RMH barrel durability?

Hi all, I am a lurker, most of the time. But as I am almost getting to the point to start building a cabin I am starting to sketch n think about an indoor rocket pizza oven.
Now my question is, if the RMH just has the barrel (not very heavy gage metal i guess) on top of the hottest point of the fire, the "rocket" part of the J, how long do those barrel tops actually last? What temps are the barrel tops reaching? This is so I can figure out how thick my oven bottom plate would have to be so it will last a couple of decades (or forever?)

thanks for sharing your experiences about durability, Hedy

Hi Hedy,     There are several factors that determine how hot the top of the barrel will get. First is the size of the combustion unit. Obviously a larger unit will put out more heat and thus make the top get hotter and vise versa. The second factor is the top gap - the distance the barrel top is from the top of the heat riser. The closer it is, from 2" (absolute minimum) to several feet will concentrate or dissipate heat differently.
Temperatures I've seen typically from myself and reported by others is generally around 700 - 1000F at the height of a burn.  

I've used my barrel for a good 4 seasons now with extremely little degradation.

I know there are a few other threads here that talk about using certain types of metal plates with good results.

I believe Ianto Evans has an 8" J that has lasted well over two decades. I can't remember where I saw that so someone fact check me, I imagine it is mentioned in his book on the topic.

Example of temperatures: my 8" J ran at about 600-700 on the lid with a 3" gap. My 8" batch rocket averages at 750F with a 12" gap. My batch has been run for only 2 seasons, but I haven't seen any sort of change in its condition.

Thank you for your helpful replies Gerry and Daniel