Effect of Internal Pressure on Flexibility and Stress-Intensification Factors of Curved Pipe or Welding Elbows

Abstract

The flexibility and stress-intensification factors presently applied in piping-flexibility analysis to account for the behavior of curved pipe in bending have been derived from theories and tests with no internal pressure. Pressure tends to reduce the effect of these factors but in smaller and relatively thick-wall piping commonly used in the past the effect is of a low order and may be neglected; in larger diameter relatively thin-wall piping the effect is pronounced and significant. Using strain-energy methods the present paper develops a theory establishing the flexibility and stresses due to in-plane and out-of-plane bending including the effect of internal pressure, and proves its adequacy by means of carefully conducted tests. In a final step, the complex theoretical formulas are reduced to a simple and readily usable approximation.