It was considered that the metal and cement pipes would be replaced by the large sized plastics pipe, and the polyethylene double walled bellows would develop greatly.

• 分析结果表明,金属管、水泥管等传统埋地管材将被淘汰,取而代之的是大口径塑料埋地管,聚乙烯双壁波纹管将会获得大发展。