Abstract
In addition to providing an overview of the ASME Boiler and Pressure Vessel Code design rules applicable to Class 2 and 3 valves, where Class is defined in Section III of the ASME Code, Sub-Article NCA-2130, this paper offers some insight as to why the rules are as they are. The motivation comes from a request by the ASME Codes and Standards Committee, Components Subgroup, for the Valve Working Group to prepare this overview. The request came after discussing a question from a participant regarding how the “(Primary Membrane or Local) plus Bending” stress category should be addressed for a valve.
The paper goes beyond a basic overview of Code rules as it includes a discussion of the underlying valve standard ASME B16.34, looks at the valve rules in relation with the rest of the Code, and contributes some historical perspective. From a perusal of the Code both in general and during preparation of this paper, it is concluded that the valve Code rules could benefit from a few clarifications; thus, changes are proposed, and the Working Group is encouraged to consider them. In answer to the underlying question regarding the primary local stress category, it is shown that the need for a local stress evaluation would be rare for a valve.
