SFA-5.12/SFA-5.12M 2011a SECTION IT, PART C

TABLE 1 CHEMICAL COMPOSITION REQUIREMENTS FOR TUNGSTEN ELECTRODES

Classification Chemical Composition Requirements

Symbol Oxide Addition Impurities, Tungsten, Color Code, <ISO 6848 Mass Mass RGB Color Value, and

Classification) Principal Oxide Mass Percent Percent Percent Color Sample"

EWP None N.A.b 0.5 max. 99.5 max. Green (WP) #008000

EWCe-2 Ce02 1.8 to 2.2 0.5 max. Balance Grey (formerly orange) rwce 2oJ #808080

EWLa-1 LazOJ 0.8 to 1.2 0.5 max. Balance Black (WLa 10) #000000

EWLa-1.5 LazOJ 1.3 to 1.7 0.5 max. Balance Gold (WLa 15) #FFD700

EWLa-2 La203 1.8 to 2.2 0.5 max. Balance Blue (WLa 20) #OOOOFF

EWTh-1 Th02 0.8 to 1.2 0.5 max. Balance Yellow (WThlOJ #FFFFOO

EWTh-2 Th0 2 1.7 to 2.2 0.5 max. Balance Red (WTh 20) #FFOOOO

<WTh 30) Th02 2.8 to 3.2 0.5 max. Balance Violet #EE82EE

EWZr-1 Zr02 0.15 to 0.50 0.5 max. Balance Brown (WZr 3) #A52A2A

EWZr-8 Zr02 0.7 to 0.9 0.5 max. Balance White rwzr 8) #FFFFFF

EWG The manufacturer The manufacturer 0.5 max. Balance The manufacturer may must identify all must state the select any color not

additions. nominal quantity already in use. of each addition.

GENERAL NOTE : Intentional additions of "doping oxides" other than indicated for a particular electrode classification is prohibited .

NOTES :

a. RGB color values and color samples can be found at the following website: http://msdn2.microsoft.com/en-us/library/ms531197 .aspx

b. N.A. = Not applicable.

3.3 Electrodes classified under one classification shall not be classified under any other classification in this speci­fication .

3.4 No electrode meeting the requirements of any other classification, shall be classified under EWG.

3.5 The electrodes classified under this specification are intended for gas tungsten arc welding (GTA W), gas tungsten arc cutting (GTAC), plasma arc welding (PAW), or plasma arc cutting (PAC), but that is not to prohibit their use with any other process for which they are found suitable. See Clause B2 for an explanation of the classifi­cation system.

4. Acceptance

Acceptance of the electrodes shall be in accordance with the provisions of AWS A5.01M:A5.01 (ISO 14344 MOD).

310

See Annex Clause B3 for further inj01mation concerning acceptance and testing of material shipped.

5. Chemical Analysis

Chemical analysis shall be performed on specimens of the electrode being classified. Any analytical technique may be used but, in cases of dispute, reference shall be made to established published methods. The referee method shall be ASTM F 288. The results of the analysis shall meet the requirements of Table 1 for the classification of electrode under test.

6. Retests

If any test fails to meet the requirement, that test shall be repeated twice. The results of both retests shall meet the requirements. Specimens for retesting may be taken

(

(

(

(

SFA-5.12/SFA-5.12M 2011a SECTION II, PART C

Lanthanated tungsten electrodes can be used for both dcen and ac applications.

B7 .4 EWTh-X Electrode Classifications. The EWTh-X electrodes are tungsten electrodes containing tho­rium oxide, referred to as thoria. The thoria in all classes is responsible for increasing the usable life of these electrodes over the EWP electrodes because of their higher electron emission, better arc starting and arc stability. They gener­ally have longer life and provide greater resistance to tung­sten contamination of the weld.

SAFETY NOTE

Thoria is a low-level radioactive material. However, if welding is to be performed in confined spaces for prolonged periods of time, or if electrode grinding dust might be ingested, special precautions relative to ventilation should be considered. The user should consult appropriate safety personnel.

The following statement was developed by the Interna­tional Institute of Welding (IIW) Commission VIII on Health and Safety:

STATEMENT OF COMMISSION VIII ON HEALTH ASPECTS IN THE USE OF

THO RIA TED TUNGSTEN ELECTRODES

"Thorium oxides are found in Thoriated Tungsten Elec­trodes {up to 4.2% (ISO 6848-WT 40 Electrode)} 6

• 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 Vill will continue to keep these aspects under review."

6 " Up to 4.2% (ISO 6848- WT 40 Electrode)" was deleted from ISO 6848 at the time of publishing 2004 edition, and it was never in AWS A5.12/A5.12M.

318

B7.4.1 EWTh-1 (WTh 10) Electrode Classification (Yellow). These electrodes were designed for direct current applications. They have 0.8-1.2 percent of thoria content dispersed throughout their entire length. They maintain a sharpened point well, which is desirable for welding steel. They can be used on alternating current work, but a satisfac­tory balled end, which is desirable for the welding of nonferrous materials, is difficult to maintain.

B7.4.2 EWTh-2 (WTh 20) Electrode Classification (Red). The higher thoria content (1.7-2.2 percent) in the EWTh-2 electrode causes the operating characteristic improvements to be more pronounced than in the lower thoria content EWTh-1.

Should it be desired to use these electrodes for alternat­ing current welding, then balling can be accomplished by briefly, and carefully, welding with direct current electrode positive prior to welding with alternating current. During alternating current welding, the balled end does not melt and so emission is not as good as from a liquid ball on an EWP electrode.

B7.4.3 (WTh 30) Electrode Classification (Violet). This 3% thoriated electrode has no commercial significance in the United States.

B7.4 EWZr-X Electrode Classifications

B7.5.1 EWZr-1 (WZr 3) Electrode Classification (Brown). The EWZr-1 electrode is a tungsten electrode containing about 0.3% zirconium oxide, referred to as zir­conia. This electrode is preferred for applications where tungsten contamination of the weld must be minimized. This electrode performs well when used with alternating current, as it retains a balled end during welding and has a high resistance to contamination.

B7.5.2 EWZr-8 (WZr 8) Electrode Classification (White). This 0.8% zirconiated electrode has no commer­cial significance in the United States.

B7.6 EWG Electrode Classification (manufacturer may select any color not already in use). The EWG electrode is a tungsten electrode containing an additive not specified by an existing classification. The purpose of the addition is to affect the nature or characteristics of the arc, as defined by the manufacturer. Although no additive is specified, the manufacturer must identify any specific addi­tions and the nominal quantities added.

B8. General Recommendations

These recommendations, when followed, should main­tain high weld quality and promote welding economy in any specific application.

B8.1 The appropriate current (type and magnitude) should be selected for the electrode size to be used. Too great a current will cause excessive melting, dripping, or

(

(