Application of Non-Destructive Testing for Condition Analysis, Repair of Damages and Integrity Assessment of Vital Steel Structures

Loads at vital steel structures occur during their production and assembly (residual stresses), during the execution of functional tasks in exploitation (stationary and dynamic loads) and during the disturbed process of exploitation (non-stationary dynamic loads). Considering the fact that stress concentrators, corrosion and unpredictable effects that occur during exploitation must be taken into account as well, it is clear that loading of vital structures during the design phase can not be represented with a model in which the parameters change uniformly. Therefore only experimental non-destructive tests performed at large steel structures during exploitation enable the assessment of their current condition, need for particular repairs and assessment of integrity. In that way the data necessary for determination of causes of degradation of material and welded joints at structures, for the evaluation of mutual influence of equipment parts, as well as for determination of functionality and reliability of operation of drive systems. This primarily refers to vital steel structures of bucket-wheel excavators, dredgers and cranes, as well as to vital steel structures at hydroelectric equipment, thermal power plant equipment, bridges etc. This paper presents the analysis of causes for the occurrence of damages at the support structure of the boom of the bucket-wheel excavator, which is operating at the open pit coal mine near Kostolac (Serbia), that was executed on the basis of non-destructive tests. The paper also contains the procedure for the repair of damaged structure through the application of adequate welding, performed at existing and newly produced components, and the assessment of structural integrity after the repair based on non-compliances detected during the design process, as well as during the making of the support structure of the bucket-wheel excavator boom due to inadequate radiuses defined during the processes of design and production and due to the existence of flaws on the surface and within welded joints.