(a) This Standard covers pressure–temperature ratings, materials, dimensions, tolerances, marking, testing, and methods of designating openings for pipe flanges and flanged fittings. Included are
(1) flanges with rating class designations 150, 300, 400, 600, 900, 1500, and 2500 in sizes NPS 1⁄2 through NPS 24, with requirements given in both metric and U.S. Customary units with diameter of bolts and flange bolt holes expressed in inch units
(2) flanged fittings with rating class designation 150 and 300 in sizes NPS 1⁄2 through NPS 24, with requirements given in both metric and U.S. Customary units with diameter of bolts and flange bolt holes expressed
in inch units
(3) flanged fittings with rating class designation 400, 600, 900, 1500, and 2500 in sizes NPS 1⁄2 through NPS 24 that are acknowledged in Annex G in which only U.S. Customary units are provided
(b) This Standard is limited to
(1) flanges and flanged fittings made from cast or forged materials
(2) blind flanges and certain reducing flanges made from cast, forged, or plate materials
Also included in this Standard are requirements and recommendations regarding flange bolting, flange gaskets,
and flange joints.
Codes, standards, and specifications, containing provisions to the extent referenced herein, constitute requirements of this Standard. These reference documents are listed in Annex H.
1.3 Time of Purchase, Manufacture, or Installation
The pressure–temperature ratings in this Standard are applicable upon its publication to all flanges and flanged fittings within its scope which otherwise meet its requirements. For unused flanges or flanged fittings maintained in inventory, the manufacturer of the flange or flanged fittings 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.
1.4 User Accountability
This Standard cites duties and responsibilities that are to be assumed by the flange or flanged fitting user in the
areas of, for example, application, installation, system hydrostatic testing, operation, and material selection.
1.5 Quality Systems
Requirements relating to the product manufacturer’s Quality System Program are described in Annex E.
1.6 Relevant Units
This Standard states values in both 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 system 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.
1.7 Service Conditions
Criteria for selection of materials suitable for particular fluid service are not within the scope of this Standard.
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.
1.9.1 Pressure Rating Designation.
Class, followed by a dimensionless number, is the designation for pressure–temperature ratings as follows: Class 150 300 400 600 900 1500 2500
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
2 PRESSURE-TEMPERATURE RATINGS
Pressure-temperature ratings are maximum allowable working gage pressures in bar units at the temperatures
in degrees Celsius shown in Tables 2-1.1 through 2-3.17 for the applicable material and class designation. Tables F2-1.1 through F2-3.17 of Annex F list pressure-temperature ratings using psi units for pressure at the temperature
in degrees Fahrenheit. For intermediate temperatures, linear interpolation is permitted. Interpolation between class designations is not permitted.
2.2 Flanged Joints
A flanged joint is composed of separate and independent, although inter-related components: the flanges, the gasket, and the bolting, which are assembled by another influence, the assembler. Proper controls must be exercised in the selection and application for all these elements to attain a joint that has acceptable leak tightness. Special techniques, such as controlled bolt tightening are described in ASME PCC-1.
2.3 Ratings of Flanged Joints
Pressure-temperature ratings apply to flanged joints that conform to the limitations on bolting in para. 5.3 and on gaskets in para. 5.4, which are made up in accordance with good practice for alignment and assembly (see para. 2.2). Use of these ratings for flanged joints not conforming to these limitations is the responsibility of the user.
2.3.2 Mixed Flanged Joints.
If the two flanges in a flanged joint do not have the same pressure–temperature rating, the rating of the joint at any temperature is the lower of the two flange ratings at that temperature.
2.4 Rating Temperature
The temperature shown for a corresponding pressure rating is the temperature of the pressure-containing shell of the component. In general, this temperature is the same as that of the contained fluid. Use of a pressure rating corresponding to a temperature other than that of the contained fluid is the responsibility of the user, subject to the requirements of applicable codes and regulations. For any temperature below −29°C (−20°F), the rating shall be no greater than the rating shown for −29°C (−20°F). See also paras. 2.5.3 and 5.1.2.
2.5 Temperature Considerations
Use of flanged joints at either high or low temperatures shall take into consideration the risk of joint leakage due to forces and moments developed in the connected piping or equipment. Provisions in paras. 2.5.2 and 2.5.3 are included as advisory with the aim of lessening these risks.
2.5.2 High Temperature.
Application at temperatures in the creep range will result in decreasing bolt loads as relaxation of flanges, bolts, and gaskets takes place. Flanged joints subjected to thermal gradients may likewise be subject to decreasing bolt loads. Decreased bolt loads diminish the capacity of the flanged joint to sustain loads effectively without leakage. At temperatures above 200°C (400°F) for Class 150 and above 400°C (75
0°F) for other class designations, flanged joints may develop leakage problems unless care is taken to avoid imposing severe external loads, severe thermal gradients, or both.
2.5.3 Low Temperature.
Some of the materials listed in Tables 1A and 1B, notably some carbon steels, may undergo a decrease in ductility when used at low temperatures to such an extent as to be unable to safely resist shock loading, sudden changes of stress, or high stress concentration. Some codes or regulations may require impact testing for applications even where temperatures are higher than −29°C (−20°F). When such requirements apply, it is the responsibility of the user to ensure these requirements are communicated to the manufacturer prior to the time of purchase.
2.6 System Hydrostatic Testing
Flanged joints and flanged fittings may be subjected to system hydrostatic tests at a pressure of 1.5 times the 38°C (100°F) rating rounded off to the next higher 1 bar (25 psi) increment. Testing at any higher pressure is the responsibility of the user, taking into account the requirements of the applicable code or regulation.
2.7 Welding Neck Flanges
Ratings forwelding neck flanges covered by this Standard are based upon their hubs at the welding end having thickness at least equal to that calculated for pipe having 276 MPa (40,000 psi) specified minimum yield strength.1 In order to ensure adequate flange hub thickness for flange sizes NPS 2 and larger, the bore of a welding neck flange, dimension B in the various dimensional tables.
2.8 Straight Hub Welding Flanges
Straight hubwelding flanges are an extension ofwelding neck flanges and have straight hubs of uniform thickness.
With the exception of the following, the straight hub welding flanges shall have dimensions of the welding neck flanges of the size and class set forth in Tables 8, 11, 14, 16, 18, 20, and 22 (Tables F8, F11, F14, F16, F18,F20, and F22 of Annex F). See Fig. 15.
2.8.1 Length Through Hub.
The length through hub shall be 229 mm (9 in.) for NPS 4 and smaller and 305mm (12 in.) for larger than NPS 4. Other lengths may be furnished by agreement between the end user and the manufacturer.
The bore diameter shall be equal to B dimension of the welding neck flange. Other bores may be furnished by agreement between the end user and the manufacturer. In no case shall the bore diameter exceed the bore of the same size and class lapped flange.
2.8.3 Hub End.
The standard flange shall be provided with square cut end. The end user may specify welding end preparation in accordance with para. 6.7.
2.9 Multiple Material Grades
Material for flanges and flanged fittings may meet the requirements of more than one specification or the requirements of more than one grade of a specification listed in Table 1A. In either case, the pressure-temperature ratings for any of these specifications or grades may be used provided the material is marked in accordance with para. 4.2.8.
3 COMPONENT SIZE
3.1 Nominal Pipe Size
As applied in this Standard, the use of the phrase “nominal pipe size” or the designation NPS followed by a dimensionless number is for the purpose of pipe, flange, or flanged fitting end connection size identification. The number is not necessarily the same as the flange or flanged fitting inside diameter.
3.2 Reducing Fittings
Reducing fittings shall be designated by the NPS for the openings in the sequence indicated in the sketches
of Fig. 2.
3.3 Reducing Flanges
Reducing flanges shall be designated by the NPS for each opening. See examples in Note (4) of Table 6 (Table
F6 of Annex F).
Except as modified herein, flanges and flanged fittings shall be marked as required in MSS SP-25, except as
noted in para. 4.2.
4.2 Identification Markings
The manufacturer’s name or trademark shall be applied.
Material shall be identified in the following way:
(a) Cast flanges and flanged fittings shall be marked with the ASTM specification,2 grade identification symbol
(letters and numbers), and the melt number or melt identification.
(b) Plate flanges, forged flanges, and flanged fittings shall be marked with the ASTM specification number and grade identification symbol.2
(c) Amanufacturer may supplement these mandatory material indications with his trade designation for the material grade, but confusion of symbols shall be avoided.
(d) For flanges and flanged fittings manufactured from material that meets the requirements of more than one specification or grade of a specification listed in Table 1A, see para. 4.2.8.
4.2.3 Rating Designation.
The flange or flanged fitting shall be marked with the number that corresponds to its pressure rating class designation (i.e., 150, 300,400, 600, 900, 1500, or 2500).
The designation B16 or B16.5 shall be applied to the flange or flanged fitting, preferably located adjacent to the class designation, to indicate conformance to this Standard. The use of the prefix ASME is optional.
Temperature markings are not required on flanges or flanged fittings, however, if marked, the temperature shall be shown with its corresponding tabulated pressure rating for the material.
The NPS designation shall be marked on flanges and flanged fittings. Reducing flanges and reducing flanged fittings shall be marked with the applicable NPS designations as required by paras. 3.2 and 3.3.
4.2.7 Ring Joint Flanges.
The edge (periphery) of each ring joint flange shall be marked with the letter R and the corresponding ring groove number.
4.2.8 Multiple Material Marking.
Material for components that meet the requirements for more than one specification or grade of a specification listed in Table 1A may, at the manufacturer’s option, be marked with more than one of the applicable specification or grade
symbols. These identification markings shall be placed so as to avoid confusion in identification. The multiple marking shall be in accordance with the guidelines set out in ASME Boiler and Pressure Vessel Code, SectionII, Part D, Appendix 7.
Materials required for flanges and flanged fittings are listed in Table 1A with the restriction that plate materials shall be used only for blind flanges and reducing flanges without hubs. Recommended bolting materials are listed in Table 1B (See para. 5.3). Corresponding materials listed in Section II of the ASME Boiler and Pressure Vessel Code may be used provided that the requirements of the ASME specification are identical to or more stringent than the ASTM specification for the Grade, Class, or type of material.
Criteria for the selection of materials are not within the scope of this Standard. The possibility of material deterioration in service should be considered by the user. Carbide phase conversion to graphite and excessive oxidation of ferritic materials, susceptibility to intergranular corrosion of austenitic materials, or grain boundary attack of nickel base alloys are among those items requiring attention. A discussion of precautionary considerations can be found in ASME B31.3, Appendix F; Section II, Part D, Appendix 6; and Section III, Division 1, Appendix W of the ASME Boiler and Pressure Vessel Code.
Some of the
materials listed in Table1A undergo a decrease in toughness when used at low temperatures, to the extent that Codes referencing the Standard may require impact tests for application even at temperatures higher than −7°C (+20°F). It is the responsibility of the user to assure that such testing is performed.
When service conditions dictate the implementation of special material requirements [e.g., using a Group 2 material above 538°C (1000°F)], it is the user’s responsibility to so specify to the manufacturer in order to ensure compliance with metallurgical requirements listed in the notes in Tables 2-1.1 through 2-3.17 (Tables F2-1.1 through F2-3.17 of Annex F):
5.1.4 Cast Surfaces.
Cast surfaces of component pressure boundaries shall be in accordance with MSS SP-55 except that all Type I defects are unacceptable and defects in excess of Plates “a” and “b” for Type II through Type XII are unacceptable.
5.2 Mechanical Properties
Mechanical properties shall be obtained from test specimens that represent the final heat treated condition
of the material required by the material specification.
Bolting listed in Table 1B is recommended for use in flanged joints covered by this Standard. Bolting of other material may be used if permitted by the applicable code or government regulation. Bolting materials are subject to the limitations given in paras.5.3.2, 5.3.3, 5.3.4, and 5.3.5.
5.3.2 High Strength Bolting.
Bolting materials having allowable stresses not less than those for ASTM A 193 Grade B7 are listed as high strength in Table 1B. These and other materials of comparable strength may be used in any flanged joint.
5.3.3 Intermediate Strength Bolting.
Bolting materials listed as intermediate strength in Table 1B, and other bolting of comparable strength, may be used in any flanged joint provided the user verifies their ability to seat the selected gasket and maintain a sealed joint under expected operating condition.
6.1 Flanged Fittings Wall Thickness
For inspection purposes the minimum wall thickness tm of flanged fittings at the time of manufacture shall be as shown in Tables 9 and 12 (Tables F9 and F12 of Annex F), except as provided in para. 6.1.2. Additional metal thickness needed to withstand installation bolt-up assembly stresses, shapes other than circular, and stress concentrations must be determined by the manufacturer, since these factors vary widely. In particular, 45-deg laterals Tee, true Ys, and crosses may require additional reinforcement to compensate for inherent weaknesses in these
6.3 Flat Face Flanges
This Standard permits flat face flanges in all classes.
A raised face may be removed from a raised face flange to convert it to a flat face flange provided that the required dimension tf, shown in Fig.7 (Fig. F7 of Annex F) is maintained.
The flat face flange facing finish shall be in conformance with para. 6.4.5 for the full width of the seating surface for the gasket.
6.4 Flange Facings
Figure 7 (Fig. F7. of Annex F) shows dimensional relationships for various flange types and for pipe lap facings to be used with lap joints. Table 4(Table F4 of Annex F) lists dimensions for facings other than ring joint. Table 5 (Table F5 of Annex F) lists dimensions for ring joint facings. Classes 150 and 300 pipe flanges and companion flanges of fittings are regularly furnished with 2 mm (0.06 in.) raised face, which is in addition to the minimum flange thickness, tf. Classes 400, 600, 900, 1500, and 2500 pipe flanges and companion flanges of fittings are regularly furnished with 7 mm(0.25 in.) raised face, which is in addition to the minimum flange thickness,