SOCKET WELD / THREADED FITTINGS ASME B16.11
Forged fittings are widely used in the petrochemical industry for smaller size pipelines and piping systems (generally, below 2 inches). They are used to implement specific pathways for the pipeline, and / or branch / close it. Forged fittings are, as the name evocates, manufactured out of forged steel (whereas butt weld fittings are produced from pipes and plates). Butt weld and forged fittings overlap somehow in the limit range 1/2 to 4 inches. Forged fittings manufactured in accordance with the ASME B16.11 norm are compatible with ASME B36.10 (carbon / alloy steel) and ASME B36.19 pipes (stainless steel / duplex and other lightweight corrosion resistant materials).
There are several types of forged fittings, in terms of shapes, sizes and material grades (the most common are ASTM A105, ASTM A350 and ASTM A182). The main classification is between:
SOCKET WELD PIPE FITTINGS
Socket weld fittings are recommended for connections that require strenght and duration. These type of forged fittings have a socket where the connecting pipe has to be sitted and welded (with a fillet-type seal weld) for installation. Socket weld connections are very reliable but require remarkable installation time due to the laborius welding operations. They are available in sizes up to 4 inches and in pressure ratings from class 3000 to 6000 and 9000. Manufacturers refer to the ASME / ANSI B16.11 for dimensions and tolerances of socket weld fittings.
Typical applications of socket weld fittings are:
- Explosive fluids / gas
- Acids and toxic fluids
- Long service / durable installations
The image shows a comparison between a socket weld and a butt weld fitting: the first requires only a fillet weld, wherease butt weld fittings imply more extensive welding of the butt weld ends.
THREADED PIPE FITTINGS
Threaded fittings are common for non critical pipeworks such as water distribution, fire protection and cooling systems (low pressure applications, or installations that are not subject to vibration, elongation and bending forces). Threaded fittings shall be avoided when the temperature of the fluid is subject to consistent variations, as sudden temperature changes would crack the threaded connection between the fitting and the pipe. The most common materials used for threaded fittings are gray cast iron, malleable iron, carbon steel A105, stainless steel A182. Threaded fittings are available in sizes up to 4 inches and in pressure ratings from class 3000 to 6000 and 9000. The reference standard, also for threaded fittings, is the ANSI / ASME B16.11. The most common type of threading in oil & gas is the NPT type.
The main types of socket weld / threaded pipe fittings are:
- 45 , 90 degrees elbows
- equal and reducing tees
- street elbows
The same product in the socket weld (left) / threaded (right) configuration.
OTHER FORGED FITTINGS FOR PIPES
Other forged products belong to the family of forged fittings, namely:
- Plugs: round / square / hex head shaped
- Bushings: flush / hexagonal
- Couplings: half / full
- Reducers and reducer inserts (type 1/2)
- Unions: male / female, female / female, lug nut, rockwood type (MSS SP 83)
- Welding bosses
This Standard covers ratings, dimensions, tolerances, marking and material requirements for socket-welding and threaded forged fittings. These fittings are designated as Class 2000, 3000, and 6000 for threaded end fittings and Class 3000, 6000, and 9000 for socket-weld end fittings. B16.11 is to be used in conjunction with equipment described in other volumes of the ASME B16 series of standards as well as with other ASME standards, such as the Boiler and Pressure Vessel Code and the B31 Piping Codes. (source: ASME)