SY/T 6996-2024 Assessment ofsteel oil & gas pipelines with dent English, Anglais, Englisch, Inglés, えいご
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ICS
E
Professional standard of the People's Republic of China
SY/T 6996-2024
Assessment of steel oil & gas pipelines with dent
钢质油气管道凹陷评价方法
(English Translation)
Issue date: 2024-09-24 Implementation date: 2025-03-24
Issued by National Development and Reform Commission, P.R.C
Contents
Foreword
1 Scope
2 Normative References
3 Terms and Definitions
4 Abbreviations
5 Design Conditions
5.1 Environmental Conditions
5.2 Design Cases
5.3 Vessel Parameters
6 Design Criteria
6.1 General Requirements
6.2 Design Life
6.3 SPM Location and Spatial Requirements
7 Design Requirements
7.1 Turret System
7.2 Mooring System
7.3 Mooring Foundation
7.4 Dynamic Risers and Umbilicals
8 Construction and Inspection
8.1 General Requirements
8.2 Construction Materials
8.3 Welding
8.4 Quality Control and Inspection
9 Offshore Installation
9.1 General Requirements
9.2 Installation of Mooring Foundation
9.3 Laying of Mooring Lines
9.4 Hook-up of Mooring Lines
Evaluation Method for Dents in Steel Oil and Gas Pipelines
1 Scope
This document specifies the methods and procedures for the detection and evaluation of dents in in-service steel oil and gas pipelines.
This document applies to the evaluation of dents in onshore carbon steel and low alloy steel oil and gas pipelines. The evaluation of dents in submarine oil and gas pipelines may refer to this document.
2 Normative References
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 27699 Technical specification for in-line inspection of steel pipelines
SY/T 6151 Methods for evaluating metallic loss defects of steel pipeline
SY/T 6597 Technical specification for in-line inspection of oil and gas pipelines
3 Terms and Definitions
The following terms and definitions apply to this document.
3.1
dent
Local elastic-plastic deformation on the pipeline surface caused by external impact or compression, resulting in a significant change in curvature.
3.2
smooth dent
A dent where the pipe wall curvature changes smoothly.
3.3
kinked dent
A dent where the pipe wall curvature changes sharply, and the radius of curvature at the sharpest part is less than 5 times the wall thickness in any direction.
3.4
plain dent
A smooth dent without associated metal loss, cracks, or other defects, and which does not alter the curvature of adjacent girth welds or seam welds.
3.5
constrained dent
A dent that cannot spring back or reround freely due to the presence of external constraints.
Note: Dents located at the bottom of the pipeline (4:00-6:00-8:00 o'clock orientation) are typically constrained dents, such as dents formed by compression against bottom rocks.
3.6
unconstrained dent
A dent where external constraints have been removed, allowing free elastic spring back and free rerounding under subsequent changes in internal pressure.
Note: Dents located on the top of the pipeline (8:00-12:00-4:00 o'clock orientation) are typically unconstrained dents.
3.7
spring back; rebound
The reduction in dent depth resulting from elastic unloading of the pipe after the removal of external constraints.
3.8
rerounding
The reduction in dent depth under the action of internal pressure.
3.9
dent depth
The maximum reduction in the external diameter of the pipeline at the dent location compared to the original external diameter.
Note: 'd' in Figure 1 represents dent depth.
3.10
dent length
The axial length along the pipeline passing through the deepest point of the dent, measured between points on both sides of the deepest point where the depth is 50% of the maximum depth.
Note: 'L' in Figure 1 represents dent length.
3.11
dent width
The circumferential arc length along the pipe wall passing through the deepest point of the dent, measured between points on both sides of the deepest point where the depth is 50% of the maximum depth.
Note: The circumferential arc length corresponding to 'W' in Figure 1 represents dent width.
3.12
response
Actions such as repair, pressure reduction, or other risk mitigation measures taken for pipelines containing defects.
3.13
specified minimum yield strength (SMYS)
The minimum yield strength specified in the technical requirements for a given type of pipe material.
[Source: GB 32167-2015, 3.13]
4 General Principles and Requirements
4.1 Relevant information required for the evaluation shall be collected, available dent morphology data shall be analyzed, appropriate evaluation methods shall be selected according to the provisions of this document, the evaluation object shall be assessed, and evaluation conclusions shall be provided.
4.2 Information prepared before evaluation includes, but is not limited to:
a) Data on pipeline steel grade, diameter, wall thickness, material mechanical properties, burial depth, elevation, etc.;
b) Data on geological conditions along the pipeline route and surrounding environment;
c) Historical operating data such as pipeline transported medium, pressure, temperature, etc.;
d) Pipeline in-line inspection (ILI) and external inspection data;
e) Relevant information related to third-party construction activities.
4.3 Dent evaluation methods include depth-based evaluation and strain-based evaluation. Depth-based evaluation methods are typically used, and when necessary, strain-based evaluation should be further conducted.
4.4 The dent type, constraint state, and circumferential stress level shall be determined before evaluation. If the constraint state cannot be clearly determined, the dent should be evaluated as an unconstrained dent.
5 Dent Detection
