Material properties like stresses and strains are defined precisely to cancel effects of geometry like specimen thickness. If you increase the thickness of your pipe, you increase both the area and the force needed to deform it; the definition of stress serves to cancel this.

This should be explained in any introductory text on materials science (like Frost/Ashby or our own book by Rösler/harders/Bäker)

Tensile properties of any materials are not affected by the geometry. The stress just represents the unit of strength of the material.....