Views: 26 Author: Monica Publish Time: 2025-09-12 Origin: Site
A threaded flange is a pipe flange with a thread cut into its bore. Instead of being welded to the pipe, it screws directly onto the pipe's own external thread, so the joint is made with a wrench and a gasket and nothing else.
That single difference drives everything else about this flange type. Because no arc and no flame are involved, a threaded flange can be fitted in a hazardous area where a hot work permit would never be issued. Because the joint is mechanical, it can be broken and remade for maintenance without cutting the pipe. And because no heat goes into the metal, the corrosion resistance of an expensive alloy such as Inconel 625 or Hastelloy C276 is left exactly as the mill delivered it.
The table below is the whole specification on one screen. If your duty falls inside the last row, a threaded flange is almost certainly the fastest and cheapest answer; if it does not, choose a welded type instead.
Use a threaded flange whenever you need a flanged joint on small-bore pipe and you cannot, or should not, weld. It is the standard answer for DN15-DN150 (1/2"-6") lines at Class 150-300 in hazardous areas, on frequently opened lines, and on high-alloy piping.
Every other common flange type, including slip-on, socket weld, weld neck and lap joint, ends in a weld. The threaded flange is the exception. Inside its bore is a standard pipe thread, NPT or BSPT, that matches the thread cut on the pipe. You wrap the pipe thread with sealing tape, screw the flange on, drop in a gasket, bolt the two flanges together, and the line is complete.
Because the connection is mechanical, a threaded joint can be broken and remade any number of times. And because there is no molten metal, no heat-affected zone and no welder qualification required, threaded flanges are widely used in fuel-gas and refinery piping, instrument hook-ups, temporary lines, and repair work on operating plants where a welding permit would be impossible to obtain.
The trade is a narrower service envelope. A thread holds by friction, so pressure, temperature cycling and vibration all work against it. That is why the standards keep threaded ends in the lower pressure classes, and why the honest answer to "can I use a threaded flange here" is usually decided by three numbers: size, class and temperature.
Four design features define a threaded flange: a standard pipe thread in the bore, a choice of flat or raised sealing face, small-diameter sizing, and completely weld-free installation. Together they make it the fastest flange to install and the easiest to take apart.
The bore carries a standard pipe thread, NPT on ASME flanges and BSPT or BSPP on EN flanges, cut to the same gauges used for threaded pipe and forged pipe fittings. Taper threads, NPT and BSPT, wedge tight and seal on the flanks of the thread itself, which is why thread sealant or PTFE tape is still required. The thread does the mechanical gripping; a gasket between the flange faces does the primary pressure sealing.
Flat Face (FF): mates with a full-face or flat gasket; used on brittle mating parts such as cast iron and some plastics, and on low-pressure utilities where uneven bolt tightening would warp a raised face.
Raised Face (RF): a 1.6 mm (1/16") raised ring for Class 150-300 concentrates gasket stress; pairs with flexible graphite or spiral-wound gaskets for better sealing at higher pressure. Higher classes use a 6.4 mm (1/4") raised face.
Thread seal: on taper threads the helical path itself is a secondary seal once PTFE tape or pipe dope is applied, so one joint carries two sealing systems.
Threaded flanges are made and stocked primarily for DN15-DN150 (1/2"-6"). Threading larger bodies is possible but pointless: above 6" the wrench torque needed to make a threaded joint exceeds the cost of a weld, and the pressure capability of the thread drops. Larger lines use welded flange types such as slip-on and weld neck.
Installation adds no heat-affected zone, no weld residual stress and no distortion. That matters for thin-wall pipe, and it matters for corrosion-resistant alloys whose properties are set by solution annealing and must not be disturbed by field heat input. With nickel alloys the saving is measured in days of qualified weld procedure, filler matching and post-weld pickling that simply do not happen.
Threaded flanges are typically 30-50% cheaper to install than butt-weld flanges, go on in minutes without a welder or a welding permit, and can be dismantled and remade repeatedly. Their hard limits are just as clear: no Class 600 and above, no sustained service above roughly 300 °C, and no severe vibration.
Advantages:
Speed of installation: wrap the thread, screw on the flange, bolt up. For small-diameter pipe this is often faster than welding, and it needs no welder, no power supply and no post-weld inspection.
Repeated disassembly: the joint can be broken for maintenance, cleaning, inspection or line modification and then remade with a new gasket, and the pipe itself is never cut.
Lower installed cost: the flange is cheaper than the equivalent butt-weld flange, and you save all welding labour and post-weld heat treatment where it would apply.
Safety in hazardous areas: no arc, no flame and no hot work permit, a decisive advantage in oil and gas, chemical and pharmaceutical plants where welding near flammable media is restricted or forbidden.
Alloy economy: with nickel alloys and duplex, skipping field welding avoids costly qualified weld procedures and pickling of the weld zone.
Limitations to Respect
The reason is mechanical, not metallurgical. A thread is a helical wedge: pressure and temperature cycles work it back and forth until friction alone cannot hold the joint. Standards therefore keep threaded flanges in the classes where thread loosening is not the governing failure mode, and direct high-duty service to socket-weld or butt-weld joints.
Five threaded flange types cover almost every requirement: the standard threaded flange for general duty, the socket-weld threaded hybrid for small-bore high pressure, the lap-joint threaded flange for frequent dismantling, the reducing threaded flange for size changes, and the threaded blind flange for closing line ends.
The workhorse: flat or raised face, internal NPT or BSP thread, Class 150-300, with 600# available for special cases. It serves water, air, low-pressure steam and general plant utilities, and it is the type most buyers of this guide will order. For the full product range see JN ALLOY threaded flanges.
This design adds a socket recess behind the thread: the pipe is first screwed into the thread, then fillet-welded at the socket for extra stability. It combines the alignment ease of a thread with the strength of a weld, and suits small-bore, higher-pressure systems built to ASME B16.11 class 3000/6000 forged fittings.
A lap-joint flange slips over a stub end that carries the gasket face. The backing flange can rotate, so bolt holes align without turning the pipe, which is ideal for frequent dismantling and for dissimilar-material economics: only the stub end needs to be the expensive alloy. See lap joint stub ends and lap joint loose flanges.
One side carries a smaller threaded bore, so two different pipe sizes join without a separate reducer. It is common at pump inlets, valve connections and branch line reductions, and it removes one leak path from the assembly.
A solid disc with no centre bore that closes the end of a threaded pipe system. Class ratings run up to 2500# because a blind has no pipe thread in service, only the bolted gasket joint carries pressure. Typical uses are hydrotest closure, maintenance isolation and future-expansion caps. See blind flanges.
Threaded flange dimensions come from three standards families: ASME B16.5 for NPT threads, EN 1092-1 for BSPT and BSPP threads with PN ratings, and JIS B2220 for PT and PF threads with K classes. Always check the dimension against the mating standard, because a Class 150 flange and a PN16 flange of the same nominal size are close but not identical.
The tables below give representative dimensions for each family. For procurement, always confirm against the current edition of the standard or the manufacturer's certified drawing.
Pressure classes 150#, 300#, 600#, 900#, 1500# and 2500# all exist in the standard, but threaded ends are normally supplied in 150# and 300#. The values below are Class 150, the most frequently ordered rating.
Thread type: NPT (National Pipe Taper) to ASME B1.20.1 for ASME flanges.
Raised face height: about 1.6 mm (1/16") for Class 150-300, and about 6.4 mm (1/4") for higher classes.
Bolt hole count and bolt circle change with nominal size, so always order bolts against the flange drawing rather than the pipe size.
PN ratings are PN6, PN10, PN16, PN25 and PN40. PN16 and PN40 correspond approximately to Class 150 and Class 300.
Thread type: BSPT (taper) or BSPP/G (parallel). Parallel threads seal on a gasket or O-ring, not on the thread flanks.
PN16 is treated as the practical equivalent of Class 150, and PN40 of Class 300.
EN flanges are dimensioned in millimetres throughout, so bolt patterns are not interchangeable with ASME sizes even where the bores match.
JIS pressure ratings are 5K, 10K, 16K, 20K, 30K, 40K and 63K. Threaded flanges are most common in 10K and 16K.
Thread type: PT (taper, JIS B 0203) or PF (parallel, JIS B 0202).
Confirm K-class pressure-temperature ratings from JIS B2220 for your design condition.
JIS and ASME flanges of the same nominal size do not share a bolt pattern, so a mixed-standard line needs an adaptor or a pair of companion flanges.
Use Class 150 or Class 300, which map to PN10-PN40 and to JIS 10K and 16K. Higher classes exist in the standards but are rarely recommended for threaded ends, because threads lose their grip under high pressure, high temperature and cyclic loading: above Class 300, switch to welded ends.
Three rating systems describe the same idea in different regions: ASME classes in North America, PN ratings under EN 1092-1 in Europe, and K classes under JIS in Japan. The table below shows the practical equivalences for threaded flanges.
Every class rating is temperature-dependent: a Class 300 carbon-steel flange does not carry its full rating at 400 °C. Always read your design pressure against the pressure-temperature table of the governing standard for the specific material, and remember that for a threaded joint the temperature limit of the thread, roughly 300 °C, is normally reached before the pressure limit of the flange is.
Threaded flanges are forged in four material families: carbon steel such as A105, LF2 and A694 for general and low-temperature duty, stainless steel such as A182 F304 and F316L plus duplex F51 and F53 for corrosion resistance, Cr-Mo alloy steel F11, F22 and F91 for high temperature, and nickel alloys including B564 Monel 400, Inconel 625 and Hastelloy C276 for severe corrosion service.
The no-weld advantage matters most in the last row of that table. Field-welding Inconel 625 or Hastelloy C276 demands qualified procedures, matching filler and pickling of the weld zone; a threaded connection avoids all of it. That is why threaded nickel-alloy flanges are routine in chemical equipment and water treatment installations, even though the flange itself costs more per kilogram.
The grades most often ordered for threaded flanges, with the service each one is bought for:
ASTM A105 carbon steel: the default for non-corrosive utilities, air, water and low-pressure steam.
ASTM A350 LF2: the low-temperature carbon steel, impact tested for service down to about -46 °C.
ASTM A182 F304 and F316L: general corrosion resistance for chemical, food and pharmaceutical duty; see stainless steel 316L.
ASTM A182 F321 and F347: stabilized grades for service in the sensitizing range where weld or thermal exposure would otherwise cause intergranular attack.
ASTM A182 F51 (S31803/S32205) and F53 (S32750): duplex and super duplex for chloride and seawater service, see duplex S32205 and super duplex S32750.
ASTM A182 F11, F22 and F91: Cr-Mo alloy steels for high-temperature steam, refining and hydrogen service.
ASTM B564 UNS N04400 (Monel 400): seawater, brine and hydrofluoric acid service, see Monel 400.
ASTM B564 UNS N06625 (Inconel 625): mixed acids, seawater and high-temperature oxidation, see Inconel 625 flanges and the Inconel 625 guide.
ASTM B564 UNS N10276 (Hastelloy C276): the broadest corrosion resistance of the common flange alloys, see Hastelloy C276 flanges and the Hastelloy C276 hub guide.
ASTM B564 UNS N08825 (Incoloy 825) and UNS N08020 (Alloy 20): sulfuric and phosphoric acid service, see Alloy 20 and Incoloy 825.
For deeper material background, see the JN ALLOY guides to stainless steel 304, stainless steel 316 and 316L, 904L stainless, 254SMo and Monel 400.
Choose the flange by joining method, not by price alone: threaded for no-weld small-bore duty up to Class 300; socket weld for small-bore high pressure with vibration; butt weld, usually a weld neck, for critical high-pressure and high-temperature service; slip-on for low-pressure economy in larger sizes; lap joint with stub end where alignment, inspection or alloy cost saving drives the design.
The comparison below is the selection table most buyers ask for. Read the row that matches your pressure and dismantling needs, then confirm the size range covers your line.
Three practical rules shorten the decision. If you cannot weld, choose threaded. If you need more than Class 300, choose welded ends. If the line comes apart more than once a year, choose threaded or lap joint, because every welded flange removal means a cut, a bevel and a re-weld.
Detailed comparisons of individual welded and alloy types are covered in the JN ALLOY guides to Hastelloy C276 flanges, Inconel 600 flanges, Incoloy 825 flanges and duplex S32205 flanges.
Match the gasket to the facing and the bolt torque to the gasket: full-face soft gasket on a flat face, spiral-wound or flexible graphite on a raised face, and bolts tightened in a star pattern in at least three passes. Most threaded joint leaks are gasket or torque faults, not thread faults.
Flat face: use a full-face non-asbestos fibre or EPDM gasket covering the whole face, so bolt load spreads across the full area instead of bending the flange.
Raised face: use a spiral-wound gasket with a centring ring, or flexible graphite, sized to sit on the raised ring and not on the bolt circle.
Bolt-up: tighten in a star pattern in at least three passes, roughly 30%, 70% and 100% of target torque, then re-check after the first thermal cycle.
Lubrication: lubricate bolt threads and nut faces so the torque figure actually produces the intended bolt preload; dry threads can waste half the torque in friction.
Re-torque: a new gasket creeps. Plan a re-torque after 24 hours of service and after the first heat-up.
Where the flange material is much nobler than the pipe, for example a stainless flange on carbon steel pipe in wet service, break the galvanic couple by matching materials or by insulating the joint. Galvanic corrosion at a thread root removes metal from the thinnest section of the assembly first.
Threaded flanges dominate four duty classes: utility and instrument piping in process plants, fuel-gas and fire-protection lines where hot work is banned, maintenance isolation and hydrotest closures, and high-alloy small-bore lines where field welding would be expensive.
Oil and gas and refining: fuel-gas headers, small-bore process lines and repair work on operating units; see JN ALLOY oil and gas solutions.
Chemical and pharmaceutical processing: lines that must stay contamination free and are opened for cleaning, plus alloy threaded flanges on acid circuits in chemical equipment.
Water treatment and marine: duplex and super duplex threaded flanges for chloride resistance and Monel 400 for seawater; see water treatment and marine engineering.
Power and utilities: air, water and low-pressure steam up to Class 300.
Instrumentation: impulse lines and hook-ups, where fittings are forged to ASME B16.11 and the flange must match the fitting class; see forged pipe fittings and pipe nipples.
Aerospace and test rigs: small-bore high-alloy lines that are reconfigured often; see aerospace.
Correct installation is a five-step sequence: verify thread compatibility, seal the thread, screw the flange home without over-torque, seat the gasket, and tighten the bolts in a star pattern to the specified torque. Most threaded joint leaks trace back to a skipped step in this sequence.
Verify thread compatibility. NPT and BSPT are not interchangeable; confirm NPS/DN, class and thread type against the pipe schedule before assembly.
Seal the thread. Wrap the male thread with two or three turns of PTFE tape, or apply anaerobic pipe sealant, winding in the direction of the thread so tightening does not peel it back.
Screw the flange on by hand to full engagement, then wrench-tighten 1.5 to 3 turns beyond finger-tight for taper threads, enough to wedge the thread and not enough to split the flange.
Seat the gasket. Match gasket to facing: non-asbestos or EPDM full-face on flat face, flexible graphite or spiral-wound on raised face, centred on the raised face.
Bolt in a star pattern to the specified torque in at least three passes, 30%, 70% and 100%, and re-check after the first thermal cycle. Safety note: never loosen or break a threaded joint under pressure. Depressurise, drain and lock out the line first, because thread engagement can hide trapped pressure behind the flange face.
Two field checks catch most assembly errors before start-up. First, confirm that the pipe end does not protrude past the flange face; a protruding pipe end prevents the gasket seating. Second, confirm that the flange has not been over-tightened, since a split hub usually cracks at the thinnest section behind the thread.
The three real-world failure modes of threaded flanges are thread loosening under vibration or cyclic load, leak paths through under-sealed threads, and galvanic or crevice corrosion at the thread root. All three are manageable with correct selection and inspection, and none is a reason to avoid the type within its Class 300 and 300 °C envelope.
Vibration is the classic thread killer: a helical wedge needs friction, and sustained vibration un-wedges it. If the line cannot be braced or damped, move to socket-weld or butt-weld ends. Crevice corrosion concentrates in the thread gap of stainless joints in chloride media, and the answer is a higher-alloy grade such as duplex F51 or super duplex S32750 rather than more sealant. Galvanic couples between carbon-steel pipe and a stainless flange in wet service should be broken by matching the flange material to the pipe.
A complete threaded flange purchase order names seven things: the dimensional standard, the nominal size, the pressure class, the thread standard, the facing, the material specification with grade, and the certification required. Miss any one of them and the quotation cannot be compared like for like.
Dimensional standard: ASME B16.5, EN 1092-1 or JIS B2220, and state the edition.
Nominal size and schedule: NPS or DN, plus the pipe schedule the external thread will be cut on.
Pressure class: Class 150 or Class 300 in practice, or the PN or K rating.
Thread standard: NPT to ASME B1.20.1, BSPT or BSPP, or PT or PF for JIS work.
Facing: flat face or raised face, and the raised face height if the class is above 300.
Material: the ASTM or EN specification and grade, for example ASTM A182 F316L or ASTM B564 N10276.
Certification: EN 10204 3.1 as a minimum, plus impact testing and any NDE the code requires.
A worked example: ASME B16.5 threaded flange, NPS 2", Class 300, NPT thread to ASME B1.20.1, raised face, ASTM A182 F316L, 20 off, EN 10204 3.1 certification, impact tested to -46 °C. Send that line, or your drawing, to JN ALLOY through the contact page and you will get a comparable quotation back.
If you are still choosing between types, the JN ALLOY flange product range lists the full set, including slip-on flanges, socket weld flanges, weld neck flanges, orifice flanges, spectacle blinds and plate flanges.
Inspect a threaded joint on three occasions: at assembly, after the first thermal cycle, and on a periodic walk-down if the line vibrates. The inspection itself takes minutes and catches the two faults that matter, loosening and crevice corrosion.
At assembly: confirm thread engagement, confirm the pipe end does not protrude past the face, and confirm the gasket is centred and undamaged.
After the first thermal cycle: re-check bolt torque, because new gaskets creep and the taper thread settles.
Periodic: on vibrating or cycling lines, listen and look for weeping at the thread, and check for corrosion product at the thread-crevice line.
On every break: treat the male thread and the gasket as consumable. Clean and re-tape the thread and fit a new gasket.
Records: keep the heat number and the EN 10204 certificate against the line tag so the material can be traced years later.
A threaded flange screws onto the pipe thread, so it needs no welding, no welder and no hot work permit.
Its service envelope is DN15-DN150 (1/2"-6"), Class 150-300, and roughly 300 °C; beyond any of those three, choose welded ends.
NPT, BSPT and BSPP are not interchangeable, and ASME, EN and JIS flanges do not share bolt patterns.
The thread grips and gives a secondary seal; the gasket is the primary pressure boundary, so gasket selection and star-pattern torque decide whether the joint leaks.
Material choice follows the service: A105 for utilities, F316L for chemical duty, duplex and Monel for seawater, B564 nickel alloys for severe corrosion.
Threaded flanges win on installed cost and on disassembly; they lose on vibration, thermal cycling and high class duty.
Specify all seven purchase-order items, standard, size, class, thread, facing, material and certification, and you will get quotations that can actually be compared.
A threaded flange connects small-diameter pipes, valves and instruments without welding: it screws directly onto the pipe's external thread (NPT or BSPT). It is the preferred connection wherever hot work is forbidden, for example on fuel-gas lines, repairs on operating plants and in hazardous areas, and on high-alloy piping where field welding is costly. Typical duty is DN15-DN150 (1/2"-6") at Class 150-300.
ASME B16.5 flanges use NPT (tapered) threads to ASME B1.20.1; EN 1092-1 flanges use BSPT (tapered) or BSPP/G (parallel). NPT and BSPT both seal on the thread flanks with sealant, while parallel BSPP seals on a bonded gasket or O-ring at the end face. The two families share nominal sizes but are not interchangeable: a 1" NPT male will not seal in a 1" BSPT female.
Choose Class 150 for utilities and Class 300 as the practical upper limit. Class 600 and higher threaded flanges exist in the standards but are rarely recommended, because a thread can loosen under high pressure, temperature cycling or vibration. Above Class 300, switch to socket-weld or butt-weld ends. European equivalents are PN16 for Class 150 and PN40 for Class 300.
Yes. Common forgings include ASTM A182 F304/304L and F316/316L stainless, F321 and F347 stabilized grades, F51 and F53 duplex for chloride service, and ASTM B564 nickel alloys such as UNS N04400 (Monel 400), N06625 (Inconel 625) and N10276 (Hastelloy C276). The no-weld advantage is greatest with nickel alloys, because it avoids qualified weld procedures and weld-zone pickling.
About 300 °C is the practical service ceiling for a threaded joint, and that limit is set by thread loosening rather than by the metal. ASME pressure-temperature tables allow several forged grades to go higher, but sustained operation above roughly 300 °C, or severe thermal cycling, should move to welded flange ends for long-term leak integrity.
Seal the thread and control the torque. Wrap the male thread with two or three turns of PTFE tape or apply anaerobic pipe sealant, wrench-tighten 1.5 to 3 turns beyond finger-tight, use the correct gasket for the raised or flat face, tighten bolts in a star pattern to specification, and re-check after the first thermal cycle. Inspect vibration-exposed joints periodically for loosening.
Yes. Threaded flange, screwed flange and screwed-on flange are three names for the same ASME B16.5 type: a flange whose bore carries an internal pipe thread. The term "threaded flange" is standard in North America, while "screwed flange" is common in older British and Commonwealth pipework specifications. Both describe a flange with no weld to the pipe.
Not as a pressure-retaining weld. A standard threaded flange is designed to grip the pipe mechanically, and adding a fillet weld over the thread does not reliably seal the helical leak path and can crack the thread root. If your design needs a weld, specify a socket-weld threaded hybrid, which has a socket recess behind the thread that takes a proper fillet weld, or move to a socket weld flange or weld neck flange.
Yes. The thread does the mechanical gripping and gives a secondary seal once tape or dope is applied, but the primary pressure boundary is the gasket between the two flange faces. Use a full-face non-asbestos or EPDM gasket on a flat face, and a flexible graphite or spiral-wound gasket centred on a raised face.
Standard stock runs from DN15 to DN150, that is 1/2" to 6" NPS. Above 6" the wrench torque needed to make a threaded joint rises steeply, the pressure capability of the thread falls, and a welded flange becomes cheaper and safer. Large-diameter lines therefore use slip-on, weld neck or lap joint types.
ASME B31.3 permits threaded joints, but with restrictions set out in the chapter on joints: they are limited to smaller nominal sizes, they are not permitted where severe erosion, crevice corrosion, shock or vibration is expected, and they are excluded from the more severe fluid service categories. Confirm the size limit and fluid service category against the current edition of the code before specifying.
NPT (National Pipe Taper) is a tapered thread that wedges tight and seals on the thread flanks with sealant. NPS (National Pipe Straight) is a parallel thread that does not seal on the flanks and needs a gasket, O-ring or seal weld. Flanges used for pressure piping are normally NPT to ASME B1.20.1.
Yes, provided the external thread can be cut to the full ASME B1.20.1 length and the remaining wall still meets the code minimum. Heavy wall such as Schedule 80 and Schedule 160 leaves less metal at the thread root after cutting, so confirm the remaining wall thickness against the design code, and note that cutting a thread always removes material from the thinnest part of the joint.
There is no code limit, but good practice is to treat the male thread as consumable. Each make-up work-hardens the taper thread and compresses the sealant, so plan to clean and re-tape the thread and fit a new gasket every time the joint is broken. If a line is opened more than a few times a year, a lap joint with a stub end is usually the more economical long-term design.
They do, provided the alloy matches the chloride load. Duplex F51 and super duplex F53 resist chloride pitting and crevice attack, and Monel 400 is the traditional choice for seawater and brine. In seawater the thread crevice is the weak point, so specify the higher alloy plus a crevice-resistant gasket rather than relying on sealant. See JN ALLOY marine engineering for service guidance.
Vibration and thermal cycling. A taper thread is a helical wedge held by friction, and repeated pressure or temperature reversals walk it back until friction alone cannot hold the joint. Crevice corrosion at the thread root and galvanic attack between dissimilar pipe and flange metals accelerate the process. Brace the line, match the flange alloy to the pipe, and re-torque after the first cycle.
A compliant ASME B16.5 forging is stamped with the manufacturer's name or trademark, the material specification and grade such as ASTM A182 F316L, the pressure class, the nominal size, the thread standard, and the heat number for traceability. Ask your supplier for the EN 10204 3.1 certificate that matches the heat number before the flange goes into service.
The flange itself is usually cheaper to install than a slip-on flange, because a slip-on needs two fillet welds plus a welder, welding consumables and inspection. On paper the slip-on flange body can be the cheaper item; on an installed-cost basis the threaded flange usually wins in sizes up to 4". See the slip-on flange page for the welded alternative.
Yes, for low-pressure steam up to Class 300 and within the joint temperature limit of roughly 300 °C. Above that, carbon steel loses allowable stress and the thread loosens, so welded ends are specified. For saturated steam at typical plant pressures, a Class 300 threaded flange with a spiral-wound gasket is a standard, serviceable choice.
State the standard, nominal size, pressure class, thread type, facing, material specification and grade, quantity, and the certification you need. For example: ASME B16.5 threaded flange, NPS 2", Class 300, NPT thread per ASME B1.20.1, raised face, ASTM A182 F316L, 20 off, EN 10204 3.1, with impact test if the design temperature requires it. Send the drawing to JN ALLOY for a quotation.
Standards and sources behind the dimensions, ratings and material grades quoted in this guide:
ASME B16.5, Pipe Flanges and Flanged Fittings: NPS 1/2 through NPS 24, the governing dimensional standard for ASME threaded flanges.
ASME B1.20.1, Pipe Threads, General Purpose (Inch): the NPT thread form and engagement lengths.
ASME B16.11, Forged Fittings, Socket-Welding and Threaded: the 3000# and 6000# classes used for small-bore hook-ups.
ASME B16.47, Large Diameter Steel Flanges: NPS 26 through NPS 60, referenced where large-diameter companion flanges are needed.
ASME B31.3, Process Piping: the restrictions on where threaded joints may be used.
EN 1092-1, Flanges and their joints: circular flanges for pipes, valves, fittings and accessories, PN designated.
JIS B2220, Steel pipe flanges: the K-class rating system used in Japan.
ASTM A105, A350, A182, A694 and B564: the forging specifications for carbon, low-temperature, stainless, high-yield and nickel alloy flanges.
MSS SP-43 and MSS SP-44: stub ends and steel pipeline flanges used in lap joint and large-diameter assemblies.
JN ALLOY product and application references: threaded flanges, flange range, Inconel 625, Hastelloy C276, Monel 400, duplex S32205, Alloy 20, oil and gas, chemical equipment.
Threaded flanges are one of JN's specialties. As a flange manufacturer in China, we specialize in custom flanges ranging from 1/2 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. Browse the full product catalogue or start with the threaded flange product page.
