What Is a Nipolet?

A nipolet is a one-piece forged branch connection fitting that provides a threaded (NPT) outlet from a pipe header. It combines the contoured base of a weldolet with an extended nipple body that terminates in a female threaded end. The header end is welded to the pipe, while the branch end accepts a threaded pipe or instrument connection. Nipolets are covered under MSS SP-97 (branch connection fittings).

Property	Detail
Standard	MSS SP-97
Branch angle	90° to header
Branch end	Female NPT thread
Header end	Contoured to match header OD (weld-on)
Size range	Header: NPS 2 to NPS 36; Branch: NPS 1/2 to NPS 4
Materials	ASTM A105 (CS), A182 F11/F22 (alloy), A182 F304/F316 (SS), A350 LF2 (low-temp)
Pressure class	3000# and 6000#

Nipolet vs Threadolet

Both fittings provide threaded branch outlets, but their geometry differs:

Feature	Nipolet	Threadolet
Outlet type	Female NPT (internal thread)	Female NPT (internal thread)
Body length	Extended nipple body	Short body (flush with header)
Reinforcement	More (thicker, longer body)	Standard
Use case	Instrument taps, vent/drain valves	General threaded branches
Pipe extension needed	No (nipple is integral)	Often requires a pipe nipple
Accessibility	Better (extended reach)	Closer to header surface

The key distinction is the extended body. A nipolet projects the threaded connection away from the header pipe surface, providing clearance for wrenches, instrument connections, and valve bonnets. A threadolet sits close to the header, which can make connections difficult on large-diameter pipes with heavy insulation.

Applications

Nipolets are standard fittings for:

• Instrument taps: Pressure gauges, transmitters, and temperature wells on process headers
• Vent connections: Small-bore vent valves on high points of liquid-filled piping
• Drain connections: Small-bore drain valves at low points of piping systems
• Sample points: Chemical sampling connections on process lines
• Thermowell bosses: Extended reach for thermowells on large-diameter headers

Installation

1. Mark the branch location on the header pipe
2. Cut a hole in the header matching the nipolet bore
3. Fit the contoured base to the header OD, ensuring full contact
4. Weld the nipolet to the header with a full-penetration weld
5. Thread the instrument, valve, or pipe nipple into the female NPT end

The weld between the nipolet and header is inspected per the piping specification, typically by magnetic particle or liquid penetrant testing for small-bore connections.

Nipolet vs Weldolet + Nipple

An alternative to a nipolet is a weldolet plus a separate pipe nipple plus a coupling. The nipolet eliminates two threaded joints and one weld, reducing potential leak paths from three to one (the header weld).

Configuration	Joints	Leak Paths	Parts
Nipolet	1 weld + 1 thread	2	1 fitting
Weldolet + nipple + coupling	1 weld + 2 threads	3	3 parts
Threadolet only	1 weld + 1 thread	2	1 fitting

For critical services where minimizing leak paths matters, the nipolet or threadolet is preferred over multi-piece assemblies. The nipolet adds the benefit of extended reach.

Read the full guide to pipe fittings