Forged Fittings: SW & Threaded (B16.11)

Quick Reference

ASME B16.11 forged fittings for small bore pipes: Socket weld (SW) connected via fillet welds, Threaded (NPT/BSP) for non-critical systems. Sizes: 1/8” to 4” NPS. Classes: 3000# (Sch 80 pipe), 6000# (Sch 160), 9000# (XXS). Materials: ASTM A105 (CS), A182 (SS/alloy), A350 (low-temp). For pipes >2”, use ASME B16.9 BW fittings.

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Need a printable version? Download the ASME B16.11 Forged Fittings Chart for socket weld and threaded fitting dimensions.

Forged Fittings ASME B16.11

What Are Forged Fittings?

ASME B16.11 covers socket-welding and threaded forged fittings, the workhorses of small-bore piping. If you have been around any plant long enough, you have seen thousands of these: every instrument connection, every drain, every vent, every small process tie-in.

The forging process shapes solid steel billets under high pressure, which produces a tighter grain structure than casting. In practice, this means forged fittings handle pressure, thermal cycling, and vibration far better than cast equivalents. They are the default choice for high-pressure, high-temperature, and corrosive service.

Classification of forged fitting types (ASME B16.11)

Socket/Threaded Fittings in ASME B16.11

FOrged fittings by end connection

The two connection types in B16.11 differ fundamentally in how they join to pipe:

Connection	Method	Typical Use
Socket Weld (SW)	Pipe inserts into fitting socket; fillet weld applied around the joint	High-pressure, critical service (steam, hydrocarbons, toxic fluids)
Threaded (THD)	Pipe screws into fitting via NPT or BSP threads	Lower-pressure, non-critical service (utilities, drains, instrument taps)

Sizes and Pressure Ratings

B16.11 covers NPS 1/8” through 4”. Class ratings match specific pipe schedules; get this wrong and you create a weak point at the joint (see the caution note below).

Pro Tip

When installing socket weld fittings, always maintain a 1/16” (1.6mm) gap between the pipe end and the socket bottom before welding. This expansion gap prevents cracking during thermal cycling. Insert the pipe fully, mark it, then withdraw it slightly before tacking. Fittings welded with zero gap crack in high-temperature service.

What Does “Class” Mean for Forged Fittings?

The class number roughly corresponds to the maximum cold working pressure in psi. More importantly, it tells you which pipe schedule the fitting pairs with:

Class	Max Pressure (approx.)	Matching Pipe Schedule
2000	Up to 2,000 psi	Sch 40 (threaded only)
3000	Up to 3,000 psi	Sch 80
6000	Up to 6,000 psi	Sch 160
9000	Up to 9,000 psi	XXS

Actual allowable pressure drops with temperature. B16.11 has detailed P/T tables by material grade. Always check these tables rather than assuming room-temperature values apply at operating conditions. Select class based on maximum operating pressure, design temperature, and material compatibility with the process fluid.

Forged vs. Buttweld Fittings

Aspect	Forged (B16.11)	Buttweld (B16.9)
Size range	NPS 1/8”-4” (2000#/3000#) or 1/8”-2” (6000#/9000#)	NPS 1/2” and up
Raw material	Solid steel billets, machined to shape	Seamless or welded pipe, cut and formed
Connection	Socket weld (fillet weld) or threaded	Butt weld (full-penetration weld)
Specs	ASME B16.11, MSS SP-75, SP-83, SP-95	ASME B16.9

Forged fittings pair with ASME B36.10 and B36.19 small-bore pipes in carbon, alloy, stainless, and nickel alloy grades.

Applicable Specifications (ASME/MSS/API)

Specification	Scope
ASME B16.11	Socket weld and threaded forged fittings, NPS 1/8-4”, Class 2000-9000
MSS SP-79	Insert-type socket-welding fittings from bar stock, NPS 1/2-4”
MSS SP-83	Class 3000 and 6000 threaded and socket-welding pipe unions
MSS SP-97	Integrally reinforced forged branch outlet fittings (Weldolets, Threadolets, Sockolets)
API 602	Compact steel gate, globe, and check valves, NPS 1/8-4” (refinery/petrochemical)

When specifying forged fittings, match the material grade to the pipe grade, select the class for the design pressure/temperature, and verify the correct specification applies. In practice, ASME B16.11 covers 90% of what you will encounter on small-bore piping in oil and gas or power plant work.

Types of Forged Fittings

Forged fittings are classified two ways: by connection type (socket weld vs. threaded) and by body shape (elbow, tee, coupling, etc.).

Socket Weld vs. Threaded Fittings Types

Socket weld fitting (left), threaded fitting (right)

Socket Weld Fittings (“SW”)

The pipe slides into the fitting socket and a fillet weld seals the joint. Available in NPS 1/8”-4”, Class 2000-9000.

Socket weld is the go-to connection for small-bore high-pressure work: steam lines, instrument piping on process units, chemical injection. The fillet weld joint is strong, leak-tight, and can be radiographed if required. The downside is labor: welding hundreds of small-bore connections on a plant turnaround is slow and expensive. But for steam, hydrocarbons, toxic fluids, and any service where you cannot tolerate a leak, socket weld is the right choice.

Compared to buttweld fittings, socket weld connections are quicker to fit up (no precise bevel prep needed) and work better in tight spaces. The trade-off is that buttweld joints give a smoother internal bore and better flow characteristics, and they are the only option above NPS 4”.

Remember the 1/16” (1.6mm) expansion gap between pipe end and socket bottom before welding. This is not optional.

Socket weld fittings (left) vs. Threaded fittings (right)

Socket-Weld vs. Butt-Weld Fittings

Aspect	Socket Weld	Butt Weld
Pipe size	Small bore (up to NPS 4”)	NPS 1/2” and up, typically >2”
Weld type	Fillet weld (external)	Full-penetration butt weld
Fit-up	Simpler, no bevel needed	Requires precise alignment and bevel prep
Internal bore	Slight step at socket	Smooth, continuous
Leak risk	Very low (welded joint)	Lowest (full-pen weld, smooth transition)

Fillet weld vs. Butt Weld: a butt welding connection fills the gaps between two devices, that are beveled at 30 degrees.

Threaded Fittings (“THD” or “THDD”)

Threaded fittings screw onto the pipe, no welding required. They are the fastest fittings to install and the easiest to disassemble for maintenance. You will find them on utility water, cooling water, fire protection, low-pressure drains, and instrument connections where socket weld is not justified.

The flip side: threaded joints are the weakest link in a piping system. Threads cut into the pipe wall, reducing its effective thickness. They can back out under vibration, and thermal cycling loosens them over time. Never use threaded fittings on lines subject to significant vibration, thermal shock, or hazardous fluid service. Most engineering specs restrict threaded connections to NPS 2” and below, Class 2000 or 3000, in non-critical service.

Available shapes include elbows (45/90 deg), tees (equal/reducing), couplings (full/half/reducing), caps, nipples, unions, and bushings. Materials are the same as socket weld: ASTM A105, A182, A350 in the standard grades.

Types of Threads for Threaded Fittings

The two major thread standards are BSP (55 deg angle) and NPT (60 deg angle). They are not interchangeable; cross-threading BSP into NPT (or vice versa) is a common field mistake that results in leaks and damaged fittings.

BSP Fittings (BSPT/BSPP)

BSP (British Standard Pipe) is the dominant thread standard in the UK, Europe, Asia, and Australia. It comes in two variants:

Type	Sealing Method	Description
BSP Parallel (BSPP)	Bonded or metal seal compressed between mating surfaces	Constant diameter (G-thread); used where a fluid-tight seal is required on the threads’ periphery
BSP Tapered (BSPT)	Thread interference (similar to NPT)	Diameter tapers down, providing a tighter seal as threads engage; pressure-tight seal without additional sealing mechanism

BSPP is common in hydraulic and water systems; BSPT seals by thread interference and is used on pressurized oil and gas piping. Outside North America, BSP fittings are standard stock.

NPT Fittings

NPT (National Pipe Taper) is the North American standard, per ANSI/ASME B1.20.1. The threads taper at 1 deg 47’ per side, so they wedge tighter as you screw them in.

Feature	Description
Tapered Threads	Tapered at 1°47’24” (1.7899°) per side; diameter decreases towards the fitting end for interference fit
Sealing Mechanism	Achieved through thread deformation when tightened; requires sealant (Teflon tape or pipe dope)
Standards	Must conform to ANSI/ASME B1.20.1 specifications

NPT threads alone do not seal reliably; always use Teflon tape or pipe dope. Over-tightening cracks the fitting body (especially in stainless steel, which galls easily). NPT fittings can be reused if threads are undamaged, but apply fresh sealant every time.

NPT threading is covered by the ASME B1.20.1 specification and is based on 60° thread flank angles (vs. 55° of the BSP type).

BSP (BSPP/BSPT) vs NPT: thread angle 55 vs 60 Deg.

Forged Fittings by Shape

ASME B16.11 Forged Fittings Classification

Forged Elbow 45/90 Degrees

Forged elbows change the direction of flow. Available in socket weld or threaded, in all standard material grades per ASME B16.11. Three main types:

• 45-Degree Elbow: Makes a gentler turn that produces less pressure drop than a 90. Use these where you can get away with two 45s instead of one 90, as the flow characteristics are noticeably better.
• 90-Degree Elbow: The standard quarter-turn. The most common forged fitting you will order on any project.
• Street Elbow: Has one male end and one female end, so it threads directly into another fitting without needing a nipple. Invaluable in tight spots where you cannot fit an extra piece of pipe between fittings.

Forged Tee (Equal/Reducing)

Forged tees split or combine flow. An equal tee has the same bore on all three ends; a reducing tee has a smaller branch connection. Available with socket weld or threaded connections per ASME B16.11 and MSS SP-75.

Forged Lateral

A forged lateral branches off the main line at 45 degrees (or sometimes 30 degrees) rather than the 90 degrees of a tee. The Y-shape gives much better flow characteristics than a tee branch: lower pressure drop, less turbulence at the junction. You will see laterals specified on drain headers and anywhere the designer wants to minimize erosion at the branch takeoff.

Forged Plug (Round, Squared, Hex)

Forged plugs close off (blind) the end of a fitting, valve, or pipe section. Available in round, square, and hex head configurations. Hex and square heads allow torque with a wrench; round plugs give a flush, clean appearance. You will order dozens of these for hydrotest blanking and dead-end terminations.

Bushings

A forged bushing reduces the bore of a larger fitting, valve, or pipe to accept a smaller pipe. One end has male threads that screw into the larger connection; the other end has female threads for the smaller pipe. Bushings are quick, cheap reducers, though for process piping, most specs prefer a reducing coupling or a proper concentric/eccentric reducer for better flow.

Couplings (Half, Full)

Couplings are the simplest forged fitting: they join two pipes in a straight line.

• Full Coupling: Socket or threaded ends on both sides; joins two pipes of the same diameter.
• Half Coupling: Socket or threaded on one end only, the other end is butt-welded or fillet-welded to a pipe, vessel, or header. Half couplings are commonly used as instrument or branch connections on larger pipe.
• Reducing Coupling: Different bore on each end, connecting two different pipe sizes in line.

Reducers and Reducer Inserts

Forged reducers connect pipes of different diameters. Two types:

• Concentric Reducer: Centerlines aligned, the standard choice for vertical lines and anywhere air/sediment entrapment is not a concern.
• Eccentric Reducer: One side flat (top or bottom aligned). On horizontal lines, install flat-on-bottom (“FOB”) to prevent liquid pockets, or flat-on-top (“FOT”) at pump suctions to prevent vapor pockets.

Reducer Inserts

Reducer inserts slip into the socket of a larger fitting or valve to accept a smaller pipe, an economical, space-saving alternative to a full reducing coupling. ASME B16.11 defines two types:

Type	Use	Installation
Type 1	Flow from larger to smaller bore	Insert sits in the socket; pipe enters through the insert. Gives a smooth internal transition.
Type 2	Flow from smaller to larger bore, or where Type 1 geometry does not suit	Similar installation, but oriented for reverse flow or specific assembly constraints.

Both types must be carefully aligned in the socket before welding. A misaligned reducer insert creates a step in the bore that traps solids and disrupts flow.

Union

A forged union is a three-piece fitting (male end, female end, and nut) that allows disconnection without cutting pipe. You will find unions wherever maintenance access is needed: at control valves, instruments, and equipment connections that require periodic removal. The nut draws the two halves together with a metal-to-metal or gasket seal.

Unions come in male-to-female, female-to-female, lug-nut, and Rockwood designs. They comply with MSS SP-83.

Welding Boss

A forged welding boss provides a take-off point on a pipe or vessel for instrument connections (pressure gauges, thermowells, level transmitters) or small branch lines. The boss is welded directly to the pipe surface and has a threaded or socket outlet for the instrument or branch connection. You will see welding bosses on every process line that carries instrumentation; they are the standard method for mounting a thermowell or a pressure tap on small-to-medium bore piping.

Swage Nipple

Swage nipple ASME B16.11

A swage nipple (or swage reducer) transitions between two different pipe sizes with a gradual conical taper. Think of it as a short reducer with plain, beveled, or threaded ends on each side. Swage nipples are manufactured by forging or by machining from solid bar stock.

Two configurations:

• Concentric: Uniform taper, centerlines aligned. Standard choice when alignment matters.
• Eccentric: Off-center taper, one side flat. Used on horizontal runs where you need flat-on-bottom for drainage or flat-on-top at pump suctions.

End connections can be plain (for butt welding), threaded (NPT/BSP), or a combination (e.g., one end threaded, the other beveled). Match the material and pressure rating to the connected piping; the swage nipple must be at least as strong as the weakest pipe it joins.

Forged Fittings Materials

Carbon Steel Fittings ASTM A105 (Forged)

ASTM A105 is the standard carbon steel forging for socket weld and threaded fittings. It pairs with ASTM A53, A106, and API 5L pipe in high-temperature service. For low-temperature service (below -29 deg C / -20 deg F), switch to ASTM A350 fittings to match ASTM A333 low-temp pipe.

A105 Forged Fittings Materials, Chemical Composition %

Material Grade	Grade or Class	C	Si	Mn	S	P	Cu	Ni	Cr	Mo	V	Cb/Nb
ASTM A105		0.35	0.10-0.35	0.60-1.05	0.04	0.035	0.4	0.4	0.3	0.12	0.08
ASTM A181	60	0.35	0.10-0.35	1.1	0.05	0.05
	70	0.35	0.10-0.35	1.1	0.05	0.05
ASTM A266	1	0.3	0.15-0.35	0.40-1.05	0.025	0.025
	2	0.3	0.15-0.35	0.40-1.05	0.025	0.025
	3	0.35	0.15-0.35	0.80-1.35	0.025	0.025
	4	0.3	0.15-0.35	0.80-1.35	0.025	0.025
ASTM A350	LF1	0.3	0.15-0.30	0.60-1.35	0.04	0.035	0.4	0.4	0.3	0.12	0.08	0.02
	LF2-1	0.3	0.15-0.30	0.60-1.35	0.04	0.035	0.4	0.4	0.3	0.12	0.08	0.02
	LF2-2	0.3	0.15-0.30	0.60-1.35	0.04	0.035	0.4	0.4	0.3	0.12	0.08	0.02
	LF3-1	0.2	0.20-0.35	0.9	0.04	0.035	0.4	3.30-3.70	0.3	0.12	0.03	0.02
	LF3-2	0.2	0.20-0.35	0.9	0.04	0.035	0.4	3.30-3.70	0.3	0.12	0.03	0.02
	LF5-1	0.3	0.20-0.35	0.60-1.35	0.04	0.035	0.4	1.00-2.00	0.3	0.12	0.03	0.02
	LF5-2	0.3	0.20-0.35	0.60-1.35	0.04	0.035	0.4	1.00-2.00	0.3	0.12	0.03	0.02
	LF6-1	0.22	0.15-0.30	1.15-1.50	0.025	0.025	0.4	0.4	0.3	0.12	0.04-0.11	0.02
	LF6-2	0.22	0.15-0.30	1.15-1.50	0.025	0.025	0.4	0.4	0.3	0.12	0.04-0.11	0.02
	LF6-3	0.22	0.15-0.30	1.15-1.50	0.025	0.025	0.4	0.4	0.3	0.12	0.04-0.11	0.02
	LF9	0.2		0.40-1.06	0.04	0.035	0.75-1.25	1.60-2.24	0.3	0.12	0.03	0.02
	LF787-2	0.07	0.4	0.40-0.70	0.025	0.025	1.00-1.30	0.70-1.00	0.60-0.90	0.15-0.25	0.03	0.02 min
	LF787-3	0.07	0.4	0.40-0.70	0.025	0.025	1.00-1.30	0.70-1.00	0.60-0.90	0.15-0.25	0.03	0.02 min

A105 Forged Fittings, Mechanical Properties

Material Grade	Grade or Class	Tensile Strength min, Ksi	Yield Strength Ksi @ 0.2%	Elongation in 2 in, %
ASTM A105	-	70	36	22
ASTM A181	60	60	30	22
ASTM A181	70	70	36	18
ASTM A266	1	60-85	30	23
ASTM A266	2	70-95	36	20
ASTM A266	3	70-95	36	20
ASTM A266	4	75-100	37.5	19
ASTM A350	LF1	60-85	30	25
ASTM A350	LF2-1	70-95	36	22
ASTM A350	LF2-2	70-95	36	22
ASTM A350	LF3-1	70-95	37.5	22
ASTM A350	LF3-2	70-95	37.5	22
ASTM A350	LF5-1	60-85	30	25
ASTM A350	LF5-2	70-95	37.5	22
ASTM A350	LF6-1	66-91	52	22
ASTM A350	LF6-2	75-100	60	20
ASTM A350	LF6-3	75-100	60	20
ASTM A350	LF9	63-88	46	25
ASTM A350	LF787-2	65-85	55	20
ASTM A350	LF787-3	75-95	65	20

Low-Alloy Steel Fittings ASTM A182 (Forged)

Low-alloy forged fittings match chrome-moly ASTM A335 pipes: P5/F5, P9/F9, P11/F11, P22/F22, P91/F91. Always keep the fitting grade consistent with the pipe grade. Mixing, say, F11 fittings on P22 pipe is a common procurement error that creates a weak point in the system.

Low-Alloy Forged Fittings Materials	A182 F5	A182 F9	A182 F11	A182 F22	A182 F91
C	0.15 Max	0.15 Max	0.10-0.20 (2)	0.05-0.15	0.08-0.12
Mn	0.30-0.60	0.30-0.60	0.40-0.65	0.30-0.60	0.30-0.60
P	0.035 Max	0.030 Max	0.025 Max	0.035 Max	0.020 Max
S	0.030 Max	0.030 Max	0.040 Max	0.040 Max	0.010 Max
Si	0.50 Max	0.50-1.00	0.50-0.80	0.50 Max	0.20-0.50
Ni	0.50 Max	-	-	0.40 Max
Cr	4.0-6.0	8.0-10.0	1.00-1.50	2.00-2.50	8.0-9.5
Mo	0.44-0.65	0.90-1.10	0.44-0.65	0.90-1.10	0.85-1.05
V	-	-	-	0.18-0.25
Cu	-	-	-	-
Other	-	-	-	Cb, 0.06-0.10; N, 0.03-0.07; Al, 0.04 max.

Stainless Steel Fittings ASTM A182 (Forged)

Stainless steel forged fittings match ASTM A312 pipes. The most commonly specified grades are F304/F304L and F316/F316L. For high-temperature service, use the “H” grades (F304H, F316H) which have controlled carbon ranges for creep resistance.

ASTM A182 Forged Fittings Materials, Chemical Composition %

A182 Grade	C	Mn	P	S	Si	Ni	Cr	Mo	Nb	Ti	Others
F304(1)	0.08	2.0	0.045	0.030	1.0	8.0-11.0	18.0-20.0
F304H	0.04-0.10	2.0	0.045	0.030	1.0	8.0-11.0	18.0-20.0
F304L(1)	0.030	2.0	0.045	0.030	1.0	8.0-13.0	18.0-20.0
F304N(2)	0.08	2.0	0.045	0.030	1.0	8.0-10.5	18.0-20.0
F304LN(2)	0.030	2.0	0.045	0.030	1.0	8.0-10.5	18.0-20.0
F309H	0.04-0.10	2.0	0.045	0.030	1.0	12.0-15.0	22.0-24.0
F310	0.25	2.0	0.045	0.030	1.0	19.0-22.0	24.0-26.0
F310H	0.04-0.10	2.0	0.045	0.030	1.0	19.0-22.0	24.0-26.0
F310MoLN	0.030	2.0	0.030	0.015	0.40	21.0-23.0	24.0-26.0	2.0-3.0			N 0.10-0.16
F316	0.08	2.0	0.045	0.030	1.0	10.0-14.0	16.0-18.0	2.0-3.0
F316H	0.04-0.10	2.0	0.045	0.030	1.0	10.0-14.0	16.0-18.0	2.0-3.0
F316L(1)	0.030	2.0	0.045	0.030	1.0	10.0-15.0	16.0-18.0	2.0-3.0
F316N(2)	0.08	2.0	0.045	0.030	1.0	11.0-14.0	16.0-18.0	2.0-3.0
F316LN(2)	0.030	2.0	0.045	0.030	1.0	11.0-14.0	16.0-18.0	2.0-3.0
F316Ti	0.08	2.0	0.045	0.030	1.0	10.0-14.0	16.0-18.0	2.0-3.0		(3)	N 0.10 max
F317	0.08	2.0	0.045	0.030	1.0	11.0-15.0	18.0-20.0	3.0-4.0
F317L	0.030	2.0	0.045	0.030	1.0	11.0-15.0	18.0-20.0	3.0-4.0
F321	0.08	2.0	0.045	0.030	1.0	9.0-12.0	17.0-19.0			(4)
F321H	0.04-0.10	2.0	0.045	0.030	1.0	9.0-12.0	17.0-19.0			(5)
F347	0.08	2.0	0.045	0.030	1.0	9.0-13.0	17.0-20.0		(6)
F347H	0.04-0.10	2.0	0.045	0.030	1.0	9.0-13.0	17.0-20.0		(7)
F348	0.08	2.0	0.045	0.030	1.0	9.0-13.0	17.0-20.0		(6)		Co 0.20Ta 0.10
F348H	0.04-0.10	2.0	0.045	0.030	1.0	9.0-13.0	17.0-20.0		(7)		Co 0.20Ta 0.10

Forged fittings are also available in duplex (ASTM A182 F51), super duplex (F53/F55), and various nickel alloys (Inconel, Incoloy, Monel, Hastelloy) for severe corrosion or extreme temperature service.

Forged Fittings Manufacturers

• Anvil/JB Smith
• Beck
• Bonney Forge
• Del Corte
• General Plug and Manufacturing
• IML/OMC
• Interfit Vallourec
• Lame Fittings
• Jefferson Union
• Mega Mex
• M.E.G.A.
• Mueller Industries
• Nicholson
• Penn Machine
• Phoenix/Capitol
• Ulma
• Ward
• Westbrook
• WFI
• Viar

Common Mistake

Using threaded fittings in vibrating service or high-cycle applications. Threads back out under vibration regardless of how much sealant you use. For instrument connections on rotating equipment or reciprocating compressors, specify socket weld or use locking compounds designed for vibration service.

Field Note

Match the fitting class to your pipe schedule - Class 3000 pairs with Schedule 80 pipe, Class 6000 with Schedule 160. Installing Class 3000 fittings on Schedule 160 pipe creates a wall thickness mismatch at the joint, weakening the system at exactly the point where you need strength.

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