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Comprehensively understand the inspection data comparison technology in long-distance oil and gas pipelines

2021-08-03 04:43:41
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As my country's demand for oil and natural gas energy is increasing, the role of oil and gas pipelines, known as the "national lifeline", has become more and more prominent. In recent years, oil and gas pipeline accidents have occurred frequently, and the safe operation of pipelines has also been paid more and more attention.


Now that the era of big data management has arrived, making big data more effective in pipeline integrity management and safety assessment has become a hot topic in the oil and gas industry.


Internal inspection is a vital part of integrity management and evaluation content, and it is also the main data source of pipeline big data. In recent years, domestic oil and gas pipelines have gradually carried out internal inspections, and some pipelines have undergone two or more rounds of internal inspections, but the mining and use of a large amount of internal inspection data has been relatively lagging. The comparison of inspection data within two or more rounds has become a research content that is convenient for data mining and can be effectively used. It can not only evaluate the equipment performance and inspection results of the inspection contractor, but also improve and modify the basic information of the pipeline being inspected. Grasping the change of defects, predicting the remaining life of the pipeline and evaluating the application effect of control measures, etc., have an important guiding role for the scientific management and operation and maintenance of the pipeline.


Overview of the development of domestic and foreign pipeline inspection data comparison technology

The data comparison work of foreign oil and gas pipeline internal inspection technology started earlier. Some foreign pipeline operators and inspection contractors have conducted data comparisons for multiple pipelines that have been inspected within two or more rounds.


The research progress of domestic internal testing data comparison is relatively lagging, and there have been related literature reports since 2015. However, it has developed rapidly in recent years. Data comparison technology and comparison software have gradually been applied in China, and data comparison standards have been compiled. , Such as SY/T 0087.5-2016 "Steel Pipeline and Storage Tank Corrosion Evaluation Standard Part 5 Comprehensive Analysis of Oil and Gas Pipeline Corrosion Data" standardizes the process and method of data comparison analysis.


The main content of internal test data comparison

With the maturity of our domestic testing technology, the gap between domestic and foreign technology is gradually narrowing, and there are more and more domestic contractors carrying out internal testing services. Domestic and foreign inspection contractors mainly carried out deformation, metal loss and IMU internal inspections, and provided inspection reports.


The main content of the routine internal inspection report information table includes feature name, feature type, mileage, reference positioning point, relative mileage, front and rear weld number, pipe section length, distance, length, width, hour position, degree, Surface position, wall thickness, ERF (estimated repair ratio), remarks, coordinate information, etc.


Although inspectors have their own data format, feature expression method, report and information table format, etc., the feature information can be matched one-to-one through comparison and sorting, and then manual alignment or software + manual alignment can be used to achieve the comparison of internal test data. Yes.


1

Comparison of basic characteristics of pipelines

The basic features of internal inspection pipelines include welds (circumferential welds, spiral welds, straight welds), straight pipes, elbows or elbows, valves, tees, flanges, external metal objects, and references set by the inspector Positioning points, etc. Among them, the reliability of the internal inspection data of the girth weld is relatively high, and it is also the primary object of comparison.


The research results and application experience of domestic and foreign inspection data comparison show that the successful alignment of the girth weld is the primary task of the overall data comparison, and it also lays a good foundation for the comparison of defects. In the process of girth weld alignment, other basic feature information such as pipe section length, elbows or pipes, valves, tees (including rerouted tees), straight welds or spiral welds intersections, etc. can assist in the inspection and judgment of girth welds The accuracy of seam alignment can be corrected in time until the comparison of all basic features is completed. The following conclusions can be drawn from the comparison results of girth weld features:


(1)

Due to the slip of the mileage wheel, data loss, line change or pipe replacement, etc., there is a certain difference in information such as the mileage of the girth weld and the length of the pipe section.

(2)

The main reasons for the failure to achieve complete alignment of the girth welds are the different marking methods of the girth welds near the accessories such as the receiving and dispatching balls and valves, line or pipe replacement, loss of inspection data or missing features, etc.

(3)

Because the inspection companies have different ways of defining the intersection information of straight welds or spiral welds and girth welds, their clock positions are inconsistent, but they can be adjusted to be consistent through mutual correction.

(4)

Due to the different reference positioning points set by the inspector, the relative mileage is of little reference for the comparison of the girth welds.

2

Comparison of pipeline defects

The characteristics of internal inspection pipeline defects mainly include deformation defects, metal loss defects (corrosion defects, mechanical scratches or manufacturing defects) and weld defects. Based on the results of two or more rounds of comparison of defects, it is possible to analyze the changes in the number and degree of defects, thereby assessing the severity of the damage to the pipeline.

01

Comparison of deformation defects

According to the publicly published literature, the author has not found that deformation defects are included in the internal inspection data comparison category, but geometric deformation inspection is a very important link in the internal inspection of oil and gas pipelines, and deformation defects are a common form of pipeline defects , It threatens the safe operation of the pipeline, and even causes the failure of the pipe body. Therefore, it is necessary to compare the deformation defects detected twice or more.


Deformation defects mainly include depression, folds, buckling and so on. Based on the alignment of the basic features of the pipeline, the deformation defects are mainly aligned on the basis of features with small differences in data such as the relative distance between the front and rear circumferential welds and the position of the hour. Because the length, width, and depth of deformation defects are generally larger and their number is relatively small, it is easier to achieve comparison.


For defects with increased deformation after alignment, the growth rate and development of deformation defects can be evaluated and predicted by referring to the calculation method of the full life growth rate of corrosion defects. The calculation method is shown in the following formula:


RD = (D2-D1)·r / (T2-T1)

Where: RD is the growth rate of deformation defects; r is the outer diameter of the pipeline; D2 is the degree of deformation in the next round of inspection; D1 is the degree of deformation in the previous round of inspection, if not, it means that the pipeline has no deformation; T2 is the next The year of the round of inspection; T1 is the year of the last round of inspection.


The following conclusions can be drawn from the comparison results of deformation defects:


(1)

The difference in the number or size of deformation defects is caused by the different accuracy and confidence of the deformation detector or the different working environment, and the overall alignment rate is relatively high.

(2)

It can identify new deformation defects, and predict the development of deformation defects by calculating the growth rate, providing a basis for formulating repair plans and the next round of inspections.

(3)

By comparing the repaired deformation defects, especially the deformation defects of springback or rounding after the constraint is removed, it is possible to evaluate the deformation after springback and the repair effect.

02

Comparison of metal loss defects

Metal loss defects are key factors that affect the safe operation of pipelines, mainly including corrosion, mechanical scratches, and manufacturing defects. According to the literature and engineering experience published at home and abroad, it is found that the comparison of internal inspection data is mainly carried out with the growth rate of metal loss defects and new points as the research object.


On the basis of the alignment of the basic features of the pipeline, the metal loss defects are mainly aligned based on features with small data differences such as the relative distance between the front and rear circumferential welds, the position of the hour and the surface position. Considering that the length, width and depth of metal loss defects are generally small, their number is large and sometimes they are densely distributed. Therefore, parameters such as mileage, relative mileage, depth, length and width cannot be used as alignment references. Increase the alignment and The difficulty and workload of the comparison.


After the alignment of metal loss defects, the comparison work first sets the threshold for evaluating the change of metal loss defects based on the accuracy, confidence, or detection error of the known defect data in two or more rounds of detection data sources, which can be divided into active defects ( Depth increase ≥ threshold), inactive defects (depth increase <threshold), new defects (new depth increase ≥ threshold) and other defects. By calculating the growth rate of new defects, the remaining life of pipeline corrosion can be evaluated, and reasonable maintenance and repair plans can be formulated to meet the needs of pipeline integrity management. The calculation method of the growth rate of metal loss is shown in the following formula:

RML = ΔMd·WT/Δt

Where: RML is the growth rate of metal loss; ΔMd is the increase in metal loss depth within Δt; WT is the pipe wall thickness.


If the whole life method is adopted, Δt is the interval between the inspection date and the last round of inspection date; if the half-life method is adopted, Δt is half of the interval between the inspection date and the last round of inspection date.


The remaining corrosion life of pipelines is calculated using the method of "Regular Inspection Rules for Pressure Pipelines and Long-distance (Oil and Gas) Pipelines". The specific method is shown in the following formula:

RL = C×SM·(t/GR)

Where: RL is the remaining life of the pipeline; C is the correction factor, C=0.85; GR is the corrosion rate; t is the nominal thickness; SM is the safety margin.

The following conclusions can be drawn from the comparison results of metal loss defects:

(1)

The number of metal loss defects or the length, width and depth data of some defects are quite different. This is due to the different accuracy and confidence of the detector or the different working environment, but most of the defects can be compared.

(2)

Other types of defects refer to defects that have been misdetected or missed in the most recent inspection.

(3)

By comparing the repaired metal loss defects, the repair effect of the defects can be evaluated, and certain guidance can be provided for the later defect repair.

03

Comparison of weld defects

In recent years, there have been many accidents caused by the failure of pipeline welds at home and abroad, which has caused serious harm. Weld defects are one of the main failure modes of oil and gas pipelines and have become a key risk point for major pipeline operating companies.


Weld defects mainly include circumferential weld defects, spiral weld defects and straight weld defects. Although the accuracy of defect identification and size quantification is relatively low, in-pipe inspection is still the most important source of weld defect feature data for buried pipelines, and the main basis for pipeline operation companies to investigate and manage weld defects. At present, domestic and foreign pipeline internal inspection companies are working on the internal inspection technology of weld defects and improve the inspection accuracy.


Based on the alignment of the basic features of the pipeline, the weld defects can be aligned based on features with small differences in data such as the position of the hour and the surface position. Due to the limitations of internal inspection capabilities, data errors such as the length, width and degree of weld defects are relatively large, so it is relatively difficult to compare weld defects, especially those of different inspectors.


In view of the fact that there is currently no domestic welding seam abnormal classification evaluation standard based on internal inspection methods, China Petroleum Pipeline Inspection Technology Co., Ltd., China Special Equipment Inspection and Research Institute, etc. The seam abnormalities are classified as mild, moderate and severe, which are used as the calculation and evaluation method for the growth rate of weld defects and the prediction of remaining life. The following conclusions can be drawn from the comparison results of weld defects:


(1)

The growth and development of weld defects can be estimated, and the causes of weld defects can be analyzed.

(2)

Most of the weld defects are produced during the construction and manufacturing stage, and there are many inactive defects.

(3)

It is recommended that the pipeline operating company conduct negative reassessment or selective excavation according to the degree of weld defects, and adopt effective non-destructive testing methods for inspection and evaluation.

3

Pipeline coordinate comparison

Loading IMU on pipeline detectors has become a commonly used surveying method for long-distance oil and gas pipelines at home and abroad. Coordinate matching of IMU data with internal detection data such as deformation, magnetic flux leakage, and ultrasonic can obtain all the characteristics of the pipeline and the coordinates of the center line. The alignment of the basic feature of the pipeline and the feature of the defect means that the coordinate data has also been aligned. The following conclusions can be drawn from the comparison results of the test data in the IMU:

(1)

By mutually verifying the pipeline characteristics of different inspection vendors and the coordinate accuracy of the center line, and combining more accurate pipeline coordinate data sources (correction points) to correct the coordinates, higher precision pipeline coordinates can be obtained.

(2)

As a new positioning method for pipeline features, the accuracy of pipeline defects and basic feature coordinates is improved, which greatly meets the needs of quickly and accurately positioning pipeline features (such as welds, defects, etc.), which not only greatly reduces the workload and cost of excavation, but also Contribute to the formulation of maintenance plans and ensure the timeliness of maintenance.

(3)

Based on two or more rounds of IMU inspection centerline surveying and mapping data, the strain and displacement changes across the pipeline can be calculated, so as to identify defects or other characteristic points with larger or faster displacement changes, which is convenient for the repair and maintenance of pipeline defects. At the same time, it helps to monitor and warn the location of pipelines that may cause high-risk and high-consequence areas.

(4)

The pipeline coordinate accuracy obtained by the combination of internal inspection and IMU is affected by the accuracy of the IMU itself, the coordinate accuracy of the reference correction point, and the data settlement and integration technical capabilities. This is also the cause of problems in the coordinate data comparison.

Suggestion

In-pipe inspection technology is currently the method used by major pipeline companies to inspect pipeline conditions and location information and support integrity management. On the road to the development of big data in the pipeline system, how to apply and manage the detection data in the pipeline to ensure the safe operation of the pipeline is an urgent task at present. The author puts forward the following suggestions on the comparison of test data in the pipeline:

1


Internal inspection and pipeline operation companies should increase research on the in-depth mining and comprehensive utilization of internal inspection data, especially in terms of multiple rounds of internal inspection data comparison, and establish a pipeline system data platform and comprehensive analysis mechanism.

2


When the pipeline operating company conducts the next round of internal inspections, it should clarify the starting point and end point of the inspection, reference positioning points, a unified internal inspection data list, etc., which is conducive to the subsequent internal inspection data comparison work.

3


There is no mature application of pipeline inspection data comparison and analysis system in China. Only a few units have developed internal testing data comparison and analysis software, but the application effect remains to be verified. It is recommended to conduct in-depth research on the internal inspection data comparison and analysis system, and gradually realize the intelligent analysis of manual alignment to automatic alignment + manual correction to fully automatic alignment, as well as multiple rounds of internal inspection mass data comparison.

4


There are few standard specifications for internal test data comparison. It is recommended to formulate targeted standards and specifications as soon as possible to provide clear guidance for internal test data comparison.



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