ASME B16.34:2017 pdf free download – Valves – Flanged, Threaded, and Welding End
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 Table 2-1.1 throughTable2-3.19 for−29°C (−20°F). Someofthemate- rials listed in Table 1, notably some carbon steels, may undergo adecreaseinductilitywhenusedatlowtempera- turestosuchanextentastobeunabletosafelyresistshock loading, sudden change of stress, or high stress concen- tration. 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 manufac- turer prior to the time of purchase.
2.3.3 Fluid Thermal Expansion. Under certain condi- tions, some double-seated valve designs are capable of sealing simultaneously against pressure differential from the center cavity to the adjacent pipe in both direc- tions. Acircumstance in which the centercavityis filled or partially filled with liquid and subjected to an increase in temperaturecanresultinanexcessivebuildup ofpressure in the center cavity that may lead to pressure boundary failure. An example is apipingsystem inwhich liquidfrom the condensing, cleaning, or testing fluids accumulates in the centercavityofa closed valve. Such accumulation may resultfrom leakage pastthe upstream seatofthe valve. If, during subsequentstartup, the valve is notrelieved ofthe liquid by partial opening of the valve or by some other method, the retained liquid may be heated during warm-up of the system. Where such a condition is possible, it is the responsibility of the user to provide, or require to be provided, means in design, installation, or operation procedure to assure that the pressure in the valve will notexceed thatallowed bythis Standard for the attained temperature.
2.4 Guidance for the Use of Flanged Valve Ratings
Application offlanged-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. Precautions regarding the bolting of raised face flanges to cast iron flanges are given in ASME B16.5 and ASME B16.47.
5.1.1 Application. Itisnotrequiredthatidenticalmate- rial ormaterial form be used forbodyand bonnetorcover parts. The rating applied, however, shall be based on the valve body. The bonnet or cover shall be designed and material selected so as to comply with the body pres- sure–temperature rating. Selection of stems, disks, and other parts, such as bonnet gaskets and bolting, subject to pressure and other loading, must be consistent with the applicable valve pressure–temperature rating.
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 ofvalves NPS 4 and smaller where the ratings do not exceed Class 600, therequirements ofthe ASTM specifications referred to in Table 1 shall be met, exceptthatitis permissible to deter- mine mechanical and chemical properties from a master heatandtousea25 mmgagelength× 6.25 mmdiameter(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.