Sep. 29, 2026
A threaded pipe flange is a flanged fitting with internal threads that connect directly to the external threads on a pipe. Unlike a weld neck or slip-on flange, it normally does not require welding during installation, which can simplify work where hot work is restricted or impractical. I recommend using a threaded pipe flange when the pipe material, wall thickness, service conditions, and thread compatibility are all suitable for a threaded connection. For high-temperature, high-cyclic, or highly critical services, I advise buyers to evaluate a welded flange alternative with an engineer before ordering.
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A threaded pipe flange, also called a screwed flange in some markets, has a female thread machined into the bore. The pipe is prepared with a matching male thread and then screwed into the flange. Bolts pass through the flange holes to connect it to another flanged component, such as a valve, pipe spool, equipment nozzle, or second flange.
The flange creates a bolted connection and provides a face for a gasket where the joint design requires one. The threaded bore transfers the connection to the pipe without a field weld. Because the pipe is not welded to the flange, installation can reduce the need for welding equipment, welding procedures, and post-weld activities, although proper assembly and inspection remain essential.
The primary function is to join a threaded pipe to another flanged component in a way that can be disassembled. This is useful for maintenance, equipment replacement, and modular piping layouts. The bolted flange connection also allows the installer to select a suitable gasket and tightening method for the service.
Threaded flanges are manufactured with standardized outside diameters, bolt-hole arrangements, flange thicknesses, and bore dimensions when produced to a recognized dimensional standard. ASME B16.5, for example, covers many flanges and flanged fittings from NPS 1/2 through NPS 24, although the applicable standard must be confirmed for the project. I do not recommend selecting a flange by nominal size alone because pressure class, facing, thread form, and material are equally important.
In areas where hot work permits, welding access, or welding inspection creates project challenges, a threaded connection may be more convenient. This does not mean that threading is suitable for every service. The connection still requires accurate machining, compatible threads, controlled tightening, and an engineering review when pressure, temperature, vibration, or safety consequences are significant.
I generally suggest evaluating a threaded pipe flange for relatively small-diameter piping, utility lines, instrument connections, and systems where field welding is restricted. It can also be considered for installations that need a removable flanged connection without welding the flange to the pipe. The actual decision should be based on the piping code, design pressure, design temperature, fluid, pipe wall, vibration level, and maintenance requirements.
Threaded flanges are often easier to consider in smaller sizes because thread engagement and installation torque become more demanding as pipe size increases. The maximum practical size is not determined by flange dimensions alone; it also depends on pipe wall thickness, thread strength, installation access, and the governing design code. I recommend obtaining written technical approval before using a threaded connection in a critical process line.
A threaded pipe flange may be a poor choice for severe vibration, repeated thermal cycling, high bending loads, or services where leakage has serious consequences. The threaded joint can be affected by assembly quality, thread damage, corrosion, and differential movement between components. For these conditions, a weld neck, socket weld, or another engineered connection may provide a more appropriate design solution.
Threading also removes material from the pipe wall and requires sufficient wall thickness for safe thread engagement. Thin-wall pipe may not provide the required strength or sealing reliability. Corrosive fluids, hazardous media, elevated temperatures, and frequent pressure fluctuations deserve particular attention from the responsible engineer.
The flange facing determines how the flange contacts the gasket and the mating flange. Raised face, flat face, and other facing arrangements may be specified depending on the standard and application. The mating flange, gasket, bolt set, and tightening procedure must be compatible; mixing unplanned facing or bolting configurations can compromise joint performance.
For stainless steel pipe systems, common material discussions may include austenitic grades such as 304 or 316, subject to the purchaser’s specification and the service environment. Grade selection should consider chloride exposure, chemical compatibility, temperature, cleaning agents, and galvanic contact with other metals. I provide material options according to the required standard and documentation rather than treating one stainless steel grade as suitable for every application.
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Carbon steel, alloy steel, duplex stainless steel, and other materials may be considered for different combinations of strength, corrosion resistance, temperature, and cost. Availability, machinability, and thread quality should also be reviewed before finalizing the material. If the project requires a specific chemical composition, heat treatment, inspection record, or marking method, those requirements should appear clearly in the purchase specification.
Before ordering, I recommend confirming the nominal pipe size, flange standard, pressure class, facing type, bore, thread standard, material grade, and dimensional tolerances. ASME pressure classes commonly include Class 150, Class 300, and higher classes, but the correct class must be selected from the system design rather than from price or availability. The thread designation should identify the applicable thread form and size, such as NPT or another regional standard where appropriate.
| Specification | Why It Matters |
|---|---|
| Nominal size | Must match the pipe and connected equipment. |
| Pressure class | Determines the applicable dimensional and pressure-rating requirements. |
| Thread type | Must match the pipe thread to achieve proper fit and engagement. |
| Material grade | Influences corrosion resistance, strength, and service compatibility. |
| Facing and bore | Must align with the mating flange, gasket, and pipe configuration. |
| Inspection and marking | Support identification, incoming inspection, and project traceability. |
For dimensional planning, buyers should pay attention to the complete flange envelope, not only the nominal bore. A threaded pipe flange may be supplied for sizes such as 1/2 in or larger sizes up to the limit of the selected standard, but product availability and engineering suitability can differ by material and pressure class. I can review a drawing or specification sheet to identify missing details before quotation.
Start with the medium, operating pressure, operating temperature, design pressure, design temperature, and expected vibration. Add information about outdoor exposure, corrosive chemicals, cleaning cycles, and installation limitations. These factors determine whether a threaded flange is appropriate at all.
Confirm the pipe outside diameter, wall thickness, thread form, thread size, and available thread length. Do not assume that two components are compatible because they share the same nominal size. Thread standards, pitch, taper, and tolerances must be checked against the project requirements.
Verify the pressure class, facing, bolt-hole pattern, flange thickness, gasket dimensions, and mating component. The flange should be compatible with valves, pumps, tanks, or other equipment in the line. If the piping system includes a different flange standard, an adapter or revised design may be required.
Specify quantity, packaging, marking, material documentation, inspection requirements, and delivery expectations. Minimum order quantity and lead time can vary with size, material, machining complexity, and whether the item is standard or customized. I recommend requesting a formal quotation that lists every technical assumption.
At Longrun, I support buyers sourcing threaded pipe flanges for stainless steel pipe and related piping applications. Our technical discussion can cover size, pressure class, thread standard, flange facing, material grade, dimensions, surface condition, marking, packaging, and required documents. This helps reduce the risk of quoting a flange that looks correct by size but does not match the full connection design.
For repeat orders, I can also help establish a consistent specification and inspection checklist for future purchasing. For custom requirements, buyers should provide a drawing, applicable standard, material specification, quantity, and delivery destination. Where the application is outside normal threaded-flange use, I will recommend that the purchaser obtain approval from the responsible piping or mechanical engineer rather than relying on a catalog selection.
A threaded pipe flange is a practical option when you need a detachable flanged connection without field welding and when the pipe, thread, material, pressure, and service conditions support that design. It is most suitable for selected small-bore and utility applications, but it should not be treated as a universal replacement for welded flanges. The next step is to confirm the service data, pipe and thread details, flange standard, pressure class, facing, and material grade.
Send Longrun your required size, thread type, material, pressure class, quantity, and technical drawing if available. I can then help clarify the specification and prepare a B2B quotation for your threaded pipe flange requirements.
Contact us to discuss your requirements of Threaded Pipe Flange. Our experienced sales team can help you identify the options that best suit your needs.
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