Piping Codes provide equations to calculate the stress due to moments applied to piping components.The calculated stresses are then compared with the allowable stresses.If the calculated stresses do not exceed limits prescribed in the Code, the piping is deemed to be Code-acceptable in-so-far as the components in the piping system are concerned.The calculated stresses make use of -indices and -indices, Ref. [3] in the report, or stress intensification factors, Refs. [1, 2, 4] in the report. Reference [5] in the report suggested standardized methods for developing stress intensification factors.The magnitudes of the moments used in Code equations for stresses come from piping system analyses.There are many sources of uncertainty in piping system analyses.One source, addressed herein, is the use of in-accurate flexibility of components in piping systems.This is particular true for components with high stress indices or stress intensification factors which, usually, also have significant flexibility.Piping system analyses are based on beam-element models. The analyses may use stiffness factors rather than flexibility factors; however the translation from flexibility factors to stiffness factors is relatively simple.At present, most piping system analyses only use the flexibility of straight pipe and elbows or curved pipe.This PVRC project was initiated by a request from the B31 Mechanical Design Technical Committee.The purpose of this report is to suggest standardized methods for developing flexibility factors.Part 2 of this report discusses definitions of flexibility factors.Available data is discussed in Part 3; knowledge of existing data is deemed essential in planning the development of additional flexibility factors. Part 4 gives simple examples of the potential effect of flexibility factors on results obtained from piping system analyses. Part 5 discusses present Code guidance relevant to flexibility of components in piping systems; in general, this guidance is inadequate. Part 6.1 introduces Appendix A of the report which gives detailed suggestions for developing additional flexibility factors from test data.Part 6.2 discusses the development of additional flexibility factors from analytical data. While a “conservative” stress index or stress intensification factor is definable, a “conservative” flexibility factor is not definable. Thus, the goal is to develop best estimates of flexibility factors.