AS 2574:2000 pdf free download – Non-destructive testing- Ultrasonic testing of ferritic steel castings

AS 2574:2000 pdf free download – Non-destructive testing- Ultrasonic testing of ferritic steel castings.
3.6.2 Scanning
3.6.2.1 General
Scanning shall be carried out using probes selected in accordance with Clause 3.5. from the surfaces nominated and to the extent of coverage required. The scanning rate shall not exceed 150 mm/s.
Twin crystal probes should he used for the detection of flaws located close to the entry surface.
3.6.2.2 Scanning sen. iii rifv
Scanning shall he carried out using a gain of at least dH greater than that required to bring the signal from a 6 mm diameter flat bottom hole reference reflecwr at the maximum beam path length to 40% graticule height. For long items, the beam path may be divided into sections to improve clarity of presentation.
3.6.3 Evaluation and recording sensitivity
Unless otherwise agreed by contracting parties, the sensitivity used for the evaluation of discontinuities shall be that necessary to enable comparison with either a 6 mm diameter flat-bottom hole or a reflector with equivalent reflectivity, at the same beam path distance.
Discontinuities shall be evaluated and recorded for rellectivity. dimension, including length. width and where possible. section depth (see Section 4) and location, using one of the following levels:
(a) Level I—For the DAC method, a discontinuity is evaluated and recorded if its amplitude is equal to or greater than one half of the amplitude resulting from a 6 mm diameter flat-bottom hole. For the DGS method, a discontinuity is evaluated and recorded if its amplitude is equal to or greater than the amplitude resulting from a 4 mm diameter flat-bottom hole.
The choice of probes for the examination of any casting is usually a compromise between the optimum type and what is economically practical. The examination of a casting should be conducted in such a manner as to ensure that the best possible ultrasonic detection and resolution is obtained by using the highest possible frequency consistent with adequate acoustic penetration and an acceptable noise (interference) level.
The determination of the best possible compromise on the type of probe should be made with regard to the following features of the casting:
(a) Geometrical shape and surface condition. The access to areas suspected of containing discontinuities and the availability of a suitable scanning surface will depend on the shape of the casting.
(b) Size.
(c) Metallurgical structure.
(d) The nature, position and orientation of possible discontinuities.
Guidance on the selection of probes is given in Paragraph B2.
B2 PROBE ChARACTERISTICS
112.1 Frequency
In most applications of ultrasonic testing of steel castings the test frequency will be within the range 2 MFlt to 5 MHt, Other frequencies may be used where specified.
The following factors will influence the choice of frequency:
(a) Nature of the metal through which the beam will pass When testing coarse-grained steel, higher frequencies will he attenuated w a greater extent than lower frequencies; e.g. where 1 MHz is required to give satisfactory penetration. 4 MHz would give unsatisfactory results because the ultrasonic beam would attenuate to a greater extent and therefore result in less penetration.
(h) Size of discontinuity to he derecu’d In general, the size of the discontinuity which may be detected is proportional to the wavelength of the ultrasonic beam. The higher the frequency the shorter the wavelength and the smaller the discontinuity which may he detected. It also follows that better resolution is possible at higher frequencies.
(c) Beami, path length Where long beam path lengths are to he used it may he advantageous to use a lower frequency to result in less attenuation.
B2.2 Beam angle
The objective in the selection of the beam angle is to produce an ultrasonic beam having an axis normal to the maximum reflecting surface or surfaces of any discontinuity.