Experimental Stress Analysis for Four 24-in. ANSI Standard B16.9 Tees

Abstract

This paper describes the experimental stress analysis of low cycle fatigue tests of four tees tested by Combustion Engineering, Inc. (C-E) under subcontract to Union Carbide Nuclear Division. These tests are part of the ORNL Design Criteria for Piping and Nozzles Program which is being conducted for the development of design criteria for nuclear power plant service piping components. The test assemblies were fabricated at C-E from commercially obtained ANSI B16.9 tees and matching diameter steel pipes welded to the tees, with suitable end closures and fixtures for applying the loads. The tees tested and discussed in this report are described in the following: Tee Number/Material/Nominal Size: T–11/carbon steel/24″ ×24″ ×24″ sch 160; T–12/carbon steel/24″ ×24″ ×10″ sch 40; T–13/carbon steel/24″ ×24″ ×10″ sch 160; T–16/stainless steel/24″ ×24″ ×24″ sch 10. Each tee test assembly was instrumented with approximately 240 rectangular strain gage rosettes for determining elastic stress distributions, and six linear variable displacement transducers for determining flexibility factors. Elastic-response tests were conducted for 12 loading conditions consisting of internal pressure, pure bending and torsional moments and direct force loads applied individually to the branch pipe extension and to one end of the run pipe. The other run pipe extension was fixed rigidly to the loading frame. Automatic data handling equipment and data reduction techniques were used to process the strain gage readings. For each loading condition, stress distributions were determined and the locations and magnitudes of the maximum stresses were identified. Test results are presented and compared with appropriate design formulas of the ASME Boiler and Pressure Vessel Code, Section III. After the elastic-response tests were completed, three of the tees were low-cycle fatigue tested by pressure cycling using transformer oil. The T-11 and T-13 tees were pressure cycled for 100 psig (790 kPa) to 7000 psig (48 360 kPa); whereas, the T-12 tee was pressure cycled from 0 psig (100 kPa) to 1800 psig (12 510 kPa). A low-cycle fatigue test was performed on the T-16 tee assembly by applying a bending moment to the branch pipe in the plane of the tee with the tee pressurized to a constant internal pressure of 300 psig (2170 kPa). All low-cycle fatigue tests were performed until a through-the-wall fatigue crack occurred as evidenced by a leak. Subparagraph NB-3653.6 of ASME Code, Section III, Division I, Nuclear Power Plant Components was used to calculate the fatigue design life and comparisons were made with the experimentally determined fatigue life.