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法兰水线标准中是有规定的。ASME B16.5、API600、API610等标准中均规定水线要求，如水线粗糙度、水线间距等；无水线的法兰也是有的，不仅仅是平面法兰、即使突面法兰（RF）也可以不加工水线，一般情况下，默认是带水线的，带水线的密封性更好，至于哪种情况不带水线的法兰密封性优于带水线的法兰有待探讨。
法兰水线有以下好处：
一是增加垫片与法兰间的阻力，防止在管道负压的时候垫片被吸进去；
二是增加密封性；
三是方便在法兰连接面有漏点时，拆下垫片可直接观察是否垫片问题；
凹凸法兰不在上述优点。
水线也有缺点，尤其是使用石棉垫一段时间后，清除法兰面上的石棉比较困难。根据HG20592规定，只有PN≤4.0MPa（美标≤5.0MPa）的突面法兰，采用非金属平垫片、聚四氟乙烯包覆垫和柔性石墨复合垫时，可车制水线，密封面代号为RF(A)。
Waterline standard flange is provided. ASME B16.5, API600, API610 and other standards require water line requirements, such as water line roughness, water line spacing; water line of the flange are some exceptions, not just a flange, even if the face or flange ( RF) can not process the waterline, under normal circumstances, the default is with a water line, with a waterline seal better, as each case without the water line than the flange sealing flange with water line await further study. Flange waterline has the following benefits: One is to increase the resistance between the gasket and flange, to prevent negative pressure in the pipe when the washer is sucked; Second is to increase the seal; Third, facilitate the flange surface Youlou point, remove the gasket can directly observe whether the gasket problem; Not the merits of concave and convex flange. Water line has its drawbacks, particularly the use of asbestos pad for some time, the surface of the asbestos removal flange difficult. According HG20592, only PN ≤ 4.0MPa (American standard ≤ 5.0MPa) of the face or flange, using non-metallic flat gasket, PTFE coated mat and the flexible graphite composite mat, the system can be car waterline, sealed area code for the RF (A).