What is Tungsten?

Tungsten is a rare steel-grey colored metal and an element on the periodic table, represented by the symbol W. Tungsten has the highest melting point of all known elements, with a melting point of 6,192° F (3,422° C).

What are Electrical Characteristics of Tungsten?

The current carrying capacity of tungsten electrodes is dependent upon

Classification or Type of Tungsten
Current Type and Polarity
- DCEN Direct : Current Electrode Negative (best capacity)
- AC : Alternating Current
- DCEP : Direct Current Electrode Positive (worst capacity)
Diameter of Tungsten
Torch head air cooled or water cooled
Shielding gas used

How is Tungsten Used In Welding?

Tungsten electrodes are non-consumable in that they do not intentionally become part of the weld metal as do electrodes used as ﬁller metals. The function of a tungsten electrode is to initiate and provide an arc which supplies the heat required for welding or cutting.

Tungsten Types for Welding

The alloys or additional elements added to tungsten are referred to as “doping oxides” by the A5.12 standard.

EWP : Pure - GREEN

EWP is commercially pure tungsten identified by the color green.

Current carrying capacity is lower than the alloyed tungsten types. EWP has good stability when used with balanced alternating current. When being used on AC EWP will maintain a smooth balled or spherical end which has traditionally been preferred for aluminum welding. If too much current is passed through the tungsten for its given diameter the ball on the end of the tungsten will become fluid, dance around and in some cases become ejected into the weld puddle. As with any of the other applications properly size the tungsten for the given application.

EWCe-2 : 2% Ceriated - GREY

“-2” Ceriated tungsten is identified by the color Grey (formerly Orange), and contain 2% cerium oxide (1.8-2.2 wt.%).

The addition of ceria to pure tungsten improves the ease of arc initiation, arc stability, and reduces the rate of vaporization or burn-off. Unlike thoria, ceria is not radioactive. EWCe-2 operates successfully with alternating current or direct current.

EWLa-1 : 1% Lanthanated - BLACK

“-1” lanthanated tungsten is identified by the color Black, and contains 1% lanthanum oxide (0.8-1.2 wt.%).

The advantages and operating characteristics of this electrode type are very similar to those of EWCe-2.

EWLa-1.5 : 1.5% Lanthanated - GOLD

“-1.5” lanthanated tungsten is identified by the color Gold, and contains 1.5% lanthanum oxide (1.3-1.7 wt.%).

The increased proportion of lanthanum enhances arc starting and stability, reduced tip erosion rate, and increased current range. Lanthanated tungsten can be used for both DCEN and AC applications.

EWLa-2 : 2% Lanthanated - BLUE

“-2” lanthanated tungsten is identified by the color Blue, and contains 2% lanthanum oxide (1.8-2.2 wt.%).

The increased proportion of lanthanum enhances arc starting and stability, reduced tip erosion rate, and increased current range. Lanthanated tungsten can be used for both DCEN and AC applications.

More recent trends of GTAW aluminum welding use EWLa-2 on AC with a sharpened or pointed tip with improved performance over EWP balled tungsten.

ETh-1 : 1% Thoriated - YELLOW

“-1” thoriated tungsten is identified by the color Yellow, and contains 1% thorium oxide (0.8-1.2 wt.%).

Thoria is effective at increasing the usable life of the tungsten in comparison to EWP electrodes. Thoriated tungsten has higher electron emission, better arc starting and arc stability, they generally have longer life and provide greater resistance to tungsten contamination of the weld when used on DCEN.

ETh-2 : 2% Thoriated - RED

“-2” thoriated tungsten is identified by the color Red, and contains 2% thorium oxide (1.7-2.2 wt.%).

Thoriated tungsten maintains a sharpened point well which is desirable for DCEN welding.

Thoriated electrodes are not acceptable for DCEP or AC welding as the tip of the tungsten does not ball, but under the DCEP portion of the electrical cycle causes miniscule splintering that has a tendency to spit small pieces of tungsten which contaminates the weld.

EWZr-1 : 1% Zirconiated - BROWN

“-1” zirconiated tungsten is identified by the color Brown, and contains 0.3% thorium oxide (0.15-0.50 wt.%).

This electrode is preferred for applications where tungsten contamination of the weld must be minimized. This electrode is best used with alternating current, as it retains a balled end during welding and has a high resistance to contamination.

EWZr-8 : 8% Zirconiated - WHITE

“-8” zirconiated tungsten is identified by the color White, and contains 0.8% thorium oxide (0.15-0.50 wt.%).

This electrode is best used with alternating current, as it retains a balled end during welding and has a high resistance to contamination.

EWG : General Classification

“G” tungsten is a general classification defined by the manufacturer, and includes proprietary additives not defined by the A 5.12/SFA 5.12 specification. The manufacturer defines the color to identify the tungsten, so the color cannot be compared between different companies.

Tungsten Specification

The SFA 5.12 standard speciﬁes requirements for classiﬁcation of non-consumable tungsten electrodes for inert gas shielded arc welding, and for plasma welding, cutting, and thermal spraying.

The classification of tungsten electrodes is based upon its chemical composition.

The ASME SFA-5.12 standard is an adoption of the AWS A5.12 standard, and the ASME SFA-5.12 can be found in ASME Section II Part C.

Safety

The following statement has been developed by the International Institute of Welding (IIW) Commission VIII on Health and Safety…

“Thorium oxides are found in Thoriated Tungsten Electrodes . Thorium is radioactive and may present hazards by external and internal exposure. If alternatives are technically feasible, they should be used”.

“Several studies carried out on Thoriated Electrodes have shown that due to the type of radiation generated, external radiation risks during storage, welding, or disposal of residues are negligible under normal conditions of use”.

“On the contrary, during the grinding of electrode tips there is generation of radioactive dust, with the risk of internal exposure. Consequently, it is necessary to use local exhaust ventilation to control the dust at the source, complemented if necessary by respiratory protective equipment. The risk of internal exposure during welding is considered negligible since the electrode is consumed at a very slow rate.

“Precautions must be taken in order to control any risks of exposure during the disposal of dust from grinding devices”.

“The above statement is based on a considered view of the available reports. Commission VIII will continue to keep these aspects under review”.

Tungsten for Welding SFA 5.12