... /W≤4.8GB/T3139-2005 Advantages(1)High strength, Used for the carriageways directly buried, don’t need concrete cover, Can ... , flame retardant, heat resistant performance is good, can be use for a long time in 130 degrees heat and not easy ... , bridge construction The type of pipe's coupling 1). Sole sealing ring socket coupling: suitable for medium pressure 2). Double sealing ring ...