5.3 Essential Welding Definitions and Terminology
Key Takeaways
- Definitions/terminology account for ~12% of Part A — the largest single topic area
- Key geometry terms: root opening, root face, groove angle, bevel angle, weld toe, weld face, weld root
- Three throat measurements: theoretical (0.707 × leg), effective (diagram), actual (includes penetration)
- DCEP = DC Electrode Positive (formerly Reverse Polarity); DCEN = DC Electrode Negative (formerly Straight)
- Heat input formula: HI (kJ/in) = (V × A × 60) / (Travel Speed × 1,000)
- Essential variables require re-qualification if changed; non-essential variables do not
5.3 Essential Welding Definitions and Terminology
Definitions and terminology account for approximately 12% of Part A — the largest single topic area. Precise understanding of these terms is essential because exam questions often hinge on the exact definition.
Weld Joint Geometry Terms
| Term | Definition |
|---|---|
| Root opening | The separation between members at the root of the joint |
| Root face (land) | The unbeveled portion of the groove face at the root |
| Groove angle | The total included angle of the groove between the members |
| Bevel angle | The angle of the bevel on a single member (groove angle = sum of bevel angles) |
| Root | The point where the members are closest together before welding |
Weld Metal Terms
| Term | Definition |
|---|---|
| Weld face | The exposed surface of a weld on the side from which welding was done |
| Weld toe | The junction between the weld face and the base metal |
| Weld root | The point where the back of the weld intersects the base metal surface |
| Weld reinforcement | Weld metal built up above the surface of the base metal |
| Weld throat (theoretical) | Minimum distance from root to face in a fillet weld (0.707 × leg for equal legs) |
| Weld throat (effective) | Minimum distance from root to face of the diagrammatic weld cross-section |
| Weld throat (actual) | Minimum distance from root to face of the actual weld — accounts for penetration beyond the root |
| Leg size | The distance from the root to the toe of a fillet weld, measured along each member |
Electrode and Process Terms
| Term | Definition |
|---|---|
| DCEP (DC Electrode Positive) | DC Reverse Polarity — electrode is positive terminal |
| DCEN (DC Electrode Negative) | DC Straight Polarity — electrode is negative terminal |
| Arc length | Distance from the electrode tip to the surface of the weld pool |
| Travel speed | Speed of the electrode along the weld joint |
| Contact tip-to-work distance (CTWD) | Distance from the contact tip to the workpiece (GMAW/FCAW) |
| Stickout (electrical stickout) | Length of electrode extending beyond the contact tip |
| Deposition rate | Weight of weld metal deposited per unit time (lbs/hr) |
| Deposition efficiency | Ratio of weld metal deposited to filler metal consumed (%) |
| Duty cycle | Percentage of 10-minute period that equipment can operate at rated output |
Heat Input
Heat input is the amount of energy delivered to the weld per unit length. It is critical for controlling HAZ properties, distortion, and microstructure.
Formula:
Heat Input (kJ/in) = (Voltage × Amperage × 60) / (Travel Speed in in/min × 1,000)
Or with metric units:
Heat Input (kJ/mm) = (V × A × 60) / (Travel Speed in mm/min × 1,000)
Important: Some codes and applications include a process efficiency factor (η):
- SMAW: η ≈ 0.80
- GMAW/FCAW: η ≈ 0.80
- GTAW: η ≈ 0.60
- SAW: η ≈ 0.95
Inspection and Quality Terms
| Term | Definition |
|---|---|
| Acceptance criteria | Specified limits for discontinuity size, type, and distribution that determine accept/reject |
| Procedure Qualification Record (PQR) | Record of welding variables used to produce a test weldment and the test results |
| Welding Procedure Specification (WPS) | Document providing required welding variables for a specific application |
| Welder Performance Qualification (WPQ) | Test demonstrating a welder's ability to produce sound welds per WPS |
| Essential variable | A welding variable that, if changed beyond specified limits, requires re-qualification |
| Non-essential variable | A welding variable that can be changed without requiring re-qualification |
For the Exam: Know the exact definitions for weld face, weld toe, weld root, weld throat (all three types), reinforcement, and leg size. Also know DCEP vs. DCEN and the heat input formula. These terms appear in multiple choice questions where incorrect options use similar-sounding but wrong definitions.
What is the theoretical throat of an equal-leg fillet weld with 1/2" legs?
DCEP (DC Electrode Positive) is also known as:
Using the heat input formula, what is the heat input for: 25V, 200A, travel speed 10 in/min?