A non-destructive crack detection method for steel jacket offshore platforms based on global and local responses

Abstract

A crack detection method for steel jacket offshore platforms based on global (displacement) and local (strain) responses is presented in this paper. One side panel of an idealized three-dimensional space frame structure was used in the numerical analysis; substructuring technique in finite element method was utilized as the numerical analysis procedure. Isoparametric thin shell elements, with reduced Gaussian integration, were used to discretize the whole structure. ABAQUS finite element software was used to solve the problem and process all information relating to the above-mentioned global and local responses. Numerical results obtained in the analysis have been compared with those obtained using other types of elements available in ABAQUS. The global and local parameters (displacements and strains) have been normalized using those obtained from the uncracked structure. It has been observed that the largest changes (in strain and stress) occur around the crack, but significant changes occur even away from the cracking weld toe. For cracks occurring at "one or both" saddle point(s), significant differences in strain exist to identify whether the cracking is on one side or on both sides. Significant change in slope of normalized global displacements, obtained around the crack, indicates the location of crack.Key words: crack detection, global and local responses, substructuring.