FEM analysis of inspection manhole on large steel tanks

Abstract

The aim of this paper is to demonstrate how the correct application of FEM analysis can be used to find effective solutions for the design of mechanical structures. The design of the inspection openings on the tanks is being considered. There are several existing tanks of the same dimensions (20 m high and diameter 10,2 m), but they have different wall thicknesses (9,6; 15; 20 and 25 mm). For inspection purposes, assembly of manhole hatch on all tanks is required. The manhole hatch is designed applying standard API 650. All tanks are filled with the water to the top 20 m high. Several different analyses have been carried out in order to ensure that there are not too high stresses in the materials of the existing tanks due to the insertion of the manhole hatch and finally qualify construction according to EN-13445 norm. The elastic analysis shows that stresses in the material are too high and the design hasn’t been approved. In order to avoid redesign procedures, which can be expensive and sometimes difficult to do in reality, plastic analysis has been done. After plastic analysis, the design could be approved with the restriction on the max. preload force in the bolts 40 kN/per bolt.