Background on the New ASME PCC-1-2010 Appendices D O 'Guidelines for Allowable Gasket Contact Surface Flatness and Defect Depth' 'Assembly Bolt Load Selection'

摘要

ASME PCC-1 "Guidelines for Pressure Boundary Bolted Joint Assembly" has recently been published and includes several new or extensively revised appendices. Among those is a new Appendix D "Guidelines for Allowable Gasket Contact Surface Flatness and Defect Depth", which outlines a more practical approach, based on the gasket type being used, to determining acceptable surface flatness and defect tolerances. The approach is based on basic gasket elastic compressibility properties and follows a methodology similar to vessel flaw evaluation to provide guidance for the acceptable depth and size of flange seating surface defects. It will enable independent assessment of the acceptability of defects on a flange facing by inspection personnel without the need for experienced-based judgment for each individual defect by others. An additional new appendix is Appendix O "Assembly Bolt Stress Determination". In this appendix an alternative, more advanced method compared to the previous method employed in PCC-1 is outlined for the determination of the optimal assembly bolt stress for any bolted joint. The method is based on the maintenance of an acceptable level of gasket stress, with consideration of operating loads or effects acting on the joint. Sufficient data is contained within the appendix to enable the creation of site-specific target assembly bolt torque charts for all standard size flanges. In addition the method can be applied to non-standard joints for a site-wide approach to determining target assembly bolt stress levels on a systematic basis. This paper outlines the background into thedevelopment of both of these new appendices and includes further examples of the use of Appendix O.