Derivation of Stress Intensification Factors for a Special, Contoured, Integrally Reinforced Branch Connection

Abstract

The results of an extensive experimental investigation of a contoured, integrally reinforced branch connection in a cylindrical pressure vessel (or run pipe) have been reported [1]. One size model, specifically a 12 in. (0.375) × 6 in. (0.280) standard weight header was studied by three-dimensional photoelasticity using the stress-freezing and slicing technique. Loads applied were internal pressure, plus in-plane and out-of-plane bending moments on the branch; one model was used for each mode of loading. In addition, carbon steel headers were fatigue tested by longitudinal and transverse moments cyclically applied to the branch pipes. A model was required for each mode of loading for each level of amplitude of applied nominal stress. Stress concentration factors (stress indices) were derived from the photoelastic tests, whereas, the fatigue tests produced stress intensification factors. The stress indices and stress intensification factors derived from the tests apply only to 12 × 6 standard weight headers, or geometrically identical headers, with the particular type of branch connection. This paper describes how generalized stress intensification factor equations were derived to cover a broad range of sizes and thicknesses of headers incorporating the same type of branch fitting. In this paper the term “header” applies to a single branch connection in a pipe remote from all other discontinuities.