武汉市汉口地区自上世纪八十年代开始使用以直立炉煤气、水煤气和油制气混合的人工煤气,其输送管网绝大部分采用柔性接口灰口铸铁管和球墨铸铁管。至2004年天然气进汉后,汉口地区人工煤气于2005年11月初全部置换为天然气,即由湿气改为干气。此后,由于柔性机械接口的橡胶圈在湿气环境下被膨胀,改输干气后,橡胶圈有所收缩, Hankou in Wuhan City since the eighties of last century began to use upright furnace gas, water gas and oil gas mixture of artificial gas, the vast majority of its transmission network using a flexible interface gray cast iron pipe and ductile iron pipe. After the natural gas came into the country in 2004, the artificial gas in Hankou area was completely replaced by natural gas in early November 2005, that is, it was changed from moisture to dry gas. Since then, the rubber ring of the flexible mechanical interface is expanded under the moisture environment, and the rubber ring is shrunk after changing the dry gas,