Stress Intensity Factor Calculation And Safety Assessment Of Fillet Weld Toe Surface Crack Of Large Storage Tank

The research of the article relies on the project of China Special EquipmentInspection Institute “Research on the Safety Assessment Technology of LargeStorage Tank”. The article studied the fillet weld crack which is the main failuremode of large storage tank. The calculating method and safety assessmenttechnology of fillet weld toe surface crack of large storage tank was mainlyresearched.To get the accurate stress field of fillet weld toe, four types of finite modelsincluding2D bottom plate-foundation contact model and3D LINK10bilinear modelwere built. On this basis,3D simplified constraint model was presented to calculatestress intensity factor of variable parameter crack.The1/4node singular element method was used to build the semi-ellipticalcrack model. A mixed mesh expanding method was presented to expand the cracksingular element. The detailed process for mixed mesh expanding method wasintroduced. Compared to the method of modeling node by node, the mixed meshexpanding method reduced the workload and can realize connection to complexwhole model. The accuracy of finite model was certified by comparing to thecalculated results of empirical formula.The surface semi-elliptical model of fillet weld toe of storage tank was built bymixed mesh expanding method. The stress distribution of storage tank was got by3D simplified constraint model and the stress intensity factor was got further. Theeffect of variable parameter a/c, a/t, Lw/t and θ to stress intensity factor value wasdiscussed. The calculated results showed that stress intensity factor values of storagetank fillet weld toe present U distribution along the crack front. The maximum stressintensity factor value emerges at the surface point. As the a/c or a/t increased, thestress intensity factor value went down. The results fit the variety law of radialdirection stress along the depth direction. Compared to the stress intensity factor calculated results of plate T-joint fillet weld toe surface crack with pure tension state,the stress intensity factor variation gradient of fillet weld toe surface crack of storagetank is much bigger at the surface point and the deepest point.A crack case was assessed using the general failure assessment diagram(FAD)of GB19624《Safety assessment for in-service pressure vessels containing defects》and whether the crack initiation emerges. The stress intensity factor data calculatedby the crack model built by the method presented in this article can be used tocalculate the Krof FAD. This article is a practice that stress intensity factorcalculated by using finite element method applies to engineering practice cracksafety assessment.