The welding methods used to connect flanges to pipe will often depend on the type of flange you are preparing to weld and the base metal that you will be welding it onto. But the overall welding process is primarily the same as other welding processes you are familiar with. If you are going to weld a Neck and Lap Joint Stub and Flange you will need a root gap spacing between the pipe and the flange of 1/16” to 1/8”. Your first bead should penetrate uniformly to the interior of the wall of the flange and pipe assembly to insure that a strong joint is created. Your last bead should be built up higher than the pipe O.D. at approximately 1/16 of an inch. The type of joint created using this method is preferred because of the safety and lack of fatigue. It can be used in all pressures and temperatures.
If you are using a slip-on flange be prepared to reface the finished product once the weld has been completed. This extra step of having to reface the finished pipe and flange often makes this process more demanding and costly than the more common method of welding neck types of connections. This process is mostly used when smooth bores that are free of pockets are needed. Slip on flanges can be used on weights ranging from 150 pounds to 300 pounds. Due to the lower safety factor in pressure resistance and fatigue this type of weld is not recommended for use above 750 degrees Fahrenheit. Slip-On flanges are often preferred over Welding Neck Flanges because of the low production cost and because it requires the welder to perform less accurate cuts but still allows for the alignment of bolt holes and the squaring of flange faces with less difficulty.
Socket weld flanges are recommended when the running of an internal weld is difficult. In pipes four inches and smaller this type of weld is preferred. A socket weld also eliminates internal pockets while the amount of warping is decreased because of the lack of heat and spatter on the face of the flange. This process offers the same resistance to high internal pressure as the Slip-On Flanges and provides longer fatigue life to the joint. This connecting process is best suited for sizes ranging from 50 pounds to 300 pounds. This makes it one of the most adaptable types of welds to produce.
