Meaning of E7018 Welding Rod
E7018 is one of the most frequently used SMAW/ stick welding low hydrogen electrodes for mild steel and Carbon Steel welding. The electrode coating are made with inorganic coverings that contain minimal moisture thus provide a weld deposit with lowest hydrogen in weldment, thus giving name to these electrodes as Low Hydrogen Electrodes. Low-hydrogen electrode coverings can be designed to resist moisture absorption for a considerable time in a humid environment so, even they kept in a humid place, they will need significant time to absorb the moisture. E7018 electrodes also contains relatively high percentage of iron powder added into the coating which gives higher productivity as you will get more weld deposit compare to E7015 electrode of same diameter.
Note (Don’t try it on actual job): For understanding resistance to moisture absorption, dip a E7018 electrode in water for few minutes and weld. You will not see any porosity in the weld. Now, try similar experiment with E7010 or E6013 types & you will observe significant weld porosity.
Due to the thick covering and deep cup produced at the arcing end of the electrode, iron powder electrodes can be used very effectively with a “drag” technique. This technique consists of keeping the electrode covering in contact with the workpiece at all times, which makes for easy handling. However, a technique using a short arc length is preferable if the 3/32 in or 1/8 in [2.5 mm or 3.2 mm] electrodes are to be used in other than flat or horizontal fillet welding positions or for making groove welds.
E7018 electrode Specification & classification
E7018 electrodes are classified according to ASME Section IIC, 5.1 Specification for Carbon steel electrodes for Shielded metal arc welding. Similar to other welding electrodes, each digit in E7018-H4 electrode have its own meaning. These digit gives very valuable information about this electrode as given below:
- E stands for Electrodes for SMAW or stick welding.
- The next two digits i.e. 70 indicate the tensile strength of weld deposit is 70 KSI or 70000psi.
- The next digit 1 indicates it is all position electrode.
- The last digit 8 indicates it is a basic coated electrode with improved deposition rate ( because of added iron powder in the coating ) and low hydrogen type.
E7018 electrode Optional Supplemental Designators
Now, there are additional supplementary designation for E7018. When it is E7018 -1, So, here by 1, it means that it is suitable for low temperature application welding as the weld deposit has improved notch toughness or impact properties.
Sometimes, an Optional Supplemental Designators suffix H4 or H8 is used which indicates possible Hydrogen content in weld:
· H4 = Less than 4 ml/100 grams.
· H8 = Less than 8 ml/100 grams
H16 = = Less than 16 ml/100 grams.
Sometimes a suffix R is used which means the electrode meets the requirement of absorbed moisture test.
Hydrogen available in electrode coating or in atmosphere, finds its way in weld metal from moisture in the welding consumable so baking of E7018 electrode is very important. (Especially if the electrodes were left in atmosphere, they will absorb moisture). Electrodes shall be kept sufficiently hot in portable oven to eliminate chance of any additional moisture getting in electrode.
The diffusible hydrogen into the weld metal if presents in sufficient quantity, will cause to hydrogen cracking or cold cracking as the hydrogen atoms will gets trapped while the weld will cool fast due to rapid cooling caused by welding.
Charpy V-Notch Impact (toughness) Requirements for E7018 type electrode
E7018 require Stick welding electrode to have minimum V-Notch toughness values of 20 ft·lbf at –20°F [27 J at –30°C].
Electrodes with the optional supplemental designations which is E7018-1 shall meet the lower temperature impact requirements of 20 ft·lbf at –50°F [27 J at –45°C].
General recommendation to avoid Hydrogen Cracking
Once a steel has been selected and purchased for welding, the options available to counter the
possibility of hydrogen cracking include:
- Minimize weld joint restraint.
- Avoid notches in the area of the weld.
- Use a low hydrogen process.
- Use low hydrogen consumables and ensure their proper storage.
- Use high arc energy to reduce the cooling rate (but this may reduce other properties such as strength and toughness).
- Use preheat (and post-heat); its main function is to slow down the cooling rate below 100°C and give more time for hydrogen to diffuse out.
- It’s recommended to provide a post heat for 15 to 30 minutes period to allow hydrogen diffusion after welding finish @ 300 to 350 Deg C.
- Target to avoid hard microstructure – if weld cooling rates is high, detrimental phases such as martensite & bainite can form in weld and HAZ which are prone to Hydrogen cracking.
- Minimize restrain to allow residual stresses accommodation.
E7018 Welding electrode Polarity
E7018 electrodes are can be used with AC and DCEP polarity. The potassium based coating allow good arc characteristics using AC as well as DCEP current with E7018 electrodes.
E7018 vs E7024 Electrode
E 7024 electrodes are not suitable for all positions, as the number 2 indicates, but only for horizontal and flat/plane positions while E7018 is all position electrode. E7018 is low hydrogen potassium based coating while E7024 is rutile titania coating. Click here to learn deep about E7024 electrode.
The ASME, F numbers are completely different for both electrodes. E-7024 (Rutile iron powder flux coating) having F No. 1, is not in the same class as E-7018, , Low hydrogen-potassium-iron powder flux that have F no. 4.
The similarities of E7018 & E7024 are:
- Both are having iron powder coating.
- Both have 70ksi minimum tensile strength
E7018 welding rod uses
E7018 electrodes are basic C-Mn steel used for moderate strength purposes. These electrodes can be used for joining all mild steel, low carbon steel and medium carbon steels without any weldability issues.
Selection of current for E7018 Electrode
The correct welding amperage (current) setting mainly depends on the electrode diameter used. For example, a 1/8-inch 7018 rod runs well from 90 to 150 ampere, while a 3/16 inch 7018 rod welds at currents up to 300 ampere.
Below tables gives the recommended welding amperage for E7018 electrode diameter 3/32, 1/8, 5/32, 3/16, 7/32 & 1/4 inch sizes.