双金属的连接方式：
The connection mode of bimetallic:
外基管多数采用的是镀锌管，沿用了镀锌管成熟的连接方式：
Most of the outer base pipes are galvanized pipes, which follow the mature connection mode of the galvanized pipe:
1、螺纹连接（俗称丝扣连接），适用于DN15-DN100，执行GB7306-2和GB3287-1982标准；
1. Threaded connection (commonly known as threaded connection), suitable for DN15-DN100, the implementation of GB7306-2 and GB3287-1982 standards;
2、沟槽卡箍连接，适用DN100以上，执行CJ/T156标准；
2, groove clamp connection, the application of DN100 above, the implementation of the CJ/T156 standard;
3、法兰连接，视情况而定，一般DN100以上采用，法兰等由厂家定做，并在连接处配上专用硅胶层；
3. Flange connection, depending on the situation, generally DN100 or more used, flange, etc. by the manufacturer customized, and the connection with a special silica gel layer;
4、焊接连接，据实际工况采用焊接，执行YB/T5092-2005和JB/T4747-2002标准，一般采用三层焊，先氩弧焊封底，再焊过渡层，最后手工电弧焊填充盖面。
4. Welding joints, according to the actual working conditions using welding, the implementation of YB/T5092-2005 and JB/T4747-2002 standards, the general use of three-layer welding, argon arc welding first, then welding the transition layer, finally manual arc welding filling the cover.