Why hollow steel pipe is stronger than solid steel rod?

the question is to be rephrased,the hollow rod is stronger than the solid rod of the same solid material , that shall make the hollow rod of bigger diameter and consequently larger moment of inertia around its central axis yielding larger resistance

because of bigger inertia than steel rods which consume same quantity of material 

Because of the moment of inertia of hollow steel pipe higher than a solid steel rod.

Hollow pipe have more anertia than the solid pipe

Hollow steel pipe has higher strength to weight ratio than solid steel rod of same cross section. 

Most of the strength of a cylinder comes from the outer portions. I think the contribution goes like the cube of the radial position. So, if you took a solid rod and drilled out a half the volume from the center, you do not lose half the strength. Strength to weight ratio is better for a hollow pipe than a solid rod.

First, the wording of the question is wrong, and the hollow is not stronger unless the diameter is greater than that because it will be a difference in the moment of inertia

Industrial Manufacturing Company. The stiffness of the hollow pipe is more than the solid shaft with the SAME WEIGHT. Hollow pipes have a more polar moment of inertia, thus they can transmit more torque compared to solid shafts. Thus, hollow steel pipes are stronger than solid shafts having IDENTICAL WEIGHT.

Because it is not rustproof

because the moment of inartia of the member depends on the depth of the beam not the wheight while the weight will make more sttlement

The area of ​​​​the sector is larger and therefore bears higher stresses