ISO 5948:1994 pdf download – Railway rolling stock material 一Ultrasonic acceptance testing.
9 Setting of the sensitivity of the instrument
9.1 General
The setting of the sensitivity of the instrument shall be carried out under the same conditions (see 7.2 and clause 8) as the tests themselves.
In the case of discontinuity-detection tests, in each case the sensitivity shall be set so that, within the area to be scanned outside the “dead zone” (see note 2 to table 1), a reference reflector with a diameter specified as acceptance standard in clause 12 can, irrespective of its distance from the surface to be scanned, be detected positively.
NOTE 3 Calibration blocks applied for establishing the
DGS diagrams or for setting the sensitivity according to
9.2, 9.3 or 9.4 shall have an acoustic attenuation similar to
that of the wheels or tyres to be tested.
9.2 Sensitivity setting for wheels or tyres
9.2.1 For wheels or tyres to be tested with the beam in an axial or radial direction and to be evaluated by the distance-gain-size (DGS) method, the sensitivity is set with the help of the DGS diagram and the backwall echo occurring when axially testing the tyre or the wheel rim.
9.2.2 For wheels and tyres to be evaluated by the comparison method, the sensitivity shall be set:
a) when being tested with the beam in an axial direction, with the help of a calibration block of the type shown in figure 1 and an internal reference standard of the type shown in figure 2 (see note 4) (both may be combined in the same block); or
b) when being tested with the beam in a radial direction, with the help of a calibration block of the type shown in figure 3.
NOTE 4 In this International Standard, “internal reference standard” means a calibration block with a bore on the backwall with the position, form, depth and diameter indicated in figure 2.
9.3 Sensitivity setting for axles
9.3.1 For axles to be tested with the beam in a radial direction and to be evaluated by the DGS method, the sensitivity is set with the help of the DGS diagram and the occurring backwall echo.
method, the sensitivity shall be set, when being tested with the beam in a radial direction, with the help of a calibration block of the type shown in figure 4.
9.4 Sensitivity setting for testing the permeability of axles
For testing the permeability (ultrasonic transparency) of axles, the amplification shall be adjusted such that the height of the first backwall echo obtained on a standard axle admitted by the purchaser is 90 % of the screen height.
10 Scanning
10.1 Each individual component shall be scanned. Unless otherwise agreed in the order or its appended documents, the scanning shall be carried out on the areas indicated in table 1, column 10.
10.2 When choosing the time of scanning, it shall be taken into consideration that, depending on the heat-treatment conditions, discontinuities may occur during a certain period after the steel has reached ambient temperature.
10.3 Adequate coupling between the probe and the product shall be maintained and the probe shall be moved over the surface to be tested (see 10.1) to ensure that the maximum possible volume of the component is scanned by the ultrasonic beam.
The rate of scanning shall be selected in order to ensure that it is possible to detect all defects which are considered to be inadmissible.
11 Evaluation of indications
11.1 Estimation of the size of discontinuities
When any significant discontinuity is indicated during scanning, the operator shall use one of the following two methods to estimate its size.
a) Distance-gain-size method (DGS).
In this method, use is made of the DGS diagram.
b) Comparison method.
In this case, the height of the discontinuity echo is compared with the height of the echo of a flatbottomed hole, with its bottom situated at the same distance from the probe as the discontinuity and exhibiting the diameter specified as the ac-ceptance standard.