Break out the internal dams. A chisel can be used to remove the dams entirely.
Torch the inside of the culm. Start in the middle and work out towards the ends.
If you see a lot of flame the section isn't done yet.
Continue to heat a section (keep the flame moving) until all you have is a glowing red spot and no flame.
When you get close to an end you will see the moisture and sap bubbling out of the end grain
As you can see the outside of the culm remains unchanged, even after all that heat applied to the other side.
Wire brush off all the burned pith
Culm is ready to split. No further heat treating is needed, no oven required. I have been flaming this way for many years, and none of my rods have any sets in them, none have broken that I know of. The bamboo is as stiff and snappy as any other rod I have cast, in fact it is even more so than some rods I have seen.