Portable hardness testers for metals are compact instruments dedicated to the non-destructive hardness measurement of large, fixed or in-service metal components, or components of complex geometry, where traditional bench hardness testers cannot be used. The two main technologies are the Leeb method (dynamic rebound) and the UCI method (Ultrasonic Contact Impedance), which operate on different physical principles but both offer the portability required for field inspections. They are widely used in shipbuilding, industrial maintenance, quality control of large forgings and castings, and in-service inspection of steel structures.
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Leeb method
The Leeb method is based on the dynamic rebound of a small impact body of known mass fitted with a tungsten carbide ball: a calibrated spring propels it against the surface of the part at a defined velocity, and after impact it rebounds at a reduced velocity. The loss of velocity (energy absorbed by the part in plastic deformation) correlates with hardness: soft parts absorb a great deal of energy (low rebound), hard parts absorb little (high rebound). The ratio v_rebound/v_impact multiplied by 1000 gives the HL value (Leeb Hardness). Several impact devices are available (D, DL, C, G, S, E) with different masses and geometries, covering parts of different sizes and different hardness ranges.
UCI method
The UCI method (Ultrasonic Contact Impedance) uses a probe fitted with a small Vickers indenter (a square-based diamond pyramid) vibrating at its resonant frequency (typically 78 kHz). When the indenter presses against the part under a defined load, the contact area affects the resonant frequency, which decreases as a function of hardness (soft parts: larger contact area, lower frequency). The instrument measures the frequency shift and converts it into an HV (Vickers) hardness value. The small size of the UCI indentation (tens of µm) allows measurement on welded structures, HAZ zones, coatings and thin-walled components.
Features and conversions
Modern portable hardness testers integrate: automatic conversion of the primary scale (HL or HV) to other scales (HRC, HRB, HB, HV, estimated tensile strength σR) according to the ASTM E140 and DIN 50150 tables, with a warning about the validity limits of the conversion (which depend on the material and the range); automatic compensation for test direction (vertically downwards, horizontally, upwards – Leeb rebound varies with direction); statistics on measurement batches; GO/NOGO thresholds; Bluetooth/USB data output; PC software for advanced analysis.
Applications
Leeb hardness testers are used for: hardness checks on foundry castings, large forgings, shafts, gears, welded structures (HAZ verification), pressure vessels, shipbuilding and railway structures, pipelines and piping, and maintenance of mechanical assemblies in service. UCI hardness testers are particularly valued for: weld inspection (mapping of the heat-affected zone), thin components (where Leeb would require masses that are not available), thick coatings (hard chrome plating, galvanizing), gears with small teeth, and screw and bolt assemblies with a specified hardness grade.
Reference standards
The main standards are: ISO 16859 (Leeb hardness test method), ASTM A956 (the US equivalent); DIN 50159 (UCI hardness test). For conversion between scales: ISO 18265 and ASTM E140. Calibration of portable hardness testers uses ISO 17025 certified reference blocks with a known hardness value in the various scales (HRC, HB, HV). Performance verification and tip inspection (for UCI) are prescribed by the standard. Personnel carrying out inspections with NDT methods must be qualified (level 1, 2, 3 to ISO 9712).
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