In complex industrial piping systems, every connection point is critical. A minor oversight can lead to leaks, downtime, or even safety incidents. Flanges, as key components of pipe connections, directly impact the safety and reliability of entire systems through their selection, standards, and sealing materials. But do you truly understand how to correctly choose and apply flanges?

This guide provides a comprehensive and practical solution for flange connections, covering identification, types, standards, pressure ratings, sealing materials, and relevant specifications to help professionals in water treatment, construction, HVAC, and other industries confidently address various flange connection challenges.

I. Flange Identification and Types

As common connecting elements in piping systems, flanges come in numerous varieties with diverse standards. Accurate identification of flange types and specifications is essential for proper selection.

1. Decoding Flange Identification Codes

Take BS4504 / 111 / B – PN16 – DN400 - B4 - XXXX – 654321 as an example to interpret each component of the flange identification code:

• British Standard : BS4504 indicates compliance with British Standard BS4504.
• Flange Code Number : 111 is the code number distinguishing different flange types.
• Flange Face Type : B represents the sealing face type, possibly indicating Raised Face.
• Nominal Pressure : PN16 denotes a pressure rating of 16 bar.
• Nominal Diameter : DN400 signifies a 400mm nominal diameter.
• Material Designation : B4 identifies the material grade, potentially a specific carbon steel.
• Manufacturer : XXXX represents the manufacturer's code.
• Casting Number : 654321 is the production batch traceability number.

2. Flange Type Codes

Different flange types suit various applications. Common codes include:

• 101 – Plate flange for welding : Flat plate flanges for welded pipe connections.
• 102 – Loose plate flange with weld on plate collar : Features a welded collar allowing free rotation for bolt hole alignment.
• 104 – Loose plate flange with weld-nut collar : Similar to 102 but with welded nuts for connection.
• 105 – Blank flange : For sealing pipe ends or openings.
• 111 – Weld neck flange : Butt-welded for high-pressure/temperature applications.
• 112 – Hubbed slip-on flange for welding : Slips over pipes for welding, offering higher strength than plate flanges.
• 113 – Hubbed threaded flange : Threaded connections for low-pressure systems.
• 121 – Integral flange : Single-piece construction with pipes for superior strength at higher cost.

II. Flange Face Types

Sealing face types critically influence performance. Key variants include:

• Type A: Flat Face : For low-pressure applications with non-metallic gaskets.
• Type B: Raised Face : Versatile for various pressures/temperatures with multiple gasket options.
• Type C/D: Tongue & Groove : Interlocking design prevents gasket blowout.
• Type E/F: Spigot & Recess : Precise alignment for high-pressure systems.
• Type G: Ring Recess : For metal ring gaskets in extreme conditions.
• Type H: O-Ring Groove : Superior sealing with elastomeric O-rings.

III. Critical Parameters: DN, PCD, and Pressure Ratings

1. Nominal Diameter (DN)

DN (Diameter Nominale) is a dimensionless value approximating pipe inner diameter, bridging imperial/metric standards. Common conversions:

2. Flange PCD (Pitch Circle Diameter)

The bolt hole circle diameter is crucial for fastener selection and assembly alignment.

3. Pressure Ratings

PN (Pressure Nominale) indicates maximum working pressure at specified temperatures (e.g., PN16 = 16 bar). ANSI uses Class ratings (Class 150, 300, etc.), with cross-referencing requiring temperature/material tables.

IV. Gasket Material Selection Guide

Gasket material selection requires careful consideration of media, temperature, and pressure:

V. Industry Applications and Standards

1. Water Treatment & Construction

Ductile iron flanges with rubber gaskets are common, with bolt lengths designed for 3mm gaskets in cast iron connections.

2. HVAC (BS10 & BS1560, BS4504)

BS10 (imperial) and BS4504 (metric) standards apply, with bolt lengths calculated for 1/16" gaskets and washers.

3. CESWI 7 Compliance

The Civil Engineering Specification for Water Industry mandates full nut engagement with ≥2 exposed threads post-tightening, requiring washers under both bolt head and nut.

VI. Coatings for Bolts, Flanges, and Fittings

Common anti-corrosion treatments:

• Galvanized : Basic corrosion protection.
• Rilsan (Polyamide-11) : High-performance plastic coating meeting international standards.
• Sheraplex : Dual-layer zinc/organic system offering superior protection with better torque/load consistency and reusability.