Are these slip joints with a u shaped clamp? I don't put anything on joints. The stuff drys hard and brittle so it will crack with any movement.

If you use regular u shaped clamps, place the edge about 1/4" from the outer pipe joint, this will allow the outer pipe to crush easier.

Try stainless steel band clamps like this http://www.apexhaust.com/wp-content/uploads/2010/07/HD_Premium_Exhaust_Clamping_Products_APEC0808.pdf However you will need to see if they have metric sizes if your pipes don't match a inch standard.

I've used the "good" flat band clamps on lots of industrial exhaust applications, they work just fine and are pretty much all you see on large trucks.

On the 2nd page, the "better" narrow band clamps are to be used only with slotted pipes. ( this style goes back decades.)