Electric resistance welded (ERW) pipe is made from steel coil and the weld seam runs parallel to the pipe. The width of the coil is the same as the circumference of the pipe so diameters are limited to 24 inches. However, because the manufacturing process is fast, it is ideal for large production runs of small (<= 24 in.) diameter sections.
Galvanized iron pipes commonly used on water pipe lines, it is dipped into zinc for corrosion protection
GI Pipe is “Galvanized Iron” Pipe. Material ms is mild steel and gi is galvanized steel that has been hot dipped .These days the pipe will likely be made from steel rather than iron.