Flanges, like all pipe fittings, have two sets of specifications, one that defines the dimensions and one that defines the material.
To order flanges, you will need both specifications, along with the flange type, the pipe size and schedule (or pipe OD & ID), the pressure class, the flange facing, and the material type. Don't worry, if you don't have all this, we can help you figure it out.
Part 1 (PART 2)
Here is a list of the most Common Pipe Flange Dimensional Specifications and What They Define
Flange dimensional specifications establish critical measurements, pressure ratings, and tolerances for the manufacture, inspection, and interchangeability of pipe flanges.
They ensure that flanges from different manufacturers fit properly and perform safely within defined pressure and temperature limits.
ASME / ANSI Standards (U.S.)
|
Specification |
Title |
Defines |
|
ASME B16.1 |
Cast Iron Pipe Flanges and Flanged Fittings |
Dimensions, drilling, facing, pressure ratings, and tolerances for gray and ductile iron flanges. |
|
Pipe Flanges and Flanged Fittings |
The most common standard defines dimensions, tolerances, facing, bolting, and pressure–temperature ratings for steel flanges sizes ½" to 24" in Classes 150–2500. |
|
|
ASME B16.24 |
Bronze Pipe Flanges and Flanged Fittings |
Covers copper alloy (bronze/brass) flanges, their dimensions, drilling, pressure–temperature ratings, and materials. |
|
ASME B16.36 |
Orifice Flanges |
Defines orifice flange dimensions, pressure ratings, and drilling for flow measurement assemblies. |
|
ASME B16.42 |
Ductile Iron Pipe Flanges and Flanged Fittings |
Similar to B16.5 but for ductile iron — includes dimensions, pressure classes, and drilling patterns. |
|
ASME B16.47 |
Large Diameter Steel Flanges (NPS 26–60) |
Extends flange size range beyond B16.5, covering Series A (MSS SP-44) and Series B (API 605) flanges. Defines dimensions, bolting, and facing. |
|
ASME B16.48 |
Line Blanks |
Specifies spectacle blinds, spades, and spacers for blocking or isolating piping systems. |
API (American Petroleum Institute) Standards
|
Specification |
Title |
Defines |
|
API 6A |
Specification for Wellhead and Christmas Tree Equipment |
Flange dimensions, pressure ratings, and materials used in oilfield wellhead and high-pressure systems. |
|
API 605 |
Large Diameter Carbon Steel Flanges |
The predecessor to ASME B16.47 Series B, defines large-diameter flange dimensions and drilling for pipeline use. |
|
API 590 / API RP 590 |
Steel Flanges and Bolting for Refinery Piping |
Provides recommendations for materials, ratings, and manufacturing tolerances in refinery and process plant applications. |
MSS (Manufacturers Standardization Society) Standards
|
Specification |
Title |
Defines |
|
MSS SP-6 |
Standard Finishes for Contact Faces of Pipe Flanges and Fittings |
Defines surface finish (facing) requirements, such as serrated or smooth finishes for gasket sealing. |
|
MSS SP-9 |
Spot Facing for Bronze, Iron, and Steel Flanges |
Covers machining tolerances and finish for flange spot faces. |
|
MSS SP-25 |
Standard Marking System for Valves, Fittings, Flanges, and Unions |
Defines identification markings (manufacturer, material, pressure class, etc.) required on flanges. |
|
MSS SP-44 |
Steel Pipeline Flanges |
Defines pipeline flange dimensions for large-diameter, high-strength systems; later adopted into ASME B16.47 Series A. |
|
MSS SP-51 |
Class 150LW Flanges and Flanged Fittings, Cast Iron |
Defines lightweight flanges and fittings for low-pressure cast iron service. |
|
MSS SP-53 |
Quality Standard for Steel Castings for Flanges |
Specifies casting quality, NDE, and inspection for flange manufacturing. |
International Standards (ISO / EN / DIN / BS)
|
Specification |
Title |
Defines |
|
ISO 7005 |
Metallic Flanges |
Global standard that aligns with ASME B16.5 — defines dimensions, pressure ratings, and types (steel, cast iron, copper alloy). |
|
EN 1092-1 |
Flanges and Their Joints — Steel Flanges |
European equivalent of ASME B16.5, covering PN pressure ratings, dimensions, and tolerances. |
|
DIN 2633 / 2634 / 2635, etc. |
German Standards for Steel Flanges |
Define flange dimensions and pressure ratings (PN10–PN400) for German and EU industrial piping. |
|
BS 4504 / BS EN 1092 |
British Standard for Circular Flanges |
Defines dimensions, tolerances, and pressure designations (PN) for UK-based systems. |
|
JIS B2220 |
Japanese Industrial Standard — Steel Pipe Flanges |
Defines flange dimensions, bolt holes, and pressure ratings (5K–30K) for Japanese piping. |
What These Standards Define
Most flange dimensional specifications include detailed definitions for:
- Nominal Pipe Size (NPS) / Diameter (DN)
- Pressure Class or Rating (Class 150, 300, PN16, etc.)
- Flange Type – Weld neck, slip-on, threaded, socket weld, blind, lap joint, etc.
- Bolt Circle and Hole Diameter
- Facing Type – Raised face (RF), flat face (FF), ring-type joint (RTJ), tongue-and-groove, etc.
- Hub Dimensions
- Thickness (T)
- Outside Diameter
These parameters ensure interchangeability and compatibility between flanges, gaskets, and bolts in piping systems across industries.
Summary
In short:
- ASME B16.5 → The core standard for most industrial steel flanges.
- ASME B16.47 → Large diameter flanges.
- API & MSS → Specialized pipeline and oilfield service standards.
- ISO / EN / DIN / JIS → International equivalents ensuring global compatibility.
Together, these specifications define every dimensional, mechanical, and rating aspect required to design, build, and maintain pressurized piping systems safely.
