The radiographic examination shall comply with all of the requirements of this Standard.
The procedure shall be documented and qualified, or be previously qualified and approved.
Gamma-radiography shall only be used where the risk of HACC is ‘designed out’ from the welding procedure and where permitted by the Note in Table 17.4.
NOTES:
1 AS 2177 should be referred to for guidance.
2 The preferred technique of radiographic examination of welds in pipelines is that of using an internal orthogonal x-ray radiographic crawler as, inter alia, the detectability of imperfections including cracks is superior to that obtained using high-energy gamma rays or double-wall exposure techniques.
17.2 SAFETY AND PROTECTION FROM IONIZING RADIATION
All radiographic examination shall be carried out in accordance with statutory State and Federal health and safety regulations.
17.3 DENSITY
The radiographic density through the parent metal shall be as follows:
(a) X-radiography ... not less than 2.5 and not greater than 4.0.
(b) Gamma-radiography ... not less than 3.0 and not greater than 4.0.
The radiographic density through the weld metal shall not be less than 1.3.
Weld reinforcement shall be within the limits of Figure 15.4.2.
If the density in the parent metal falls within the range specified above but the required minimum for the weld metal is not met, then the weld reinforcement shall be ground in the regions of insufficient density and the radiograph(s) shall be retaken so that the above requirements are met.
17.4 IMAGE QUALITY
The image quality indicator (IQI) shall be a wire type complying with AS 2314.
NOTE: The specification of wire type IQI in AS 2314 complies with ISO 1027 and DIN 54109.2.
Radiographic image quality is indicated by the smallest wire visible in the radiograph assessed through the parent metal. IQI wire numbers for corresponding nominal wall thicknesses shall comply with Table 17.4.
Accessed by GHD PTY LTD on 05 Aug 2009
TABLE 17.4
IMAGE QUALITY INDICATOR (IQI) SENSITIVITY vs MATERIAL THICKNESS
IQI to DIN 54109/ISO 1027 IQI on film side
NOTE: Welds in pipe Grade AP15L X60 or lower, welded entirely with low strength electrodes and in R1 locations, may be examined using gamma-radiography. Image quality indicator wire visibility using this technique may be reduced by 1 in the first three rows.
17.5 UNDERCUT DEPTH MEASUREMENT
Where radiography is used as the only method of determining internal undercut (see Clause 15.5), the images of discontinuities that have been identified as undercut shall be assessed for depth by comparing the density of its film image with the density of the film images of grooves of given sizes cut into a comparator shim. Alternatively, undercut may be assessed for depth by comparing production radiographs with reference radiographs prepared from weldments of the same thickness and welding procedure, and where the depth of real examples of undercut has been measured by macro examination.
Undercut comparator shims shall comply with the following:
(a) Material A comparator shim shall have the same radiographic opacity as the material under examination.
(b) Dimensions The dimensions of comparator shims shall be as shown in Figure 17.5.
(c) Location A comparator shim shall match the curvature of the pipe and shall be placed alongside and parallel with the edge of the external weld with the grooves on the inside radius. The shallowest groove on the comparator shim shall be placed closest to the weld.
(d) Number of comparator shims Comparator shims shall be visible as follows:
(i) For panoramic exposures, a minimum of two comparator shims spaced approximately equidistant shall appear on the radiograph. The separation of comparator shims shall not exceed 400 mm.
(ii) Where a multi-exposure method is used, comparator shims should be located adjacent to the image quality indicators or at locations where undercut is
(iii) Where a multi-exposure or multi-film method is used, at least one shim should be visible on each cut length of film of 400 mm or less.
(e) Method of assessment of undercut using comparator shims To assess the relative depth of undercut, compare the density of the actual undercut with the density observed in the machined grooves of known depth in the undercut comparator. This may be achieved by totally masking all areas of the radiograph, with the exception of a window that is of comparable size with the actual undercut, and comparing the density observed in the same size window of the machined grooves.
NOTES:
1 Tolerance on depth of groove ±0.05 mm.
2 A Charpy V-notch tool should be used to produce the grooves.
DIMENSIONS IN MILLIMETRES
FIGURE 17.5 UNDERCUT COMPARATOR SHIM
17.6 GAS PORE DEPTH MEASUREMENT
The images of discontinuities that have been identified as gas pores (GP) shall be assessed for depth (through thickness dimension) by comparing the density of its film image with the density of the film images of flat bottom hole.
The gas pore comparator shim shall comply with the following:
(a) Material The comparator shim shall have the same radiographic opacity as the material under examination.
(b) Dimensions The dimensions of the comparator shim shall be as shown in Figure 17.6.
Accessed by GHD PTY LTD on 05 Aug 2009
(c) Method of use Reference radiographs shall be made of the comparator shim and test weld. These reference radiographs shall be used in order to assess the depth of gas pores in production radiographs.
PLAN VIEW
H o l e d e pt h s
SIDE VIEW 5 0
15 3
3
0.5 1.0 2.0 3.0 END VIEW
T h i r d a n g l e p r o te c t i o n
G a s p o r e s h i m
DIMENSIONS IN MILLIMETRES
FIGURE 17.6 GAS PORE COMPARATOR SHIM
17.7 INTEPRETATION AND ASSESSMENT OF RADIOGRAPHS
Discontinuities observed on radiographs shall be identified, sized, and assessed in accordance with Clause 22. Defects shall be correlated with the radiograph, located with respect to the weld and recorded on a test report.
Defects shall be identified, and symbolized in accordance with AS 4749.
NOTE: Where the terminology and abbreviations used in AS 4749 do not adequately describe some of the discontinuities found in pipeline welds, additional descriptive abbreviations may be required (e.g., I = internal; E = external; HB = hollow bead; AS = arc strike; WT = wagon tracks;
17.8 CRITERIA OF ACCEPTANCE The weld shall comply with Clause 22.
17.9 REPORT OF RADIOGRAPHIC EXAMINATION
A test report shall be made in accordance with AS 2177 and the requirements of this Standard.
17.10 RETENTION OF RADIOGRAPHS
Radiographs shall be retained for a minimum of three years.
Accessed by GHD PTY LTD on 05 Aug 2009