The tungsten arc welding concept, originally introduced as a practical tool in 1950, is now established as the most versatile technique for producing fusion welds to the highest quality standards.
A temperature of around 4,000ºC is generated in the arc during welding and the role played by the electrode is therefore crucial. It must have a high melting point and it must be non-consumable: tungsten quickly established itself as the most suitable material. As the knowledge of arc characteristics increased however it became clear that the use of pure tungsten presented some limitations on process development, particularly arc starting, stability and electrode wear.
Early research showed that the addition of thoria resulted in overall improvements in performance and from this work a range of tungsten electrodes containing oxide additions or ‘dopants’ were introduced progressively.
Despite the clear significance of electrode composition the last 60 years has witnessed the publication of few scientific papers of practical use. Some of these advocate the widespread use of dopants on the basis of improved welding performance, some highlight the hazards associated with them.
Evidence supporting results of these trials is flawed however and cannot be used as a basis on which to make generalised conclusions. Here we present an objective review of what has become an emotive issue – the use of dopants in tungsten electrodes.
The issues under examination fall generally into two categories; those associated with technical and commercial advantages, and those relating to health hazards.