1. Overview
Shielded Metal Arc Welding (SMAW) uses flux-coated consumable electrodes. The flux generates shielding gas, forms protective slag, stabilizes the arc, and adds alloying elements. Electrode selection directly impacts weld quality and mechanical properties.
Key Terms
| Term | Definition |
|---|---|
| Tensile Strength | Minimum weld metal tensile (ksi). Must meet or exceed base metal SMYS. |
| Deposition Efficiency | Deposited weld metal / consumed electrode weight (58-75% typical). |
| Low-Hydrogen | Electrodes with <8 ml H₂/100g. Required for thick sections (>0.5") and high-strength steel. |
| Polarity | DCEP: deeper penetration. DCEN: faster deposition. AC: alternating. |
| Position | 1G (flat), 2G (horizontal), 3G (vertical), 4G (overhead). All-position = any. |
Common Selection Errors
| Problem | Cause | Solution |
|---|---|---|
| Hydrogen cracking | High-H electrode on thick/high-CE steel | E7018 (low-H) + preheat |
| Strength mismatch | E6010 on X70 pipe | E8018-G (80 ksi tensile) |
| Poor root fusion | E7018 for root pass | E6010 for penetration |
| Porosity | Wet low-H electrodes | Store at 250-300°F |
API 1104 Note: Electrode type is an essential variable. Changing classification (e.g., E7018 to E8018-G) requires WPS requalification.
2. AWS Classification System
AWS A5.1-2012 (carbon steel) and A5.5-2014 (low-alloy steel) standardize electrode naming. Each digit conveys specific properties.
AWS A5.1 Classification Format:
E XX Y Z [-Suffix]
E = Electrode
XX = Tensile strength (×1000 psi)
60 → 62 ksi min 70 → 72 ksi min 80 → 80 ksi min
Y = Position
1 = All positions 2 = Flat/horizontal only 4 = Vertical-down
Z = Current & coating type
0 = DCEP, cellulose sodium (E6010)
1 = AC/DCEP, cellulose potassium (E6011)
2 = AC/DCEN, titania sodium
3 = AC/DC, titania potassium (E6013)
4 = AC/DC, iron powder titania (E7014)
5 = DCEP, low-H sodium
6 = AC/DCEP, low-H potassium
8 = AC/DCEP, low-H iron powder (E7018)
Alloy Suffixes (AWS A5.5)
| Suffix | Alloy | Service |
|---|---|---|
| -C1 | 2.5% Ni | Low temp to -50°F |
| -C2 | 3.5% Ni | Cryogenic to -75°F (LNG) |
| -G | Unspecified | General purpose high-strength |
| H4 | — | <4 ml H₂/100g (extra low-H) |
| H8 | — | <8 ml H₂/100g (standard low-H) |
| R | — | Moisture-resistant coating |
Mechanical Properties by Classification
| Electrode | Tensile | Yield | Elong. | Base Metal Match |
|---|---|---|---|---|
| E6010/E6011 | 62 ksi | 50 ksi | 22% | A36, X42-X52 |
| E7018 | 72 ksi | 60 ksi | 22% | A572 Gr 50, X52-X60 |
| E8018-G | 80 ksi | 68 ksi | 19% | X70 pipeline |
| E9018-G | 90 ksi | 78 ksi | 17% | X80 pipeline |
| E10018-D2 | 100 ksi | 87 ksi | 16% | X100, HY-100 |
3. Common Electrode Types
E6010 — Pipeline Root Pass
High cellulose sodium coating provides deep penetration for root passes. Fast-freezing puddle enables vertical-down welding on cross-country pipelines.
E6010 Parameters:
Polarity: DCEP only
Position: All positions, vertical-down
Penetration: Deep (0.25-0.375")
Arc: Forceful spray-type
Spatter: Moderate-high
Storage: Dry area (not moisture-sensitive)
Current (Amperes):
3/32": 40-80 A | 1/8": 75-125 A
5/32": 110-170 A | 3/16": 140-215 A
E7018 — Low-Hydrogen Standard
Workhorse for structural and pipeline fill/cap. Low hydrogen (<8 ml/100g) prevents cracking. Requires strict moisture control.
E7018 Parameters:
Polarity: AC or DCEP
Position: All positions (vertical-up preferred)
Penetration: Medium
Arc: Smooth, quiet
Slag: Heavy, self-peeling
Current (Amperes):
3/32": 70-110 A | 1/8": 100-150 A
5/32": 130-200 A | 3/16": 175-250 A
STORAGE REQUIREMENTS:
• Rod oven: 250-300°F continuous
• Field exposure: 4 hours max
• Re-bake: 700-800°F × 1 hr if exposed >4hr
Moisture Warning: Wet E7018 causes porosity and hydrogen cracking. Discard if exposed beyond limits.
Deposition Efficiency
| Electrode | Efficiency | Coating | Best Use |
|---|---|---|---|
| E6010 | 58% | Cellulosic | Root passes |
| E6013 | 65% | Titania | Sheet metal |
| E7018 | 68% | Low-H iron powder | Fill/cap passes |
| E7024 | 75% | High iron powder | Flat production |
| E8018-G | 68% | Low-H iron powder | X70 pipeline |
4. Selection Criteria
Strength Matching
Weld metal tensile must meet or exceed base metal SMYS. Target overmatch ratio: 1.2-1.4×.
Base Metal to Electrode Selection:
API 5L Grade SMYS Electrode
────────────────────────────────────
X42 42 ksi E7018
X52 52 ksi E7018
X60 60 ksi E7018 or E8018-G
X65 65 ksi E8018-G
X70 70 ksi E8018-G
X80 80 ksi E9018-G
Overmatch = Electrode Tensile / Base SMYS
E8018-G on X65: 80/65 = 1.23 ✓
Hydrogen Cracking Prevention
HIC occurs when hydrogen diffuses into HAZ. Control: hydrogen source, microstructure, and restraint.
Carbon Equivalent (IIW Formula):
CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15
CE < 0.35: Low risk
CE 0.35-0.45: Moderate - use low-H electrodes
CE > 0.45: High risk - preheat + low-H + controlled cooling
Preheat Estimate:
T (°F) = 50 + 500 × CE (for CE > 0.35)
Preheat Table (ASME B31.8)
| Wall | Ambient >50°F | 32-50°F | <32°F |
|---|---|---|---|
| <0.500" | None | 50°F | 100°F |
| 0.500-0.750" | 50°F | 100°F | 200°F |
| 0.750-1.000" | 175°F | 200°F | 250°F |
| >1.000" | 250°F | 275°F | 300°F |
Low-H required for t >0.750", SMYS >52 ksi, or prior cracking.
Interpass: Maintain preheat throughout. Max 400-500°F to prevent grain coarsening.
5. Pipeline Welding (API 1104)
Cross-country pipeline construction uses E6010 root passes and E7018 fill/cap. Standardized per API 1104.
API 1104 Standard Sequence (24" OD × 0.375" wall):
Joint Prep: 30° bevel each side (60° included)
1/16" root face (land)
3/32" root opening
ROOT (Pass 1): E6010, 5/32", 110-130A DCEP, vertical-down
HOT PASS (2): E6010, 5/32", 130-150A, wash root
FILL (3-5): E7018, 1/8", 120-180A, vertical-up
CAP (6): E7018, 1/8", 110-140A, smooth finish
Time: 25-40 min/joint | Electrodes: 15-25 rods/joint
Electrode Consumption
| Pipe | Wall | Root | Fill/Cap | Total |
|---|---|---|---|---|
| 12" OD | 0.375" | 4-5 rods | 8-10 rods | ~1.5 lb |
| 24" OD | 0.500" | 8-10 rods | 18-22 rods | ~3.5 lb |
| 36" OD | 0.625" | 12-15 rods | 35-45 rods | ~6.5 lb |
Common Defects
| Defect | Cause | Fix |
|---|---|---|
| Incomplete penetration | Low current | Increase amps, proper fit-up |
| Porosity | Moisture | Dry electrodes, clean surface |
| Slag inclusion | Poor cleaning | Wire brush each pass |
| Undercut | High current | Reduce amps, pause at edges |
| HIC cracking | Hydrogen | Low-H, preheat, slow cool |
6. Storage & Handling
Proper storage prevents moisture contamination—the primary cause of porosity and hydrogen cracking with low-H electrodes.
Storage Requirements
| Electrode | Storage | Exposure | Re-dry |
|---|---|---|---|
| E6010/E6011 | Ambient dry | N/A | Not required |
| E7018 | 250-300°F | 4 hours | 700-800°F × 1 hr |
| E7018-H4R | 250-300°F | 9 hours | 650-750°F × 1 hr |
| E8018/E9018 | 250-300°F | 4 hours | 700-800°F × 1 hr |
| E10018/E11018 | 300-350°F | 2 hours | 800-850°F × 2 hr |
Re-dry Limit: Low-H electrodes may only be re-dried ONCE. Discard if exposed twice. Excessive re-drying degrades coating.
Field Practices
- Issue 1-2 lb/welder to minimize exposure
- Heated quivers: 150-200°F for field work
- Return unused: Back to oven within exposure limit
- Inspect coatings: Discard if cracked or chipped
Applicable Codes
| Code | Scope |
|---|---|
| AWS A5.1-2012 | Carbon steel electrodes (E60XX, E70XX) |
| AWS A5.5-2014 | Low-alloy electrodes (E80XX+) |
| API 1104 | Pipeline welding, WPS qualification |
| ASME B31.8 | Gas transmission piping, preheat |
| AWS D1.1 | Structural welding |
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