Threaded Flanges

Q: When are threaded flanges the right choice?

Threaded flanges are ideal for low-pressure, non-critical piping systems, especially where welding is unsafe or impractical. They’re also convenient for temporary setups or systems needing frequent disassembly.

Q: How to install a threaded flange?

Prepare the pipeline and clean threads.Apply a thread sealant or Teflon tape.Screw the flange onto the pipe until snug.Use a wrench to tighten as needed.Align flanges for gasket seating.Insert gasket.Install bolts evenly.Perform a final torque check.

Our threaded flanges are machined from A105 forged carbon steel and 304/316 stainless steel. They conform to ANSI/ASME B16.5 standards and are available upon request. We can machine threads in any type of flange to suite your project’s needs.

Non-Welded Flange Option

About Threaded Flanges

Threaded flanges are a type of pipe fitting that connects to a pipe using screw threads instead of welding. The flange has a hole in the center with internal threads, and it fits onto a pipe that has matching external threads. This allows for a tight and secure connection without the need for welding equipment or high-heat processes. Because of this simple process, installation is usually quick and straightforward, which makes these flanges a convenient choice for many basic piping systems.

These flanges are commonly used in piping systems for water, air, oil, or gas transportation under moderate pressure and temperature conditions. They are especially useful in environments where welding is not safe or practical, such as areas with flammable gases or liquids. Threaded flanges also make maintenance easier, as they can be removed and reattached without damaging the pipe.

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Material Standards and Dimensions

Threaded flanges are manufactured according to ASME B16.5, which defines the dimensional, material, and pressure requirements for pipe flanges and fittings up to NPS 24. This standard ensures compatibility across systems and guarantees a safe connection for flanged joints.

Threaded flanges shall have a taper pipe thread conforming to ASME B1.20.1. ASME B1.20.1 is the American National Standard for General Purpose Pipe Threads, specifically covering inch-based threads. It defines the dimensional and gaging requirements for:

NPT (National Pipe Taper)
NPSC (National Pipe Straight Coupling)
NPTR (National Pipe Taper Railing)
NPSM (National Pipe Straight Mechanical)
NPSL (National Pipe Straight Loose)

Threaded Flanges have a taper conforming to ASME B1.20.1 and concentric with the flange opening to 5 mm/m.

Class 150

Class 150 flanges have no counterbore. Instead, the threads on the back face are chamfered at roughly a 45° angle down to the thread’s major diameter. This chamfer is concentric with the thread and is counted as part of the overall thread length.

Class 300 and Higher

For flanges rated Class 300 and above, the back face includes a counterbore. The threads are chamfered at about a 45° angle to the thread axis, terminating at the counterbore diameter. Both the counterbore and the chamfer are concentric with the threads.

Reducing Flange Threads

In reducing flanges, the effective thread length must be at least the same as that specified for the matching threaded‑flange class. The threads aren’t required to extend all the way to the flange face.

Thread Gaging

Internal threads must be inspected using gages equipped with a gaging notch. When using working gages, the thread depth may be one full turn over or under the notch. For Class 150 flanges with a chamfer, the inspection reference is the first thread start—unless the chamfer exceeds the thread’s major diameter, in which case you use the last visible thread mark on the chamfer cone. For Classes 300–2500 with a counterbore, the reference point is the final thread mark on the chamfer cone.

Basic Dimensions for Threaded Flanges

The following table shows dimensional ranges for ASME B16.5 threaded flanges from ½″ to 24″ nominal pipe size (NPS).

NPS Range	Outside Diameter (OD)	Bore Diameter (A)	Flange Thickness (B)
½″ – 2″	3.5″ – 6.0″	0.62″ – 2.07″	0.44″ – 0.82″
2½″ – 6″	7.0″ – 11.0″	2.47″ – 6.07″	0.88″ – 1.19″
8″ – 12″	13.5″ – 19.0″	8.07″ – 12.11″	1.31″ – 1.44″
14″ – 20″	21.0″ – 27.5″	14.13″ – 20.15″	1.62″ – 2.00″
24″	32.0″	24.15″	2.25″

* These values are based on Class 150 to 600, which are the most common pressure ratings for threaded flanges.

Threaded Flange Diagram

The diagram below shows how a threaded flange connects to a pipe or fitting.

Applications of
Threaded Flanges

Fuel and Gas Lines

Ideal in explosive environments where welding is prohibited, such as fuel depots or gas plants.

Temporary Piping Systems

Used in test setups or systems that require frequent disassembly and reassembly.

Low-Pressure Water Lines

Suitable for general plumbing and utility piping where pressure is minimal.

Fire Protection Systems

Often found in sprinkler systems because of the simple maintenance.

Chemical Storage Areas

Applied in locations where flammable or reactive media are present, minimizing ignition risk.

Threaded Flange Types

Flat Face

The entire face is flat and flush with the gasket surface. Used where space or flexibility is limited, typically in low-pressure applications.

Raised Face

Includes a raised sealing surface around the bore to improve gasket compression and leak resistance under moderate pressure.

Frequently Asked
Questions

What are threaded flanges?

Threaded flanges (also called screwed flanges) feature internal threads that allow them to be screwed directly onto the external threads of a pipe. This design enables a secure, non-welded connection and makes them ideal for systems where welding isn’t feasible or safe.

What is the difference between a threaded flange and a slip-on flange?

Threaded flanges are better suited for low-pressure systems and are easier to install without welding. In contrast, slip-on flanges require welding and are typically used in higher-pressure applications where additional strength is needed.

When are threaded flanges the right choice?

Threaded flanges are ideal for low-pressure, non-critical piping systems, especially where welding is unsafe or impractical. They’re also convenient for temporary setups or systems needing frequent disassembly.

How to install a threaded flange?

Prepare the pipeline and clean threads.
Apply a thread sealant or Teflon tape.
Screw the flange onto the pipe until snug.
Use a wrench to tighten as needed.
Align flanges for gasket seating.
Insert gasket.
Install bolts evenly.
Perform a final torque check.

How to order threaded flanges from API International?

To threaded flanges from API International, determine your required pipe size, pressure class, material, and any special standards (such as ASME B16.5). Contact API International’s experienced team, who will help you select the right flange for your application.

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Custom Solutions

Custom Requirements

Capabilities:
• Custom Bolt Holes, Overbore, Counterbore, Tapped, Welds, O-ring Grooves, Threads, Special Serrations, Bevels, Chamfers

Thread Style:
• Metric Parallel, Metric Tapered, Parallel (BSPP), Taper Thread (BSPT), UN/UNF/UNC Thread,
NPT (National Pipe Thread)

Serrations:
• MWD

Tolerances:
• Contact API’s engineering department for exact specifications and tolerances.

Materials

Plastic: Delrin, POM, Lexan, Nylon 66, Nylon 6, PEEK, PP, PE, Acetal

Rubber: EPDM, Neoprene, Buna-N, Viton

Aluminum: A2011, A2024, A2017, A5052, A5056, A6061, A6063, A6463, A6082, A7075

Copper: 3600, 3604, 3771

Titanium: 1-28

Steel Series:
• Ductile Iron: ASTM A536
• Carbon/Mild Steel: A105, A36, A516-70, A572-50, etc.
• Stainless Steel:
- 300 Series – 303, 304, 304L, 316, 316L
- 400 Series – 420J2, 430, 434, 442

Special Metals: Hastelloy, Inconel, Incoloy, Duplex 2205, Super Duplex 2507, Chrome Steel, alloys, or their equivalents

Surface Finishings (Flanges Only)

Stock Finish, Spiral Serrated (Phonographic), Concentric Serrated, Smooth Finish, Cold Water Finish, MWD, Phonographic

Coatings (Metal Finishing)

Dipped, Nickel Plating, Zinc Plating (clear, yellow, black, red, blue), Super Agitine, Powder, Painted, Galvanized, Epoxy, Lacquer

Uses (Industries)

Water/Wastewater, Irrigation, Agriculture, HVAC, Marine, Exhaust, Mining, Energy/Power Generation/Oil

Manufacturing Method

Forming:
• Forged:
- Ring Rolling:
• Materials: Carbon Steel, Stainless Steel, Duplex
• Size: 2–202”

• Cast:
- Centrifugal Casting (Industrial):
• Material: Stainless Steel
- Continuous Casting:
• Material: Stainless Steel
- Sand Casting:
• Material: A536, Stainless Steel, Ductile Iron

Machining: Milling, Turning, Facing, Boring, Drilling, Tapping, Counter Sinking, Laser Cutting, Water Jet, Plasma Cutting

All Products

Products	Type	Materials	Size Range
Flanges	Flat-Face, Raised-Face, & Plate: Slip-On/Ring Weld, Neck, Blind, Socket Weld, Orifice, Reducing, Threaded	See Materials List	5–202″
Gaskets	Molded, Extruded, sheet	EPDM, Buna-N, NBR, Non-Asbestos (GNA), Red Rubber (GRR), Viton	5–60″
Screens For Filters	Basket Screens and Cone Screens (Perforated, Mesh)	Galv. Carbon Steel, Carbon Steel, Stainless Steel	6”D x 8’-H
Rings	Exhaust Rings (Marmon Flanges for DPF Filters)	Carbon Steel, Stainless Steel, Aluminum	1–16”
Seamless Rolled Rings	Forged	Carbon Steel, Stainless Steel, Aluminum	1–165”
Square Hole Rings	Repair Couplers	Carbon Steel, Stainless Steel, Galvanized, Epoxy Coated	3–32”
Fabricated Assemblies	Weldments, Pipe Spools, Valve Bodies, Silencer Housings	Carbon Steel, Stainless Steel	2–24”
Long/Short Radius Elbows	EN 10253-2–S235, P235GH–P265GH–P265NL and ASTM A234, WPB, WPC/ A420 WPL6, WPL3/ A860 WPHY52/ ASTM A234 WP11, WP22, WP5, WP9–16Mo3	304L & 316L Stainless Steel	(45° & 90°): OD: 21.3mm (1/2”)–3048mm (120”) WT: Up to SCH. XXS/160
Miscellaneous	Tubesheets / Diffuser Plates / Baffles / Ferrules / Sleeves / Pins	Carbon Steel, Stainless Steel, Duplex	5–104”

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Why Choose Us?

Who we are

API International is a manufacturer and wholesale distributor of flanges, expansion joints, valves, other pipe fittings and custom fabricated parts. We offer a wide variety of AIS & imported flanges along with other industrial pipe fitting and accessories. Customers turn to us when they need quick delivery of parts and are looking for a higher level of customer service. Standard parts are stocked in one of our conveniently located warehouses for quick distribution throughout the United States.

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