Ever wonder what the numbers on a welding electrode mean?
All mild steel welding electrodes are designated by a code that’s printed on them. This code takes the form EXXXX, or EXXXXX. So what do they mean?
The letter E designates that is it an electrode
ENNXX, or ENNNXX
The next two numbers (n) represent the tensile strength in 1000’s of psi. For example, an E7018 would have a minimum strength of 70000 psi. There are also high strength steel rods that have five numbers. In this case, the first three numbers represent the strength. An example of this would be 11018. This particular rod would have a minimum weld strength of 110000 psi.
The next number designates the position that the rod is suitable for use in. It can be either 1,2,or 3
1 means that it’s an all position electrode.
2 means that it’s only for use in horizontal or flat positions
3 means that it’s a flat position only electrode.
The last number indicates several things such as polarity, type of current, and chemical composition. and is often combined with the third number to designate a special type of electrode.
(1) Cellulose-sodium (EXX10). Electrodes of this type cellulosic material in the form of wood flour or reprocessed low alloy electrodes have up to 30 percent paper. The gas shield contains carbon dioxide and hydrogen, which are reducing agents. These gases tend to produce a digging arc that provides deep penetration. The weld deposit is somewhat rough, and the spatter is at a higher level than other electrodes. It does provide extremely good mechanical properties, particularly after aging. This is one of the earliest types of electrodes developed, and is widely used for cross country pipe lines using the downhill welding technique. It is normally used with direct current with the electrode positive (reverse polarity).
(2) Cellulose-potassium (EXX11). This electrode is very similar to the cellulose-sodium electrode, except more potassium is used than sodium. This provides ionization of the arc and makes the electrode suitable for welding with alternating current. The arc action, the penetration, and the weld results are very similar. In both E6010 and E6011 electrodes, small amounts of iron powder may be added. This assists in arc stabilization and will slightly increase the deposition rate.
(3) Rutile-sodium (EXX12). When rutile or titanium dioxide content is relatively high with respect to the other components, the electrode will be especially appealing to the welder. Electrodes with this coating have a quiet arc, an easily controlled slag, and a low level of spatter. The weld deposit will have a smooth surface and the penetration will be less than with the cellulose electrode. The weld metal properties will be slightly lower than the cellulosic types. This type of electrode provides a fairly high rate of deposition. It has a relatively low arc voltage, and can be used with alternating current or with direct current with electrode negative (straight polarity).
(4) Rutile-potassium (EXX13). This electrode coating is very similar to the rutile-sodium type, except that potassium is used to provide for arc ionization. This makes it more suitable for welding with alternating current. It can also be used with direct current with either polarity. It produces a very quiet, smooth running arc.
(5) Rutile-iron powder (EXXX4). This coating is very similar to the rutile coatings mentioned above, except that iron powder is added. If iron content is 25 to 40 percent, the electrode is EXX14. If iron content is 50 percent or more, the electrode is EXX24. With the lower percentage of iron powder, the electrode can be used in all positions. With the higher percentage of iron powder, it can only be used in the flat position or for making horizontal fillet welds. In both cases, the deposition rate is increased, based on the amount of iron powder in the coating.
(6) Low hydrogen-sodium (EXXX5). Coatings that contain a high proportion of calcium carbonate or calcium fluoride are called low hydrogen, lime ferritic, or basic type electrodes. In this class of coating, cellulose, clays, asbestos, and other minerals that contain combined water are not used. This is to ensure the lowest possible hydrogen content in the arc atmosphere. These electrode coatings are baked at a higher temperature. The low hydrogen electrode family has superior weld metal properties. They provide the highest ductility of any of the deposits. These electrodes have a medium arc with medium or moderate penetration. They have a medium speed of deposition, but require special welding techniques for best results. Low hydrogen electrodes must be stored under controlled conditions. This type is normally used with direct current with electrode positive (reverse polarity).
(7) Low hydrogen-potassium (EXXX6). This type of coating is similar to the low hydrogen-sodium, except for the substitution of potassium for sodium to provide arc ionization. This electrode is used with alternating current and can be used with direct current, electrode positive (reverse polarity). The arc action is smother, but the penetration of the two electrodes is similar.
(8) Low hydrogen-potassium (EXXX6). The coatings in this class of electrodes are similar to the low-hydrogen type mentioned above. However, iron powder is added to the electrode, and if the content is higher than 35 to 40 percent, the electrode is classified as an (EXX18).
(9) Low hydrogen-iron powder (EXX28). This electrode is similar to the (EXX18), but has 50 percent or more iron powder in the coating. It is usable only when welding in the flat position or for making horizontal fillet welds. The deposition rate is higher than (EXX18). Low hydrogen coatings are used for all of the higher-alloy electrodes. By additions of specific metals in the coatings, these electrodes become the alloy types where suffix letters are used to indicate weld metal compositions. Electrodes for welding stainless steel are also the low-hydrogen type.
(10) Iron oxide-sodium (EXX20). Coatings with high iron oxide content produce a weld deposit with a large amount of slag. This can be difficult to control. This coating type produces high-speed deposition, and provides medium penetration with low spatter level. The resulting weld has a very smooth finish. The electrode is usable only with flat position welding and for making horizontal fillet welds. The electrode can be used with alternating current or direct current with either polarity.
(11) Iron-oxide-iron power (EXX27). This type of electrode is very similar to the iron oxide-sodium type, except it contains 50 percent or more iron powder. The increased amount of iron powder greatly increases the deposition rate. It may be used with alternating direct current of either polarity.
Occasionally you’ll see a suffix after the first set, EXXXX-XX These are used to indicate the alloy materials and their proportions. As per the AWS:
-H4, H8, and H16 Indicates the maximum diffusible hydrogen limit measured in millimeters per 100 grams. H4 =4 ml, H8 = 8 ml, H16 = 16 ml
-A1 Carbon-Molybdenum 0.40 – 0.65 Mo
-B1 Chromium-Molybdenum 0.40 – 0.65 Cr 0.40 – 0.65 Mo
-B2 Chromium-Molybdenum 1.00 – 1.50 Cr 0.40 – 0.65 Mo
-B2L Chromium-Molybdenum Lower Carbon B2
-B3 Chromium-Molybdenum 2.00 – 2.50 Cr 0.90 – 1.20 Mo
-B3L Chromium-Molybdenum Lower Carbon B3
-B4L Chromium-Molybdenum 1.75 – 2.25 Cr 0.40 – 0.65 Mo
-B5 Chromium-Molybdenum 0.40 – 0.60 Cr 1.00 – 1.25 Mo
-B6 was E502 4.6 – 6.0 Cr 0.45 – 0.65 Mo
-B8 was E505 8.0 – 10.5 Cr 0.8 – 1.2 Mo
-C1 Nickel Steel 2.00 – 2.75 Ni
-C1L Nickel Steel Lower Carbon C1
-C2 Nickel Steel 3.00 – 3.75 Ni
-C2L Nickel Steel Lower Carbon C2
-C3 Nickel Steel 0.80 – 1.10 Ni
-NM Nickel-Molybdenum 0.80 – 1.10 Ni 0.40 – 0.65 Mo
-D1 Manganese-Molybdenum 1.00 – 1.75 Mn 0.25 – 0.45 Mo
-D2 Manganese-Molybdenum 1.65 – 2.00 Mn 0.25 – 0.45 Mo
-D3 Manganese-Molybdenum 1.00 – 1.80 Mn 0.40 – 0.65 Mo
-W Weathering Steel Ni, Cr, Mo, Cu
-G No required chemistry
-M Military grade May have more requirements
Source: TC 9-237