IIW White Paper

5 Needs and challenges in welding and joining technologies

5.3.3 NDT of welds by use of electric, magnetic and thermal techniques Here, on one hand advanced developments have the ability to characterise materials in terms of mechanical hardness, to achieve yield or tensile strength by use of micro-magnetic NDT taking into account the relationships between magnetic and mechanical properties. On the other hand, new types of magnetic sensors such as giant magnetic resistors (GMR) or giant magnet impedance (GMI) became available. By use of them, magnetic testing (MT) can be performed with a high sensitivity of 10 -8 × the value of the earth magnetic field. Thermography in combination with inductive heating, can revolutionise the inspection for surface-breaking flaws. By superimposing high-powered ultrasound, the contrast can be enhanced significantly and also near-surface- hidden flaws can be detected. 5.4 NDT modelling NDT modelling plays an increasing role for designing new procedures, demonstrating performance, analysing results and providing help to experts. Modelling tools are now used for ultrasonic, eddy current and radiographic testing. For more than a decade, the CEA (French Atomic Energy Commission) has been contributing to this evolution by developing the CIVA software and integrating the research of universities from various countries. Modelling tools can be based on semi-analytical calculations or finite element analysis. The first is quicker but the latter one can help to solve more complex situations. The scope of application fields has increased a lot during past years: nuclear industry, aircraft industry, steel industry, petrochemical, railways. Generally, the user can define the shape, size and material of the part to be inspected as well as the parameters of the inspection. Different types of flaws/defects can be placed in the simulated part, then the inspection results calculated and displayed in a similar manner to what would be obtained experimentally. The main advantages of using modelling tools are to: Reduce the cost (less welded samples with representative defects are necessary to qualify a new procedure). Help to understand NDT inspection results. Perform parametric studies in order to assess procedures and NDT performance. Assess the ability to be inspected of a given part leading to possible design modifications.

Help to design new sensors optimised to reach the adequate sensitivity. Compare the performance of different NDT methods on a given part.

An example of the use of such tools is given in Figure 5.20 aiming to compare the advantages of a phased array UT inspection compared to a RT one.

Simulation of RT results

( film C3 class - Source: Ir 192)

Simulation of phased array results (16 elements 5 MHz - Shear waves)

Part modelling

Figure 5.20 Example of modelling NDT results (reproduced courtesy Institut de Soudure)

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Through Optimum Use and Innovation of Welding and Joining Technologies

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