FORGED FITTINGS ASME B16.11
In this article, we give a quick overview of forged fittings, which are products used for small diameter pipeworks. The dimensions of forged fittings are defined by ASME B16.11 (threaded and socket weld types), MSS SP 75, MSS SP 83, MSS SP 95 to match ASME B36.10 and ASME B36.19 pipes (respectively, carbon/alloy steel and stainless/nickel alloys pipes).
WHAT ARE FORGED FITTINGS?
Forged fittings are used to connect, branch, blind or deviate small diameter pipe works and piping systems (generally, below 2 inches).
Contrary to butt weld fittings, which are manufactured from pipes and plates, forged fittings are produced by forging and machining steel.
Forged fittings are available in multiple shapes, sizes (bore sizes and pressure ratings) and forged material grades (the most common are ASTM A105, ASTM A350 LF1/2/3/6 for low-temperatures, ASTM 182 for corrosive, high-temperature applications). For more details about the available material grades for forged fittings, refer to this article. Forged fittings are manufactured according to the ASME B16.11, MSS SP 75, MSS SP 83, MSS SP 95 specifications to fit ASME B36.10 carbon and alloy steel pipes and ASME B36.19 stainless steel and nickel alloy pipes.
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)
TYPES OF FORGED FITTINGS
The main types of socket weld / threaded pipe fittings are listed below.
45/90 DEGREE ELBOWS
Elbows are used to bend the pipework layout at 45 or 90 degrees. Forged elbows are manufactured according to ASME B16.11. A special type of elbow is the so-called “street” type.
EQUAL AND REDUCING TEES
Tees are forged fittings used to branch a pipe at 90 degrees. Equal tees have the same bore size for the header and the branched pipe; reducing tees have different bore sizes for the two connecting pipes. Both types are available with socket weld or threaded connections (in addition to the butt weld type, of course, used for larger pipeworks). The dimensions of tees are set by MSS SP 75 and ASME B16.11.
Laterals are forged fittings with a Y shape.
Forged plugs are available with round, squared or hexagonal head shape
Hexagonal bushings are manufactured in accordance with B16.11 and are used to join two threaded items of a different size
Couplings are forged fittings manufactured in accordance with ASME B16.11 and are used to join two pipes together. They are available in half or full size and with socket weld or threaded connections (or a combination of the two for special piping applications).
REDUCERS AND REDUCER INSERTS
Reducers are available in two main types, called 1 and 2.
Unions are available in the male to female, female to female types, lug nut, and Rockwood design. Unions comply with the MSS SP 83 standard.
FORGED FITTINGS CONNECTIONS TYPES
Forged fittings are available with two main types of connections, socket weld and threaded type (shown in the picture):
A socket weld fitting (left side) and a threaded fitting (right side)
SOCKET WELD FITTINGS
Socket weld fittings are used for applications where a strong and long-lasting connection is required. These type of pipe fittings feature a socket where the connecting pipe has to be fitted and welded (with a fillet-type seal weld). Socket weld connections are very reliable but are time-consuming to install, due to the necessary welding operations. Socket weld fittings are available in sizes from 1/8 to 4 inches and in pressure ratings from classes 2000 to 9000.
The typical applications for 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 and the different welds they require (standard butt weld and fillet weld, the same type of welds needed by slip on flanges).
Threaded fittings are used for non-critical pipeworks such as water distribution, fire protection and cooling systems (low-pressure applications not subject to vibration, elongation and bending forces). Threaded fittings are not suited for fluids with variable temperatures, as sudden changes may crack the connection. Threaded fittings are available in gray cast iron, malleable iron, carbon steel ASTM A105, stainless steel A182 F304/F316 and in sizes from 1/8 inch to 4 inches with pressure ratings between 2000 and 6000. Although different types of threads are available, the most common type is the NPT (national pipe thread).