CN113591348B - Method for calculating three-dimensional stress of weld joint of steam-water pipeline in service of thermal power plant - Google Patents
Method for calculating three-dimensional stress of weld joint of steam-water pipeline in service of thermal power plant Download PDFInfo
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Abstract
The invention discloses a three-dimensional stress calculation method for 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, and is based on the flexible design characteristics of the steam-water pipeline of the thermal power plant and the stress characteristics of a steam-water pipeline structure, and the pipeline stress caused by torque action is ignored under the assumption that the pipeline axial displacement caused by thermal expansion is completely absorbed in a pipeline. And taking hanging points adjacent to two ends of the welding line as starting endpoints, selecting the long straight pipe section containing the target welding line as a research object, compiling a pipeline stress calculation program, acquiring actual thermal displacement data of the hanging points at two ends through a high-precision three-way displacement indicator, inputting test data into the calculation program by utilizing a visual interface to obtain 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 quick and convenient measurement and calculation and low requirement on operators, the calculation precision can meet the requirements of engineering application, and the development of on-site 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 stress level of the pipeline is an important index for judging whether the pipeline can safely run or not, at present, a simplified beam model is generally adopted for calculation (software such as CAESAR II, AUTO PIPE) when the steam-water pipeline of the thermal power plant is designed, the flexibility and the overall stress level of the pipeline system are mainly analyzed, the stress analysis result is inconsistent with the actual stress distribution, the primary stress is only the axial stress of the pipeline under the action of continuous load, and the secondary stress is the maximum tensile stress of the section of the pipeline under the action of displacement load. The detailed three-dimensional stress distribution condition of the pipeline section cannot be inquired through the conventional design file, 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 of metal supervision of a thermal power plant, once defects or material performance degradation exist in the inside of the pipeline welding seam in service, safety evaluation is required 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 evaluating the service life of the pipeline in service.
At present, only finite element analysis software can be used for carrying out detailed stress analysis, the calculation process is complex and long in time consumption, and the method has certain requirements on technical capability of operators and cannot be rapidly applied to on-site detection guidance.
Disclosure of Invention
The invention aims to overcome the defects in the calculation of the weld stress of the in-service pipeline of the traditional thermal power plant, and provides the in-service steam-water pipeline weld three-dimensional stress calculation method which is simple to operate, quick to calculate and capable of meeting the actual engineering application precision.
The invention solves the problems by adopting the following technical scheme: a method for calculating the three-dimensional stress of a weld joint of an in-service steam-water pipeline of a thermal power plant is characterized by comprising the following specific steps:
the first step: when the detailed three-dimensional stress of the welding seam of the straight pipe section needs to be analyzed in detail, taking hanging points adjacent to two ends of the welding seam as starting endpoints, selecting the long straight pipe section containing the target welding seam as a research object, and measuring 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 seam 1 The specification of the pipeline is recorded, the outer diameter is Do, the wall thickness is S, and the thickness of the heat preservation layer is t.
And a second step of: three-way displacement indicators are arranged on the end face of the hanging point A and the end face of the hanging point B, and the thermal expansion displacement (x 1 、y 1 、z 1 ) The thermal expansion displacement (x 2 、y 2 、z 2 )。
And a third step of: and programming a software package of a three-dimensional stress calculation system of the welding seam of the steam-water pipeline in service of the thermal power plant by adopting a Python language, inputting measurement data by using a visual interface mode, and calculating a detailed stress value. The stress calculation formula is as follows:
hoop stress (MPa):
radial stress (MPa):
horizontal pipe axial stress (MPa):
vertical pipe axial stress (MPa):
wherein: r and theta are position parameters of the stress solving point under the polar coordinate condition; d (D) o Is the outer diameter (mm) of the pipeline; s is the wall thickness (mm) of the pipeline; l, L 1 Length of pipe section (mm); t is the thickness (mm) of the heat insulation layer; (x) 1 、y 1 、z 1 ) (x) 2 、y 2 、z 2 ) The thermal displacement value (mm) of the hanging points at the two ends; d (D) i ＝D o -2S is the pipe inner diameter (mm);
is the section moment of inertia (mm) of the pipeline 4 ) The method comprises the steps of carrying out a first treatment on the surface of the E is the elastic modulus (MPa) of the pipeline material at the working temperature; q= 24.6615 ×10 -2 (D o -S)S+4.7124×10 -2 (D o +t) t is an intermediate calculation parameter.
Fourth step: according to the stress solving formula, the position of the axial maximum tensile stress of the welding line section can be calculated. The calculation formula is as follows:
for horizontal pipes:
for vertical pipes:
a＝x 2 -x 1
b＝y 2 -y 1 。
preferably, based on the flexible design characteristics of the steam-water pipeline of the thermal power plant, the pipeline axial displacement caused by thermal expansion is assumed to be completely absorbed in the pipeline in the stress calculation process.
Preferably, based on the stress characteristics of the steam-water pipeline structure of the thermal power plant, pipeline stress caused by torque action is not considered in the stress calculation process.
Preferably, the three-way displacement indicator in the second step should have high reading accuracy, and can adopt a mechanical type or an optoelectronic type, and the reading error should be less than 0.1mm.
Preferably, under the condition that the actual thermal expansion of the pipeline is normal, the thermal expansion displacement of the lifting point measured by the three-way thermal expansion indicator in the second step can also adopt a theoretically calculated value of the thermal displacement of the lifting point.
Preferably, the program for solving the equation in the third step may be written in Python language or C, C ++, fortran, or other computing and language.
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 the on-site detection work can be better guided; (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 invention.
FIG. 3 is a software interface diagram for calculating the three-dimensional stress of a weld joint of an in-service steam-water pipeline of a thermal power plant in an embodiment of the invention.
Fig. 4 is a graph comparing stress calculations for each radial position at θ=130° in an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail by way of examples with reference to the accompanying drawings, which are illustrative of the present invention and not limited to the following examples.
Examples
Referring to fig. 1-3, in the overhaul process of a main steam pipeline of a 660MW ultra supercritical thermal power generating unit, linear defects are found in a group of welding seams on a horizontal pipe section, and the three-dimensional stress calculation method of 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 defect positions, and the operation steps are as follows:
the main steam pipe section specification phi 472.8mm×86.8mm, the material A335P 92, the design temperature 610 ℃, the design pressure 29.67MPa, the thickness t=300 mm of the aluminum silicate heat-insulating cotton, and the elastic modulus E=168.8x10 of the material at the design temperature can be known by inquiring the standard 3 MPa, in-situ measurement of l=6000 mm, L 1 =3000 mm, and the thermal expansion displacement of the suspension point a end was recorded as (x 1 ＝118.3mm、y 1 ＝-17.8mm、z 1 = -75.4 mm), thermal expansion displacement of the hanging point B end is (x) 2 ＝162.4mm、y 2 ＝-68.5mm、z 2 ＝-136.7mm)。
The defect position is at r=195 mm and θ=130°, the data are input into an in-service steam-water pipeline welding seam three-dimensional stress calculation system, and three directions of the position are calculatedThe stress is respectively as follows: sigma (sigma) r ＝-9.31MPa、σ θ ＝48.95MPa、σ L =20.87 MPa; at different radial depths, the axial maximum tensile stress is between 122 and 130 degrees in azimuth angle theta.
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 of the whole main steam pipeline, the stress calculation results of corresponding welding seams are extracted and compared, the stress calculation results of each radial position at the position of theta=130 degrees are shown in a graph like that shown in fig. 4, the comparison results show that the error of the two calculation results is within 10%, the calculation accuracy basically can meet the requirements of engineering application, and the calculation method and the assumption condition adopted by the invention are reasonable and can be used for engineering field use.
What is not described in detail in this specification is all that is known to those skilled in the art.
Although the present invention has been described with reference to the above embodiments, it should be understood that the invention is not limited to the embodiments described above, but is capable of modification and variation without departing from the spirit and scope of the present invention.
Claims (4)
1. A method for calculating the three-dimensional stress of a weld joint of an in-service steam-water pipeline of a thermal power plant is characterized by comprising the following specific steps:
the first step: when analyzing the detailed three-dimensional stress of the welding seam of the straight pipe section in detail, taking the hanging points adjacent to the two ends of the welding seam as the initial end points, selecting the long straight pipe section containing the target welding seam as a research object, and measuring 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 seam 1 Recording pipeline specifications, wherein the outer diameter is Do, the wall thickness is S, and the thickness of the heat preservation layer is t;
and a second step of: three-way displacement indicators are arranged on the end face of the hanging point A and the end face of the hanging point B, and the thermal expansion displacement (x 1 、y 1 、z 1 ) The thermal expansion displacement (x 2 、y 2 、z 2 )；
And a third step of: a software package of a three-dimensional stress calculation system of the weld joint of the steam-water pipeline in service of the thermal power plant is compiled, measurement data is input in a visual interface mode, and detailed stress values are calculated; the stress calculation formula is as follows:
hoop stress:
radial stress:
horizontal pipe axial stress:
vertical pipe axial stress:
wherein: r and theta are position parameters of the stress solving point under the polar coordinate condition; d (D) o Is the outer diameter of the pipeline; s is the wall thickness of the pipeline; l, L 1 Is the length of the pipe section; t is the thickness of the heat insulation layer; (x) 1 、y 1 、z 1 ) (x) 2 、y 2 、z 2 ) The thermal displacement value of the hanging points at the two ends; d (D) i ＝D o -2S is the inner diameter of the pipe;
is the section moment of inertia of the pipeline; e is the elastic modulus of the pipeline material at the working temperature; q= 24.6615 ×10 -2 (D o -S)S+4.7124×10 -2 (D o +t) t is an intermediate calculation parameter;
fourth step: according to the stress solving formula, calculating the axial maximum tensile stress position of the welding line section; the calculation formula is as follows:
for horizontal pipes:
for vertical pipes:
a＝x 2 -x 1
b＝y 2 -y 1 。
2. the method for calculating the three-dimensional stress of the weld joint of the steam-water pipeline in service 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 the pipeline 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 steam-water pipeline in service of the thermal power plant according to claim 1, wherein the stress of the pipeline caused by torque action 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 steam-water pipeline in service of a thermal power plant according to claim 1, wherein in the second step, the three-dimensional displacement indicator is in a mechanical or photoelectric mode, and the reading error is smaller than 0.1mm.
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