What Is a Swage Nipple?

A swage nipple is a short fitting used to connect two different pipe sizes. It functions like a reducer but is typically forged rather than formed, and it accommodates different end connections on each side: plain end (PE), butt weld (BW), threaded (T), or socket weld (SW). Swage nipples are manufactured per MSS SP-95 and available in concentric and eccentric configurations.

Property	Detail
Standard	MSS SP-95
Types	Concentric, eccentric
Size range	NPS 1/2 x 1/4 to NPS 4 x 2 (typical)
End connections	PE x PE, BW x PE, T x T, SW x SW, BW x T, BW x SW
Materials	ASTM A105 (CS), A182 F11/F22 (alloy), A182 F304/F316 (SS)
Pressure class	3000# and 6000# (forged), SCH 40/80/160 (BW end)

Concentric vs Eccentric

Feature	Concentric	Eccentric
Centerline	Same on both ends	Offset (flat side top or bottom)
Flow	Centered, symmetric	Asymmetric, one flat side
Air pocket risk	Can trap air at high points	Flat-on-top prevents air pockets
Drainage	Can trap liquid at low points	Flat-on-bottom allows full drainage
Pump suction	Not recommended	Preferred (flat on top)
Pipe support	Standard	Maintains bottom-of-pipe elevation

The selection rule mirrors that of concentric vs eccentric pipe reducers: eccentric flat-on-top for pump suction lines to prevent cavitation; eccentric flat-on-bottom for overhead lines to prevent liquid trapping.

End Connection Combinations

The flexibility of end types is the primary advantage of swage nipples over standard reducers:

Designation	Large End	Small End	Typical Use
BW x BW	Butt weld	Butt weld	Standard piping transition
BW x PE	Butt weld	Plain end	Connects BW pipe to slip-on flange
T x T	Threaded	Threaded	Small-bore threaded piping transition
SW x SW	Socket weld	Socket weld	Small-bore socket weld transition
BW x T	Butt weld	Threaded	Transition from large BW to small threaded
BW x SW	Butt weld	Socket weld	Transition from large BW to small SW

Applications

Swage nipples are commonly used in:

• Instrument connections: Transitioning from process pipe (NPS 2 or larger) to instrument taps (NPS 1/2 or 3/4)
• Vent and drain connections: Reducing from process pipe to small-bore vent or drain valves
• Sample points: Connecting process headers to sampling systems
• Branch connections: Paired with weldolets or threadolets for branch-to-instrument transitions

Swage Nipple vs Reducer

Factor	Swage Nipple	Reducer (ASME B16.9)
Manufacturing	Forged	Formed from pipe/plate
End types	Mixed (BW, SW, T, PE)	BW only
Size range	NPS 1/4 to NPS 4	NPS 1/2 to NPS 48
Body length	Short (per MSS SP-95)	Longer (per ASME B16.9)
Best for	Small-bore transitions	Large-bore transitions

For transitions above NPS 4, standard ASME B16.9 reducers are the default choice. Swage nipples fill the gap in small-bore piping where mixed end connections are needed.

Read the full guide to pipe fittings