When it comes to the fabrication of steel Lap joint pipe flanges fittings, the most common method is to extrude or draw steel pipe over a mandrel, which can be made of either welded or seamless steel pipe flange. When the threads on the ends of the pipe are smaller in diameter, they are frequently threaded together to form a larger thread. In order to accommodate the increasing size and pressure of the parts, they are frequently welded in place using either the buttweld or the socketweld methods, respectively. The use of socket-weld fittings, which are generally forged, necessitates the use of smaller pipe diameters (up to NPS 4, but usually NPS 2 or smaller) and higher pressure ratings (corresponding to Schedule 40, 80, and 160 pipe), as well as smaller threaded pipe flange diameters (up to NPS 4, but usually NPS 2 or smaller). Socket-weld fittings have pressure ratings of 3000, 6000, and 9000 pounds per square inch (psi), depending on the size. The fillet welds used to hold socket fittings in place, on the other hand, make them less strong than butt-welded fittings, which is a disadvantage. Although they are not as strong as threaded fittings, they are still preferred for high-end work because of their superior strength. Due to the requirement for an expansion gap in the fittings during operation, these fittings are not recommended for use in high-pressure food applications.

Additionally, pipe flanges can be used to join pipe sections together, with the resulting pipe sections being connected with bolts. By removing flanges from the pipeline, it is possible to access and replace valves and other components that are installed in the pipeline. Due to the same reason, flanges are also used to connect the majority of pipeline equipment, such as pumps and compressors, to the pipeline itself.

In addition to several different styles, each of which is rated according to the pressure and temperature it is intended to withstand, flange fittings are also available in a variety of sizes. Joints of various types, including lapped joints, weld neck joints, socket weld joints, ring-type joints, screwed joints, and slip-on joints, to name a few examples, are all classified as joint types. There are only a few applications in which the threaded flange is appropriate, and these are those involving low- to medium-pressure conditions. Higher pressures than those described above can be used with the other types of welded-on flanges, which are not described here. It is common to see lapped flanges used in situations where disconnections are likely to occur on a regular basis. This is due to the fact that the flange can rotate freely, which makes alignment of bolt holes much easier to achieve. As an additional feature, the so-called blind flange is used to seal the end of a pipeline while still permitting future connections between the Slip on pipe flanges or piece of equipment and any other socket weld pipe flanges or piece of equipment connected to it.

For the purpose of securing adjoining faces together, flanges can employ a variety of methods, including O-rings and seal rings, as well as other materials such as gaskets, to achieve the desired results. Comparing seal rings to flat-face gaskets, seal rings offer a significantly tighter joint and are capable of withstanding a greater amount of pressure for the same amount of bolt stress when compared to other types of seals.

International standards govern the design, manufacture, and installation of Lap joint pipe flanges. The ANSI flange is defined as follows in accordance with ASME 16.5, which is the most commonly used flange:According to ASME B16.47, applications with large diameters are divided into two series, A and B, which are further subdivided into subseries A and B. Because Series A flanges are heavier and thicker than Series B flanges when the pressure and size of both are equal, Series A flanges are used in applications where the pressure and size of both are equal. Flanges from the Series B are typically used for refurbishment work. Series B flanges are also used for new construction. To the contrary, according to ASME B16.1, the AWWS flange is only applicable to flanges used in potable water service at room temperature. Industry Standard flanges are yet another type of flange that is not defined by any government agency and instead reflects historical practice rather than being defined by a specific government agency. ANSI B16.1, which is the standard for cast-iron weld neck pipe flanges and flange fittings in the 25-125-250-inch diameter classes of pipe, is used as a guideline for the dimensions of these flanges.