ASME B16.5

ASME B16.5 Flange and Flanged Fittings Specification

ASME B16.5 is the most common use standard specification for manufacturing cast and forged steel pipe flange and flanged fittings.

Standard Scope

This standard covers pressure-temperature ratings, materials, dimensions, tolerances, marking, testing, and methods of designating openings for pipe flange and flanged fittings.

ASME B16.5 covers Steel Pipe Flanges and Flanged Fittings from NPS 1/2 through NPS 24 in pressure classes 150 to 2500.

• Flanges and flanged fittings made from cast or forged materials
• Blind flanges and certain reducing flanges made from cast, forged or plate materials
• Flange bolting, gaskets and joints

Unit

Flanges with rating classes 150#, 300#, 400#, 600#, 900# and 1500# are available in sizes NPS 1/2 to 24.

Class 2500# is available from NPS 1/2 to NPS 12. Requirements are provided in both metric and U.S. Customary units.

Flanged fittings with 150# and 300# are available in sizes NPS 1/2 to NPS 24 (inch units).

Flanged fittings with 400#, 600#, 900#, 1500# (NPS 1/2 to 24) and 2500# (NPS 1/2 to 12) are provided only in U.S. Customary units.

Pressure-Temperature Rating

The pressure-temperature rating is the maximum allowable working pressure of the material at a given temperature.

Flanged Joints

A flanged joint consists of flanges, gasket, and bolting assembled together. Proper selection and assembly are required to ensure leak tightness.

Controlled bolt tightening techniques are described in ASME PCC-1.

Mixed Flanged Joints

If flanges have different pressure-temperature ratings, the joint shall be rated according to the lower rating at that temperature.

Rated Temperature

The rated temperature corresponds to the temperature of the pressure-containing components and is generally the same as the fluid temperature.

For temperatures below −29°C (−20°F), the rating shall not exceed the rating at −29°C.

Temperature Consideration

External forces and thermal effects from piping systems should be considered to avoid leakage. Severe loads and thermal gradients should be minimized.

High Temperature

At high temperatures, bolt loads may decrease due to relaxation of components, increasing the risk of leakage.

Leakage risk increases above 200°C (Class 150) and above 400°C for other classes unless external loads and thermal gradients are controlled.

Low Temperature

Some materials lose ductility at low temperatures and may fail under impact or stress concentrations. Impact testing may be required even above −29°C.

System Hydrostatic Testing

Flanged joints may be tested at 1.5 times the pressure rating at 38°C (100°F), rounded to the next higher increment.

Identification Markings

• Manufacturer name or trademark
• Material specification
• Pressure rating (Class 150–2500)
• Standard (ASME B16.5)
• Temperature
• Size
• Ring joint marking (if applicable)
• Multiple material marking (if applicable)

Materials

Plate materials shall be used only for blind and reducing flanges without hubs.

Flanges shall be manufactured as one piece. Assembly by welding multiple parts is not permitted.

Mechanical Properties

Mechanical properties shall be determined from specimens representing the final heat-treated condition.

Bolts

Includes high, medium, and low strength bolts, as well as bolts for grey cast iron flanges.

Gasket

Gasket materials shall comply with ASME B16.20. Selection is the responsibility of the user based on operating conditions.