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SY/T 6996-2014 (SYT6996-2014)

SY/T 6996-2014_English: PDF (SYT 6996-2014, SYT6996-2014)
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Standard ID SY/T 6996-2014 (SY/T6996-2014)
Description (Translated English) Assessment of steel oil and gas pipeline with dent
Sector / Industry Oil & Gas Industry Standard (Recommended)
Classification of Chinese Standard E10
Classification of International Standard 75.010
Word Count Estimation 14,114
Date of Issue 2014/10/15
Date of Implementation 2015/3/1
Quoted Standard SY/T 6151; SY/T 6597; SY/T 6825; SY/T 6889
Drafting Organization China National Petroleum Co., Ltd. Pipeline Company
Administrative Organization Oil and gas storage and transportation industry professional Standardization Technical Committee
Regulation (derived from) State Energy Bureau Notice 2014 No. 11
Issuing agency(ies) National Energy Board
Summary This Standard specifies the depressed oil and gas pipelines in service steel testing and evaluation of the technical requirements. This Standard applies to the evaluation of carbon steel and low alloy steel onshore oil and gas pipelines recess. Depression

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 power, penetration, ultrasound, X-ray and other methods
to inspect the dent further.
6 Dent Assessment
6.1 Determination of dent type
Through the internal inspection or direct inspection results, determine the dent type;
dent can be divided into kinked dent and smooth dent. Smooth dent can be further
divided into the following ones.
a) Dent containing scratches, cracks, arc burns or weld seam defects.
b) Dent on the weld seam.
c) Dent containing corrosion.
d) Ordinary smooth dent.
6.2 Depth-based assessment
6.2.1 When the dent shape information is limited; it shall carry out dent depth
assessment. The procedure of dent-depth-based assessment can refer to Figure 1.
6.2.2 The following dents shall be repaired.
a) Kinked dent.
b) Dent containing scratches, cracks, arc burns or weld seam defects.
c) Dent on the weld seam, whose depth is more than 2% pipeline diameter.
d) Dent containing corrosion and corrosion depth is more than 40% pipeline wall
e) Dent containing corrosion and corrosion depth is 10%~40% pipeline wall thickness;
it shall be repaired as per SY/T 6151.
f) Dent whose depth is more than 6% pipeline diameter.
6.2.3 When repairing the ordinary smooth dent, it shall be sequenced as per the
ratio (d/L) between dent depth and length; the dent whose ratio is larger shall be given
priority to repair. In case the d/L values are equal, the dent whose wall thickness is
larger shall be given priority to repair.
6.3 Strain-based assessment
6.3.1 When the data of dent shape are sufficient, the strain-based assessment
against dent shall be carried out; the assessment flow can refer to Figure 2. The
calculation method of dent strain can refer to Appendix B.
Appendix A
Dent Laser Scanning Measurement
A.1 Pipeline preparation
A.1.1 Verify that the excavated dent is to-be-measured dent.
A.1.2 If it is the constrained dent, firstly remove the constraints.
A.1.3 Remove the anti-corrosion layer on the pipeline segment where the dent
exists; polish and eliminate all sediments, dirt, grease and dust, so that the pipeline
surface roughness can reach Grade 2~3.
A.2 Installation and calibration of laser scanner
A.2.1 Verify, in the target scanning area, the pipeline segment circumferential 360°’s
pipeline wall cleanliness.
A.2.2 In the pipeline’s to-be-scanned area, arrange positioning patches at certain
distance. When arranging pitch nearby the dent, ensure that the distance between
pitch and dent’s two axial ends is not less than 10mm.
A.2.3 Use calibration plate to calibrate the portable laser scanner.
A.2.4 Scan the positioning pitches.
A.3 Scanning
A.3.1 Maintain portable laser scanner perpendicular to the pipeline surface; conduct
circumferential 360° scanning.
A.3.2 As for hollow-imaging area, it shall be rescanned till it appears in the imaging
A.3.3 Set coordinate origin and coordinate axis; save the setting and scanning
A.3.4 After the completion of scanning, close the software, and remove the device.
A.4 Data extraction
Appendix B
Dent Strain Calculation Method
B.1 Strain
B.1.1 Dent strain shall, according to the dent profile obtained through the internal
and direct measurement of deformation, be calculated.
B.1.2 When coarse profile information is obtained; it can, through Interpolation
method or other mathematical method, construct more accurate dent profile
B.2 Strain calculation
B.2.1 Schematic diagram of stain calculation can refer to Figure B.1. When passing
through the cross-section of dent, determine curvature radius R1 on the dent part of
pipeline external surface. When the pipeline curvature direction is the same as the
initial surface curvature direction, R1 is positive number; when the pipeline curvature
direction is opposite to the initial surface curvature direction, R1 is negative number.
B.2.2 When pass through the axial section of dent, determine the dent’s curvature
radius R0, generally R0 is negative number.
B.2.3 Circumferential bending strain ε1 shall be calculated as per Formula (B.1).
t – Pipeline wall thickness, unit ...