Experimental Stress Analysis of 24-In. Tees

This paper describes the experimental stress analysis and low cycle fatigue test of one 24-in. dia, schedule 40 carbon steel, ASA Standrd B16.9 tee performed by Combustion Engineering, Inc. This program is part of the Oak Ridge National Laboratory Piping Program for the development of design criteria for nuclear service piping components. The tee was instrumented with 230 rectangular strain gage rosettes. Elastic data was obtained for 12 loading conditions consisting of internal pressure and orthogonal pure moment and orthogonal direct forces applied individually to the free branch and run ends of the tee. One of the run ends of the tee was “built in” throughout the test. All loads were applied through pipe extensions welded to the tee. The tee was tested to failure in a low cycle fatigue test with an in-plane bending moment on the branch pipe. The tee was pressurized to the design pressure of 1025 psig during the fatigue test. A cyclic stress of approximately ±83,600 psi was imposed on the tee and a through-the-wall fatigue crack occurred at 18,532 cycles. Significant test results are summarized and compared with design values tabulated in the current issue of the Nuclear Power Piping Code, USAS B31.7-1969.