Experimental study of behavior of austenitic stainless steel thin-walled elbows - Functional capability

Results of a serie of 15 tests on 90 large radius elbows are presented. These elbows were made from Z2 CN 18 10 steel (corresponding to ASME TP 304 L) and had an outside diameter-to-wall thickness ratio of 89.5. They were subjected to in-plane (opening and closing) and out-of-plane bending moments. Changes in elbow angular deflection and ovalization of the mid section were recorded as a function of applied moment.Measurements were made well into the plastic region. Influence of pressure, temperature and cyclic loading were also studied. The tests therefore supplied extensive data on the behavior of an austenitic stainless steel thin-walled elbow when subjected to large displacements, including its ability to carry the required flow under high loadings. Analysis per the RCC-M (1983) was also performed to quantify flow area reductions at stress limits allowed by these rules. Main results were as follow: Tested elbows exhibited satisfactory behavior in deformation and withstood large angular displacements without excessive damage. Althought tests were continued well into the plastic region, it was not possible to take these components to failure. The least favourable loading mode was in-plane bending closing the elbow. Internal pressure increased component stiffness and therefore favourably affected overall elbow behavior. Temperature and preliminary cyclic loading both had an unfavourable effect significantly lowering the experimental limit moment. Flow area reductions recorded at the experimental limit moment were low. Analysis per the RCC-M of the component under study demonstrated substantial safety margins on the experimental limit moment. If class 1 level D service limits are met, functional capability of the tested elbow is assured.