1.1 SMAW — Shielded Metal Arc Welding (Stick)

Shielded Metal Arc Welding (SMAW)

Shielded Metal Arc Welding (SMAW) — called stick welding in the field — is one of the oldest and most versatile arc processes and the one a CWI encounters most often in maintenance, repair, and field erection. Its appeal is portability: a power source, two leads, and a box of electrodes are all that is required, and the self-generated shielding tolerates moderate wind that would defeat a gas-shielded process.

SMAW uses a consumable electrode consisting of a solid core wire surrounded by a baked-on flux coating. The arc is struck between the electrode tip and the base metal, producing temperatures near 6,000–10,000°F (3,300–5,500°C) that melt both the core wire and a portion of the base metal. As the electrode burns, the coating performs four jobs the inspector must understand:

1. Decomposes into a shielding gas that displaces atmospheric oxygen, nitrogen, and hydrogen from the molten pool
2. Forms a slag that floats over the solidifying bead, slowing cooling and protecting it from the air
3. Adds deoxidizers and alloying elements (Mn, Si, Ni, Mo) per the electrode classification
4. Stabilizes the arc through ionizing salts (potassium, sodium) and provides cellulose or iron powder

Power Source and Polarity

SMAW requires a constant-current (CC), also called drooping, power source. Because the welder manually controls arc length, CC output keeps amperage nearly steady even as the arc lengthens or shortens, so the bead and penetration stay consistent. Polarity is a frequent exam point:

Electrode Classification (AWS A5.1 / A5.5)

The carbon-steel electrode classification (AWS A5.1) packs the electrode's mechanical and operating data into the digits after the letter E. Memorizing the decode is essential for Part A.

Example: E7018

Low-Hydrogen Electrodes and Storage

Low-hydrogen electrodes (E7015 DC-only, E7016 AC/DC, E7018, E7028) minimize diffusible hydrogen, the driver of hydrogen-induced (cold/underbead) cracking in hardenable and restrained steels. Because the coating absorbs atmospheric moisture, codes mandate strict handling, and AWS D1.1 Table 5.x is heavily tested:

• Store unopened rods, then hold in a rod oven at 250–300°F (120–150°C).
• Atmospheric exposure is limited (commonly 4 hours for E70 series); beyond the limit the electrode must be reconditioned/rebaked at 500–800°F (260–425°C) for 1–2 hours.
• Coatings that get wet are scrapped, not dried — moisture chemically bonds.

Exam trap: 250–300°F is the holding temperature; 500–800°F is the rebake temperature. Mixing the two is a classic wrong answer.

Heat Input and Diagnostics

SMAW deposition efficiency is only 60–65% because of stub loss (~2"), spatter, and slag. Travel speed and amperage set bead size; too-fast travel narrows the bead and can cause undercut, while too-slow travel piles up metal and risks slag inclusions. A worked heat-input example for SMAW: at 140 A, 24 V, 6 ipm, heat input = (24 × 140 × 60) / 6 = 33,600 J/in (33.6 kJ/in) — within typical structural limits.

The inspector should also understand the welder-controlled variables that the WPS pins down for SMAW: electrode size and amperage, arc length (kept roughly equal to the electrode core diameter; a long arc loses shielding and causes porosity and spatter), travel angle (drag versus push), and work angle in fillets. 1 prohibit. Restarts at the end of each electrode are also inspection points, since a cold restart can trap slag or leave incomplete fusion.

Finally, SMAW is prone to arc blow — magnetic deflection of the arc on DC, especially near the work-lead connection or at plate edges — which AC current or repositioning the ground helps control.