Views: 2 Author: Monica Publish Time: 2025-09-12 Origin: Site
Threaded flanges allow pipes, valves, equipment, or other components to be easily disconnected and reconnected for maintenance, inspection, cleaning, replacement, modification, or expansion without cutting the pipe. They are particularly suitable for applications requiring frequent disassembly.
Furthermore, threaded flanges require no welding. This is their greatest advantage over butt weld and socket weld flanges. They are screwed directly onto externally threaded fittings using the pipe threads. For small-diameter pipes, threaded connections are often faster than welding.
Threaded flange is a special type of pipe connector. Its structural feature is that the flange's inner bore is threaded, allowing it to be screwed directly onto the corresponding threaded pipe without welding.
Threaded Connection Design:
The flange's inner bore uses standard pipe threads (NPT or BSPT), allowing it to be screwed directly onto threaded pipes of the same specification. Its greatest advantage is the lack of welding. Furthermore, threaded flanges are primarily made of carbon steel and stainless steel, making them suitable for medium and low pressure applications.
Various Sealing Methods:
Flat Face Seal (FF): Used with a flat gasket, suitable for low-pressure, non-critical environments.
Raised Face Seal (RF): Used with a flexible graphite or spiral wound gasket for improved sealing.
Conical Spiral Seal (NPT): Some NPT seals have built-in sealing capabilities, reducing the risk of leaks.
Suitable for Small Diameter Pipes:
Primarily used for small-diameter pipes ranging from DN15-DN150 (½" to 6"), they are smaller than butt-weld flanges and are suitable for installation in space-constrained environments.
Solder-Free Installation:
Eliminates deformation and residual stress caused by high-temperature welding, and connection points allow for easy disassembly and reassembly.
Easy Installation:
Installation is simple; simply screw the flange onto the pipe threads and tighten with bolts. This flange is particularly suitable for applications requiring quick disassembly and assembly, such as temporary piping, repairs and replacements, and instrument connections.
Easy Adjustment and Maintenance:
It can be disassembled and reassembled multiple times without compromising pipeline integrity, making it suitable for systems with frequent maintenance. It facilitates pipeline extensions, branching, and equipment replacement.
Low Cost:
Threaded flanges are 30%-50% cheaper than butt-weld flanges. Replacement only requires replacing the flange or gasket, while welded flanges may require cutting the pipe.
Suitable for High-Risk Environments:
In industries such as oil and gas, chemicals, and pharmaceuticals, where welding can cause explosions or contamination, threaded flanges offer a safer connection method.
Note: Threaded flanges are not suitable for high-pressure (>Class 600), high-temperature (>300°C), or severe vibration environments. Long-term use can lead to leaks due to loosening of threads, so regular inspection is necessary.
Standard Threaded Flange
lDesign:
nFlat Face (FF) or Raised Face (RF) sealing surface.
nInternal pipe threads (NPT, BSP, etc.) for direct screwing onto pipes.
lStandard: ASME B16.5 / B16.47 (ANSI), EN 1092-1 (DIN), JIS B2220.
lPressure Class: 150# to 300#, some up to 600# for specific applications.
lApplications: General industrial piping, water, air, and low-pressure steam systems.
Socket Weld Threaded Flange
lDesign:
nFeatures both internal threads and a socket weld recess for added strength.
nThe pipe is first threaded and then welded in the socket for extra stability.
lStandard: ASME B16.11 for smaller sizes.
lPressure Class: 3000# to 6000#, higher pressure than pure threaded flanges.
lApplications: Small-bore high-pressure systems.
Lap Joint Threaded Flange with Stub End
lDesign:
nThreaded flange + lap joint stub end.
nNo direct sealing, it relies on a stub end and gasket.
lStandard: ASME B16.5 / MSS SP-44.
lPressure Class: 150# to 900#.
lApplications: Systems requiring frequent dismantling.
Reducing Threaded Flange
lDesign:
nOne side has a smaller threaded bore.
nUsed to connect different pipe sizes without extra fittings.
lStandard: ASME B16.5, DIN 2576.
lPressure Class: 150# to 300#.
lApplications: Pump inlets, valve connections, and branch line reductions.
Blind Threaded Flange
lDesign:
nSolid flange with threaded bolt holes with no center hole.
nUsed to seal the end of a threaded pipe system.
lStandard: ASME B16.5 / B16.47.
lPressure Class: 150# to 2500#.
lApplications: Pipeline testing, maintenance isolation, future expansion caps.
ASME B16.5 Threaded Flange Dimensions (Standard for NPT Threads)
Pressure Classes: 150#, 300#, 600#, 900#, 1500#, 2500#
Nominal Pipe Size (NPS) | Outer Diameter (OD) | Bolt Circle (BC) | Bolt Hole Dia | No. of Bolts | Min. Thread Length (NPT) |
½" (15mm) | 90mm (3.5") | 60.3mm (2.38") | 15.9mm (0.63") | 4 | 13mm (0.5") |
1" (25mm) | 108mm (4.25") | 79.4mm (3.13") | 15.9mm (0.63") | 4 | 15mm (0.59") |
2" (50mm) | 152mm (6.0") | 120.7mm (4.75") | 19.1mm (0.75") | 8 | 17mm (0.67") |
4" (100mm) | 229mm (9.0") | 190.5mm (7.5") | 19.1mm (0.75") | 8 | 22mm (0.87") |
6" (150mm) | 279mm (11.0") | 241.3mm (9.5") | 22.2mm (0.88") | 12 | 25mm (1.0") |
Notes:
Thread Type: NPT (National Pipe Thread, tapered) for ASME flanges.
Raised Face (RF) Height: ~1.6mm (1/16") for Class 150-300, ~6.4mm (1/4") for higher classes.
DIN/EN 1092-1 Threaded Flange Dimensions
PN Ratings: PN6, PN10, PN16, PN25, PN40
DN (mm) | OD (mm) | Bolt Circle (mm) | Bolt Hole Dia (mm) | Thread (BSPT/G) |
DN15 | 65 | 50 | 11 | R½" (BSPT) |
DN25 | 85 | 70 | 11 | R1" (BSPT) |
DN50 | 125 | 100 | 14 | R2" (BSPT) |
DN100 | 200 | 170 | 18 | R4" (BSPT) |
Notes:
Thread Type: BSPT (British Standard Pipe Taper) or parallel (BSPP/G).
PN16 (≈150#), PN40 (≈300#) pressure equivalents.
JIS B2220 Threaded Flange Dimensions
JIS 5K/10K/16K/20K Pressure Ratings
NPS (mm) | OD (mm) | Bolt Holes | Thread (PT, PF) |
15A | 95 | 4×14mm | PT½" (Tapered) |
25A | 115 | 4×14mm | PT1" |
50A | 165 | 4×19mm | PT2" |
Notes:
Thread Type: PT (Tapered, JIS standard), PF (Parallel).
The "grade" of threaded flange generally refers to two aspects: material grade and pressure grade. The two are closely related and together determine the flange's applicable temperature, pressure, media, and mechanical properties.
Pressure rating: This represents the maximum working pressure a flange can safely withstand. Different standards use different pressure ratings:
ASME B16.5 / ASME B16.47 (North American):
Using Class designations: Class 150, 300, 400, 600, 900, 1500, 2500.
The most common and recommended pressure ratings for threaded flanges are Class 150 and Class 300.
Threaded flanges of Class 600 and higher have extremely limited practical applications and are generally not recommended. This is because threaded connections are inherently susceptible to loosening or failure under high pressure, high temperature, cyclic loading, or vibration. High pressures require more reliable connection methods, such as butt welding.
EN 1092-1 / PN System (Europe):
Uses PN (Pressure Nominal) designations: PN 6, PN 10, PN 16, PN 25, PN 40, PN 63, PN 100, etc.
The most common and recommended pressure ratings for threaded flanges are PN 10, PN 16, PN 25, and PN 40.
Threaded flanges of PN 63 and higher are also rare and require careful evaluation for similar reasons to ASME Class 600+.
Similarly, the pressure-temperature ratings table in EN 1092-1 should be consulted based on the design pressure and temperature.
JIS B2220 System (Japan):
Uses K-Class designations: 5K, 10K, 16K, 20K, 30K, 40K, 63K.
Common threaded flanges are 10K and 16K.
Material grade: This is the specific material specification used to manufacture flanges. The material grade determines the flange's chemical composition, mechanical properties, corrosion resistance, and applicable temperature range.
Carbon Steel:
ASTM A105: Standard carbon steel forgings for ambient temperature service. The most commonly used, suitable for non-corrosive media, with a temperature range of approximately -29°C to 425°C.
ASTM A350 LF2: Low-temperature carbon steel forgings. Used at low temperatures, with improved low-temperature impact toughness.
ASTM A694: High-yield strength carbon and alloy steel forgings used in pipeline systems. Common grades include F42, F52, F60, F65, and F70.
Stainless Steel:
ASTM A182:
F304/F304L: General-purpose austenitic stainless steel, resistant to general corrosion. L stands for extra-low carbon, which offers improved resistance to intergranular corrosion.
F316/F316L: Molybdenum-containing austenitic stainless steel with better corrosion resistance than 304, especially resistance to pitting and crevice corrosion. L stands for ultra-low carbon.
F321: Titanium-containing stabilized austenitic stainless steel, resistant to intergranular corrosion.
F347: Niobium-containing stabilized austenitic stainless steel, resistant to intergranular corrosion.
F51 (2205), F53 (2507), F55 (Super Duplex): Duplex stainless steels with high strength and excellent resistance to chloride stress corrosion cracking and pitting.
Alloy Steel:
ASTM A182:
F11 (1¼Cr-½Mo), F22 (2¼Cr-1Mo): Chromium-molybdenum alloy steels with high temperature resistance (creep resistance) and hydrogen corrosion resistance. Used in high-temperature, high-pressure steam and petroleum refining.
F91 (9Cr-1Mo-V): High-strength chromium-molybdenum-vanadium alloy steel, used for high-temperature components in supercritical/ultra-supercritical power plants.
Nickel Alloys:
ASTM B564 (Forgings):
UNS N04400 (Monel 400), UNS N06625 (Inconel 625), UNS N10276 (Hastelloy C276): For use in extremely harsh corrosive environments.
Threaded flanges are JN's specialty. As a flange manufacturer in China, we specialize in custom flanges ranging from ½ inch to 250 inches in diameter. Simply provide your specifications and drawings, and JN will deliver your pipe flanges on time.
Some custom forged flange types include slip-on flanges, butt weld flanges, blind flanges, lap joint flanges, and threaded flanges. We offer custom forged flanges in a variety of materials, including carbon steel, stainless steel, nickel alloys, and duplex steel. We have the experience you need to source the right flange for your unique application in most cases.
