The following are the 6 types of Flanges most used in process piping systems. The Weld neck Flange is the most often used and is easy to recognize by the tapered hub where the pipe welds to the Flange. The Weld neck Flange is supplied with a bore that matches the pipe so there will be no restriction of product flow and to prevent turbulence and erosion at the welded joint. The tapered neck also provides stress distribution from the pipe to the bolted connection, making it the strongest of the Flanges. The Weld neck Flange is mated to the pipe with a single full penetration butt weld which can be easily radiographed to detect any flaws in the welded connection.
The Slip on Flange is the second most popular Flange type, and is installed by slipping the Flange over the pipe and securing it with two fillet welds. One weld is made on the backside of the hub on the Flange, the second fillet weld is made on the inside of the Flange sealing the pipe and Flange. Although the initial cost of the Slip on Flange is less than the Weld neck Flange, but with the extra welding and inspection time the installation cost is almost the same.
The Socket weld Flange is similar to the Slip on Flange as the pipe slips inside the Flange into a socket and is secured with a fillet weld at the hub on the back side of the Flange. Per ASME B31.3 Socket weld Flanges are only to be used in noncritical applications where pressure, temperature or product corrosion is not an issue.
The Lap Joint Flange with a Stub end is a two part assembly made with a stub end which is butt welded to the pipe and a Backing Flange. The Stub end and Lap Joint Flange are primarily used in Alloy piping systems where the Lap Joint Flange is Carbon steel thus keeping the cost lower.
The Threaded Flange is attached to the pipe with a tapered thread that conforms to ASME B1.20.1. The threaded Flanges today are used almost exclusively in smaller pipe sizes for utility service such as instrument air, plant air, nitrogen, potable and raw water up to 300# rating.
The Blind Flange is manufactured without a bore to be installed at the end of a piping system, seal off nozzles on a vessel or other piece of equipment or valve for positive isolation of that system. Contact Coastal Flange with any questions or for an inquiry tailored to your requirements.