Ultrasonic Monitoring of Electron Beam Welding

TWI Core Research Project 1134/2020

TWI undertook a Core Research Programme project to create an online monitoring tool for electron beam welding (EBW). This case study presents the scope and activities of the project as well as subsequent follow-on work.

Overview

The EBW process is currently being extended to enable the rapid welding of thick-walled components, as well as being developed for single pass application in the nuclear and the renewables sectors. It is usually performed inside large vacuum chambers, which is not ideal for many industries because of the costs of running large vacuum chambers, hence there is ongoing research and development (R&D) into reduced pressure electron beam welding (RPEBW) systems. A key part of enabling rapid production is the online monitoring of the welding to detect the emergence of any flaws which may be related to welding process parameters, such that immediate feedback loops can correct the parameters for optimum product quality.

Objectives

Investigate the possibility of using ultrasonic testing (UT) techniques to monitor the emergence of potential flaws in thick-section joints being created using RPEBW systems
Design a prototype UT system for real-time monitoring of RPEBW in process conditions

Solution

A review of potential UT techniques was undertaken including: time-of-flight diffraction (TOFD); full matrix capture/total focussing method (FMC/TFM); electro-magnetic acoustic transducer (EMAT); and PAUT. The last was chosen because (1) no magnetism, which is not agreeable to EBW, is involved, (2) the data volume is manageable in comparison to FMC/TFM, and (3) it provided options to correct for any image distortions.

The first task was to simulate the transient temperature profiles in the component during a welding event. This was done using finite element modelling. Ultrasonic simulation of the beam propagation in the component, when the metal temperature was ambient and when it was elevated, was utilised to establish the level of any distortion in the imaging, and compared with the experiment. Based on this, a prototype system was designed (see Figure 1), which has since been used in a project for EBW monitoring and is currently being considered for arc welding monitoring.

Conclusion

On completion, the project demonstrated that it is possible to undertake online monitoring of EBW, as the temperature levels it requires, using PAUT. Follow-on work then verified the efficacy of the approach for industrial use.

This project was funded by TWI’s Core Research Programme.

Figure 1. Prototype designed for EBW monitoring tool

Channa Nageswaran Technology Consultant

Channa has worked at TWI, since the beginning of 2003 on completion of an undergraduate degree in Aeronautical Engineering from Imperial College, London. Channa undertook an Engineering Doctorate degree while working in TWI with the Metallurgy Department of the University of Birmingham, delivering a thesis on the development of phased array ultrasonic techniques for inspection of heterogeneous anisotropic materials such as composites and austenitic welds.

Channa is the Chairman of the sub-commission for Ultrasonic Testing for the International Institute of Welding (IIW). Channa worked in the sub-commission to generate the ISO 23864 and ISO 23865 standards for FMC/TFM, performing the role of master editor of ISO 23865 and writing significant parts of the technical content of the document. These documents collated together best practice across industry represented by leading experts.

Channa’s current role in TWI is to be a Technology Consultant focused on R&D towards improved ultrasonic testing (UT) techniques.

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