CN113591348A - Three-dimensional stress calculation method for weld joint of in-service steam-water pipeline of thermal power plant - Google Patents
Three-dimensional stress calculation method for weld joint of in-service steam-water pipeline of thermal power plant Download PDFInfo
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- CN113591348A CN113591348A CN202110797829.9A CN202110797829A CN113591348A CN 113591348 A CN113591348 A CN 113591348A CN 202110797829 A CN202110797829 A CN 202110797829A CN 113591348 A CN113591348 A CN 113591348A
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Abstract
The invention discloses a method for calculating three-dimensional stress of a weld joint of an in-service steam-water pipeline of a thermal power plant, which belongs to the technical field of pipeline stress analysis. The method comprises the steps of taking hanger hoisting points adjacent to two ends of a welding line as starting end points, selecting a long straight pipe section containing a target welding line as a research object, compiling a pipeline stress calculation program, obtaining actual thermal displacement data of the hoisting points at the two ends through a high-precision three-way displacement indicator, inputting test data into the calculation program through a visual interface, obtaining three-dimensional stress data of any position of the section of the welding line, and calculating the position of the maximum stress. The invention has the advantages of rapid and convenient measurement and calculation and low requirement on operators, the calculation precision can meet the requirement of engineering application, and the development of field detection work can be better guided.
Description
Technical Field
The invention relates to a three-dimensional stress calculation method for a weld joint of an in-service steam-water pipeline of a thermal power plant, belongs to the technical field of pipeline stress analysis, and can be widely applied to the fields of steam-water pipeline systems and related equipment of the thermal power plant.
Background
The pipeline stress level is an important index for judging whether the pipeline can run safely, a simplified beam model is generally adopted for calculation (CAESAR II, AUTO PIPE and other software) in the design of the steam-water pipeline of the thermal power plant at present, the flexibility and the integral stress level of the pipeline system are mainly analyzed, the stress analysis result is not consistent with the actual stress distribution, the primary stress is the pipeline axial stress under the action of continuous load, and the secondary stress is the maximum tensile stress of the pipeline section under the action of displacement load. The detailed three-dimensional stress distribution condition of the pipeline section cannot be inquired through conventional design files, and the actual stress condition and the theoretical design state of the in-service pipeline may have differences.
The pipeline welding seam is an important object for metal supervision of a thermal power plant, once defects or material performance degradation exist in the in-service pipeline welding seam, safety evaluation needs to be carried out according to the actual stress state of the position, and meanwhile, the actual stress state of the welding seam is also an important parameter for service life evaluation of the in-service pipeline.
At present, only finite element analysis software can be adopted for detailed stress analysis, the calculation process is complicated and time-consuming, certain requirements are required for the technical capability of operators, and the method cannot be quickly applied to field detection guidance.
Disclosure of Invention
The invention aims to overcome the defects in the existing heat-engine plant in-service pipeline weld stress calculation, and provides an in-service steam-water pipeline weld three-dimensional stress calculation method which is simple in operation, quick in calculation and high in precision and meets the requirements of practical engineering application.
The technical scheme adopted by the invention for solving the problems is as follows: a three-dimensional stress calculation method for a weld joint of an in-service steam-water pipeline of a thermal power plant is characterized by comprising the following specific steps of:
the first step is as follows: when detailed three-dimensional stress of a straight pipe section welding line needs to be analyzed in detail, a hanger lifting point adjacent to two ends of the welding line is taken as an initial end point, the long straight pipe section containing the target welding line is selected as a research object, the length L from the end face of a lifting point A to the end face of a lifting point B and the length L from the end face of the lifting point A to the end face of the welding line are measured1Recording the specification of the pipeline, wherein the outer diameter is Do, the wall thickness is S, and the thickness of the heat-insulating layer is t.
The second step is that: three-way displacement indicators are arranged on the end surface of the lifting point A and the end surface of the lifting point B to record the thermal expansion displacement (x) of the lifting point A1、y1、z1) Recording the thermal expansion displacement (x) of the suspension point B2、y2、z2)。
The third step: a software package of a heat-engine plant in-service steam-water pipeline weld joint three-dimensional stress calculation system is compiled by adopting Python language, measurement data are input by using a visual interface mode, and a detailed stress value is calculated. The stress calculation formula is as follows:
horizontal pipe axial stress (MPa):
vertical pipe axial stress (MPa):
wherein: r and theta are position parameters of the stress solution point under the polar coordinate condition; doIs the outer diameter (mm) of the pipeline; s is the pipe wall thickness (mm); l, L1Is the length (mm) of the pipe section; t is the thickness (mm) of the heat preservation layer; (x)1、y1、z1) And (x)2、y2、z2) The thermal displacement value (mm) of the hanging points at the two ends is shown; di=Do-2S is the inner diameter (mm) of the pipe;is the pipe section moment of inertia (mm)4) (ii) a E is the elastic modulus (MPa) of the pipeline material at the working temperature; q is 24.6615X 10-2(Do-S)S+4.7124×10-2(Do+ t) t is the intermediate calculation parameter.
The fourth step: according to the stress solving formula, the axial maximum tensile stress position of the section of the welding seam can be calculated. The calculation formula is as follows:
for a horizontal pipe:
for a vertical pipe:
a=x2-x1
b=y2-y1。
preferably, the stress calculation process assumes that the axial displacement of the pipeline caused by thermal expansion is completely absorbed in the pipeline system based on the flexible design characteristics of the steam-water pipeline of the thermal power plant.
Preferably, on the basis of the stress characteristics of the steam-water pipeline structure of the thermal power plant, the pipeline stress caused by the torque action is not considered in the stress calculation process.
Preferably, the three-way displacement indicator in the second step has high reading precision, can adopt a mechanical type or a photoelectric type, and has a reading error of less than 0.1 mm.
Preferably, in the case that the actual thermal expansion of the pipeline is normal, the thermal expansion displacement of the hoisting point measured by the three-way thermal expansion indicator in the second step can also adopt the value of the thermal displacement of the hoisting point obtained by theoretical calculation.
Preferably, the program for solving the equation in the third step can be written in Python language or C, C + +, Fortran, and other calculation and languages.
Preferably, the calculation method can also be applied to three-dimensional stress calculation of any section of the straight pipe section.
Compared with the prior art, the invention has the following advantages and effects: (1) the three-dimensional stress of any position of the section of the welding seam and the position of the maximum stress can be obtained, and the development of field detection work can be guided better; (2) the measurement and calculation are quick and convenient, and the requirement on operators is low.
Drawings
FIG. 1 is a schematic diagram of horizontal pipeline test data in an embodiment of the present invention.
FIG. 2 is a schematic diagram of vertical pipe test data in an embodiment of the present invention.
FIG. 3 is a three-dimensional stress calculation software interface diagram of a weld of an in-service steam-water pipeline of a thermal power plant in an embodiment of the invention.
Fig. 4 is a graph comparing the stress calculation results at each radial position where θ is 130 ° in the embodiment of the present invention.
Detailed Description
The present invention will be described in further detail below by way of examples with reference to the accompanying drawings, which are illustrative of the present invention and are not to be construed as limiting the present invention.
Examples are given.
Referring to fig. 1 to 3, in the process of overhauling a main steam pipeline of a 660MW ultra-supercritical thermal power generating unit, a linear defect is found in a group of welding seams on a horizontal pipe section of the main steam pipeline, the three-dimensional stress calculation method for the welding seams of the steam-water pipeline in service of the thermal power plant in the embodiment is adopted to calculate the three-dimensional stress at the position of the defect, and the operation steps are as follows:
the specification of the main steam pipe section is phi 472.8mm multiplied by 86.8mm, the material is A335P 92, the design temperature is 610 ℃, the design pressure is 29.67MPa, the thickness t of the aluminum silicate heat-preservation cotton is 300mm, and the query standard shows that the elastic modulus E of the material at the design temperature is 168.8 multiplied by 103MPa, measured in situ as L6000 mm, L13000mm, the thermal expansion displacement of the A end of the lifting point is recorded by a three-way displacement indicator arranged as (x)1=118.3mm、y1=-17.8mm、z1-75.4mm) and the thermal expansion displacement at the B-end of the suspension point is (x)2=162.4mm、y2=-68.5mm、z2=-136.7mm)。
Inputting the data into an in-service steam-water pipeline welding seam three-dimensional stress calculation system at a defect position where r is 195mm and theta is 130 degrees, and calculating to obtain the three-dimensional stress of the position as follows: sigmar=-9.31MPa、σθ=48.95MPa、σL20.87 MPa; and the axial maximum tensile stress is between 122 and 130 degrees in the azimuth angle theta at different radial depths.
In order to verify the correctness of the calculation result of the invention, finite element software is adopted to carry out three-dimensional stress simulation analysis on the whole main steam pipeline, the stress calculation results of corresponding welding seams are extracted and compared, the stress calculation results of all radial positions at the position where theta is 130 degrees are shown in figure 4, the comparison result shows that the error between the two is within 10 percent, the calculation precision basically can meet the requirement of engineering application, and the calculation method and the assumed conditions adopted by the invention are reasonable and can be used for engineering field application.
Those not described in detail in this specification are well within the skill of the art.
Although the present invention has been described with reference to the above embodiments, it should be understood that the scope of the present invention is not limited thereto, and that various changes and modifications can be made by those skilled in the art without departing from the spirit and scope of the present invention.
Claims (4)
1. A three-dimensional stress calculation method for a weld joint of an in-service steam-water pipeline of a thermal power plant is characterized by comprising the following specific steps of:
the first step is as follows: when the detailed three-dimensional stress of the welding line of the straight pipe section is analyzed in detail, the hanging points of the hanging bracket adjacent to the two ends of the welding line are taken as starting end points, the long straight pipe section containing the target welding line is selected as a research object, the length L from the end face of the hanging point A to the end face of the hanging point B and the length L from the end face of the hanging point A to the end face of the welding line are measured1Recording the specification of the pipeline, wherein the outer diameter is Do, the wall thickness is S, and the thickness of the heat-insulating layer is t;
the second step is that: three-way displacement indicators are arranged on the end surface of the lifting point A and the end surface of the lifting point B to record the thermal expansion displacement (x) of the lifting point A1、y1、z1) Recording the thermal expansion displacement (x) of the suspension point B2、y2、z2);
The third step: compiling a software package of a three-dimensional stress calculation system of the in-service steam-water pipeline welding line of the thermal power plant, inputting measurement data by using a visual interface mode, and calculating a detailed stress value; the stress calculation formula is as follows:
horizontal pipe axial stress (MPa):
vertical pipe axial stress (MPa):
wherein: r and theta are position parameters of the stress solution point under the polar coordinate condition; doIs the outer diameter (mm) of the pipeline; s is the pipe wall thickness (mm); l, L1Is the length (mm) of the pipe section; t is the thickness (mm) of the heat preservation layer; (x)1、y1、z1) And (x)2、y2、z2) The thermal displacement value (mm) of the hanging points at the two ends is shown; di=Do-2S is the inner diameter (mm) of the pipe;is the pipe section moment of inertia (mm)4) (ii) a E is the elastic modulus (MPa) of the pipeline material at the working temperature; q is 24.6615X 10-2(Do-S)S+4.7124×10-2(Do+ t) t is an intermediate calculation parameter;
the fourth step: calculating the axial maximum tensile stress position of the section of the welding seam according to the stress solving formula; the calculation formula is as follows:
for a horizontal pipe:
for a vertical pipe:
a=x2-x1
b=y2-y1。
2. the method for calculating the three-dimensional stress of the weld joint of the in-service steam-water pipeline of the thermal power plant according to claim 1, wherein the axial displacement of the pipeline caused by thermal expansion is assumed to be completely absorbed in a pipeline system in the stress calculation process based on the flexible design characteristics of the steam-water pipeline of the thermal power plant.
3. The method for calculating the three-dimensional stress of the weld joint of the in-service steam-water pipeline of the thermal power plant according to claim 1, wherein the stress of the pipeline caused by the action of torque is not considered in the stress calculation process based on the stress characteristics of the steam-water pipeline structure of the thermal power plant.
4. The method for calculating the three-dimensional stress of the weld joint of the in-service steam-water pipeline of the thermal power plant according to claim 1, wherein in the second step, the three-way displacement indicator is in a mechanical or photoelectric type, and the reading error is less than 0.1 mm.
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