ASME/ANSI flanges are standardized components used to connect pipes, valves, pumps, pressure vessels, and other equipment in industrial piping systems. The modern standards governing these flanges are published by the American Society of Mechanical Engineers (ASME). People often call these flanges ‘ANSI flanges,’ but the official design and dimensional requirements fall under ASME, specifically the ASME B16.5 and ASME B16.47 standards. This guide covers everything you need to know about ASME/ANSI flanges, including how they work, different types, pressure classes, common applications, selection criteria, and comparisons between ASME standards.
1. What Are ASME/ANSI Flanges and How Do They Work?
ASME/ANSI flanges comply with the ASME’s B16 Standards Committee series standards. These flanges are manufactured to standardized designs to ensure uniformity in dimensions, tolerances, pressure-temperature ratings, and material selection across industrial systems.
Flanges function by forming a tight seal between two pipe ends using bolts and a gasket. They distribute stress evenly across the connection and allow systems to operate safely under high pressure.
Bolting Mechanism:
Bolts tighten both flanges together.
Compression presses the gasket firmly into the flange face.
The connection forms a reliable, leak-proof seal.
2. ASME B16.5 and B16.47 Standards
ASME B16.5 and B16.47 are the most common standards for ASME flanges. They define flange dimensions, pressure classes, materials, and tolerances.
| Feature | ASME B16.5 | ASME B16.47 |
|---|---|---|
| Size Range | ½″ – 24″ | 26″ – 60″ |
| Pressure Classes | 150–2500 | 75–900 |
| Series | None | Series A & B |
| Typical Use | General industrial piping | Large diameter pipelines |
3. Standard Types of ASME/ANSI Flanges
There are several common flange types defined under ASME B16 standards.
Table: Common ASME/ANSI Flange Types
| Flange Type | Description | Typical Use |
|---|---|---|
| Weld Neck (WN) | Long tapered neck, butt-welded | High pressure, high temperature |
| Slip-On (SO) | Slides over pipe, fillet welded | Low–medium pressure |
| Blind (BL) | Solid plate to close pipeline | Testing, isolation |
| Socket Weld (SW) | Pipe inserted into socket, fillet welded | Smaller pipe sizes, high pressure |
| Lap Joint (LJ) | Two-piece system with stub end | Systems requiring frequent dismantling |
| Threaded (TH) | Internal thread for screw-on connection | Low pressure, non-weld applications |
| Reducing Flange | Different bore size | Pipe size transitions |
4. ASME Pressure Class Chart
ANSI/ASME Pressure Classes (Carbon Steel A105)
(Approximate values, at 100°F)
| Class | Max Pressure (psi) | Conditions |
|---|---|---|
| 150 | 285 psi | Low pressure at near-ambient temperatures. |
| 300 | 740 psi | Moderate pressure with mild temperature demands. |
| 400 | 990 psi | Higher pressure under steady temperature conditions. |
| 600 | 1,480 psi | High pressure combined with elevated temperatures. |
| 900 | 2,220 psi | Very high pressure and increased thermal stress. |
| 1500 | 3,705 psi | Severe pressure loads with temperature fluctuation. |
| 2500 | 6,170 psi | Extreme pressure where maximum rigidity is required. |
5. Materials Used for ASME/ANSI Flanges
Flanges manufactured to ASME/ANSI standards can be produced from a wide range of materials, each chosen to meet specific pressure, temperature, and corrosion-resistance requirements. Common ASME/ANSI materials include:
1. Carbon Steel (A105, A350)
Suitable for general industrial service
Cost-effective with reliable strength
Performs well under moderate pressure and temperature
2. Stainless Steel (ASTM A182, 304/304L, 316/316L)
Provides strong corrosion resistance
Appropriate for chemical and food-grade environments
Maintains integrity at elevated temperatures
3. Duplex & Super Duplex (2205, 2507)
High mechanical strength with reduced weight
Excellent resistance to pitting and chloride attack
Used in offshore, marine, and high-salinity conditions
4. Nickel Alloys (Inconel, Monel, Hastelloy)
Exceptional resistance to aggressive chemicals
Stable under high heat and thermal cycling
Preferred for demanding, high-temperature corrosive environments
6. Applications of ASME/ANSI Flanges in Industrial Piping
ASME/ANSI flanges are widely used in industrial piping systems that handle liquids, gases, steam, and process media across a range of pressures and temperatures. These applications include:
- Oil & Gas Pipelines: Transporting petroleum products under extreme pressures.
- Chemical Processing: Resistant to corrosion and chemical exposure.
- Power Generation: Steam, cooling water, pressure vessels.
- Water & Wastewater: Municipal piping networks and treatment plants.
- Manufacturing & Industrial Facilities: Process lines, compressed air systems, mechanical equipment.
- HVAC Mechanical Systems: Chilled water, steam, hydronic heating loops.
7. Benefits of ASME/ANSI Flanges
ASME/ANSI flanges offer several operational and engineering advantages:
- Interchangeability: Globally recognized standards for flanges ensure compatibility across different manufacturers.
- High-pressure reliability: Designed to perform safely under Class 150–2,500 pressure ratings.
- Easy installation & removal: There is no need for cutting or welding pipe during maintenance.
- Material versatility: Available in carbon steel, stainless steel, duplex, nickel alloys, and more.
- Wide industrial use: From petrochemical plants to municipal water systems, standardized flanges provide dependable operation.
8. How to Choose the Right ASME/ANSI Flange
Selecting an appropriate ASME flange involves several important considerations:
- Identifying the required pressure class: The class should correspond to the system’s operating pressure and temperature, using standard ratings such as 150, 300, 400, 600, 900, 1500, and 2500.
- Selecting a suitable flange design: Weld neck, slip-on, blind, and threaded configurations each support different service conditions and installation requirements.
- Choosing the appropriate material: Options like carbon steel, stainless steel, duplex, and nickel alloys are selected based on corrosion exposure, temperature limits, and media compatibility.
- Matching pipe size and schedule: Proper alignment requires the flange to match the pipe’s outside diameter and wall thickness.
- Determining the correct gasket and face type: Raised Face (RF), Flat Face (FF), and Ring-Type Joint (RTJ) styles offer different sealing characteristics depending on system demands.
Conclusion
ASME/ANSI flanges remain a dependable choice across industrial piping systems due to their standardized design, wide material options, and proven performance in demanding conditions. At API International, Inc., we manufacture standard and custom ANSI/ASME flanges to meet the highest quality standard. Our full line of flanges can be viewed here. If our standard flanges don’t meet your requirements our Custom Machining Shop allows the manufacture of custom parts as well as modifications to stock items, so you can get exactly what you need.