ASME B16.34:2013 pdf download.Valves一Flanged, Threaded, and Welding End.
(f) Ratings intermediate to tabulated values are determined by linear interpolation between temperatures within a class number or between class numbers, except that for flanged-end valves interpolation between tabulated classes is not permitted. A further exception is that Class 400 valves having ASME B16.5 or ASME B16.47 flanged ends shall use the intermediate rating method of para. 2.1.5.
(g) In all cases, valves shall be constructed so that the body, bonnet or cover, body bolting, and bonnet or cover bolting meet the 38°C (100°F) pressure rating requirements for the designated pressure class or pressure— temperature rating. However, pressure—temperature ratings for the valve may be otherwise limited by construction details or material design considerations, in which case the requirements of paras. 4.3.3 and 7.2.6 shall be met.
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 Table 2 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 Table 2 with an identifying label “B — Special Class.” Special Class ratings shall not be used for flanged-end valves.
2.1.4 Limited Class Valves. Welding- or threaded- end valves in sizes NPS 2’/2 and smaller that conform to the requirements of Mandatory Appendix V may be designated Limited Class valves. Pressure—temperature ratings shall not exceed the values calculated in accordance with Mandatory Appendix V. Limited Class ratings shall not be used for flanged-end valves.
2.1.5 Intermediate Rated Valves. A Standard Class or Special Class welding- or threaded-end valve or a Standard Class 400 flanged-end valve may be assigned an intermediate pressure—temperature rating or Class in accordance with para. 6.1.4, provided all other applicable requirements of this Standard are met. Correspondingly, an intermediate pressure rating or Class for Limited Class valves having welding ends or threaded ends may be assigned pressure—temperature ratings as determined by the method described in Mandatory Appendix V in conjunction with the interpolation procedure described in para. 6.1.4.ASME B16.34 pdf download.