrels for trading and future use !

Personally I am not that worried about the likely hood of getting much less than 20 years out of a barrel. I will have built and rebuilt many more R.M.H.s since then, both
for the fun of it and to take advantage of new High Temperature refractory materials that will be coming on the market, and hopefully driving their price down !

We used to believe that the barrel lasted so long because there was an oxygen deficient environment within the streaming hot exhaust gases, but what testing that can be
done in that Torrid environment and further downstream shows very little Carbon Monoxide as compared to the amounts of Carbon Dioxide, and some presence of oxygen.
I Have come to believe that at these temperatures there is a natural preference of Carbon and Hydrogen that places itself above Iron! Y.M.M.V. Also there is an Affect
generally called Laminar flow, though in this case it more properly could be called laminar non-flow that protects the metal surface from the scrubbing effects of your hot
exhaust gases! I have high hopes for the future of the whole family of Rocket types, those over 25 years old, and new ones we are learning about here in these threads !

Think like Fire, flow like a Gas, Don't be the Marshmallow! As always your comments and questions are Solicited and Welcome, PYRO - Logically BIG AL

The best choice then is likely to find an older barrel( ie. thicker materiel) or make your own. On the idea of making your own, I am curious on what would be considered the ideal thicknesses of the barrel. Should the top be thicker to retain more heat, not only for better burn but a better cook surface as well? Should the sides be thicker or thinner to radiate heat better? Erica mentioned that if someone knows how or has the ability to make barrels to get a hold of them so perhaps they have some certain specs in mind.

Warren Martin : I believe that I expressed clearly what my choice is, I will take a lot of tradeoffs for the knowledge I can gain from having a barrel on my Rocket Mass Heater
with one end made removable, and sealed with a clamping band, Without unshipping the barrel from theCob of my R.M.H. I can quickly check to see the health of the inside
and outside of my Heat Riser, inspect my barrel, the transitional area where the Gases shift from falling vertically to flowing horizontally, and check on and vacuum Fy ash
out of my barrel and the Transitional area !

While I started to give a straight forward answer, I became a little tongue in cheek ! I really could have covered it all by typing Y.M.M.V.! If you are worried about it you can
weigh the barrels and tell !

Erica Wisner has learned to grow to love the functionality of 55 gal drums but would love, love to see a sleeker exterior to please a wider Audience, she is running a for fun
contest to see who can improve the drums appearance w/out destroying its functionality, a drum maker on the East Coast Would probably only want to send pictures of past
builds, and not fabricate a one off barrel on speculation, and with so many barrels on the west coast, Ernie or Erica would probably not want to pay the freight bill !

Think like fire, flow like a gas. Don't be the Marshmallow ! as always, your questions and comments are solicited and Welcomed! PYRO - Logically Big AL !

Having spent part of the last week in a lime kiln at a paper mill, I'm fully aware of the damage flames can inflict upon steel.
A lime kiln is a big long tube of steel, the shell, lined with a special brick for protection of the shell. If left unprotected, the constant extreme heat combined with the force of licking flames will eat through the shell in just a few weeks, and its 3/4" steel.

A steel barrel is much thinner, and the heat and flames are not as constant or intense. Over time, I expect some damage would occur. The steel of the drum would not fail all at once. Pinholes would appear first, allowing a small amount of smoke to alert the user of the problem. Before pinholes appear, tapping all areas of the top of the drum would offer an acoustic test of the integrity of the steel. Spots that are getting thin would have a different feel and sound.

It would be possible to protect the steel with refractory material. Install expanded metal by welding or bolting, then hand pack castable material to cover the steel. It's a simple enough process, but is not cost effective when a replacement drum can be had for 20 bucks. Alternately, welding or bolting a steel plate over the bottom of the drum can extend the life of the drum.

Ken Peavey : I absolutely agree with everything you have said, and I bow to your high temperature expertise, The mystery of what actually goes on inside the Rocket Mass Heaters
R.M.H.s barrel is beyond me, I am no kind of a metallurgist and with chemical energy I can never remember which are the Cations, and which are The Anions. I Think that in
that environment that Oxygen and Carbon and Hydrogen have such an affinity for each other that Mere Iron trapped behind the static part (my word choice )of the Laminar flow, or
no-flow, has little chance to combine with O2 and make rust ! Generally speaking, having tried to weld in these locations it appears that iron will combine with small amounts of carbon
first!

Of course in the case you mentioned there is no laminar flow to speak of and the hot gases would have a scrubbing effect !

As you said Barrels are cheap, and can easily be got and replaced, Any hole in a Commercial Fossil Fuel Fired Forced-air Furnace would be an immediate case to red tag the furnace,
as I stated earlier, few heat exchangers ever get replaced, its the whole furnace, usually long after their 20 yr guarantee !

I am afraid that any attempt to extend the life of a 55 gal drum with insulative materials will have negative effects on the drums ability to radiate off the amounts of heat energy
needed to create the Thermal Differential Engine that allows us to drive the hot exhaust gases though 30'+ of horizontal piping and then out the vertical chimney as the gas cools
and becomes more dense and heavy ! Again these are my thoughts,and partial understandings, Y.M.M.V. For the Good of the Craft , and all things permies !

Think like fire, flow like a gas, Don't be the Marshmallow ! As Always, your comments and questions are solicited and are Welcome ! PYRO - Logically BIG AL !