These pipes are used in the specific areas of natural gas network where the 4-bar pressure applied. Gas networks are consisted of 20-bar steel pipe, 4-bar mediating line and 0.4-bar intra-building lines. For the 20-bar lines, polyethylene composite pipes are started to be used for a trial purpose. Upon the relevant standards are set, their usage will be expanded. Studies on fire resistant composite pipes for the interior usage are still continuing.