CN110806191B - Circumferential weld defect pipeline safety evaluation method based on strain monitoring - Google Patents
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Abstract
The invention relates to the technical field of safety assessment, in particular to a girth weld defect pipeline safety assessment method based on strain monitoring, which comprises the following steps of S1, calculating the stress state near the girth weld defect pipeline defect: s11, arranging a strain monitoring unit near the defect of the pipeline circumferential weld, and S12, monitoring strain distribution of the cross section of the pipeline; s13, calculating the stress and the internal force of the cross section of the pipeline; s2, evaluating the safety of the girth weld defect pipeline based on strain monitoring; s21, evaluating defects based on the current stress; s22, safety early warning based on a stress threshold value; and S23, quantifying safety evaluation and risk control. The girth weld defect pipeline safety evaluation method based on strain monitoring can simplify calculation, reduce workload, reduce cost and effectively improve the safe operation condition of the pipeline.
Description
Technical Field
The invention relates to the technical field of safety assessment, in particular to a method for assessing the safety of a girth weld defect pipeline based on strain monitoring.
Background
Along with the development of urbanization and industrialization, the demand of China on energy sources such as petroleum, natural gas and the like is increasingly large. The long oil and gas transmission pipeline is one of the most important modes for long-distance oil and gas transmission. In view of the serious social, environmental and economic impacts caused by oil and gas pipeline leakage accidents, governments, society and enterprises are more and more concerned about the safety problems of oil and gas pipelines. The circumferential weld cracking is one of the main failure modes of the oil and gas pipeline, has the characteristics of long cracking length, large leakage amount and the like, is easy to cause serious threats to the safety of peripheral personnel and the environment, particularly has the characteristics of difficult emergency repair work, strict requirements on pipeline outage and transportation, more environmental sensitive points and the like, is used for timely monitoring, analyzing and evaluating the stress strain of the pipeline, repairing the circumferential weld defect and ensuring the intrinsic safety of the pipeline, and has important economic and social significance.
For example, chinese patent, publication No. CN103049648B, discloses a method for evaluating pipeline stress for engineering practical problems, which includes the following steps: (1) determining all specification types to be adopted in evaluation, determining versions of all specifications to be considered by all pipeline levels (2) included in the specifications, and special requirements in the specifications or other specifications, analyzing and evaluating a requirement code (3) to find out all load types aiming at all the specifications, classifying the same load types in all the specifications, designing a load code (4) to obtain an analysis requirement identification code (5) of each load condition according to the calculation requirements of all the specifications, classifying the analysis requirement identification codes (5) according to the calculation formulas in all the specifications, using the completely same formulas as one class to obtain various available calculation formula classes, finding an analysis requirement identification code corresponding to each different calculation formula, determining a calculation requirement code identification (6) of each formula to obtain an analysis requirement identification code of each load working condition in calculation according to the calculation requirements of a user, and according to the analysis requirement identification code of the load working condition, finding a calculation requirement coding identification (7) of a calculation formula to be adopted, calculating a stress value and a corresponding allowable stress value according to the formula of the calculation requirement coding identification, and giving an evaluation formula and a corresponding specification (8) to perform additional calculation and evaluation on the calculation requirement of the subject with additional conditions.
The technical scheme has the advantages of complex calculation, large workload and higher evaluation cost. Because the working environment of the pipeline is difficult to accurately analyze, the conveying state is changed all the time, and the actual stress condition and the safety of the pipeline are difficult to accurately evaluate in real time.
At present, domestic and international defect evaluation standards and specifications are more, but a method for synchronously obtaining a pipeline defect evaluation result by combining strain monitoring data is basically not available. Therefore, the girth weld defect pipeline safety evaluation method based on strain monitoring is combed, and is beneficial to improving the safe operation of the pipeline.
Disclosure of Invention
The invention aims to provide a girth weld defect pipeline safety assessment method based on strain monitoring, which can simplify calculation, reduce workload, reduce cost and effectively improve the safe operation condition of a pipeline.
In order to achieve the purpose, the invention adopts the following technical scheme: the method for evaluating the safety of the girth weld defect pipeline based on strain monitoring is characterized by comprising the following steps of,
s1, calculating the stress state near the defect of the circumferential weld defect pipeline, comprising the following steps:
s11, arranging a strain monitoring unit near the defect of the pipeline girth weld,
the strain monitoring unit comprises a first strain monitoring sensor group and a second strain monitoring sensor group, the two strain monitoring sensor groups are respectively arranged at two sides of the girth weld defect of the oil and gas pipeline, and each strain monitoring sensor group at least comprises 3 strain sensors; taking a circular section of the oil-gas pipeline along the airflow direction of the oil-gas pipeline, optionally selecting three points L, U, R on the circular section in a clockwise direction, wherein the included angle between a point L and a connecting line of the point U and the circle center of the circular section is equal to the included angle between the point U and a connecting line of the point R and the circle center of the circular section, and respectively arranging a strain sensor at the position of a point L, U, R;
s12, monitoring strain distribution of the cross section of the pipeline;
s13, calculating the stress and the internal force of the cross section of the pipeline;
s2, a circumferential weld defect pipeline safety evaluation method based on strain monitoring comprises the following steps:
s21, evaluating defects based on the current stress;
s22, safety early warning based on a stress threshold value;
and S23, quantifying safety evaluation and risk control.
Further, the step S21 includes,
(1) the buried straight pipe section without defects in a safe state should satisfy the following two conditions (11) and (12) at the same time:
(11) according to the specification of ASME B31.8-2016, the maximum allowable value of the axial stress of the buried constraint pipeline is 0.9 times of the minimum yield strength, namely the axial stress of the pipeline is satisfied
|σL|≤0.9σs
(12) According to the provisions of GB50251 and GB50253, the combined equivalent stress of the axial stress and the circumferential stress of the buried straight pipe section is less than 90 percent of the minimum yield strength specified by the steel pipe standard, namely the combined equivalent stress of the pipeline is required to meet the requirement
σe＜0.9σs
The conditions (11) and (12) are simultaneously met, and the pipeline safety is evaluated; otherwise, it is unsafe;
wherein: sigmas-pipe minimum yield strength (MPa);
σL-buried pipeline axial stress;
σe-pipe combined equivalent stress;
(2) a buried straight pipe section in a safe state contains a pipeline with a weld crack defect, and the following two conditions (21) and (22) are simultaneously satisfied:
(21) the evaluation condition of (11) should be satisfied;
(22) allowable axial tensile stress of pipeline
Wherein, K: a stress intensity factor;
y: a geometric factor or a shape factor;
a: crack sizes, such as: radius of circular crack, semiminor axis of elliptical crack.
Further, the step S22 includes,
based on monitoring historical data and mechanical calculation, calculating to obtain defect safety states possibly occurring in different stress states, based on the defect safety states, obtaining a stress threshold value bearable by the defect under the current working condition or the specified working condition, based on the monitoring data and the stress threshold value, obtaining a ratio of the stress to the allowable stress, setting an early warning grade based on the ratio, and performing defect early warning.
Further, the first strain monitoring sensor group and the second strain monitoring sensor group are respectively arranged at 0.5-1m positions on two sides of the girth weld defect of the oil and gas pipeline.
Further, the first strain monitoring sensor group and the second strain monitoring sensor group are symmetrically arranged on two sides of the girth weld defect of the oil and gas pipeline.
Further, the strain monitoring sensor is a vibrating wire type strain sensor.
Further, a protective cover is arranged on the outer side of the strain monitoring sensor.
The method for evaluating the safety of the girth weld defect pipeline based on the strain monitoring can simplify calculation, reduce workload and reduce cost. By the strain monitoring device, the actual stress condition of the pipeline can be accurately controlled in real time according to the working environment and the time change of the conveying state of the pipeline, the defect evaluation result can be synchronously obtained after the real-time strain monitoring data is obtained, the defect safety or unsafe conclusion and basis can be given, and the engineering decision service is provided. The method has simple and efficient evaluation process, and can evaluate the safety state of the pipeline in real time through the strain monitoring data.
Drawings
FIG. 1 is a flow chart of a method for easily assessing pipeline stress for engineering practice problems;
FIG. 2 is a schematic view of a strain sensor mounting;
FIG. 3 is a schematic view of a monitoring cross-sectional installation location;
FIG. 4 is a schematic view showing the three-fold line constitutive relation of the pipeline steel;
FIG. 5 is a flowchart of the evaluation of the safety of a girth weld defective pipeline based on strain monitoring.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In recent years, with the vigorous development of the domestic pipeline industry, a large number of newly built pipelines are built and put into production. Although a high-strength steel welding process is generally adopted for newly-built pipelines, the pipe manufacturing quality is greatly improved compared with that of the former old pipelines, the problems that pipe body preheating, heat preservation and strength group are not carried out according to the process requirements in winter construction in part of pipelines still exist, the problem of circumferential weld welding defects is obvious, and the safe operation of the pipelines is influenced. Therefore, the invention provides a girth weld defect pipeline safety assessment method based on strain monitoring, which can monitor the stress of a pipeline with defects in real time so as to comprehensively analyze and give early warning to the safety state of the pipeline.
The invention relates to a method for evaluating the safety of a girth weld defect pipeline based on strain monitoring, which comprises the following steps,
s1, calculating the stress state near the defect of the circumferential weld defect pipeline, comprising the following steps:
s11, arranging a strain monitoring unit near the defect of the pipeline girth weld,
the strain monitoring unit is arranged on the pipeline and used for monitoring the stress of the pipeline in real time. The strain monitoring unit comprises a first strain monitoring sensor group and a second strain monitoring sensor group, the two strain monitoring sensor groups are respectively arranged on two sides of the circumferential weld defect of the oil and gas pipeline, and each strain monitoring sensor group at least comprises 3 strain sensors; taking a circular section of the oil-gas pipeline along the airflow direction of the oil-gas pipeline, optionally selecting three points L, U, R on the circular section in a clockwise direction, wherein the included angle between a point L and a connecting line between the point U and the circle center of the circular section is equal to the included angle between the point U and a connecting line between the point R and the circle center of the circular section, and arranging a strain sensor at the position of a point L, U, R respectively.
The vibrating wire type strain sensor 11 is a passive sensor, is small in size, is easy to isolate extrusion of external loads after being additionally provided with the protective cover 12, is easy to perform anticorrosion treatment, can avoid sensor failure caused by soil displacement shearing, and is stable for a long time and good in durability. Pipe stress cannot be measured directly, so to determine the magnitude of stress on a pipe, it is necessary to determine the strain on the pipe directly. For the pipeline containing the defects, as the section containing the defects of the pipeline is a potential danger point, monitoring equipment is not suitable to be directly installed on the section containing the defects during strain monitoring, so that the unfavorable expansion of the defects caused by artificial defect disturbance is avoided. Therefore, when defect monitoring is carried out, 1 group of monitoring sections are respectively installed at 0.5-1m positions on two sides of the defect, and stress distribution at the defect position is obtained through calculation according to the axial stress rule of the pipeline. Namely, as shown in fig. 3, the strain monitoring sensors are respectively arranged at a first monitoring section 13 and a second monitoring section 14, and the first strain monitoring sensor group and the second strain monitoring sensor group are symmetrically arranged at two sides of the girth weld defect of the oil and gas pipeline. Through two sets of monitoring sections, the complex stress state of the monitoring pipe section can be calculated, the monitoring precision is high, the reliability is high, and the method is suitable for the girth weld defect pipeline with low risk level.
Preferably, 1 strain sensor is respectively arranged on the left side (L), the top (U) and the right side (R) of the cross section of the pipeline, strain distribution of any angle of the cross section can be calculated according to the strain distribution rule of the cross section of the pipeline after strain of three points of the same cross section is measured, and strain distribution in the wall thickness direction can also be obtained. According to the strain distribution of the monitoring section, the stress distribution and the internal force of the monitoring section can be obtained. A schematic diagram of the sensor mounting is shown in fig. 2.
S12, monitoring strain distribution of the cross section of the pipeline;
according to the principle of plane section assumption and superposition, the pipeline strain is composed of film strain, x-direction bending strain and y-direction bending strain. Thin film with monitoring sectionThe maximum y-direction bending strain and the maximum z-direction bending strain are respectively epsilonm、
And
according to the superposition principle, the strain at any point on the pipeline section is obtained as follows:
wherein,
-the angle of any point on the pipe section in the clockwise direction from the apex of the section;
r-the distance from the center of the cross section of the pipeline to any point on the cross section is between the inner diameter ri of the pipeline and the outer diameter ro of the pipeline;
the monitored strain value U (0, r) can be obtained according to a formula0)、
And
and epsilonm、
And
the relationship of (1) is:
the cross-sectional film strain (average axial strain) and the maximum y and z-direction bending expressed by the monitored strain are respectively obtained by the following formula:
the maximum bending strain in the cross section can be obtained by combining the bending strains in the y and z directions:
the angle at which the maximum bending strain is:
accordingly, the monitoring cross-sectional maximum and minimum axial strains become:
the formula-the axial strain at any point in the pipe section, represented by the monitored strain, can be found by:
similarly, the maximum axial strain of each angle of the monitoring section can be obtained by the formula:
if the defect is located in the circumferential direction of the section
σeAnd the axial strains of the inner surface and the outer surface of the pipeline at the defect position are respectively obtained by the following formula:
the calculation of the monitored cross-sectional average axial strain and bending strain can be calculated by the following formula:
monitoring the section average axial strain:
monitoring the section bending strain:
wherein epsilonL' is the cross-sectional axial average strain; epsilonrIs the section bending strain; epsilonmaxMaximum strain in cross section; epsilonminIs the minimum strain in cross section.
S13, calculating the stress and the internal force of the cross section of the pipeline;
as shown in fig. 4, the relationship between stress and strain of the pipe steel in the three-fold line is obtained by calculating the stress of the defect point in the elastic range and the stress of the defect point in the elastoplastic range according to the relationship between stress and strain of the pipe steel.
1) When tensile strain (. epsilon. ')'max) In the elastic region, i.e. ε'max＜ε1Time of flight
σ’max＝Eε‘max
2) When tensile strain (. epsilon. ')'max) In the elastoplastic region, i.e. epsilonmax’≥ε1When the temperature of the water is higher than the set temperature,
in the formula,
σs-minimum yield strength of pipe (MPa);
σb-ultimate tensile strength of the pipe (MPa);
n- - - -strain hardening index;
note: formulated from BS7910-2013 and CSA Z662.15-2015.
In summary, strain distribution of the whole monitoring section can be obtained by monitoring strain by three strain sensors of the monitoring section, and stress distribution of the monitoring section can be obtained according to the strain distribution. According to the stress distribution and the internal force definition of the monitored cross section, the axial force of the monitored cross section, the bending moment to the Y axis and the bending moment to the Z axis can be obtained according to the following formulas:
s2, a circumferential weld defect pipeline safety evaluation method based on strain monitoring comprises the following steps:
specifically, the safety assessment of the girth weld defective pipe based on strain monitoring (see fig. 5) includes the following:
s21, evaluating defects based on the current stress;
and (4) based on the monitoring strain and stress analysis results, synthesizing the current defect evaluation standard, and deducing a defect evaluation criterion based on the monitoring strain. And combining the monitored strain with the initial stress to obtain the current stress of the pipeline, carrying out simplified evaluation and conventional evaluation on the defects based on the current stress and the defect evaluation criterion, and checking the current safety state of the defects.
(1) The buried straight pipe section without defects in a safe state should satisfy the following two conditions (11) and (12) at the same time:
(11) according to the specification of ASME B31.8-2016, the maximum allowable value of the axial stress of the buried constraint pipeline is 0.9 times of yield strength, namely the axial stress of the pipeline is required to meet the requirement
|σL|≤0.9σs
(12) According to the provisions of GB50251 and GB50253, the combined equivalent stress of the axial stress and the circumferential stress of the buried straight pipe section is less than 90 percent of the minimum yield strength specified by the steel pipe standard, namely the combined equivalent stress of the pipeline is required to meet the requirement
σe＜0.9σs
The conditions (11) and (12) are simultaneously met, and the pipeline safety is evaluated; otherwise, it is not safe.
Wherein: sigmas-pipe minimum yield strength (MPa);
σL-buried pipeline axial stress;
σe-pipe combined equivalent stress;
(2) a buried straight pipe section in a safe state contains a pipeline with a weld crack defect, and the following two conditions (21) and (22) are simultaneously satisfied:
(21) the evaluation condition of (11) should be satisfied;
(22) allowable axial tensile stress of pipeline
Wherein, K: a stress intensity factor;
y: a geometric factor or a shape factor;
a: crack sizes, such as: radius of circular crack, semiminor axis of elliptical crack.
S22, safety early warning based on stress threshold
Based on monitoring historical data and mechanical calculation, calculating to obtain defect safety states possibly occurring in different stress states, based on the defect safety states, obtaining a stress threshold value bearable by the defect under the current working condition or the specified working condition, based on the monitoring data and the stress threshold value, obtaining a ratio of the stress to the allowable stress, setting an early warning grade based on the ratio, and performing defect early warning.
S23, quantitative safety evaluation and risk control
When the pipeline risk evaluation is carried out based on the strain monitoring data, the danger degree of the monitoring pipeline section is required to be higher than that of the non-monitoring pipeline section. Therefore, strain monitoring of pipelines requires that the monitoring be focused on High Risk (HRA) and High Consequence (HCA) pipe sections. If the data show that monitoring section pipeline is safe, can guarantee that other pipelines will also be in safe state, and then guarantee to reduce the pipeline operation risk by the biggest.
The method for evaluating the safety of the girth weld defect pipeline based on the strain monitoring can simplify calculation, reduce workload and reduce cost. By the strain monitoring device, the actual stress condition of the pipeline can be accurately controlled in real time according to the working environment and the time change of the conveying state of the pipeline, the defect evaluation result can be synchronously obtained after the real-time strain monitoring data is obtained, the defect safety or unsafe conclusion and basis can be given, and the engineering decision service is provided. The method has simple and efficient evaluation process, and can evaluate the safety state of the pipeline in real time through the strain monitoring data.
The method is successfully applied to a pipeline body strain monitoring project of a pipeline defect section at 2 positions of a desert area, a pipeline body strain monitoring project of 126m upstream of GP228 pipeline defect sections of the west gas east China second line Ganzhou station, and a safety monitoring project of a west gas east China second line Wu acupoint station-Nanchang station serial No. 43640 circular weld defect epoxy casing pipe repairing construction process, and the pipeline body strain monitoring unit is stable in operation and normal in work.
It will be understood that modifications and variations can be made by persons skilled in the art in light of the above teachings and all such modifications and variations are intended to be included within the scope of the invention as defined in the appended claims.
Claims (6)
1. The method for evaluating the safety of the girth weld defect pipeline based on strain monitoring is characterized by comprising the following steps of,
s1, calculating the stress state near the defect of the circumferential weld defect pipeline, comprising the following steps:
s11, arranging a strain monitoring unit near the defect of the pipeline girth weld,
the strain monitoring unit comprises a first strain monitoring sensor group and a second strain monitoring sensor group, the two strain monitoring sensor groups are respectively arranged at two sides of the girth weld defect of the oil and gas pipeline, and each strain monitoring sensor group at least comprises 3 strain sensors; taking a circular section of the oil-gas pipeline along the airflow direction of the oil-gas pipeline, optionally selecting three points L, U, R on the circular section in a clockwise direction, wherein the included angle between a point L and a connecting line of the point U and the circle center of the circular section is equal to the included angle between the point U and a connecting line of the point R and the circle center of the circular section, and arranging a strain sensor at the position of a point L, U, R respectively;
s12, monitoring strain distribution of the cross section of the pipeline;
s13, calculating the stress and the internal force of the cross section of the pipeline;
s2, a circumferential weld defect pipeline safety evaluation method based on strain monitoring comprises the following steps:
s21, evaluating defects based on the current stress;
s22, safety early warning based on a stress threshold value;
s23, quantifying safety evaluation and risk control;
wherein the step S21 includes the steps of,
(1) the buried straight pipe section without defects in a safe state should satisfy the following two conditions (11) and (12) at the same time:
(11) according to the specification of ASME B31.8-2016, the maximum allowable value of the axial stress of the buried constraint pipeline is 0.9 times of the minimum yield strength, namely the axial stress of the pipeline is satisfied
|σL|≤0.9σs
(12) According to the provisions of GB50251 and GB50253, the equivalent stress of the combination of the axial stress and the circumferential stress of the buried straight pipe section is less than 90 percent of the minimum yield strength specified by the steel pipe standard, namely the equivalent stress of the pipeline combination is required to meet the requirement
σe＜0.9σs
The conditions (11) and (12) are simultaneously met, and the pipeline safety is evaluated; otherwise, it is unsafe;
wherein: sigmas-minimum yield strength of the pipe in MPa;
σL-buried pipeline axial stress;
σe-pipe combined equivalent stress;
(2) a buried straight pipe section in a safe state contains a pipeline with a weld crack defect, and the following two conditions (21) and (22) are simultaneously satisfied:
(21) the evaluation condition of (11) should be satisfied;
(22) allowable axial tensile stress of pipeline
Wherein, K: a stress intensity factor;
y is a geometric factor or a shape factor;
a, crack size: radius of circular crack, semiminor axis of elliptical crack.
2. The method for evaluating the safety of the girth weld defect pipeline based on the strain monitoring as claimed in claim 1, wherein the step S22 comprises,
based on monitoring historical data and mechanical calculation, calculating to obtain defect safety states possibly occurring in different stress states, based on the obtained defect safety states, obtaining a stress threshold value bearable by the defect under the current working condition or the specified working condition, based on the monitoring data and the stress threshold value, obtaining a ratio of the stress to the allowable stress, and setting an early warning grade based on the ratio and carrying out defect early warning.
3. The pipeline safety assessment method based on the strain monitoring circumferential weld defect of claim 1, wherein the first strain monitoring sensor group and the second strain monitoring sensor group are respectively arranged at 0.5-1m positions on two sides of the circumferential weld defect of the oil and gas pipeline.
4. The pipeline safety assessment method based on strain monitoring and circumferential weld defect of claim 1, wherein the first strain monitoring sensor group and the second strain monitoring sensor group are symmetrically arranged on two sides of the circumferential weld defect of the oil and gas pipeline.
5. The method for evaluating the safety of the girth weld defect pipeline based on the strain monitoring as claimed in claim 3 or 4, wherein the strain monitoring sensor is a vibrating wire type strain sensor.
6. The method for evaluating the safety of the girth weld defect pipeline based on the strain monitoring as claimed in claim 5, wherein a protective cover is arranged on the outer side of the strain monitoring sensor.
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| CN112504112B (en) | 2020-12-01 | 2022-04-05 | 西南石油大学 | Safety pipe ring and method for monitoring pipeline strain in mountainous area |
| CN113295313B (en) * | 2021-05-20 | 2023-02-28 | 中国大唐集团科学技术研究院有限公司中南电力试验研究院 | Pipeline welded junction stress monitoring and evaluating method |
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