Pipe support vs structural support

Er,
You will notice I changed your first line "I am using structural supports " to "I am using structural shapes". It is a minor thing but is more understandable.

The use of structural shapes vs. pipe (shapes) for certain types of secondary(*) pipe supports is more a matter of company personality than real engineering. If the Secondary Pipe Supports were developed by the Structural Department then more likely than not, structural shapes were used. However if these same supports were developed by the Piping Department then piping shapes were more likely to be used.
Both methods do the same job and are equal in strength and reliability.
Both have good points and bad points'
- In Hydrogen Service service the Structural shapes should be used to prevent hydrogen pockets.
- In really bad corrosive atmospheres structural shapes allows for inspection for corrosion.
- Using pipe shapes is cheaper and easier to weld.
- Use of pipe shapes makes some types of supports easier (Adjustable Base Supports)


(*) For a better understanding of Primary and Secondary Pipe Supports see:
pipingdesigners.com/Training%20-%20section%203.htm
Read both A and B