Salient point of ASME B16.5–Piping Stress Engineer

Salient point of ASME B16.5 a piping stress engineer needs to know

1) Flanges with rating class designations 150,300,400,600,900 and 1500 in sizes NPS 1⁄2 through NPS 24 and flanges with rating class designation 2500 in sizes NPS 1⁄2 through NPS 12, with requirements given in both metric and U.S. Customary units with diameter of bolts and flange bolt holes expressed in inch units.

2) 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 material.

3) 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 that appear in Mandatory Appendix II. 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.

4) 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

5) 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:

NPS DN
1/2 15
3/4 20
1 25
1 1/4 32
1 1/2 40
2 50
2 1/2 65
3 80
4 100

GENERAL NOTE: For NPS ≥ 4, the related DN = 25 multiplied by the NPS number.

6) 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 2-3.19 for the applicable material and class designation. Tables II-2-1.1 through II-2-3.19 of Mandatory Appendix II 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.

7) A flanged joint is composed of separate and independent, although interrelated components: the flanges, gasket, and 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.

8) 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.

9) 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).

10) 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 (750°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.

11) 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.

12) 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.

13) 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.

14) Material. Material shall be identified in the following way:

  1. 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.
  2. Plate flanges, forged flanges, and flanged fittings shall be marked with the ASTM specification number and grade identification symbol.2

( 2 An ASME Boiler and Pressure Vessel Code, Section II specification number may be substituted for an ASTM specification number provided the requirements of the ASME specification are identical to or more stringent than the ASTM specification for the Grade, Class, or Type of material.)

15) 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. Flanges and flanged fittings shall be manufactured as one piece in accordance with the applicable material specification. Assembly of multiple pieces into the finished product by welding or other means is not permitted by this Standard.

16) Recommended bolting materials are listed in Table 1B.

17) 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.

18) High-Strength Bolting. Bolting materials having allowable stresses not less than those for ASTM A193 Grade B7 are listed as high strength in Table 1B. These and other materials of comparable strength may be used in any flanged joint.

19) 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 conditions.

20) Low-Strength Bolting. Bolting materials having no more than 206 MPa (30 ksi) specified minimum yield strength are listed as low strength in Table 1B. These materials and others of comparable strength are to be used only in Class 150 and 300 flanged joints and only with gaskets described in para. 5.4.2. Flanged assemblies using low-strength carbon steel bolts should not be used above 200°C (400°F) or below −29°C (−20°F).

21) Bolting material shall not be used beyond temperature limits specified in the governing code.

22) ASME Boiler and Pressure Vessel Code, Section II materials may also be used, provided the requirements of the ASME specification are identical or more stringent than the corresponding ASTM specification for the Grade, Class, or Type listed.

23) Repair welding of bolting material is prohibited.

24) Ring joint gasket materials shall conform to ASME B16.20. Materials for other gaskets are described in Nonmandatory Appendix B. The user is responsible for selection of gasket materials that will withstand the expected bolt loading without injurious crushing and that are suitable for the service conditions.

Sources:

  • ASME B16.5-2013 (Revision of ASME B16.5-2009)

Pipe Flanges and Flanged Fittings (NPS 1⁄2 Through NPS 24 Metric/Inch Standard)

Note: For above mentioned table and paragraph and also for more detail please refer the code.

Leave a Reply

Your email address will not be published. Required fields are marked *