ISO 10893-7:2019 pdf download – Non-destructive testing of steeltubes — Part 7: Digital radiographic testing of the weld seam of welded steel tubes for the detection of imperfections.
Detector-side positions typically show 1 or 2 more wires, or holes, than if the same IQI was on the source side, Customers may ask for a trial exposure to be carried out on a sample piece of pipe, with IQIs placed on both source and detector sides as a comparison, see ISO 17636-2:2013,6.7, for details When the tubes under inspection have the same dimensions and grade, it is sufficient to use the IQI only every 4 h, or twice a shift, to check image sensitivity. When carrying out the sensitivity checks, though. the IQI shall be placed on the source side.
The parameters used with the trial exposures (settings of X-ray source, detector and geometry) shall not be changed for the subsequent images acquired with detector-side lQls. For stable systems and processes, such as automated testing systems using DDAs, it is sufficient to prove the image quality once per shift as long as the tube dimension, tube material and testing parameters remain unchanged. In this case, the image quality proof should be performed only with source side 1Q15.
By usage of the duplex wire lQl, conforming to ISO 19232•5, the image unsharpness, 11g. shall be measured,
The read-out unsharpness. 11g. value for the duplex wire IQI is the smallest wire pair element number (largest wire diameter) with a dip separation below 20 %. measured with a profile plot across the duplex wire in the digital image.
The duplex wire IQI should be positioned on the surface of parent metal at an approximately 50 angle towards the pixel orientation in order to avoid aliasing effects.
7.2 The basic spatial resolution of the digital detector, Rh%drtrr. which is fixed by the construction and hardware parameters, shall be determined by placing the duplex wire IQI directly in front of the detector. In this case, Rbsdetector, is given by Formula (3):
Compensation principle: If both lQl sensitivities of Tpbles 1 and 2 (wire or hole and duplex wire IQI) cannot be achieved by the detector system used, an increase in single wire visibility can compensate too high unsharpness values. This compensation shall be limited to max 3 IQI values.
EXAMPLE For 10 mm wall thickness, class B; it is necessary to use wire number W14 and duplex Dli. 111)11 cannot be reached. compensation Is possible: two steps down from Dli to 09, but increasing two steps up from Wl4 to Wl6,
The contrast sensitivity for digital detectors depends on the integration time and tube current (mA) used for the acquisition of the radiographic images for a given distance and tube voltage, so the single wire visibility can be increased by an increased exposure time and mA setting.
7.3 The two image quality classes are defined in Ta.l1es1 and 2. The minimum normalized S/Nnorm in the base material should be > 70 for testing class A and> 100 for testing class B. The normalized S/N,ior,ii shall be calculated from the measured S/N in the image at base material adjacent to the welding seam and normalized by the basic spatial resolution of the detector system:
NOTE For details of SNR measurement, see. br example. EN 14784-i. ASTM E2446-05 or ASTM E2597-07. IQI quality For larger wall thicknesses is available in Iso 17636-2.
7.4 For the double wall penetration technique, the Image quality value for use shall be taken as that corresponding to twice the specified wall thickness.
73 Where available, the performance of the digital system should also be measured, using representative quality Indicators (RQls). RQls should he of the same dimensions and radiographic
absorption characteristics as the tubes under inspection.RQIs use are advised in order to ensure digitalset-up is capable of meeting inspection specifications.
7.6 The two image quality classes are defined in Tables 1 and 2.