阅读说明：本技术 一种含腐蚀缺陷的海底管道结构弯曲失效评估方法 (Submarine pipeline structure bending failure assessment method containing corrosion defects ) 是由 杨冬平 王强 郭爱洪 丛军 王伟斌 牛更奇 支景波 朱丽国 高莎莎 马文峰 于 2018-08-13 设计创作，主要内容包括：本发明公开了一种含腐蚀缺陷的海底管道结构弯曲失效评估方法,具体为：检测管道最大尺寸腐蚀缺陷位置及腐蚀尺寸；根据管道检测数据、工况条件及环境条件计算管道承受的波浪及海流载荷,最终确定出被测管道所承受的最大弯矩位置和最大弯矩值；推导出含腐蚀缺陷管道的塑性极限弯矩公式,按照该公式可计算被测管道的塑性极限承载弯矩；将计算得到的最大弯矩值与塑性极限弯矩进行比较,在考虑安全系数的前提下判断被测管道是否失效。本发明的有益效果是：本发明能够对含有任意位置的小范围长轴向腐蚀缺陷的管道,进行整体弯曲强度计算评估,省去了有限元建模及分析过程,降低了计算难度,提高了计算的效率,同时又满足结果精度要求。(The invention discloses a submarine pipeline structure bending failure evaluation method containing corrosion defects, which comprises the following steps: detecting the position of the corrosion defect of the maximum size of the pipeline and the corrosion size; calculating wave and ocean current loads borne by the pipeline according to the pipeline detection data, the working condition and the environmental condition, and finally determining the maximum bending moment position and the maximum bending moment value borne by the pipeline to be detected; deducing a plastic limit bending moment formula of the pipeline containing the corrosion defects, and calculating the plastic limit bearing bending moment of the detected pipeline according to the formula; and comparing the calculated maximum bending moment value with the plastic limit bending moment, and judging whether the tested pipeline fails or not on the premise of considering the safety coefficient. The invention has the beneficial effects that: the method can be used for carrying out overall bending strength calculation and evaluation on the pipeline with the short-range long-axis corrosion defect at any position, so that the finite element modeling and analyzing process is omitted, the calculation difficulty is reduced, the calculation efficiency is improved, and the result precision requirement is met.)

1. A submarine pipeline structure bending failure evaluation method containing corrosion defects is characterized by comprising the following specific steps:

step S1: selecting an active pipeline as a tested pipeline, and detecting the position and corrosion size of the maximum-size corrosion defect of the tested pipeline;

step S2: according to the detection data of the step S1, calculating sea wave load and ocean current load, and determining the bending moment and the bending direction borne by the pipeline to be detected, so as to determine the maximum bending moment position and the maximum bending moment value borne by the pipeline to be detected;

step S3: deducing a plastic limit bending moment formula of the pipeline containing the corrosion defects, and calculating the plastic limit bending moment of the detected pipeline according to the plastic limit bending moment formula according to the detection result of the step S1;

step S4: comparing the maximum bending moment value calculated in the step S2 with the plastic limit bending moment calculated in the step S3, and if the maximum bending moment value is equal to or greater than the plastic limit bending moment, the detected pipeline fails; if the maximum bending moment value is smaller than the plastic limit bending moment, the tested pipeline does not fail;

and when the safety factor needs to be considered in the actual evaluation, replacing the plastic limit bending moment calculated in the step S3 with the allowable plastic limit bending moment for comparison, wherein the allowable plastic limit bending moment is a value obtained by dividing the plastic limit bending moment calculated in the step S3 by the safety factor n, and the safety factor n is determined according to the pipeline specification requirement.

2. The method for subsea pipeline structure bend failure evaluation containing corrosion defects according to claim 1, wherein in step S1, the location of the corrosion defect comprises a corrosion pit location angle.

3. The subsea pipeline structure bend failure evaluation method containing corrosion defects according to claim 1 or 2, wherein in step S1, the corrosion dimensions comprise corrosion width, corrosion depth and corrosion length of the corrosion pit.

4. The method for evaluating structural bending failure of a submarine pipeline containing corrosion defects according to any one of claims 1 to 3, wherein said step S2 is implemented by using a wave spectrum to calculate wave loads, and taking into account the combined effect of sea current loads.

5. The method for evaluating the structural bending failure of the submarine pipeline containing the corrosion defects according to any one of claims 1 to 4, wherein the calculation process of the plastic limit bending moment of the pipeline to be measured in the step S3 is as follows:

step S301: determining the position of a plastic neutral axis according to the position of the corrosion defect and the corrosion size of the measured pipeline, and calculating the area A of a tension area of the measured pipeline according to a formula (1) and a formula (2)_IAnd area A of compression zone_Π：

A_Ι＝2R_mtβ (1)

A_Π＝2R_mt(π-β)-2Rhθ (2)

Wherein:

step S302, according to the position and corrosion size of the corrosion defect of the detected pipeline, the angle β of the plastic neutral axis, the position angle α of the corrosion defect and the included angle gamma between the plastic neutral axis and the horizontal axis can be obtained, and then the centroid coordinates (y) of the tension area and the compression area are obtained according to the formulas (3) to (6)_c1，z_c1) And (y)_c2，z_c2)

Step S303: if the tested pipeline is in a plastic limit bearing state, the following two conditions should be met:

a) the method comprises the following steps The centroid connecting the tension zone and the compression zone is parallel to the z-axis, i.e. y_c1＝y_c2；

b) The method comprises the following steps The area of the tension zone is equal to that of the compression zone, namely A is A_I＝A_Π；

From the above two conditions, it can be calculated:

step S304: according to the calculation result of the step S303, the ultimate bending moment of the measured pipeline in the plastic ultimate bearing state is further obtained as follows:

M_p＝σ_yA(z_c2-z_c1)＝σ_y(4R_m ²tsinβcosγ-2R_m ²hsinθcosα) (9)

when the defect is symmetrical about the z-axis, i.e., α γ 0, its plastic limit bears a bending moment:

M_p＝σ_yA(z_c2-z_c1)＝σ_y(4R_m ²tsinβ-2R_m ²hsinθ) (10)

step S305: and substituting the corrosion defect position and the corrosion size of the measured pipeline into a formula (9) or a formula (10) to obtain the plastic limit bending moment of the measured pipeline.

6. A calculation method for submarine pipeline plastic limit bending moment is characterized by comprising the following steps:

step S1: determining the position of a plastic neutral axis according to the position of the corrosion defect and the corrosion size of the measured pipeline, and calculating the area A of a tension area of the measured pipeline according to a formula (1) and a formula (2)_IAnd area A of compression zone_Π：

A_Ι＝2R_mtβ (1)

A_Π＝2R_mt(π-β)-2Rhθ (2)

Wherein:

step S2, obtaining the angle β of the plastic neutral axis, the position angle α of the corrosion defect and the plastic neutral axis according to the position and the corrosion size of the corrosion defect of the detected pipelineThe included angle gamma with the horizontal axis, and then the centroid coordinates (y) of the tension area and the compression area are obtained according to the formulas (3) to (6)_c1，z_c1) And (y)_c2，z_c2)

Step S3: if the tested pipeline is in a plastic limit bearing state, the following two conditions should be met:

a) the method comprises the following steps The centroid connecting the tension zone and the compression zone is parallel to the z-axis, i.e. y_c1＝y_c2；

b) The method comprises the following steps The area of the tension zone is equal to that of the compression zone, namely A is A_I＝A_Π；

From the above two conditions, it can be calculated:

step S4: according to the calculation result of the step S303, the ultimate bending moment of the measured pipeline in the plastic ultimate bearing state is further obtained as follows:

M_p＝σ_yA(z_c2-z_c1)＝σ_y(4R_m ²tsinβcosγ-2R_m ²hsinθcosα) (9)

when the defect is symmetrical about the z-axis, i.e., α γ 0, its plastic limit bears a bending moment:

M_p＝σ_yA(z_c2-z_c1)＝σ_y(4R_m ²tsinβ-2R_m ²hsinθ) (10)

step S5: and substituting the corrosion defect position and the corrosion size of the measured pipeline into a formula (9) or a formula (10) to obtain the plastic limit bending moment of the measured pipeline.

7. The method for calculating a plastic limit bending moment of a subsea pipeline according to claim 6, wherein in step S1 the location of the corrosion defect comprises a corrosion pit location angle.

8. The method for calculating the plastic limit bending moment of subsea pipelines according to claim 6 or 7, wherein said corrosion dimensions comprise corrosion width, corrosion depth and corrosion length of the corrosion pit in step S1.

Technical Field

The invention relates to the technical field of submarine pipeline failure evaluation, in particular to a submarine pipeline structure bending failure evaluation method containing corrosion defects.

Background

In recent years, the demand of our country for resources such as petroleum and natural gas has been increasing. The development and utilization of resources such as oil and natural gas are also becoming more and more important. The submarine pipeline is used as a 'life line' for development, production and transportation of oil and gas resources, and plays an extremely important role in ensuring the safety of a pipeline structure. Because of the complex marine environment, subsea pipelines are often suspended by erosion and seawater. When the outer anticorrosive coating of the submarine pipeline is damaged, seawater can corrode along the damaged direction of the anticorrosive coating, and a long corrosion defect (a corrosion defect with small circumferential size and large axial length, ideally, the axial corrosion length is not less than that of the pipeline)

Wherein R is a pipeRadius, t is the pipe thickness). After the pipeline is corroded, the pipeline is locally thinned, and the limit bearing capacity is reduced. Corrosion of pipelines is one of the important causes of damage to subsea pipelines. In addition, the submarine pipeline is often subjected to natural disasters such as landslide and riverbed deformation, and is suspended due to erosion and seawater scouring, and at the moment, the bending moment load becomes a main factor causing damage to the submarine pipeline.

Accurate assessment of the ultimate bearing capacity or ultimate bending moment of a corroded pipe (the ultimate bending moment can be calculated through the ultimate bearing capacity, and the ultimate bearing capacity and the ultimate bending moment can be converted mutually) is a precondition for ensuring normal operation of the pipe. On the basis of experimental research and theoretical simulation, scholars at home and abroad carry out a great deal of research on the ultimate bearing capacity of the corroded pipeline. In the 70 s of the 20 th century, the American society of mechanical Engineers proposed the specification of ultimate internal pressure load of corrosive pipes: ASME B31G, is still the most widely used specification for the ultimate bearing capacity assessment of pipelines. Considering that the B31G is conservative in evaluating the extreme internal pressure load of the corrosion pipeline, the Kiefer and the Vieth improve parameters such as flow stress, Folias coefficient and the like in the B31G, and further propose a revised extreme internal pressure load specification: MB31G (0.8 dl). In the early 21 st century, norwegian classification (DNV) proposed the evaluation specification of the ultimate bearing capacity of a DNV-RP-F101 corrosion pipeline by a series of numerical simulations and experimental studies on submarine corrosion pipelines, taking into account axial pressure and bending loads. In 2003, Choi et al performed blasting tests and numerical simulation on X65 natural gas corrosion pipelines, and regressed a limit internal pressure formula of pipelines containing rectangular corrosion defects and elliptical corrosion defects. Zhu and Leis, etc. apply finite strain theory and distortion instability theory, propose a plastic failure model suitable for intact pipelines, and extend the model into corrosion-defective pipelines.

However, in the current method for evaluating the ultimate bearing capacity of the submarine pipeline in plastic failure under bending action, the corrosion defect is mostly set at the position with the maximum bending stress, so that the lower limit of the critical load of the submarine pipeline with corrosion in plastic failure is obtained. However, the corrosion position of the surface of the actual submarine pipeline has arbitrariness, namely, the corrosion position is not necessarily located at the position with the maximum bending stress, so that the method for researching the bending plasticity limit bearing capacity of the submarine pipeline containing any position has more practical application value, and the failure judgment of any corrosion position defect can be realized only by establishing a pipeline finite element model to perform simulation analysis.

Disclosure of Invention

The invention provides a submarine pipeline structure bending failure evaluation method containing corrosion defects, which comprises a calculation method of submarine pipeline bending plastic limit bearing bending moment at any position, and is not limited to the situation that the corrosion defects only exist at the maximum pipeline bending position.

The invention provides a submarine pipeline structure bending failure evaluation method containing corrosion defects, which comprises the following steps:

step S1: selecting a service pipeline as a detected pipeline, and detecting the position and corrosion size of the maximum-size corrosion defect of the detected pipeline;

step S2: according to the detection data of the step S1, calculating sea wave load and ocean current load, and determining the bending moment and the bending direction borne by the pipeline to be detected, so as to determine the maximum bending moment position and the maximum bending moment value borne by the pipeline to be detected;

step S3: deducing a plastic limit bending moment formula of the pipeline containing the corrosion defects, and calculating the plastic limit bearing bending moment of the detected pipeline according to the plastic limit bending moment formula according to the detection result of the step S1;

step S4: comparing the maximum bending moment value obtained by calculation in the step S2 with the plastic limit bearing bending moment obtained by calculation in the step S3, and if the maximum bending moment value is equal to or greater than the plastic limit bearing bending moment, the tested pipeline fails; if the maximum bending moment value is smaller than the plastic limit bearing bending moment, the tested pipeline does not fail; and when the safety factor needs to be considered in the actual evaluation, replacing the plastic limit bending moment calculated in the step S3 with the allowable plastic limit bending moment for comparison, wherein the allowable plastic limit bending moment is a value obtained by dividing the plastic limit bending moment calculated in the step S3 by the safety factor n, and the safety factor n is determined according to the pipeline specification requirement.

In step S1, the location of the etch defect includes an etch pit location angle α, and the etch size includes an etch width 2R θ, an etch depth h, and an etch length L of the etch pit.

In step S2, a wave spectrum is used to calculate the wave load, and the combined action of the wave load is considered.

The calculation process of the plastic limit bearing bending moment of the pipeline to be measured in the step S3 is specifically as follows:

step S301: determining the position of a plastic neutral axis according to the position of the corrosion defect and the corrosion size of the measured pipeline, and calculating the area A of a tension area of the measured pipeline according to a formula (1) and a formula (2)_IAnd area A of compression zone_Π：

A_Ι＝2R_mtβ (1)

A_Π＝2R_mt(π-β)-2Rhθ (2)

Wherein:

is the average radius; r is the radius of the outer wall of the pipeline; t is the thickness of the measured pipeline, and t is far less than R; h is the corrosion depth, and theta is the half angle of the corrosion width;

step S302, according to the position and corrosion size of the corrosion defect of the detected pipeline, the angle β of the plastic neutral axis, the position angle α of the corrosion defect and the included angle gamma between the plastic neutral axis and the horizontal axis can be obtained, and then the centroid coordinates (y) of the tension area and the compression area are obtained according to the formulas (3) to (6)_c1，z_c1) And (y)_c2，z_c2)

Step S303: if the tested pipeline is in a plastic limit bearing state, the following two conditions should be met:

a) the method comprises the following steps The centroid connecting the tension zone and the compression zone is parallel to the z-axis, i.e. y_c1＝y_c2；

b) The method comprises the following steps The area of the tension zone is equal to that of the compression zone, namely A is A_I＝A_Π；

From the above two conditions, it can be calculated:

step S304: according to the calculation result of the step S303, the ultimate bending moment of the measured pipeline in the plastic ultimate bearing state is further obtained as follows:

M_p＝σ_yA(z_c2-z_c1)＝σ_y(4R_m ²t sinβcosγ-2R_m ²h sinθcosα) (9)

when the defect is symmetrical about the z-axis, i.e., α γ 0, its plastic limit bears a bending moment:

M_p＝σ_yA(z_c2-z_c1)＝σ_y(4R_m ²t sinβ-2R_m ²h sinθ) (10)

step S305: and substituting the corrosion defect position and the corrosion size of the measured pipeline into a formula (9) or a formula (10), so as to obtain the plastic limit bearing bending moment of the measured pipeline.

In order to achieve the above object, the present invention further provides a method for calculating the plastic limit bearing bending moment of the submarine pipeline, wherein the method specifically comprises:

step S1: determining the position of a plastic neutral axis according to the position of the corrosion defect and the corrosion size of the measured pipeline, and calculating the area A of a tension area of the measured pipeline according to a formula (1) and a formula (2)_IAnd area A of compression zone_Π：

A_Ι＝2R_mtβ (1)

A_Π＝2R_mt(π-β)-2Rhθ (2)

Wherein:

is the average radius; r is the radius of the outer wall of the pipeline; t is the thickness of the measured pipeline, and t is far less than R; h is the corrosion depth, and theta is the half angle of the corrosion width;

step S2, according to the position and corrosion size of the corrosion defect of the detected pipeline, the angle β of the plastic neutral axis, the position angle α of the corrosion defect and the included angle gamma between the plastic neutral axis and the horizontal axis can be obtained, and then the centroid coordinates (y) of the tension area and the compression area are obtained according to the formulas (3) to (6)_c1，z_c1) And (y)_c2，z_c2)

Step S3: if the tested pipeline is in a plastic limit bearing state, the following two conditions should be met:

a) the method comprises the following steps A tension zone andthe centroid of the compression zone being parallel to the z-axis, i.e. y_c1＝y_c2；

b) The method comprises the following steps The area of the tension zone is equal to that of the compression zone, namely A is A_I＝A_Π；

From the above two conditions, it can be calculated:

step S4: according to the calculation result of the step S303, the ultimate bending moment load bending moment of the measured pipeline in the plastic ultimate load state is further obtained as follows:

M_p＝σ_yA(z_c2-z_c1)＝σ_y(4R_m ²t sinβcosγ-2R_m ²h sinθcosα) (9)

when the defect is symmetrical about the z-axis, i.e., α γ 0, its plastic limit bears a bending moment:

M_p＝σ_yA(z_c2-z_c1)＝σ_y(4R_m ²t sinβ-2R_m ²h sinθ) (10)

step S5: and substituting the corrosion defect position and the corrosion size of the measured pipeline into a formula (9) or a formula (10), so as to obtain the plastic limit bearing bending moment of the measured pipeline.

In step S1, the location of the etch defect includes an etch pit location angle α, and the etch size includes an etch width 2R θ, an etch depth h, and an etch length L of the etch pit.

The invention has the beneficial effects that: the method can calculate the ultimate bearing bending moment of the corrosion pipeline under the pure bending moment load aiming at the small-range long corrosion defect of any position of the pipeline, and compares the ultimate bearing bending moment with the maximum bending moment position and the maximum bending moment value born by the pipeline to evaluate the integral strength of the corrosion-containing pipeline, thereby saving the finite element modeling calculation process of the bending failure evaluation of the tubular structure containing the corrosion defect, reducing the calculation difficulty of engineering application, improving the calculation efficiency and simultaneously meeting the requirement of the accuracy of the result.

Drawings

FIG. 1 is a finite element grid diagram of a pipeline containing corrosion defects in accordance with an embodiment of the present invention.

FIG. 2 is a graph of finite element analysis failure in accordance with an embodiment of the present invention.

FIG. 3 is a graph illustrating finite element bending moment versus end turn angle in accordance with an embodiment of the present invention.

FIG. 4 shows the test piece size and the corrosion defect size in the second comparative test of the present invention.

Detailed Description

Because the marine environment is complex, the submarine pipeline is often in a suspended state due to elutriation and seawater scouring, and the bending moment load becomes a main factor for the damage of the submarine pipeline. When the outer anticorrosive coating of submarine pipeline appears damaging, the sea water can take place to corrode along the direction that the anticorrosive coating damaged, forms long corrosion defect in pipeline outside optional position very easily. The method is used for deducing a limit bending moment calculation formula under the pure bending moment load by carrying out numerical simulation and finite element analysis aiming at the short-range long corrosion defect at any position, comparing the limit bending moment calculation formula with a finite element analysis result, and verifying the accuracy of the calculation formula.

In order to clearly illustrate the technical features of the present solution, the present solution is explained below by way of specific embodiments.