SMAW (Shielded Metal Arc Welding) Fundamentals
This domain tests SMAW (MMAW) fundamentals: electrode classification, current and polarity, arc length, electrode angle, slag control and electrode storage. The exam expects you to match an electrode and technique to the joint and code requirement.
Electrode and technique
- In the AWS classification E7018, the 70 means 70,000 psi minimum tensile strength; the 1 indicates all-position capability; the 8 indicates a low-hydrogen iron-powder coating.
- E6013 is a general-purpose rutile electrode with easy restriking and a smooth finish; E7018 is low hydrogen and needs dry storage.
- Hold a short arc-about the electrode core diameter-and use a work angle near 90° to the plate.
- Remove slag between passes; trapped slag causes lack of fusion.
Worked example
A fillet weld on 10 mm carbon steel must meet a low-hydrogen requirement. Reasoning: choose E7018, follow the manufacturer’s current range (for example, about 110–140 A for 3.2 mm), use DCEP or AC as approved, and store the electrodes in a heated quiver after drying. Clean the joint, strike the arc just ahead of the start, keep a short arc, and chip and brush each pass. E6013 might weld easily but does not meet the low-hydrogen control by itself.
Traps
Do not use damp E7018; moisture raises hydrogen cracking risk. Do not long-arc to spread heat; it increases spatter and fume and reduces penetration. Do not assume all electrodes run on the same polarity. Do not leave slag on a pass and weld over it.