4 A Commentary for Understanding and Applying the Principles of the ASME Boiler and Pressure Vessel Code Available to Purchase

This chapter provides a commentary on the principles of the ASME Boiler and Pressure Vessel Code to help users apply common sense when using the Code. It provides engineers, owners, inspectors, regulatory institutions, and other Code users with a better understanding of the basic principles of the Code. The chapter begins with a discussion on the design factors used by the ASME Committee to determine allowable stress and the requirements for a Design Specification and a Stress Report. It then provides information on the seismic design requirements and describes the use of Service Levels A, B, C, and D to provide increased allowable stresses for upset, emergency, and faulted plant conditions, as appropriate. The chapter emphasizes the need for good engineering judgment by knowledgeable professional engineers. This is essential for understanding which computer output should be used or how the output must be modified. The chapter discusses the revision made in the Foreword to the ASME Code in the 1992 Addenda to specify that engineering dimensions require tolerances and that Code-specified dimensions are based on nominal sizes. A brief note is provided on the identification of the proper allowance for erosion and corrosion caused by service conditions. The chapter also points out concerns with the use of finite element analysis in design activities. Forming operations for pressure vessels and postweld heat treatment of some welded configurations are briefly covered. In addition, the chapter discusses the importance of performance-based quality assurance programs and the use of thermal relief devices to protect pressure vessels or piping against pressure that results from the heat of the fluid contained in the component. Other issues addressed include the evaluation of new hypothetical loads on equipment that has been Code Stamped, and the purpose of hydrostatic testing of pressurized equipment.