1.1 SMAW — Shielded Metal Arc Welding (Stick)
Key Takeaways
- SMAW uses a consumable flux-coated electrode that provides shielding gas, slag, and alloying elements
- SMAW requires a constant current (CC) power source and operates on AC, DCEP, or DCEN depending on electrode type
- E7018 is the most common structural electrode — low-hydrogen, all-position, AC or DCEP
- Low-hydrogen electrodes must be stored at 250–300°F and reconditioned if exposed to atmosphere for more than 4 hours
- The electrode classification system (e.g., E7018) encodes tensile strength, positions, and coating/current type
- SMAW deposition efficiency is only about 60–65% due to stub loss, spatter, and slag
1.1 SMAW — Shielded Metal Arc Welding (Stick)
Shielded Metal Arc Welding (SMAW), commonly called stick welding, is one of the oldest and most versatile arc welding processes. It is the most widely used process in field welding, maintenance, and repair work due to its portability and ability to weld in all positions.
Process Fundamentals
SMAW uses a consumable electrode coated in flux. The arc is struck between the electrode tip and the base metal, generating intense heat (approximately 6,000–10,000°F / 3,300–5,500°C) that melts both the electrode core wire and a portion of the base metal. As the electrode melts, the flux coating:
- Decomposes to produce a shielding gas that protects the molten weld pool from atmospheric contamination (oxygen, nitrogen, hydrogen)
- Forms a slag layer over the solidifying weld metal, providing additional protection during cooling
- Adds alloying elements to the weld metal (depending on electrode classification)
- Stabilizes the arc through ionizing compounds in the coating
SMAW Equipment
| Component | Function |
|---|---|
| Power source | Provides constant current (CC) — either AC, DC+, or DC- |
| Electrode holder (stinger) | Clamps the electrode and conducts welding current |
| Work clamp (ground clamp) | Completes the electrical circuit by connecting to the workpiece |
| Welding cables | Carry current from the power source to the holder and clamp |
| Electrodes | Consumable filler metal with flux coating |
Electrode Classification System (AWS A5.1 / A5.5)
The AWS electrode classification system for carbon steel electrodes (A5.1) uses a standardized naming convention:
Example: E7018
| Character | Meaning |
|---|---|
| E | Electrode |
| 70 | Minimum tensile strength in ksi (70,000 psi) |
| 1 | Usable positions (1 = all positions; 2 = flat and horizontal only) |
| 8 | Coating type and current type (8 = low-hydrogen potassium, AC/DCEP) |
Common Electrode Types:
| Electrode | Coating | Current | Positions | Key Characteristics |
|---|---|---|---|---|
| E6010 | Cellulosic (high) | DCEP only | All | Deep penetration, fast-freeze, great for root passes and pipe |
| E6011 | Cellulosic (high) | AC or DCEP | All | Similar to 6010 but works on AC — versatile field electrode |
| E6013 | Rutile | AC, DCEP, DCEN | All | Light penetration, smooth arc, good for thin materials |
| E7018 | Low-hydrogen iron powder | AC or DCEP | All | Most widely used structural electrode, low-hydrogen reduces cracking risk |
| E7024 | Iron powder rutile | AC, DCEP, DCEN | Flat/Horizontal | High deposition rate, heavy iron powder coating |
| E7028 | Low-hydrogen iron powder | AC or DCEP | Flat/Horizontal | Similar to 7018 but higher deposition for flat/horizontal only |
Low-Hydrogen Electrodes — Critical Knowledge
Low-hydrogen electrodes (E7015, E7016, E7018, E7028) are essential for welding high-strength steels, thick sections, and restrained joints because they minimize the amount of diffusible hydrogen introduced into the weld — the primary cause of hydrogen-induced cracking (cold cracking).
Storage requirements for low-hydrogen electrodes:
- Store in a heated rod oven at 250–300°F (120–150°C) after removing from sealed packaging
- If exposed to atmosphere for more than 4 hours, they must be reconditioned (rebaked) at 500–800°F (260–425°C) for 1–2 hours
- Some codes limit the number of times an electrode can be reconditioned
For the Exam: Low-hydrogen electrode storage and reconditioning requirements are heavily tested on Part A. Remember: 250–300°F holding temperature and 4-hour maximum atmospheric exposure before reconditioning is required.
Advantages and Limitations
| Advantages | Limitations |
|---|---|
| Highly portable — minimal equipment | Lower deposition rate than semi-automatic processes |
| Works outdoors in wind (self-shielded) | Requires frequent electrode changes (stub loss) |
| Welds all positions | Slag must be removed between passes |
| Welds most ferrous metals and many alloys | Operator skill significantly affects quality |
| Low equipment cost | Typical deposition efficiency only 60–65% |
| Excellent for field/maintenance/repair work | Arc time limited by electrode length |
What type of power source characteristic does SMAW require?
What does the "18" in E7018 indicate?
At what temperature should low-hydrogen electrodes (E7018) be stored in a holding oven?
Which SMAW electrode is most commonly used for structural steel welding and is classified as low-hydrogen?