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Also called: 1/2" NTP. National Pipe Thread Tapered Thread. This type of pipe thread is tapered so that the fit tightens as the pipe is twisted in. [[File:120x120_12galvpipethread.jpg|left]]Also called: 1/2" NTP. National Pipe Thread Tapered Thread. This type of pipe thread is tapered so that the fit tightens as the pipe is twisted in. Common residential NTP pipe use is for water and natural gas. Although galvanized (zinc-coated) pipe is still considered to be a safe transport material for drinking water, there are some potential health concerns because this type of pipe tends to corrode over years of use. == Galvanized Steel Pipe ==Galvanized pipe is steel pipe covered with a protective coating of zinc which greatly reduces its tendency to corrode and extends its life expectancy. Public water supplies treat their water to make it essentially non-corrosive. However, plumbers will tell you that when they remove galvanized pipe, it is typically internally full of corrosion. Galvanized pipe is no longer commonly installed in residential water systems. Galvanized pipe was used extensively as water supply lines in new construction prior to the 1960's.Calcium buildup and oxidation occur internally, causing a loss of water pressure as the opening inside the pipe decreases. A moderate level of calcium helps form a protective coating on the pipe, which may slow down corrosive effects. Even so, the pipe still corrodes over time, and fills with rust. Over time, the pipes might corrode to the point where the pipes are completely restricted due to rust. If the water system has been shut off for a period of time, such as between home owners, this can accelerate the level of corrosion internally, causing the pipe to rust from the inside out, and even leak when pressure is reintroduced. Galvanized steel can last roughly forty years until it needs to be replaced. Hard water in the home generally reduces the life expectancy of galvanized pipe.