Infrared Inspection of Steel Structures Under Load

Abstract

This paper presents in detail the experimental methodologies and the results of the infrared investigation of the steel samples under load. Moreover the second, electromagnetic method (EM) for non destructing evaluation was used for monitoring the fatigue process. The IRT allows to observe the general global condition of the material while the EM to carry out local, detail examination of the fatigue stage in critical region. The presented inspection results are compared and discussed. 1. Introduction The dynamic development of many modern industries is associated with the production of the steel structures with a high level of complexity. It is expected that these structures meet the highest standards of safety. However, maintaining relatively low manufacturing costs are also crucial. The success of many companies and corporation is mainly based on the possibility of the long term and low cost product usage. Therefore the continuous and systematic monitoring of the changes in the material properties of the steel structures is very important. The crucial feature of such a monitoring is the necessity of observation the structure under load. The estimation of fatigue failure risk requires to carry out the analysis and prediction algorithms taking into consideration initial strength capacity, production technology and types of possible flaws introduced during production or operation period [1]. The process requires also determination of local condition of the material, which involves evaluation of its microstructure, applied and residual stress values in accordance to strain state as well as crack grow area within the examined region. Therefore, the need for application of nondestructive testing and evaluation methods contributing the process of determining the state of stress and damage in the material emerges [1, 2]. There are many methods, that can be useful in steel structures monitoring (electromagnetic, magnetic, radiographic and ultrasound). In the recent times the increased importance of thermographic method may be also observed [3]. Active infrared thermography is one of the methods that are widely used in the non-destructive testing of materials. Internal structure of the tested material, in particular defects (such as cracks or weakening of the structure caused by the mechanical stress) affect the free flow of heat. Sensitive infrared camera is used to observe the temperature distribution on the sample's surface. The high temperature resolution allows to observe even small internal inhomogeneities in the form of the overheated or colder places, showing the location, size and type of defects. The purpose of this paper is to present and compare the results of fatigue monitoring carried out by electromagnetic and infrared thermography method [4]. 2. Experimental methods and systems