Photoelastic Study and Fatigue Tests of a Contoured, Integrally Reinforced Branch Connection

The paper describes the results of an extensive study of a contoured, integrally reinforced branch connection in a cylindrical pressure vessel (or run pipe). Three epoxy models were tested by means of three-dimensional photoelasticity using the stress-freezing and slicing technique. Loads applied were internal pressure, a longitudinal moment on the branch, and a transverse bending moment on the branch; one model was required for each mode of loading. Stress distribution curves are given. In addition, thirteen geometrically similar steel headers were fatigue tested by longitudinal and transverse forces cyclically applied to the branch pipes. Tests were conducted over a range of nominal stress in the branch. Stress concentration factors or stress indices from the photoelastic tests for bending and stress intensification factors from the bending fatigue tests are compared. Stress concentration factors for internal pressure loading, as derived from the photoelastic tests, are presented. Since stress intensification factors are not used to describe fatigue behavior under pulsating pressure, a similar comparison is not possible. Owing to the amount of data accumulated, only the most pertinent are presented; in every instance this includes the area of maximum stress.