layer 3 (bottom): port tube original
layer 2 (middle): flame footage, masked to only necessary video area
layer 1 (top): port tube, masked to reveal only the front section of the tube.
In After Effects, you can composite fire by using an unmultiply plugin like Unmult from
redgiant software (I think it's still free), or you can try to use a transfer mode like Add or Screen to eliminate the darkest parts of the fire video.
Unfortunately there usually isn't an easy way to composite fire into something and make it look good. You need to consider the lighting changes that the introduced fire element creates, and it starts to go uphill from there.
But after 10 years - - welcome to the AE club. There are a lot of tools already in there that will help you get the job done.