scope:

General

This Standard covers pressure-temperature ratings, materials, dimensions, tolerances, marking, and testing for pipe flanges in sizes NPS 26 through NPS 60. Included here are flanges with rating class designations 75, 150, 300, 400, 600, and 900 with requirements given in both SI (metric) and U.S. Customary units, with diameter of bolts and flange bolt holes expressed in inch units.

This Standard is limited to

(a) flanges made from cast or forged materials

(b) blind flanges made from cast, forged, or plate materials (see Tables 1 and 2)

Also, included in this Standard are requirements and recommendations regarding flange bolting, flange gaskets, and flange joints.

Flange Series

This Standard provides two series of flange dimensions. Series A specifies flange dimensions for general use flanges. Series B specifies flange dimensions for compact flanges that, in most cases, have smaller bolt circle diameters than Series A flanges. These two series of flanges are, in general, not interchangeable. The user should recognize that some flanged valves, equipment bolted between flanges, and flanged equipment may be compatible with only one series of these flanges.

Time of Purchase, Manufacture, or Installation

The pressure-temperature ratings in this Standard are applicable upon its publication to all flanges within its scope that otherwise meet its requirement. For unused flanges maintained in inventory, the manufacturer of the flange may certify conformance to this Edition, provided that it can be demonstrated that all requirements of this Edition have been met. Where such components were installed in accordance with the pressure-temperature ratings of an earlier edition of this Standard, those ratings are applicable, except as may be governed by the applicable code or regulation.

User Accountability

This Standard cites responsibilities that are to be assumed by the flange user in the areas of, for example

(a) application

(b) installation

(c) system pressure testing

(d) operation

(e) material selection

Quality Systems

Requirements relating to the product manufacturer's Quality System Program are described in Mandatory Appendix II.

Relevant Units

This Standard states values in both SI (metric) and U.S. Customary units. As an exception, diameter of bolts and flange bolt holes are expressed in inch units only. These systems of units are to be regarded separately as standard. Within the text, the U.S. Customary units are shown in parentheses or in separate tables. The values stated in each systemare not exact equivalents; therefore, it is required that each system of units be used independently of the other. Except for diameter of bolts and flange bolt holes, combining values from the two systems constitutes nonconformance with the Standard.

Service Conditions

Criteria for selection of materials suitable for particular fluid service are not within the scope of this Standard.

Convention

For the purpose of determining conformance with this Standard, the convention for fixing significant digits where limits, maximum and minimum values are specified, shall be rounded as defined in ASTM Practice E 29. This requires that an observed or calculated value shall be rounded off to the nearest unit in the last right hand digit used for expressing the limit. Decimal values and tolerances do not imply a particular method of measurement.

Denotation

Pressure Rating Designation.

Class, followed by a dimensionless number, is the designation for pressure-temperature ratings (i.e., class 75, class 150, class 300, class 400, class 600, class 900).

Size.

NPS, followed by a dimensionless number, is the designation for nominal flange size. NPS is related to the reference nominal diameter, DN, used in international and other standards. For the sizes covered in this Standard, the relationship is: DN = 25 x NPS.