Electrode Classification, Handling and Storage
Decoding the AWS classification
Under AWS A5.1 (carbon steel), E7018 reads: E = electrode; 70 = 70,000 psi minimum tensile strength; 1 = usable in all positions (2 means flat and horizontal fillets only); 8 = coating and current type. Coating digits you must know: 0 = cellulosic sodium, DCEP only, deep penetration (E6010); 1 = cellulosic potassium, AC or DC (E6011); 3 = rutile, easy arc, shallow penetration, sheet metal (E6013); 4 = iron-powder rutile, high deposition, flat and horizontal only (E7024); 8 = low-hydrogen iron powder, AC or DCEP (E7018).
Suffixes carry real meaning: -1 indicates improved notch toughness, H4 means a maximum of 4 mL diffusible hydrogen per 100 g of deposited metal, and R means a moisture-resistant coating.
Storage rules
E7018 must go from the sealed pack into a holding oven at 120-150 degrees C. If it has absorbed moisture, rebake at 370-430 degrees C for at least an hour. Exposure out of the oven is commonly limited to about four hours, after which it is rebaked or discarded. Cellulosic electrodes (E6010, E6011) must stay dry but must never be baked at those temperatures - the cellulose coating degrades. Discard electrodes with cracked, swollen or flaking coatings, or rusted cores.
Worked example
E7018-1 H4R: 70 ksi minimum tensile, all position, low-hydrogen iron-powder coating for AC or DCEP, improved toughness, 4 mL/100 g maximum diffusible hydrogen, moisture-resistant coating. The H4R classification does not remove the holding-oven requirement once the pack is opened.
Traps
- Baking E6010 at 400 degrees C.
- Leaving E7018 in an open can overnight and welding with it.
- Bending electrodes to reach a restricted joint.