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Single Sensor Top-Face Monitoring of Weld Penetration


Top-Face Monitoring of Weld Penetration Using a Single Sensor with Two Assessment Parameters

TWI Industrial Member Report Summary 619/1997

P C J Anderson and J Tapp

A top-face sensor system has been developed to monitor the depth of weld penetration during autogenous TIG welding.


For high integrity components, there is a need for a system to accurately determine weld bead penetration. Currently there are a number of sensor systems but each has generic limitations that define its application.

Previous work [1] suggested that a combination of sensor types may allow the restrictions of individual methods to be overcome, as the information made available by one sensor can be used to counteract the limitations of another. In particular, a system based upon simultaneous weld pool viewing and thermal sensing with a single infra-red camera was proposed.

  • Sensing by weld pool viewing does not appear to be affected by the surface condition of the workpiece, but is less reliable when used to detect variations in the component thickness and joint fit-up.
  • Thermal sensing with an infra-red camera can provide a qualitative indication of variations in these factors, although its quantitative accuracy for penetration control is adversely affected by variations in the surface emissivity of the component material.

Both techniques function independently of welding process, position and joint type.

This report details firstly the sensor system design, and secondly the operation of the sensor system on some autogenous TIG trial welds. The trial welds demonstrate that the sensor is able to detect changes in the thermal properties of a weld and, from that information conclude changes in the material thickness.


The objective of this project is to develop a top-face penetration control system for TIG welding.

The objectives of this phase of work were:

  • To design a top-face monitoring system using an infra-red camera such that it can detect variations in the weld pool shape and thermal information during TIG welding.
  • To use this information to determine changes in plate thickness.
  • To establish potential of the system for use as a control system.

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