Measuring Instruments in Welding — Complete Practical Guide
Introduction
Accurate measurement is fundamental to welding quality control. From joint preparation to final inspection, welders and inspectors use various instruments to verify dimensions meet WPS tolerances and applicable standards (ISO 5817, EN 1090, AWS D1.1).
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Vernier Callipers
The most versatile workshop instrument. Measures external, internal dimensions and depths. Resolution: 0.05mm (vernier) or 0.01mm (digital).
Applications: plate thickness, pipe diameter, bead width and height, bevel depth, wire and electrode diameter, root gap.
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Micrometer
Higher precision than callipers (0.001mm). Measures external dimensions in limited range (0-25mm, 25-50mm). Always use the ratchet for constant pressure. Zero-check before each measurement session.
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Welding Gauges
Purpose-built instruments for weld measurement: HI-LO gauge (misalignment), fillet weld gauge (leg and throat), Bridge Cam universal gauge (bevel angle, gap, root face, reinforcement, undercut, fillets), reinforcement gauge.
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Squares
Combination square (90° and 45°) for checking perpendicularity. Bevel protractor for measuring preparation angles to 1° accuracy.
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Feeler Gauges
Calibrated steel blades (0.05 to 1.00mm) for measuring root gap. Typical gap: SMAW 2.0-3.0mm, GMAW 1.0-2.0mm, GTAW 0.5-1.5mm.
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Thermometers and Pyrometers
Measure preheat and interpass temperatures. Types: contact thermocouple (±1°C), IR pyrometer (non-contact), temperature crayons (±1%). Measure 50-75mm from bevel (EN 1011-1).
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Summary Table
| Instrument | Resolution | Application | Approx. cost |
|---|---|---|---|
| Digital callipers | 0.01mm | Thickness, diameters | €20-80 |
| Micrometer | 0.001mm | Precise thickness | €30-100 |
| HI-LO gauge | 0.5mm | Misalignment | €30-60 |
| Fillet gauge | 1mm | Leg and throat | €15-40 |
| Bridge Cam | 0.5mm | Complete weld measurement | €40-80 |
| Combination square | 1° | Perpendicularity | €15-40 |
| Feeler gauges | 0.05mm | Root gap | €10-20 |
| Contact thermocouple | ±1°C | Preheat | €50-200 |
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*Article based on ISO 17025, AWS Welding Handbook, ISO 5817:2014, EN 1090-2:2018. Published at WeldFC Academy.*