1. ASME B16.5 (Most Common Standard)

Full Title: Pipe Flanges and Flanged Fittings, NPS 1/2 through NPS 24

Size range: NPS ½" ~ NPS 24"

Pressure Classes: Class 150, 300, 400, 600, 900, 1500, 2500

Covers flange types: Weld Neck, Slip-On, Blind, Threaded, Lap Joint, Socket Weld

Specifies dimensions, bolt layout, pressure-temperature ratings, facing types (RF, FF, RTJ), tolerances, marking and testing.

Widely used in oil & gas, chemical, power, general industrial piping.

2. ASME B16.47 (Large Diameter Steel Flanges)

Full Title: Large Diameter Steel Flanges, NPS 26 through NPS 60

Size range: NPS 26" ~ NPS 60"

Two series:

Series A: Originated from MSS SP-44

Series B: Originated from API 605

Pressure Classes: 75, 150, 300, 400, 600, 900

Used for big transmission pipelines, water lines, power plant large bore piping.

3. Special-purpose ASME flange standards

ASME B16.36: Orifice Flanges (for flow measurement, with pressure tap holes)

ASME B16.48: Spectacle Blinds & Spacers (Figure-8 blinds for pipeline isolation)

ASME B16.1: Gray Iron Pipe Flanges (Class 25, 125, 250, cast iron only)

ASME B16.24: Cast Copper Alloy Flanges

Quick Selection Rule

NPS ≤ 24″ → ASME B16.5

NPS ≥ 26″ → ASME B16.47

Typical specification example for ordering

Weld Neck Flange, NPS 6, Class 300, RF, ASME B16.5, ASTM A105