ELASTIC STRESSES AND LIMIT BENDING MOMENTS OF CONCENTRIC AND ECCENTRIC REDUCERS SUBJECTED TO BENDING MOMENTS

In order to assess the safety of concentric reducers and eccentric reducers, the meridian stress and circumferential stress of the reducers subjected to in-plane bending moments are calculated based on the membrane theory. Solutions of limit bending moments are derived by using the approach with the equivalent stress and engineering coefficient. The solutions for both reducers are identical, as the formulas are composed of a base term multiplied by a bending moment coefficient. The limit bending moments are dominated by the small end of the reducers. The value of limit bending moment of the reducers is 14.6% more than that of a thin wall reducing elbow with same diameter and thickness when corresponding bending coefficient lambda>3.0. But comparison with a straight pipe which has the same diameter and thickness as the small end of the reducers, the limit bending moment of the reducers is 11.1% lower and the constant in the formula for the reducers is 3.6 instead of 4.0 for straight pipe. It could be dangerous to determine the limit bending moment of concentric reducers and eccentric reducers directly from the formula of limit bending moment for a thin wall pipe.