Name: Forged Threaded Boss
Brand: Cunimet Alloy International

Product Overview

Forged Threaded Boss

The Forged Threaded Boss, also referred to as a weld-on NPT nozzle boss or screwed boss, is a compact forged nozzle fitting with a flat circular base and a cylindrical boss body. The base is fillet-welded directly to the outer surface of a pipe or pressure vessel wall at a drilled or punched opening. The bore running through the boss body carries a female NPT internal thread per ASME B1.20.1, providing a screwed connection point for instrument valves, gauge connections, chemical injection quills, pressure transmitters, thermowells and similar accessories.

The threaded boss serves the same purpose as a weld-on half coupling but with a larger, flat base footprint that distributes the connection load over a greater area of the parent pipe or vessel shell, improving structural integrity at the tapping point. It is particularly useful on thin-wall vessels and pipes where the contact area of a standard half coupling is insufficient, and on curved surfaces where the flat base of the boss can be profiled (saddle-cut) to conform to the parent pipe curvature.

Cunimet Alloy International manufactures threaded bosses through closed-die forging in Stainless Steel 304/316, Duplex Steel and Super Duplex Steel. All female NPT bores are CNC-machined to ASME B1.20.1 tolerances and 100% go/no-go gauge inspected. EN 10204 3.1 material test certificates are supplied as standard.

ASME B1.20.1 (NPT) ASTM A182 ASME B31.3 ASME VIII Div.1 1/4" to 4" NPS Female NPT Bore Flat Circular Base

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ASMEThread StandardB1.20.1 (NPT)

F.NPTBore ThreadFemale NPT Internal

1/4–4"Size RangeNPS

FilletWeld TypeFlat Base to Pipe/Vessel

3Material GradesSS / Duplex / S.Duplex

Technical Dimensions

Threaded Boss — Standard Dimensions

“D” = Base outer diameter (flat circular base). “H” = Overall height from base face to top face. Female NPT thread runs from top face down through the bore. Thread form per ASME B1.20.1. All dimensions in millimetres.

NPS	Nominal NPT Bore	Base Dia. “D” (mm)	Overall Height “H” (mm)	TPI	Thread Engagement (mm)
1/4"	13.7 mm (0.540")	44	25	18	11
1/2"	21.3 mm (0.840")	57	32	14	14
3/4"	26.7 mm (1.050")	67	38	14	14
1"	33.4 mm (1.315")	83	44	11.5	17
1-1/4"	42.2 mm (1.660")	102	51	11.5	17
1-1/2"	48.3 mm (1.900")	114	57	11.5	17
2"	60.3 mm (2.375")	140	64	11.5	17
2-1/2"	73.0 mm (2.875")	159	76	8	22
3"	88.9 mm (3.500")	191	89	8	22
4"	114.3 mm (4.500")	229	102	8	22

Custom heights and base diameters available on request. Base can be profiled (saddle-cut) to match parent pipe curvature on request. BSP threads to BS EN 10226 available. All dimensions in millimetres.

Product Comparison

Threaded Boss vs Half Coupling vs SW Boss

Threaded Boss

Large flat circular base fillet-welded to pipe or vessel OD surface
Female NPT internal thread in bore for screwed connections
Best load distribution; suited to thin-wall pipe and vessel shells
Standard: ASME B1.20.1 NPT, ASME VIII Div.1, ASME B31.3

Half Coupling

Cylindrical body fillet-welded to pipe OD; narrower base contact than boss
Female NPT thread at one end; opposite end is the weld end
Standard weld-on threaded nozzle for heavy-wall pipe and header tapping
Standard: ASME B16.11, ASME B31.3

SW Boss

Same flat circular base geometry as threaded boss
Socket weld bore instead of NPT thread — pipe is inserted and fillet-welded inside
Used where a welded connection to the branch line is preferred over a screwed one
Standard: MSS SP-83, ASME B31.3

Available Materials

Material Grades for Threaded Bosses

Grade 01

Stainless Steel 304 / 316

Austenitic stainless steel threaded bosses for weld-on instrument and gauge tapping points on chemical, pharmaceutical, food and water treatment process vessels and pipelines. SS 316 specified where chloride exposure at the boss bore and weld zone is a design consideration.

ASTM A182 F304ASTM A182 F316ASME B1.20.1

Grade 02

Duplex Steel

High-strength duplex alloy threaded bosses for instrument tapping and chemical injection nozzle connections on offshore process vessels, pressure vessels and piping in desalination and chloride-bearing environments where weld zone corrosion resistance must match the parent material.

ASTM A182 F51UNS S31803UNS S32205

Grade 03

Super Duplex Steel

Premium super duplex threaded bosses with PREN greater than 40 for instrument and injection nozzle connections on seawater service vessels, offshore topsides pressure equipment and subsea pipelines where the highest available corrosion resistance at every nozzle weld joint is required by design code.

ASTM A182 F53UNS S32750UNS S32760

Quality & Compliance

Standards, Testing & Documentation

Applicable Standards

Standard	Description
ASME B1.20.1	NPT Pipe Threads — thread form, dimensions and tolerances
ASTM A182	Material specification for forged alloy and stainless steel fittings
ASME B31.3	Process Piping — nozzle, branch and attachment requirements
ASME VIII Div.1	Pressure Vessel Code — nozzle attachment requirements
BS EN 10226	BSP pipe threads — available on request
EN 10204	3.1 MTC standard; 3.2 with TPI on request

Quality Tests Performed

Test	Method / Scope
Chemical Analysis	OES per ASTM A182 for each heat of material
Mechanical Testing	Tensile, yield, elongation and Charpy impact where specified
Hardness Testing	Brinell or Vickers per ASTM A182 requirements
Thread Gauging	100% female NPT go/no-go per ASME B1.20.1 on every boss
PMI	100% XRF Positive Material Identification on request
Dimensional Inspection	100% — base OD, height, thread depth and bore concentricity

Applications

Where Threaded Bosses Are Used

01

Pressure & Temperature Instrument Tappings

Providing weld-on NPT tapping points for pressure gauges, pressure transmitters and thermowells on process vessels, heat exchangers and pipeline manifolds where the larger base diameter of the boss distributes the instrument connection load over a wider area of the vessel shell.

02

Chemical Injection Nozzles

Creating small-bore chemical injection nozzle connections on offshore process piping and vessels in Duplex or Super Duplex Steel, where the threaded boss provides a robust fillet-welded connection point for injection quill assemblies without penetrating the pipe with a full-bore branch outlet.

03

Vent & Drain Points on Vessels

Forming weld-on vent and drain nozzle connections on pressure vessels and storage tanks where a female NPT threaded boss provides a screwed tapping that can be closed with a threaded plug or fitted with a gate or globe valve for process drain and vent service.

04

Thin-Wall Pipe & Vessel Connections

Where the base footprint of the threaded boss distributes the bending moment from the instrument or valve connection over a larger area of thin-wall pipe or vessel shell than a half coupling, reducing local stress concentration at the nozzle-to-shell junction per ASME VIII requirements.

Forged Threaded Boss

Forged Threaded Boss

Threaded Boss — Standard Dimensions

Threaded Boss vs Half Coupling vs SW Boss

Threaded Boss

Half Coupling

SW Boss

Material Grades for Threaded Bosses

Stainless Steel 304 / 316

Duplex Steel

Super Duplex Steel

Standards, Testing & Documentation

Applicable Standards

Quality Tests Performed

Where Threaded Bosses Are Used

Pressure & Temperature Instrument Tappings

Chemical Injection Nozzles

Vent & Drain Points on Vessels

Thin-Wall Pipe & Vessel Connections

Similar Weld-On Fittings

SW Boss

Threaded Half Coupling

Threaded Plug

Branch Outlets

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