CN112347414A - Single-defect bent pipe limit internal pressure calculation method - Google Patents
Single-defect bent pipe limit internal pressure calculation method Download PDFInfo
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- CN112347414A CN112347414A CN202011191942.4A CN202011191942A CN112347414A CN 112347414 A CN112347414 A CN 112347414A CN 202011191942 A CN202011191942 A CN 202011191942A CN 112347414 A CN112347414 A CN 112347414A
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Abstract
The invention belongs to the technical field of petroleum and natural gas industry, and discloses a single-defect bent pipe limit internal pressure calculation method, which is characterized in that on the basis of a defect straight pipe limit load evaluation standard and a defect-free bent pipe limit load formula, the change of defect depth, length and width is considered, a 1stopt software fitting formula is utilized to obtain a prediction formula of the single-defect bent pipe limit internal pressure, and the accuracy of the formula is verified according to blasting test data. The method can obtain the ultimate internal pressure of the single-defect bent pipe of the booster station through formula calculation, provides reference for the calculation standard of the failure pressure of the single-defect bent pipe formulated by China, and provides important theoretical support for the design and safety evaluation of the bent pipe of the gas transmission pipeline.
Description
Technical Field
The invention belongs to the technical field of petroleum and natural gas industry, and particularly relates to a method for calculating the limit internal pressure of a single-defect bent pipe.
Background
The elbow is a key part in an oil and gas pipeline conveying system and can be used for changing the trend of a pipeline and bearing elastic deformation to a certain degree; because the bent pipe is of a double-curvature structure, the bent pipe can be eroded in the process that fluid flows through the bent pipe, in addition, both a medium in the pipe and soil outside the pipe can corrode the pipe wall, and the bent pipe is more prone to defects such as pits and local thinning compared with a straight pipe; the existence of the defects can reduce the pressure bearing capacity of the elbow pipe and influence the safe operation of a station yard; therefore, a calculation formula for the limit pressure-bearing capacity of the bent pipe needs to be established, the limit internal pressure of the bent pipe is accurately calculated, a maintenance decision is made, and the safety of station operation is guaranteed.
At present, domestic and foreign researchers mostly aim at straight pipes in the research of failure pressure of corrosion defect pipelines and provide a series of safety evaluation standards, such as ASME B31G, Modified B31G, DNV-RP-F101 and the like, but the research on bent pipes with defects is less, a set of mature method suitable for safety evaluation of the defective bent pipes is not formed, and the safety evaluation standard of the defective bent pipes is not formed.
For the bent pipe and the straight pipe with the same diameter-thickness ratio and the local thinning defect, the limit internal pressure is greatly different, and if the limit pressure-bearing capacity of the straight pipe is adopted to calculate the limit pressure-bearing capacity of the bent pipe, the result is possibly inaccurate. A plurality of defect conditions of the typical bent pipe phi 508 multiplied by 16mm and the material API X60 are calculated by taking as an example, the calculated values of the standard evaluation method of AMSE B31G-2009, DNV-RP-F101 and PCORRC volume type defect pipelines are compared with finite element results, and statistics is shown in Table 1. The error between the standard value and the calculated value is large, and the maximum error reaches 14.5 percent.
TABLE 1 comparison of the calculated values of the standard evaluation methods with the finite element results
Disclosure of Invention
In order to solve the problems in the background art, the invention provides a method for calculating the ultimate internal pressure of a single-defect bent pipe, and the ultimate bearing capacity of the single-defect bent pipe under the action of the internal pressure has important engineering significance on the safe operation of a pipeline in a station.
The invention provides a method for calculating the ultimate load of a single-defect bent pipe, which comprises the following steps:
step 1: determining basic parameters of the bent pipe with the defects according to design data of the booster station: the pipe diameter of the bent pipe, the wall thickness of the bent pipe, the curvature radius of the bent pipe, the tensile strength of the bent pipe, the defect length, the defect width and the defect depth;
step 2: calculating a defect axial length coefficient a, a defect circumferential width coefficient b and a defect depth coefficient c of the single-defect bent pipe;
and step 3: and (4) bringing the various calculated parameter values into corresponding calculation formulas to determine the limit internal pressure value of the single-defect bent pipe. A novel limit load calculation method for a single-defect bent pipe is provided. On the basis of a defect-free bent pipe ultimate load formula, the change of defect depth, length and width is considered, under the action of internal pressure, a bent pipe failure point may be at the center point of an inner arch and also may be in a defect area, in order to enable a calculation result to be more accurate, the analysis needs to be carried out by dividing into two conditions, namely when a defect depth coefficient c is less than 0.3 and the defect depth coefficient c is more than or equal to 0.3, a 1stopt software fitting formula is utilized to obtain a prediction formula of the single-defect bent pipe ultimate internal pressure.
When the defect depth coefficient c is less than 0.3, the failure area of the bent pipe is positioned at the center point of the inner arch, the calculation result is similar to the limit internal pressure of the non-defective bent pipe, and the limit internal pressure of the single-defect bent pipe can still be calculated by adopting a Goodall theoretical formula under the non-defective condition:
when the defect depth coefficient c is larger than or equal to 0.3, the failure point of the bent pipe is located in the defect area, and the limit internal pressure of the single-defect bent pipe is calculated by adopting the following formula:
P＝P0·[1-c(1-(1.393(1-b)0.464+3.532·exp(-0.628·a))·(1-c)1.946)]
in the formula, P is the limit internal pressure of the defect bent pipe, MPa;
P0-non-defective bend ultimate internal pressure, MPa;
σf-rheological stress, taken here as the minimum tensile strength limit 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-the coefficient of axial length of defect,
b-the circumferential width coefficient of the defect,
θ is the defect circumferential angle, °; the value range of b is [0,1]]；
c-defect depth coefficient, c ═ d/t, d is defect depth, mm; c is in the range of [0,1 ].
The invention has the advantages and positive effects that:
on the basis of the evaluation standard of the ultimate internal pressure of the defective straight pipe and the ultimate internal pressure formula of the non-defective bent pipe, the invention considers the change of the depth, the length and the width of the defect, obtains a prediction formula of the ultimate internal pressure of the single-defect bent pipe by fitting through 1stopt software, and finally verifies the accuracy of the formula through comparative analysis of blasting experiments, wherein the average relative error is 3.62 percent, the prediction error of the invention in a given range is less than 10 percent, and the prediction precision is higher.
The method provides theoretical support and certain reference value for the calculation standard of the failure pressure of the single-defect bent pipe formulated in China, and the limit internal pressure of the single-defect bent pipe is determined by establishing an auxiliary function f (a, b and c) related to a, b and c in a form of combining a calculation formula of the limit internal pressure PCORRC of the defect straight pipe; the single-defect elbow limit internal pressure prediction formula can calculate the limit internal pressure value of the elbow with single volume defect, and provides important reference basis and theoretical support for the design and safety evaluation of the gas transmission pipeline elbow.
Drawings
FIG. 1 is a flow chart of a method for calculating the limit internal pressure of a single-defect elbow according to an embodiment of the present 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 examples. It should be understood that the specific examples described herein are intended to be illustrative only and are not intended to be limiting.
The conditions of the single-defect bent pipe limit internal pressure calculation method provided by the embodiment of the invention are as follows:
the natural gas pipeline of the pressurization station is used as an example, wherein the natural gas pipeline is X60 steel grade, the pipe diameter is 508mm, the wall thickness is 22.23mm, the curvature radius R is 1.5D, the bending radius is 762mm, the yield strength is 450MPa, the tensile strength is 542MPa, the design pressure is 10MPa, and the operating pressure is 6.49-8.13 MPa.
(1) When the defect depth coefficient c <0.3 calculation example:
step 1: counting relevant size parameters of the defects;
step 2: calculating a defect axial length coefficient a, a defect circumferential width coefficient b and a defect depth coefficient c of the single-defect bent pipe;
and step 3: and (3) bringing the parameter values obtained by calculation into corresponding calculation formulas:
determining the limit internal pressure value of the single-defect bent pipe, wherein the statistical result is shown in the following table 2:
TABLE 2 failure calculation of center point of inner arch of elbow
(2) And when the defect depth coefficient c is more than or equal to 0.3, the failure point of the bent pipe is positioned in the defect area.
Step 1: counting relevant parameters of the defects;
step 2: calculating a defect axial length coefficient a, a defect circumferential width coefficient b and a defect depth coefficient c of the single-defect bent pipe;
and step 3: and (3) bringing the parameter values obtained by calculation into corresponding calculation formulas:
P＝P0·[1-c(1-(1.393(1-b)0.464+3.532·exp(-0.628·a))·(1-c)1.946)]
determining the limit internal pressure value of the single-defect bent pipe, wherein the statistical result is shown in the following table 3:
TABLE 3 failure examples for defective areas of inner arch of bent pipe
In the single-defect elbow limit internal pressure calculation method provided by the embodiment of the invention, in order to check and analyze the correctness of the fitting formula and the applicability under other steel grades, pipe diameters and pressure conditions, the limit internal pressure test data of the elbow containing the local thinning defect under the action of internal pressure in the literature is collected and sorted, and is shown in table 4:
TABLE 4 parameters and test data for local thinning defect contained in elbow
In order to check and analyze the correctness of the fitting formula, the fitting formula is used for calculating the limit internal pressure of the bent pipe containing the local thinning defect in the upper table, the result is compared with the existing blasting test value, and statistics is shown in table 5, so that the calculated result of the fitting formula containing the limit internal pressure of the local thinning bent pipe is well matched with the blasting test data, and the minimum relative error is 0.38%, the maximum relative error is 7.41%, the average relative error is 3.62% and the accuracy is higher as can be seen from table 5.
TABLE 5 comparison of measured values to fitting formula values
The above description is only a preferred embodiment of the present invention, and should not be taken as limiting the invention, and any modifications, equivalents, improvements, etc. made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (3)
1. The single-defect bent pipe limit internal pressure calculation method is characterized in that on the basis of a defect straight pipe limit internal pressure evaluation standard and a defect-free bent pipe limit internal pressure formula, the change of defect depth, length and width is considered, the positions of failure points of bent pipes are classified differently, a 1stopt software fitting formula is utilized to obtain a prediction formula of the single-defect bent pipe limit internal pressure, and the accuracy of the formula is verified through blasting test data.
2. A single-defect elbow limit internal pressure calculation method is characterized by comprising the following steps:
step 1: determining basic parameters of the bent pipe with the defects according to design data of the booster station: the pipe diameter of the bent pipe, the wall thickness of the bent pipe, the curvature radius of the bent pipe, the tensile strength of the bent pipe, the defect length, the defect width and the defect depth;
step 2: calculating a defect axial length coefficient a, a defect circumferential width coefficient b and a defect depth coefficient c of the single-defect bent pipe;
and step 3: and according to the values of a, b and c, substituting the various calculated parameter values into a proposed calculation formula to determine the limit internal pressure value of the single-defect bent pipe.
3. A single-defect elbow limit internal pressure calculation method is characterized in that an elbow failure point can be at an inner arch center point or in a defect area and discussed in two conditions (namely according to the defect depth coefficient c), and a prediction formula of the ultimate pressure of an elbow of a booster station is obtained:
when c < 0.3:
when c is more than or equal to 0.3:
P＝P0·[1-c(1-(1.393(1-b)0.464+3.532·exp(-0.628·a))·(1-c)1.946)]
in the formula, P is the limit internal pressure of the defect bent pipe, MPa;
P0-non-defective bend ultimate internal pressure, MPa;
σf-rheological stress, taken here as the minimum tensile strength limit 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-the coefficient of axial length of defect,
b-the circumferential width coefficient of the defect,
θ is the defect circumferential angle, °; the value range of b is [0,1]]；
c-defect depth coefficient, c ═ d/t, d is defect depth, mm; c is in the range of [0,1 ].
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113504024A (en) * | 2021-09-10 | 2021-10-15 | 西南石油大学 | Safety evaluation method for polyethylene gas pipeline under ground contact impact of demolition blasting collapsed body |
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Application publication date: 20210209 |