Threaded Pipe Flange: Types, Standards, Applications, and Selection Guide

A threaded pipe flange connects to a pipe through internal threads rather than a welded joint. It can be useful when welding is impractical or undesirable, but correct selection depends on matching the flange thread to the pipe, confirming the applicable flange standard and pressure-temperature rating, and checking whether threaded construction suits the service conditions. A flange’s pressure class alone does not establish a safe operating pressure for every material and temperature.

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In this guide, we explain common threaded flange options, relevant standards, typical applications, and a practical purchasing checklist. At Longrun, we recommend that buyers share the complete piping specification—not just the nominal pipe size—when requesting a quotation.

Who This Guide Is For

This guide is for engineers, procurement teams, distributors, and project buyers sourcing threaded pipe flanges, including those used with stainless steel piping. It is intended to help you prepare a specification and compare supplier offers. Final selection should follow the project’s governing code, design documents, and qualified engineering review.

How a Threaded Pipe Flange Works

Basic design and function

A threaded flange has internal threads in its hub or bore that engage with external threads on a pipe. The flange face is then bolted to a matching flange, valve, or other piping component, with a gasket selected for the service. The threaded connection avoids a flange-to-pipe weld, but it does not remove the need to verify thread engagement, sealing method, alignment, and bolting requirements.

Threaded flanges are sometimes called screwed flanges. The term describes how the flange attaches to the pipe; it does not by itself define the flange’s facing, material, dimensions, pressure rating, or thread form. Those details must be specified separately.

Types, Materials, and Standards

Thread forms and flange styles

Common pipe thread systems include NPT, BSPT, and BSPP. NPT is a tapered thread form covered by ASME B1.20.1, while BSPT and BSPP refer to different British Standard Pipe thread forms addressed by separate standards. These thread forms are not interchangeable by default, so buyers should state the required designation and standard rather than using a general description such as “pipe thread.”

Flange design and dimensions are a separate specification from the pipe thread. ASME B16.5 covers pipe flanges and flanged fittings in its stated scope, including nominal pipe sizes from NPS 1/2 through NPS 24; this scope does not mean that every flange type, class, material, or size combination is available. European projects may use EN 1092-1, while other projects may specify different standards. Confirm the governing standard and edition with the project documents and supplier.

Materials for stainless steel piping

Stainless steel threaded flanges may be specified in grades such as 304 or 316, subject to the relevant product standard and service requirements. Grade selection should account for the process fluid, temperature, corrosion exposure, and the material of the connected pipe and mating flange. A grade name alone is not enough: ask for the applicable material specification, product form, and any required traceability documents.

Dimensions, pressure class, and sealing

Nominal pipe size is a designation, not a direct measurement of the pipe’s outside diameter. For example, NPS 2 pipe has an outside diameter of 2.375 in under standard pipe dimension tables; its wall thickness depends on the specified schedule. The flange bore and thread must be ordered to suit the actual pipe specification, not inferred from nominal size alone.

ASME B16.5 includes pressure classes from Class 150 through Class 2500 within its scope, but these class numbers are not direct pressure values in psi. Allowable pressure depends on factors including material and temperature, and not all classes apply to all product configurations. Confirm the applicable pressure-temperature table and design conditions rather than treating a class marking as a universal working-pressure guarantee.

Flange facing and gasket details also matter. A raised face, flat face, or other specified facing must match the mating equipment and project requirements. The threaded pipe connection and the bolted flange joint are distinct interfaces, and both need an appropriate installation and sealing method.

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Applications and Suitability

Threaded flanges may suit piping where welding is restricted, where field welding is inconvenient, or where a mechanically assembled connection is preferred. They can be considered for certain utility, maintenance, and process connections when the design code and operating conditions permit. Their suitability must be assessed for the actual pressure, temperature, fluid, and installation environment.

They are not automatically the best choice for every line. Thread roots can create potential leakage paths, and threaded connections may be less suitable where vibration, thermal cycling, or severe cyclic loading is a concern. For hazardous or highly critical services, engineering requirements may call for a different connection type, additional controls, or a project-specific qualification.

Selection Framework for Buyers

Step 1: Define the service conditions

Record the design pressure and temperature, fluid composition, corrosion considerations, and any vibration or cycling concerns. Include the applicable piping code and project requirements. These inputs determine whether a threaded connection is permitted and help establish the material and rating requirements.

Step 2: Match the pipe and thread

Specify nominal pipe size, pipe schedule or wall thickness, and the required thread standard and designation. State whether the thread is NPT, BSPT, BSPP, or another specified form, and clarify any thread direction or inspection requirement that applies. Do not assume that similar-looking threads will seal or fit correctly.

Step 3: Confirm the flange interface

Identify the flange standard, pressure class or rating, facing, material grade, and required dimensions. Check the mating flange, gasket, and bolting details as a complete joint. If the project uses a non-standard, legacy, or mixed-standard connection, provide drawings and request confirmation before ordering.

Step 4: Review documents and supply details

Before placing an order, agree on inspection scope, marking, documentation, packaging, and delivery terms. Ask the supplier to identify any exclusions or deviations from the inquiry. For projects requiring material test reports, special inspection, or traceability, state these requirements in the request for quotation.

Pricing, MOQ, and Lead Time

Threaded flange pricing can vary with material grade, size, pressure class, standard, thread form, facing, order quantity, and documentation or inspection requirements. Minimum order quantities and lead times depend on the requested specification and current production or stock position, so they should be confirmed in a written quotation. Comparing prices is most useful when each supplier is quoting the same complete specification.

Supplier Evaluation Checklist

• Can the supplier confirm the flange standard, thread standard, material, size, class, and facing against your inquiry?
• Will the quotation clearly state any limitations, substitutions, or deviations?
• Can the supplier provide the documents and identification required by your project?
• Are inspection expectations, packaging, delivery terms, and order quantities stated clearly?
• Can the supplier support technical clarification before production and shipment?

At Longrun, we work with B2B buyers sourcing stainless steel piping products and related flange requirements. Share your drawing or specification, service conditions, quantity, and destination so our team can review the requested details and confirm availability, documentation, and commercial terms for your inquiry.

Key Takeaways and Next Steps

A threaded pipe flange joins to pipe through matching internal and external threads, making it a possible option where a welded attachment is not preferred or practical. The right choice depends on more than nominal size: verify the thread form, flange standard, material, pressure-temperature requirements, facing, and service suitability together. Threaded construction should be evaluated carefully where vibration, cycling, or leakage consequences are significant.

To move toward a reliable purchase, prepare a complete specification and have the supplier confirm it in writing before ordering. Include the pipe size and schedule, thread standard, flange standard and class, material, facing, operating conditions, quantity, documentation needs, and delivery location. Contact Longrun with these details to discuss your stainless steel flange sourcing requirements and request a project-specific quotation.