Threaded Flanges eliminate field welding for small-bore utility lines. Class 150 / Class 300 / PN 16 in NPT / BSP / JIS threads.
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Not recommended for cyclic service or where leakage constitutes a fire/process-safety hazard (ASME B31.3).
Threaded Flanges (Th) are internally-threaded pipe connectors that screw onto a matching pipe thread (NPT per ASME B1.20.1, BSP per ISO 228, or JIS B0203), eliminating field welding on small-bore utility lines. As an ASME B16.5 threaded flange manufacturer and supplier based in Hebei, China, we produce Th flanges to ASME B16.5 (1/2"–3" NPS preferred, 4"–24" rare), Class 150 (285 PSI) and Class 300 (740 PSI), EN 1092-1:2018 Type 13, and JIS B2220 Th.
Threaded flanges are limited to Class 300 because threaded joints have lower fatigue resistance than welded; ASME B31.3 §A328.5 restricts their use where leakage constitutes a fire or process-safety hazard. Threaded joints are NOT recommended for service temperatures above 200°C, NACE MR0175 sour service, or any service where thermal cycling occurs.
Common applications: utility air, instrument air, hydraulic oil lines, low-pressure water service, oilfield production manifolds where weld inspection is not feasible, and explosive atmospheres where ASME B31.1 §A1.6 restricts welding. Threaded joints allow rapid assembly/disassembly for field repair without requiring certified welding crews.
Threaded joints require thread sealant (Teflon tape, pipe dope, or anaerobic sealant) and torque verification during installation. ASME B1.20.1 NPT thread taper is standard (1° 47' taper, 16 threads per inch for NPS 1/2"); BSP parallel thread per ISO 228 is available on request for European and Middle East customers.
Materials: A105 carbon steel (default), A350 LF2 low-temperature carbon steel, A182 F304/F316 stainless steel. All supplied with EN 10204 3.1 mill certificate. ISO 9001:2015 quality management. PED CE-marking available on request.
Manufacturing process: Threaded flanges are machined from forged billet. The threaded bore must match the mating pipe thread standard: ASME B1.20.1 NPT (American standard taper pipe thread, 1° 47' taper, 16 threads per inch for NPS 1/2"), ISO 228 BSP parallel (British standard pipe parallel, for European markets), or JIS B0203 (Japanese standard taper pipe thread). The thread root radius and crest truncation must be per ASME B1.20.1 to ensure sealing under pressure. Thread sealants (PTFE tape, anaerobic resin, pipe dope) are recommended at installation.
Pressure-temperature rating: Class 150 Th flanges rated for 285 psi at 38°C, dropping to 150 psi at 200°C (above 200°C, threaded joints are not recommended per ASME B31.3). Class 300 rated for 740 psi at 38°C, dropping to 415 psi at 200°C. Per ASME B16.5 §6.1, threaded flanges are dimensionally defined for NPS 1/2" through NPS 24", but preferred NPS range is 1/2"–3" because larger threads become difficult to machine accurately.
Common applications: oilfield Christmas tree assemblies (low-pressure utility lines, wellhead isolation), instrument air systems, hydraulic oil lines in non-critical service, water treatment skids, wellhead flowlines, and modular skid-mounted equipment where field welding is restricted.
Limitations: Threaded joints are NOT suitable for: (1) service temperatures above 200°C (PTFE tape degrades; thread galling risk increases), (2) NACE MR0175 sour service (threaded crevices concentrate H2S corrosion), (3) cyclic pressure service (fatigue failure at the thread root), (4) any service where leakage constitutes a fire or process safety hazard per ASME B31.3 §A328.5.
Shipping: Standard NPS 1/2"–2" Class 150 Th flanges in A105 carbon steel ship in 15–20 days. Non-stocked sizes and Class 300 ship in 25–40 days. Sea freight from Shanghai/Qingdao to major ports in 14–30 days. Third-party inspection by SGS / BV / TUV / Intertek available on request.
No. ASME B16.5 Threaded Flanges are dimensionally defined only for Class 150 and Class 300. ASME B31.3 §A328.5 restricts their use to Class 300 maximum because threaded joints have lower fatigue resistance than welded joints. For Class 600 and above, use Weld Neck (WN) or Socket-Weld (SW, NPS ≤ 3) flanges. Threaded joints are also not recommended for service temperatures above 200°C or any cyclic pressure service.
Threaded flanges are preferred when: (1) field welding is impractical or forbidden (e.g. explosive atmospheres per ASME B31.1 §A1.6, or where certified welding crews are unavailable), (2) rapid assembly/disassembly is required (e.g. instrument manifolds, frequent maintenance), (3) the pipe is small-bore (NPS ≤ 3) and socket-weld would create crevice corrosion risk, (4) the service is low-pressure non-cyclic utility. Threaded flanges are NOT preferred for service temperatures > 200°C, NACE MR0175 sour service, or cyclic pressure service.
Standard thread is ASME B1.20.1 NPT (American standard taper pipe thread). For European and Middle East customers, we can supply ISO 228 BSP parallel thread on request. For Japanese customers, JIS B0203 taper pipe thread. The thread form must be specified at the time of order, threaded flanges cannot be re-threaded in the field without specialized equipment. We also supply NPTF (dryseal) threads on request for higher-pressure service.
Yes. NPT threads are tapered but rely on thread sealant to achieve pressure-tight sealing. Acceptable sealants: PTFE tape (Teflon), anaerobic pipe sealant (Loctite 567, 577), or pipe dope (pipe thread compound). PTFE tape is standard for water and air service. Anaerobic sealant is preferred for high-pressure service and where vibration is present. Pipe dope is preferred for steam and high-temperature service. For sour service, use PTFE-free anaerobic sealant rated for H2S exposure.
Threaded Flanges (Th) are internally-threaded pipe connectors that screw onto a matching pipe thread (NPT per ASME B1.20.1, BSP per ISO 228, or JIS B0203), eliminating field welding on small-bore utility lines. They conform to ASME B16.5 (1/2" to 3" NPS preferred, 4" to 24" rare), Class 150 (285 PSI) and Class 300 (740 PSI), and EN 1092-1:2018 Type 13. Threaded flanges are limited to Class 300 because threaded joints have lower fatigue resistance than welded; ASME B31.3 restricts their use where leakage constitutes a fire or process-safety hazard. They are the standard specification for small-bore utility and field-repairable connections.
Source: ASME B16.5-2020; EN 1092-1:2018.
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