scope:

General

This Standard covers Classes 25, 125, and 250 Gray Iron Pipe Flanges and Flanged Fittings. It includes:

(a) pressure-temperature ratings;

(b) sizes and method of designating openings of reducing fittings;

(c) marking;

(d) materials;

(e) dimensions and tolerances;

(f) bolting and gaskets;

(g) pressure testing.

Quality Systems

Requirements relating to the product manufacturer's Quality System Programs are described in Appendix A.

Relevant Units

This Standard states values in both SI 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. Within the text, the U.S. Customary units are shown in parenthesis or in separate tables. The values stated in each table are 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 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 tolerance 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 as follows:

Size.

NPS, followed by a dimensionless number, is the designation for nominal flange or flange fitting size. NPS is related to the reference nominal diameter, DN, used in international standards. The relationship is, typically, as follows:

For NPS ≥ 4, the related DN is: DN = 25 x (NPS)