Claude, the aluminum strap should not be placed directly on the carbon pipe. In the past, I have always protected my pipe by adding a layer of rubber directly where the aluminum would hold the pipe. This isn't elaborate....I used a short length, 20-25mm, of bicycle inner tube of about 1 1/2" OD. The diameter isn't critical. Just slide the rubber tube over the pipe.

My pipe mounting method now is much different and doesn't use straps; the carbon pipe doesn't require protection because the soft mounting is epoxied directly onto the pipe (I use regular epoxy, not high temperature). If you look back at some of my threads I show how this is done. I think I have it in my Derivative thread. It is more secure, far simpler, and much lighter way to soft mount the pipe.