GI pipes vs MS pipes: which one do you need?

Mild steel pipe is bare steel — strong, cheap, and fine for indoor structural work where it won't see moisture. Galvanized pipe is the same steel with a zinc coating bonded on, built specifically to survive water and weather.

If the pipe is going into plumbing, irrigation, scaffolding, or anything exposed outdoors, GI is the only sensible choice — the zinc layer sacrifices itself to corrosion so the steel underneath doesn't.

For dry, indoor, load-bearing frames where cost matters more than corrosion resistance, MS pipe does the job without paying for a coating you don't need.

One mistake worth avoiding: mixing the two on the same run without a plan. Coupling GI to MS at a bare joint sets up galvanic corrosion right at the connection, which is usually the first point to fail. If a transition is unavoidable, use a dielectric fitting or paint the joint after assembly to keep the two metals from being in direct electrical contact.