OK, can anyone help me out, this hypothetical question is driving me mad.

You have three stainless steel pipes, one has an internal diameter of 10mm and an external diameter of 20mm. The second pipe has an external diameter of 20mm, and an internal diameter of 15mm. The third pipe has an external diameter of 15mm, and an internal diameter of 10mm.

If pipes 2 and 3 are sleeved (slipped into each other) will they be stronger or weaker than pipe 1. My gut says that the sleeved pipes will be stronger, but to be honest I'm not sure. Any one have any idea?