A New Design Method for Obround Shells

Abstract

Abstract The design of obround components has been difficult and complex due to the absence of a suitable theoretical solution. Current design codes use empirical formulas based on assumptions to determine the minimum required thickness for obround components. The design process involves iteration. The results obtained are far from accurate. Based on a recently proposed closed-form solution, a new design method for obround components is developed. In the new method, an obround shell is imagined as being stretched laterally from a cylindrical shell or parent cylinder. With the flattened shell increasing, the thickness of the obround shell should increase accordingly, to keep the maximum hoop stress of obround shell consistent with the maximum hoop stress of the parent cylinder. The minimum requested thickness (MRT), of the obround shell is related to the MRT of the parent cylinder and the flattened shell length of the obround shell. Through parametric studies, those relationships are investigated. Empirical expressions are used to describe those relationships. Using the proposed design method, the determination of the MRT of obround members becomes the determination of the MRT of the parent cylinders and additional parameters. The MRT of obround members is determined directly. The case study demonstrates that the proposed method is an efficient and accurate design process for obround members. The use of new method for fitness-for-service was explored. The new method can be used to reassess operational safety in the event of vessel materials' deterioration.