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SY/T 6996-2014

Chinese Standard: 'SY/T 6996-2014'
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ICS 75.010
E 10
Registration No.. 48247-2015
Assessment of Steel Oil & Gas Pipeline with Dent
Issued by. National Energy Administration
Table of Contents
Foreword ... 3 
1 Scope ... 4 
2 Normative References ... 4 
3 Terms and Definitions ... 4 
4 Information Preparation ... 5 
5 Dent Inspection ... 6 
5.1 Internal inspection ... 6 
5.2 Direct inspection ... 6 
6 Dent Assessment ... 7 
6.1 Determination of dent type ... 7 
6.2 Depth-based assessment ... 7 
6.3 Strain-based assessment ... 7 
7 Dent Repair ... 8 
Appendix A (Informative) Dent Laser Scanning Measurement ... 11 
Appendix B (Informative) Dent Strain Calculation Method ... 13 
Appendix C (Informative) Dent Strain Calculation Method ... 15 
Bibliography ... 16 
Assessment of Steel Oil & Gas Pipeline with Dent
1 Scope
This Standard specifies the technical requirements for test and assessment of
under-construction steel oil & gas pipeline with dent.
This Standard is applicable to the assessment of land carbon steel and low-alloy steel
oil & gas pipeline with dent.
2 Normative References
The following documents are essential to the application of this document. For the
dated documents, only the versions with the dates indicated are applicable to this
document; for the undated documents, only the latest version (including all the
amendments) are applicable to this standard.
SY/T 6151 Assessment of Corroded Steel Pipelines
SY/T 6597 Technical Standard of Intelligent Pigging on Steel Pipeline
SY/T 6825 In-line Inspection Systems Qualification
SY/T 6889 In-line Inspection of Pipelines
3 Terms and Definitions
The following terms and definitions are applicable to this document.
3.1 Dent
The local elastic-plastic deformation of significant change on the curvature of pipe
surface that is caused by external impact or squeeze.
3.2 Smooth dent
Dent, of which the pipe-wall curvature is changed smoothly.
3.3 inked dent
Dent, of which the pipe-wall curvature is changed significantly; the sharpest part’s
5 Dent Inspection
5.1 Internal inspection
5.1.1 As for pipeline dent, apply the internal inspection to inspect; and implement as
per SY/T 6597, SY/T 6825 and SY/T 6889.
5.1.2 Apply deformation, magnetic-leakage or ultrasound and other internal
inspection technologies; detect the dent position (absolute distance, relative distance,
clock direction), depth, axial length and circumferential width or overall outline; give
out the position relationship between dent and pipeline weld seam, as well as other
defect information relevant to the dent such as corrosion, scratches, cracks, arc burns
and etc.
5.2 Direct inspection
5.2.1 Get rid of the anti-corrosion layer of pipe section where the dent exists; if the
dent belongs to constrained dent, then firstly remove the constraint against the dent.
5.2.2 Precisely measure the dent shape; give out the dent’s maximum depth, axial
length, circumferential width, axial and circumferential profile shape through the
maximum depth position, and the overall shape of dent. The available shape
measurement methods include but not limited to.
a) Laser scanning measurement. this method, through laser, scans the dent area; it
can accurately record and describe the overall shape of dent. The implementation
can refer to Appendix A.
b) Profile gauge measurement. divide the external surface of dent along the
circumferential direction at equal distance; use profile gauge, successively at
different segmentation line, along the axis, to tightly attach to the dent surface;
according to the gauge shape, obtain the dent outline at different section, and
describe the dent shape.
c) Template measurement. divide equal-distance grid on the external surface of the
dent; use template to measure the deformation depth on each grid; according to
the measurement data, describe the dent shape.
NOTE. After removal constraints from the constrained dent, it appears to spring back and
rebounding, which have certain influence on the measurement result.
5.2.3 Through visual observation, check the positions relationship among dent, weld
seam and other defects, such as corrosion, scratches, cracks, arc burns, and etc.; if
necessary, apply magnetic p......
Related standard:   SY/T 6986.3-2016  SY/T 5918-2017
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