NDT.net 1998 Oct, Vol.3 No.10

Table of Contents ECNDT '98

Session: Chemical, Petrochemical

The Possibilities of Mobile Hardness Testing
A User-Related Hardness Testing Comparison of the Static UCI Method and the Dynamic Rebound Method

Dr. Jörg Sommer*
Krautkrämer GmbH & Co., Hürth, Germany



The UCI method

The Rebound or Leeb's method

Fig.9: Conversion of Hardness Leeb, HL, into HRC as a typical example for conversion tabless stored in rebound hardness testers. These curves are experimentally generated by material samples of different hardness measured by rebound and rockwell test.

Selecting the Method

Application UCI testing Rebound testing
Solid parts + ++
Coarse grain materials - ++
Steel and aluminum casted alloys o ++
HAZ with welds ++ -
Tubes: wall thickness > 20 mm ++ ++
Tubes: wall thickness < 20 mm ++ -
HAZInhomogeneous surfaces - +
Thin layers ++ -
Difficult to access positions + -
  ++ especially suited/ + well suited/ o suited sometimes/ - not recommended
Table 1: Applications for UCI and rebound hardness testing.

Importance of indentation size

Fig. 11:
Critical area of HAZ, schematically (left) and prepared for testing on a tube used in the offshore industry (right).

Fig. 12:
Schematic drawing of several indentation sizes for different hardness tests (right) inside the coarse-grain zone of a HAZ and as a simulation in the photo of Fig. 11 (left)

Wall thickness requirements

Hardness testing method Wall thickness in mm Wall thickness in inches
Rebound 20mm 7.9
UCI 2-3 mm 0.8 - 1.2
Table 3: Recommended minimum wall thickness.
Certain geometries could stiffen the test piece
allowing measurement of lower wall thickness.

Surface Quality

Dyna D
3 mm ball
11 Nmm
Dyna G
6 mm ball,
100 Nmm
MIC 2010
98 N
10 kp
MIC 205
50 N
5 kp
MIC 201
10 N
1 kp
MIC 2103
3 N
300 p
Rt value <=10µm <=30µm <=15µm <=10µm <=5µm <=2,5µm
Table 4: Maximum surface finish according to the Vickers standard.

Fig. 14: Hardness versus surface preparation. HVR indicates converted Vickers hardness values measured by rebound hardness testing.


  1. Kleesattel, C., Gladwell, G.M.L.: The Contact-Impedance Meter, Ultrasonics 6 (1968), 175-180 and 244-251.
  2. Kleesattel, C.: Das UCI Härteprüfverfahren, Krautkrämer Sonderdruck, Echo 27.
  3. Leeb, D.: Definition of the hardness value "L" in the Equotip dynamic measurement method. VDI Berichte 583 (1986), 109-133.
  4. Haas, R.: Erfahrungen mit einem mobilem Rückprall-Härteprüfgerät, Ambulante Härteprüfung am Bauteil, Lehrgangsunterlagen, Schweißtechnische Lehr-und Versuchsanstalt.
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