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6. OPERATION PROCEDURE
6.1. Measurement of mechanical stress of metal of
steel products, metal structures
Measurement of the mechanical stress of the metal of a
steel product or metal structure consists in magnetizing the
inspected area of the metal with a constant magnetic field,
measuring the strength of the field of residual magnetization
over this surface, and evaluating the mechanical stress of the
metal.
Note: the dynamic measurement mode of the stress
scanner is the main mode of operation for continuous
monitoring of the stress-strain state of the metal of extended
steel products and structures.
The static measurement mode of the stress scanner is
auxiliary and is used mainly to refine location, verify and
confirm the surface of a steel product or structure where an
area with an increased stressed state of the metal is detected.
6.1.1. Enable the dynamic measurement mode of the
metal stress scanner. Install the magnetic measuring unit at the
beginning of the inspected area of the metal surface of the steel
product, metal structure and smoothly bring it into
translational motion along the inspected surface.
6.1.2. Measure the values and get a graph on the stress
scanner screen of the distribution of the field strength of the
residual magnetization of the metal (in mT) on the inspected
surface of the steel product, metal structure.
6.1.3. Based on the analysis of the graph of the
distribution of the residual magnetic field strength of the metal
on the inspected surface of the steel product, structure:
- presence of areas with increased stressed state of the
metal;
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- coordinates of the location of areas with increased
stressed state of metal on steel products, metal structures;
- actual mechanical stress value in the area with
increased stressed state of the metal.
6.1.3.1. The stress scanner readings in the area with
increased stress-strain state of the metal will have the highest
values.
6.1.3.2. The location of the amplitude on the graph of
field strength distribution of the residual magnetization of
metal will correspond to the location of the region with the
greatest mechanical stress of the metal on the surface of steel
products, steel structures.
6.1.3.3. To estimate the value of mechanical stress in
an area with an increased stress-strain state of the metal:
- determine the value of the signal amplitude according
to the graph on the stress scanner screen corresponding to the
area with an increased stressed state of the metal;
- set the value of the mechanical stress of the metal (in
MPa) for the received signal amplitude in the area with an
increased stressed state of the metal. For this purpose, the
curves of the dependence of the field strength of the residual
magnetization on the value of the mechanical stress of the
metal, previously obtained on standard samples of structural
steels, are used.
Note: if the calibration constants previously obtained
for structural steels of different grades are stored in the
electronic memory of the stress scanner during its manufacture
(see Appendix), the readout the stress scanner screen will
correspond to the value of the mechanical stress of the metal
for this steel grade (in MPa).
