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I have 1/2" and 3/8" thick x 24" diameter steel pipes that are typically used for natural gas transport, but in my case they take the shape of horizontal wood-burning cookers. I am building wood fires inside these pipes and will do this hundreds of times over my lifetime. The fire sits directly on the "bottom" wall of the pipe.

On the one hand this is a lot of steel so it seems nearly impervious to damage; on the other hand, fire is very hot and I don't know anything about metals!

I'm not concerned about superficial damage or minor rust or perhaps losing .5mm of material over 20 years, but anything more than that might cause me to take preventative action.

Will burning fires inside these pipes damage them in the long run?

If so, do we have some idea of the extent of the damage?

Lastly, what would be a good preventative measure? Some people put grates at the bottom of their cookers to keep the coals off the metal a bit. I could also put firebrick underneath the wood/fire.

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  • $\begingroup$ Hint: look at any charcoal grille's body and/or cooking surfaces $\endgroup$
    – Carl Witthoft
    Sep 20, 2022 at 15:05
  • $\begingroup$ Seen 3/4 bar that has bent over time due to the temperature and mass. $\endgroup$
    – Solar Mike
    Sep 20, 2022 at 15:15
  • $\begingroup$ @CarlWitthoft this is only partly helpful and I'm not sure which direction you're going with! Plenty of grills get pretty wrecked with time but I don't know if that is due to corrosion, thin gauge of metal, or fire damage. $\endgroup$
    – Behacad
    Sep 20, 2022 at 15:16

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They will oxidize depending on time and temperature. Higher temperatures cause faster metal loss ; "Red heat" ( about 1200 F) will accelerate metal loss. The pipe should be satisfactory for the use. Lining the inside with fire brick would significantly extend life.

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  • $\begingroup$ Be careful -- the OP has no idea what sort of temperatures he's going to achieve. $\endgroup$
    – Carl Witthoft
    Sep 20, 2022 at 19:07
  • $\begingroup$ @CarlWitthoft OP did mention wood fires. Can wood fire temperatures still cause an issue with steel? I don't see how it sounds any different than barbeque or wood burning stove which are, presumably, just made of mild steel. $\endgroup$
    – DKNguyen
    Sep 20, 2022 at 20:19
  • $\begingroup$ @blacksmith37 thanks for this, though I don't feel quite satisfied by the answer. You say (1) they will oxidize, (2) higher temps cause faster oxidization, and (3) that the pipes will be satisfactory. Unfortunately I don't know how fast they will oxidize and what they'll look like in 30 years. Will these pipes appear seemingly the same as they do today (not including surface rust and discoloration)? You mention firebrick would extend life which is obvious but I'm not sure if that is needed or not. $\endgroup$
    – Behacad
    Sep 20, 2022 at 23:22
  • $\begingroup$ @DKNguyen Wood fires can get pretty dang hot with the proper enclosure and air (oxygen) feed rates. Take a look at brick-oven pizza places, for example. $\endgroup$
    – Carl Witthoft
    Sep 21, 2022 at 12:42
  • $\begingroup$ For a more impressive answer , I looked in ASM vol.13 Corrosion, 1987. No data for heating steel in air; The data is all for steel containing something like water, steam ,oil, flue gas, etc. And metal loss is apparently mostly on the inside. Your system would not qualify as "flue gas" because of free air access.. Good luck finding a more scientific answer. At a very minimum your will need data of "hours at temperature xxx". $\endgroup$
    – blacksmith37
    Sep 21, 2022 at 21:47
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A wood-burning stove with 1/4" thick mild steel plate construction will last at least 30 years before it burns through as long as you line the bottom (which is the hottest part) with firebrick.

The cause of the burn-through will be oxidation of the surface which is triggered by condensation of water vapor during a cold start, which is then accelerated by high temperature and the presence of oxygen as the stove comes up to operating temperature and the unreacted water gets boiled off.

The standard corrosion rate specification for things like metal in contact with sea water or hot flue gases is quoted in units of mils per year or MPY where one mil is a thousandth of an inch. So if the experimentally-determined corrosion rate is 100 MPY a one-inch thick piece of the metal will last 10 years in service, if it is being attacked from one side or half that if both sides are exposed to attack.

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  • $\begingroup$ Very informative, thank you! The "problem" is that I've never heard of anyone lining the bottom of their BBQ with firebrick to protect the metal. Everyone raw dogs it, which is why I'm wondering if I need to. $\endgroup$
    – Behacad
    Sep 21, 2022 at 16:01

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