Flange Dimension Quick View: Sizes, Specs & Standards

Flange Dimension Quick View — Fast Reference ChartA clear, concise flange dimension quick view chart is an essential tool for engineers, designers, fabricators, and maintenance personnel who work with piping systems. This article provides a comprehensive reference covering common flange types, standard dimensions, selection tips, measurement methods, and quick lookup charts you can use on the job or include in design documentation.

What is a flange?

A flange is a projecting flat rim, collar, or rib on a component used for strength, alignment, or attachment. In piping systems, flanges are used to connect pipes, valves, pumps, and other equipment to create a sealed joint that can be assembled and disassembled for maintenance. Flanges are typically joined by bolting and sealed with gaskets.

Common flange types

• Weld neck flange: Tapers to a long hub and is welded to the pipe. Good for high-pressure and cyclic applications.
• Slip-on flange: Slides over the pipe and is fillet-welded. Easier to align and install but less strong than weld neck.
• Blind flange: Solid plate used to close off a pipeline or vessel opening.
• Socket weld flange: Pipe inserts into a recessed area and is fillet-welded; used for smaller pipe sizes and higher pressures.
• Threaded (screwed) flange: Threads onto the pipe; used where welding is impractical.
• Lap joint flange: Used with a stub end; beneficial for frequent disassembly.
• Ring-type joint (RTJ) flange: Uses a metal ring gasket for high-pressure and high-temperature applications.

Standard flange dimensions and specifications

Flanges are manufactured to international standards that specify dimensions, materials, pressure ratings, and testing requirements. Common standards include:

• ASME/ANSI B16.5 — Pipe flanges and flanged fittings for NPS ⁄₂ through 24 and pressure classes up to 2500.
• ASME B16.47 — Large diameter steel flanges NPS 26 through 60 (Series A and B).
• EN 1092-1 — European standard for flanges (PN ratings).
• ISO 7005 — International standard for metallic flanges.
• API 6A — Flanges and bolting for the oil and gas industry (wellhead equipment).

Key dimensional parameters specified by these standards include:

• Nominal Pipe Size (NPS) or DN (diameter nominal)
• Pressure class (e.g., 150, 300, 600, 900, 1500, 2500 for ASME)
• Outside diameter (OD) of the flange
• Bolt circle diameter (BCD) or pitch circle diameter (PCD)
• Number of bolt holes
• Diameter of bolt holes
• Hub diameter and thickness
• Flange thickness (face-to-face or raised face height)
• Raised face (RF) or flat face (FF) or ring joint (RJ) dimensions

Quick reference measurement terms

• Bore (D): Internal diameter of the flange matching the pipe bore.
• Outside Diameter (OD): Full outside diameter of the flange body.
• Pitch Circle Diameter (PCD): Diameter of the circle that passes through the centers of the bolt holes.
• Bolt Hole Diameter (d): Diameter of each bolt hole.
• Number of Bolts (n): Total bolt holes equally spaced around the PCD.
• Flange Thickness (t): Thickness of the flange between the face and the back.
• Raised Face (RF) Height (h): Height of the raised sealing surface above the flange face.
• Hub Diameter (H): Diameter of the welded hub (for weld neck flanges).
• Bore Tolerance: Allowable variation for bore to fit pipe.

Example quick reference charts (ASME B16.5 — common sizes)

Below are compact charts for some commonly used ASME B16.5 flange sizes and classes. Values are illustrative; always verify with the applicable standard or manufacturer’s data before fabrication.

• NPS ⁄₂, Class 150: OD = 95 mm, PCD = 60 mm, n = 4, bolt dia = 14 mm, t = 14 mm, RF h = 2 mm
• NPS 1, Class 150: OD = 114 mm, PCD = 75 mm, n = 4, bolt dia = 14 mm, t = 15 mm, RF h = 2 mm
• NPS 2, Class 150: OD = 152 mm, PCD = 110 mm, n = 4, bolt dia = 18 mm, t = 19 mm, RF h = 2 mm
• NPS 4, Class 150: OD = 229 mm, PCD = 180 mm, n = 8, bolt dia = 18 mm, t = 23 mm, RF h = 2 mm
• NPS 8, Class 150: OD = 318 mm, PCD = 266 mm, n = 8, bolt dia = 22 mm, t = 27 mm, RF h = 2 mm

How to use a quick view chart effectively

1. Identify the pipe nominal size (NPS/DN) and pressure class.
2. Confirm the flange face type (RF, FF, RJ) required for your gasket and service conditions.
3. Cross-check the flange OD, PCD, bolt count and bolt hole diameter to ensure proper mating with existing components.
4. Verify material and rating compatibility (temperature, pressure, corrosion).
5. For weld neck flanges, confirm hub dimensions and bevel preparation for welding.
6. When in doubt, reference the full ASME/EN/ISO standard or supplier drawings.

Selection tips and common pitfalls

• Mismatched flange faces (RF vs FF) can cause sealing failure — always match face types.
• Bolt length must account for flange thickness, gasket thickness, and nut engagement.
• Ring-type joint flanges require precise groove dimensions and gaskets — do not substitute RF gaskets.
• For retrofit work, measure the existing PCD and bolt hole diameters rather than assuming sizes.
• Consider corrosion allowances and coatings for service in aggressive environments.

Measurement and inspection best practices

• Use calipers or micrometers for bore, bolt hole diameter, and raised face height.
• Use an engineered template or coordinate measuring machine (CMM) to verify PCD and bolt hole positions for precision applications.
• Inspect flange faces for warpage and surface finish because sealing depends on flatness and finish.
• Check bolts and nuts for grade markings and full engagement; torque according to standard bolting procedures (e.g., cross-pattern tightening).

Example application scenarios

• Plant maintenance: Keep a laminated quick view chart with common flange sizes in the tooling area to speed part identification.
• Design office: Include a one-page flange quick view in project specifications for fast reference by engineers and drafters.
• Fieldwork: Use a smartphone photo of the chart for rapid on-site verification when replacing flanged components.

Quick printable checklist (one-line format)

• Confirm NPS/DN and pressure class.
• Verify flange face type.
• Check OD, PCD, bolt count and bolt hole dia.
• Confirm material and temperature rating.
• Measure and confirm hub/weld prep (if applicable).
• Verify gasket type and dimensions.
• Determine correct bolt length and torque.

Closing notes

A well-organized flange dimension quick view chart saves time and reduces errors across design, fabrication, and maintenance activities. Always validate critical dimensions against the relevant standard (ASME/EN/ISO) or supplier drawings before finalizing designs or purchasing components.