| 摘要 |
PURPOSE:To prevent the spread of a fire in a tunnel without generating a poisonous gas by providing a polyethylene resin layer, which is made fire retardant by the addition of an inorg. metal hydrate, to the outermost layer. CONSTITUTION:An org. corrosion-resistant coating layer 3 with thickness of 0.4mm or more is bonded to the outer peripheral surface of a steel pipe main body 1 through a sticking layer and the outer peripheral surface of said layer 3 is coated with a polyethylene resin layer 4. Magnesium hydroxide is added to the polyethylene resin layer 4 as an inorg. metal hydrate within the range of 50-70%. Since a predetermined amount of magnesium hydroxide is added to the polyethylene resin layer 4 being the outermost layer, excellent fire retardancy can be developed. Further, magnesium hydroxide generate no poisonous gas even when it is exposed to high temp. at the time of a fire. Therefore, even when a fire occurs in a tunnel having a fire retardant multiple coated steel pipe laid thereto, it can be prevented that a human body is exposed to a poisonous gas. |
