7 - Testing and evaluation of weld cracking in ferrous alloys

Abstract

Ferrous alloys are extensively used as structural materials in various industries due to their widely different metallurgical and mechanical properties. Quality assurance programmes play a crucial role for ferrous alloys and ferritic steel welded components. In general, testing and evaluation of materials and components are an integral part of a quality assurance programme. For an effective quality assurance programme, integrated use of destructive, semi-destructive and non-destructive testing techniques is essential. In this chapter, the importance of the quality assurance programme for ensuring the integrity of ferritic steel welded components and the application of various destructive, semi-destructive and non-destructive testing techniques is discussed. Destructive techniques such as tensile testing and impact testing, semi-destructive techniques such as hardness, corrosion and metallography, and non-destructive testing techniques such as X-ray, ultrasonics and acoustic emission are discussed. Emphasis is given to testing techniques such as ultrasonics, X-ray and metallography due to their applicability in all stages of the ferrous alloy welded components, starting from the fabrication stage to plant maintenance and in the life extension programme. The importance of understanding the formation and quantitative estimation of residual stresses and distortion in welds is also included. Semi-destructive hole-drilling and non-destructive X-ray and ultrasonic techniques for the quantitative estimation of residual stresses are discussed in detail. The applicable codes and standards for welding of ferrous alloy components and destructive and non-destructive testing techniques for evaluation of welded components are also identified in this chapter.