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ASME B16.34-2020 pdf download

ASME B16.34-2020 pdf download.Valves — Flanged, Threaded, and Welding End.
2.1.2 Standard Class Valves. Valves conforming to the requirements of this Standard, except for those meeting the additional requirements of section 8 for Special Class valves or of Mandatory Appendix V for Limited Class valves, shall be designated Standard Class valves. Ratings shall not exceed the values that are listed in Tables 2-1.1 through 2-3.19 (Tables 2-1.1C through 2-3.19C) with an identifying label “A — Standard Class.” 2.1.3 Special Class Valves. Threaded- or welding-end valves that conform to all the requirements of para. 2.1.2, and in addition have successfully passed the examinations required by section 8, may be designated Special Class valves. Pressure–temperature ratings shall not exceed the values that are listed in Tables 2-1.1 through 2-3.19 (Tables 2-1.1C through 2-3.19C) with an identi- fying label “B — Special Class.” Special Class ratings shall not be used for flanged-end valves. 1 Throughout this Standard the metric unit used for pressure is bar where 1 bar is equivalent to 0.1 MPa. Use of the term bar for pressure is an aid in distinguishing between values for pressure and stress where stress values are given in MPa units. This also recognizes the common usage of the term bar for pressure in International Standards for piping components such as valves and fittings.
2.3.2 Low Temperature. The pressure rating for service at any temperature below −29°C (−20°F) shall be no greater than the rating shown in Tables 2-1.1 through 2-3.19 (Tables 2-1.1C through 2-3.19C) for −29°C (−20°F). Some of the materials listed in Table 1, 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 change 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 require- ments are communicated to the manufacturer prior to the time of purchase. 2.4 Guidance for the Use of Flanged Valve Ratings Application of flanged-end valves at either high or low temperatures or in a service subject to rapid fluid temperature variations entails some risk of flanged joint leakage. Guidance in this regard is provided in ASME B16.5 and more extensively in ASME PCC-1. Precau- tions regarding the bolting of raised face flanges to cast iron flanges are given in ASME B16.5 and ASME B16.47. 2.5 Variances Except as provided in paras. 2.5.1, 2.5.2, and 2.5.3, the pressure–temperature ratings are the maximum allow- able working pressure for the corresponding tempera- ture. 2.5.1 Safety Valves, Relief Valves, or Rupture Disk Operation. Under conditions of safety valve, relief valve, or rupture disk operation, pressure may exceed the rated pressure for a valve furnished under this Stan- dard by no more than 10% of that defined by the pressure– temperature rating. Such conditions are necessarily of limited duration. Damage that may result from pressure excursions in excess of the aforementioned is solely the responsibility of the user.5.1.2 Carbon Steel Bonnet or Cover Bolting. It is permissible to use carbon steel, for example, ASTM A307, Grade B, for bonnet or cover bolting only for Class 300 and lower, provided the service temperature is limited to 200°C (400°F) and marking is in accordance with para. 4.3.3. 5.1.3 Investment Castings. When investment castings are used for bodies, bonnets, or cover plates of valves NPS 4 and smaller where the ratings do not exceed Class 600, the requirements of the ASTM specifications referred to in Table 1 shall be met, except that it is permissible to deter- mine mechanical and chemical properties from a master heat and to use a 25 mm gage length × 6.25 mm diameter (1 in. × 0.25 in. diameter) tensile specimen in place of the standard 2 in. tensile specimen. A master heat is previously refined metal of a single furnace charge. Tensile specimens shall be cast in molds of the same refractory as the castings and shall be given the same heat treatment as the castings. When investment castings are used for sizes and pressure classes greater than those described in this paragraph, all the requirements of the applicable material specification listed in Table 1 shall be met.

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