The GI pipes, also called pre galvanized steel pipes, are cold rolled round pipes made by galvanized steel strips. The GI pipes are widely used in scaffolding construction, greenhouse pipes, fence pipes, agricultural pipes and other areas. There are two kinds of galvanization: hot dipped galvanization and pre galvanization. Pre galvanization is also declined to hot dipped galvanization, which the zinc coating formed by immersing steel pipes into the melting zinc. The difference between hot dipped galvanization and pre galvanization pipes is that pre galvanized pipes are made by galvanized steel coils directly. While hot dipped galvanized pipes are made by black steel coils into black pipes at first, then immerse the black pipes into zinc pond. Tianjin Friend Steel Pipe CO.LTD has more than 15 years experience in steel pipe, we have always tried our best to provide high quality pipes for you.