ANSI Standard Flange

ANSI Standard Flange Description

Overview:

An ANSI Standard Flange is a circular, bolted piping connector built to precise US dimensional and mechanical standards. It provides a standardized method for joining process piping, equipment, and valves, allowing for quick assembly, disassembly, cleaning, or line modification without cutting the pipes.

Core ANSI/ASME Specifications:

- ASME/ANSI B16.5: Covers pipe flanges and flanged fittings from NPS 1/2 through NPS 24 (Nominal Pipe Size).

- ASME/ANSI B16.47: Covers large-diameter steel flanges from NPS 26 through NPS 60 (Series A and Series B).

- ASME/ANSI B16.36: Covers orifice flanges used for flow measurement.

Pressure Classes (Pressure-Temperature Ratings):

ANSI flanges are categorized into standard pressure classes measured in "Class" (often referred to as # or lb):

- Class 150

- Class 300

- Class 600

- Class 900

- Class 1500

- Class 2500

Higher class ratings indicate thicker walls, larger bolt circles, and greater ability to withstand elevated operating pressures and temperatures.

Common Types of ANSI Flanges:

1. Weld Neck Flange (WN): Features a long tapered hub welded directly to the pipe; best for high-pressure, severe-stress conditions.

2. Slip-On Flange (SO): Slides over the end of the pipe and is welded inside and outside; cost-effective and easy to align.

3. Blind Flange (BL): Solid disc used to seal off pipeline ends or pressure vessel openings.

4. Threaded Flange (TH): Connects via NPT screw threads without welding; ideal for low-pressure or hazardous areas where welding is prohibited.

5. Socket Weld Flange (SW): Pipe inserts into a recessed socket and is fillet-welded; used for smaller diameter, high-pressure lines.

6. Lap Joint Flange (LJ): Used in conjunction with a stub-end fitting; allows easy alignment of bolt holes during installation.

Facing Types:

- Raised Face (RF): Standard 1/16 in or 1/4 in raised surface that focuses pressure on the gasket area.

- Flat Face (FF): Entire face is flat, preventing cracking when mating to cast-iron or brittle material flanges.

- Ring Type Joint (RTJ): Deep groove machined into the face for a metal ring gasket, used in extreme high-pressure/high-temperature environments.

Common Materials:

- Carbon Steel: ASTM A105 (Standard high-temperature carbon steel), A350 LF2 (Low-temperature).

- Stainless Steel: ASTM A182 F304/304L, F316/316L (Corrosion-resistant applications).

- Alloy Steel: ASTM A182 F11, F22, F91 (High-temperature power generation).