CN112347583B - Method for calculating limit internal pressure of double-defect-contained bent pipe of booster station - Google Patents

Abstract

Translated fromChinese

本发明公开了一种增压站含双缺陷弯管极限内压的计算方法，包括以下步骤：首先根据增压站弯管的资料，确定弯管、弯管缺陷的基础数据，然后根据轴向和环向相互作用极限距离的判定条件，判断缺陷之间是否存在相互影响，如果缺陷之间相互影响很小，则可以按照单个缺陷计算方法来处理，如果缺陷间的相互影响不可忽略，则弯管极限内压必须考虑缺陷之间的相互影响；本发明揭示了双缺陷间相互影响对弯管极限载荷的影响，并确定了双缺陷间发生相互影响的临界距离，提出了适用于增压站内双缺陷弯管极限载荷的预测公式，对于保障管道安全运行及减少经济损失意义重大。

The invention discloses a method for calculating the ultimate internal pressure of a double-defect elbow in a booster station, comprising the following steps: first, according to the elbow data of the booster station, determine the basic data of elbow and elbow defects, and then according to the axial direction and the judgment condition of the hoop interaction limit distance, to judge whether there is mutual influence between the defects. If the mutual influence between the defects is small, it can be processed according to the calculation method of a single defect. If the mutual influence between the defects is not negligible, the bending The ultimate internal pressure of the pipe must consider the interaction between the defects; the invention discloses the influence of the interaction between the double defects on the ultimate load of the elbow, and determines the critical distance for the interaction between the double defects. The prediction formula of the ultimate load of double-defect elbows is of great significance to ensure the safe operation of pipelines and reduce economic losses.

Description

Method for calculating limit internal pressure of double-defect-contained bent pipe of booster station

Technical Field

The invention relates to a method for calculating the limit internal pressure of a bent pipe with defects in a pressurizing station, in particular to a method for calculating the limit internal pressure of a bent pipe with double defects.

Background

At present, domestic and foreign researchers generally have two analysis methods aiming at the research of the limit load of the bent pipe with the defect: the first method is a calculation method for the limit internal pressure of the elbow pipe with the defects based on a straight pipe formula, and the second method is a calculation formula for the limit internal pressure which is fitted according to finite element results; however, the influence of the single defect on the limit load of the bent pipe is mainly considered, the defects caused by corrosion, erosion and the like of the actual pipeline often appear in the form of double defects and multiple defects, and adjacent defects may have mutual influence under the conditions of the double defects and the multiple defects, so that the calculation is inaccurate according to the single-defect bent pipe limit internal pressure formula. The interaction criterion of the corrosion defects proposed by the current scholars at home and abroad is mostly established on the basis of the axial or annular double-point corrosion defects of the straight pipe, and whether the influence of the change of the distance between the double-point corrosion defects of the bent pipe on the extreme pressure is still consistent with the influence rule of the double-point corrosion defects of the straight pipe is to be further researched.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a method for calculating the limit internal pressure of a double-defect bent pipe of a booster station, which comprises the following steps:

the method comprises the following steps: according to the related data of the bent pipe of the booster station, the outer diameter D, the wall thickness t, the bending radius R and the tensile strength sigma of the bent pipe are determined_bDefect length L, depth d, width w, axial spacing S_lAnnular spacing S_c；

Step two: when the double defects are mutually influenced, the following two conditions are simultaneously met:

(1) when the positions of the two defects cannot meet the conditions at the same time, the mutual influence between the two defects can be ignored, the limit internal pressure of the bent pipe when the two single defects exist can be respectively calculated, then the smaller value of the limit internal pressure is taken as the limit internal pressure of the bent pipe with the double defects, and the axial length coefficient, the circumferential width coefficient and the depth coefficient of the defects meet the following conditions:

l is the single defect axial length;

b is w/pi D, w is the single defect annular width;

d is the single defect depth;

(2) when two adjacent defects simultaneously satisfy the above conditions, it is indicated that mutual influence occurs between the two defects, and the lengths of the two defects are respectively L₁And L₂Defect widths are w respectively₁And w₂The depth of the defect is d₁And d₂Axial spacing of defect S_lDistance S in circumferential direction_cThen, there are:

equivalent length of defect: l is_eq＝L₁+S_l+L₂；

Equivalent width of defect: w is a_eq＝w₁+S_c+w₂；

Equivalent depth of defect:

at the moment, the axial length coefficient, the circumferential width coefficient and the depth coefficient of the defect meet the following conditions:

L_eqis the equivalent length of the defect;

b＝w_eq/πD，w_eqis the equivalent width of the defect;

c＝d_eq/t,d_eqis the equivalent depth of the defect;

step three: and (3) substituting the parameters into the following extreme internal pressure calculation formula, and finally calculating the extreme internal pressure of the double-defect bent pipe:

in the formula, P is the limit internal pressure of the defect bent pipe, MPa;

P₀-defect free bend limit internal pressure, MPa;

σ_f-the flow stress, taken here is the tensile strength of the bend, MPa;

t is the wall thickness of the bent pipe, mm;

r-bend radius, mm;

r is the bending radius of the bent pipe, mm;

a-defect length coefficient;

b-defect width factor;

c-defect depth coefficient.

The invention has the advantages and positive effects that:

the invention provides a method for calculating the limit internal pressure of a double-defect bent pipe of a booster station, which is based on a single-defect bent pipe limit internal pressure calculation formula, considers the influence of the interaction between adjacent defects on the limit internal pressure of the bent pipe, combines the judgment conditions of axial and circumferential interaction limit distances, provides a method for calculating the limit internal pressure of the double-defect bent pipe, and perfects the method for calculating the limit internal pressure of the defective bent pipe. Compared with the ABAQUS software numerical simulation result, the method has the advantages of small error and good applicability, and can provide suggestions for timely maintenance and replacement of the pipeline.

Drawings

FIG. 1 is a flow chart of a method for calculating the limit internal pressure of a double-defect-containing elbow of a booster station provided by the invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The application of the principles of the present invention will now be further described with reference to specific examples.

Example (c): the gas transmission elbow pipe in a certain pressurizing station is made of X60 steel, the pipe diameter is 508mm, the wall thickness is 22.23mm, the working pressure is 8Mpa, and the inner wall of the elbow pipe is eroded by scouring of the transmission medium.

The first step is as follows: the basic data for determining the elbow based on the elbow related data of the booster station are shown in the following table 1.

TABLE 1 supercharging station bend basic data

Two adjacent defects are assumed to be defects with the same size, and the sizes, the axial spacing and the circumferential spacing of the defects are shown in table 2.

TABLE 2 Dual Defect size and location data

The second step is that: according to the judgment condition of the axial and circumferential interaction limit distance, judging that the double defects of the bent pipe in 9 calculation examples have mutual influence, wherein the related parameters of the calculated defects are shown in the following table 3:

TABLE 3 Defect-related parameters

According to the coefficient formula, the results of calculating the axial length coefficient, the circumferential width coefficient and the depth coefficient of the defect are shown in the following table 4.

L_eqIs the equivalent length of the defect;

b＝w_eq/πD，w_eqis the equivalent width of the defect;

c＝d_eq/t,d_eqis the equivalent depth of the defect;

TABLE 4 Defect correlation coefficients

The third step: and (3) substituting the parameters into the following extreme internal pressure calculation formula, and finally calculating the extreme internal pressure of the double-defect bent pipe:

the ultimate pressure of the composite double-defect bent pipe in the table is calculated according to the method, and the result obtained by formula calculation is compared with the finite element result for verification, as shown in table 4.

TABLE 4 comparison of ABAQUS analog values with formula calculation results

The comparison of formula calculation values and finite element simulation results in the table shows that the calculation results of the two methods are relatively close, the maximum error is 8.1%, the minimum error is 1.0%, and the average error is 5.1%. The method can be used for calculating the limit internal pressure of the elbow containing the double defects.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims (1)

1. A method for calculating the limit internal pressure of a double-defect bent pipe of a pressurizing station comprises the following steps:

the method comprises the following steps: according to the related data of the bent pipe of the booster station, the outer diameter D, the wall thickness t, the bending radius R and the tensile strength sigma of the bent pipe are determined_bDefect length L, depth d, width w, axial spacing S_lAnnular spacing S_c；

Step two: when the double defects are mutually influenced, the following two conditions are simultaneously met:

(1) when the positions of the two defects cannot meet the conditions at the same time, the mutual influence between the two defects can be ignored, the limit internal pressure of the bent pipe when the two single defects exist can be respectively calculated, then the smaller value of the limit internal pressure is taken as the limit internal pressure of the composite double-defect bent pipe, and the axial length coefficient, the circumferential width coefficient and the depth coefficient of the defects meet the following conditions:

l is the single defect axial length;

b is w/pi D, w is the single defect annular width;

d is the single defect depth;

(2) when two adjacent defects simultaneously satisfy the above conditions, it is indicated that mutual influence occurs between the two defects, and the lengths of the two defects are respectively L₁And L₂Defect widths are w respectively₁And w₂The depth of the defect is d₁And d₂Axial spacing of defect S_lDistance S in circumferential direction_cThen, there are:

equivalent length of defect: l is_eq＝L₁+S_l+L₂；

Equivalent width of defect: w is a_eq＝w₁+S_c+w₂；

Equivalent depth of defect:

at the moment, the axial length coefficient, the circumferential width coefficient and the depth coefficient of the defect meet the following conditions:

L_eqis the equivalent length of the defect;

b＝w_eq/πD，w_eqis the equivalent width of the defect;

c＝d_eq/t,d_eqis the equivalent depth of the defect;

step three: and (3) substituting the parameters into the following extreme internal pressure calculation formula, and finally calculating the extreme internal pressure of the double-defect bent pipe:

in the formula, P is the limit internal pressure of the defect bent pipe, MPa;

P₀-defect free bend limit internal pressure, MPa;

σ_f-the flow stress, taken here is the tensile strength of the bend, MPa;

t is the wall thickness of the bent pipe, mm;

r-bend radius, mm;

r is the bending radius of the bent pipe, mm;

a-defect length coefficient;

b-defect width factor;

c-defect depth coefficient.

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