What is the most common flange type used in industrial applications?

Weld neck flanges are the most common type used in industrial applications, especially in high-pressure and high-temperature systems. They offer superior stress distribution and fatigue resistance. Slip-on flanges are second most common for lower-pressure, less critical applications where cost is a factor.

When should I use a slip-on flange instead of a weld neck flange?

Use slip-on flanges when: the application is Class 150-300 pressure rating, you need to save cost, the system is not subjected to high temperatures (above 600°F), vibration levels are moderate, and you have adequate space for welding both inside and outside the flange. For critical or high-pressure applications, always choose weld neck.

Can I use a blind flange as a permanent end cap?

Yes, blind flanges are commonly used as permanent end caps on pipe and vessel nozzles. They are bolted to the other component with the same gasket and bolt configuration as standard flanges. Ensure proper gasket selection for the fluid, temperature, and pressure conditions.

What are the advantages of threaded flanges?

Threaded flanges require no welding, making them ideal for small-diameter systems, field repairs, and applications where welding equipment is unavailable. They are easily removable for maintenance. However, they are limited to lower pressure classes (typically 150-300) and smaller sizes.

How do spectacle blinds help during system maintenance?

Spectacle blinds (also called spectacle flanges) allow you to isolate a section of piping by rotating a two-disc assembly. One disc is solid (blocking flow) and one is open (allowing flow). This enables maintenance without breaking the connection or using a separate isolation valve, saving cost and space.

What is the difference between a lap joint flange and a hub flange?

A lap joint flange is a two-piece system with a separate stub end and flange. The stub end is welded to the pipe and supports the flange. A hub flange (or hub assembly) is essentially a simplified stub end designed to work with a matching flange. Hub flanges are more common in pressure vessel applications.

Why are orifice flanges used instead of regular flanges with separate orifice plates?

Orifice flanges are precision-designed with pre-drilled tap holes for differential pressure transmitters used in flow measurement. Using dedicated orifice flanges ensures accurate pressure tap placement per ASME and ISO standards, improves measurement accuracy, and reduces the number of connections needed.

Are plate flanges acceptable for high-pressure applications?

Plate flanges are generally not recommended for high-pressure applications (above 600 psi). They are cost-effective for large-diameter, low-pressure applications like water systems. Forged flanges (weld neck, slip-on) are always preferred for critical and high-pressure services due to superior material quality and fatigue resistance.

The Complete Flange Types Guide: 15 Types Explained

Introduction to Flange Types

Flanges are critical components in piping systems, enabling the connection of pipes, valves, pumps, and other equipment. Understanding the different flange types and their characteristics is essential for proper system design, safety, and reliability. This comprehensive guide covers 15 major flange types used across industrial, utility, and commercial applications worldwide.

What You'll Learn

Characteristics and design features of each flange type
Advantages and disadvantages for different applications
Applicable standards (ASME B16.5, API, ASTM, etc.)
Real-world applications and industry usage patterns
Practical guidance for selecting the right flange type

Whether you are designing a new piping system, specifying replacement components, or troubleshooting an existing installation, this guide provides the technical depth needed to make informed decisions. Each flange type section includes definition, characteristics, pros/cons, typical applications, applicable standards, and available face finish options.

Definition

A weld neck flange features a long tapered hub that is welded to the pipe. The tapered design provides stress relief and distributes loads gradually, reducing stress concentration at the weld. This is the most commonly used flange type in high-pressure and high-temperature applications.

Flange Diagram

Weld Neck Flange illustration would appear here

Key Characteristics

•Long tapered hub with gradual transition to pipe
•Excellent stress distribution properties
•Higher cost than slip-on due to machining and material
•Requires full penetration weld for structural integrity
•Bore matches pipe ID (butt weld compatible)
•Available in standard and long weld neck (LWN) configurations

Advantages

✓Superior stress distribution and reduced fatigue loading
✓Best for high-temperature and high-pressure services
✓Excellent corrosion resistance at weld area due to gradual transition
✓Lower vibration and deflection
✓Most common type - proven track record in critical applications
✓Better for thick-wall piping systems

Disadvantages

✗Higher cost compared to slip-on flanges
✗Requires skilled welders for proper installation
✗More complex machining increases lead times
✗Rigid connection reduces flexibility for misalignment
✗Difficult to repair or remove without cutting pipe

Typical Applications

→High-pressure steam and hot water systems
→Petrochemical and chemical processing plants
→Power generation (steam, combined cycle, geothermal)
→Oil and gas pipelines
→Cryogenic services (LF2 material)
→High-temperature thermal applications
→Severe service and critical pressure systems

Applicable Standards

◆ASME B16.5 (Classes 150-2500)
◆ASME B16.47 Series A & B (large diameter)
◆API 6A (wellhead equipment)
◆EN 1092-1 (European standard)

Available Face Finishes

Raised Face (RF)Ring Joint (RTJ)Flat Face (FF)Tongue & Groove (T&G)

Flange Type Comparison Table

Flange Type	Welding Required	Max Pressure	Cost Relative	Best For
Weld Neck	Full pen weld	2500+ psi	★★★	High-pressure, high-temp critical
Slip-On	Fillet welds	600 psi	★	Low-cost, moderate pressure
Blind	Bolted only	2500+ psi	★★	End caps, vessel closure
Threaded	None	300 psi	★	Small bore, low pressure
Socket Weld	Fillet weld	2500 psi	★★	High-temp, small bore
Lap Joint	Stub end weld	300 psi	★★	Frequent maintenance access
Reducing	Full pen weld	2500 psi	★★★	Size transitions
Long Weld Neck	Full pen weld	2500+ psi	★★★★	Critical high-temp/pressure
Orifice	Full pen weld	600 psi	★★	Flow measurement
Plate	Full pen weld	300 psi	★	Large diameter, low pressure

Flange Selection Decision Tree

Step 1: Determine Pressure Rating Required

Low Pressure (under 150 psi): Consider slip-on, threaded, or plate flanges

Moderate Pressure (150-600 psi): Slip-on, socket weld, or weld neck options available

High Pressure (600-2500 psi): Weld neck or socket weld required

Very High Pressure (above 2500 psi): Weld neck or long weld neck only

Step 2: Consider Operating Temperature

Low Temperature (-20°F to 200°F): Any flange type acceptable; consider cost

Moderate Temperature (200-600°F): Avoid threaded flanges; use weld neck preferred

High Temperature (600-1100°F): Weld neck or socket weld with alloy steel

Extreme Temperature (above 1100°F): Long weld neck with special alloys required

Step 3: Evaluate System Type and Function

Isolation/Dead Leg: Blind flanges or spectacle blinds

Flow Measurement: Orifice flanges with pressure taps

Frequent Maintenance: Lap joint or hub flanges

Size Transition: Reducing flanges (weld neck or slip-on)

Exhaust Application: Exhaust flanges (low pressure, high temperature)

Step 4: Verify Piping Constraints

Limited Space Available: Socket weld or slip-on flanges more compact

Alignment Issues: Slip-on or lap joint flanges more forgiving

Vibration Environment: Weld neck flanges have superior performance

Corrosive Service: Weld neck preferred (stress relief reduces corrosion)

Step 5: Check Code and Standards Compliance

ASME Section I (Boiler Code): Weld neck preferred, slip-on limited

ASME Section VIII (Pressure Vessels): All types permitted; weld neck critical

API 6A (Wellhead Equipment): Weld neck or hub, specific material grades

AWWA (Water Systems): Plate flanges and galvanized options common

The Complete Flange Types Guide

On This Page

Introduction to Flange Types

What You'll Learn

Weld Neck Flange

Definition

Key Characteristics

Advantages

Disadvantages

Typical Applications

Applicable Standards

Available Face Finishes

Slip-On Flange

Blind Flange

Threaded Flange

Socket Weld Flange

Lap Joint Flange

Reducing Flange

Long Weld Neck Flange (LWN)

Orifice Flange

Spectacle Blind (Isolation Plate)

Plate Flange

Backing Ring (Backup Ring)

Exhaust Flange

Hub Flange (Stub End Assembly)

Swivel Ring Flange

Flange Type Comparison Table

Flange Selection Decision Tree

Step 1: Determine Pressure Rating Required

Step 2: Consider Operating Temperature

Step 3: Evaluate System Type and Function

Step 4: Verify Piping Constraints

Step 5: Check Code and Standards Compliance

Frequently Asked Questions

Ready to Select Your Flange?

Related Resources

Pressure-Temperature Ratings

Material Grade Reference

Corrosion Prevention Guide