CN112630075B - Method for evaluating material state of low-hardness P91 pipe fitting based on partition - Google Patents

Method for evaluating material state of low-hardness P91 pipe fitting based on partition Download PDF

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CN112630075B
CN112630075B CN202011304081.6A CN202011304081A CN112630075B CN 112630075 B CN112630075 B CN 112630075B CN 202011304081 A CN202011304081 A CN 202011304081A CN 112630075 B CN112630075 B CN 112630075B
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hardness
test
square
pipe fitting
temperature
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CN112630075A (en
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贾若飞
李梁
王鹏
何晓东
陈征
王强
李东江
王亮
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Xian Thermal Power Research Institute Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/40—Investigating hardness or rebound hardness
    • G01N3/42—Investigating hardness or rebound hardness by performing impressions under a steady load by indentors, e.g. sphere, pyramid
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
    • G01N3/18—Performing tests at high or low temperatures
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/30—Investigating strength properties of solid materials by application of mechanical stress by applying a single impulsive force, e.g. by falling weight
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0014—Type of force applied
    • G01N2203/0016—Tensile or compressive
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0058—Kind of property studied
    • G01N2203/0076—Hardness, compressibility or resistance to crushing
    • G01N2203/0078—Hardness, compressibility or resistance to crushing using indentation

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  • Life Sciences & Earth Sciences (AREA)
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Abstract

The invention discloses a material state evaluation method of a low-hardness P91 pipe fitting based on partition, which comprises the following steps: processing an original sample to be detected into a plurality of P91 square strips; carrying out Brinell hardness test on each P91 material square strip, and dividing each P91 material square strip into a plurality of different hardness groups; carrying out normal-temperature short-time tensile test, test high-temperature short-time tensile test and room-temperature impact test on the P91 square strips with different hardness groups; performing metallographic examination on the P91 square strips with different hardness groups; 6) Calculating the residual life of the original sample to be detected; according to the residual life of the original sample to be detected, the result of the normal-temperature short-time tensile test, the result of the high-temperature short-time tensile test and the result of the room-temperature impact test, the material state of the low-hardness P91 pipe fitting based on the partition is evaluated, and the material state of the low-hardness P91 pipe fitting can be accurately evaluated.

Description

Method for evaluating material state of low-hardness P91 pipe fitting based on partition
Technical Field
The invention belongs to the technical field of thermal power generation metal inspection, and relates to a material state evaluation method of a low-hardness P91 pipe fitting based on partition.
Background
In recent years, with the improvement of parameters and efficiency of thermal power generating units, the grade of steel selected by the units is continuously improved, and P91 is used as a steel grade with mature technology and is widely applied to domestic thermal power generating units in recent years. P91 is an improved 9Cr-1Mo high-strength martensitic heat-resistant steel developed by reducing the carbon content, adding alloy element V, nb and controlling the content of N on the basis of P9, has good heat resistance, high strength and toughness, good hardenability, good weldability, high heat conductivity and small linear expansion coefficient, and is an excellent alternative material for a high-temperature component of a fire discovery unit.
The hardness of the P91 material pipe fitting is required to be not more than 250HB according to the ASME SA335 standard, and the hardness of the P91 material steel pipe is required to be 185HB-250HB according to the DL/T438-2016 technical rules of metal supervision of thermal power plants. However, in the physical and chemical inspection performed on site, it has been found that the lower hardness of the P91 pipe is a common problem whether it is an imported material or a domestic material. The running pipe fitting made of the P91 material has a large number of low hardness phenomena, which brings serious potential safety hazards to long-term stable running of the unit. The hardness characterizes the comprehensive mechanical property of the material to a certain extent, and various researches show that the endurance strength is also severely reduced when the hardness is reduced. In addition, because the field conditions are limited, the Brinell hardness test is limited, and the test result of the Brinell hardness tester has a certain deviation from the actual Brinell hardness, so that if a low-hardness P91 pipe fitting is encountered in the test, the test personnel and equipment management personnel can not easily make a decision on the processing mode.
For example, in the inspection process of a certain power plant, a large number of main steam pipeline pipe fittings made of P91 material are found to have the hardness lower than the lower limit of the standard requirement, including parts such as an elbow tee joint, the site is subjected to the Brinell hardness inspection and the cloth hardness rechecking, the hardness is found to be 140HB-HLD (the cloth hardness rechecking is 155 HB), the abnormal hardness parts are not uniformly distributed, the same elbow or straight section is provided with different hardness value distribution areas, and the difference value can be maximally close to 100HB-HLD. In order to ensure the safety of the unit, the factors of construction period and expense are comprehensively considered, the power plant determines to directly replace the pipe fitting and the pipeline with the hardness of 160HB or below, and evaluates the pipe fitting with the hardness of 160HB to 180HB to determine whether the pipe fitting can be used safely continuously or not. The quality state of the pipe fitting with the hardness of 160HB to 180HB is determined, and the methods of site Brinell hardness test, cloth hardness test, metallographic structure test and the like are generally adopted, so that the method has the defects of large test data discreteness, limited test position, large pipe fitting hardness distribution difference and the like, and the evaluation accuracy is poor.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a material state evaluation method of a low-hardness P91 pipe fitting based on partition, which can accurately evaluate the material state of the low-hardness P91 pipe fitting.
In order to achieve the above objective, the method for evaluating the material state of a low-hardness P91 pipe fitting based on partition according to the present invention comprises the following steps:
1) Selecting an original sample to be detected;
2) Processing an original sample to be detected into a plurality of P91 square strips;
3) Carrying out Brinell hardness test on each P91 material square bar, wherein a plurality of measuring points are selected on each cross section of the P91 material square bar for hardness test, when the difference of hardness results on the same cross section is smaller than or equal to a preset value, the hardness results are recorded, the P91 material square bar is reserved, when the difference of hardness results on the same cross section is larger than the preset value, the P91 material square bar is discarded, and finally, the reserved P91 material square bars are respectively divided into a plurality of different hardness groups;
4) Carrying out normal-temperature short-time tensile test, test high-temperature short-time tensile test and room-temperature impact test on the P91 square strips with different hardness groups;
5) Performing metallographic examination on the P91 square strips with different hardness groups;
6) Carrying out high-temperature endurance strength test on the P91 square strips in each hardness group;
7) Drawing isothermal extrapolation endurance strength curves of different hardness groups according to high-temperature endurance strength test results, and calculating 10 according to the isothermal extrapolation endurance strength curves 5 The endurance strength of the sample at h time;
8) Determining the maximum stress position and the maximum stress sigma max under the working condition of the sample and combining 10 5 Calculating the residual life of the original sample to be detected by the lasting strength of the sample in h time;
9) And evaluating the material state of the low-hardness P91 pipe fitting based on the partition according to the residual life of the original sample to be detected, the result of the normal-temperature short-time tensile test, the result of the high-temperature short-time tensile test and the result of the room-temperature impact test.
The length, width and height of the square strips made of the P91 material are respectively 20mm, 20mm and 200mm, and the number of the square strips made of the P91 material is more than or equal to 100.
And 2) processing the original sample to be detected into a plurality of P91 square strips by using oxyacetylene flame and linear cutting.
In the step 3), when the difference of the hardness results on the same cross section is less than or equal to 10%, the hardness results are recorded, the P91 square bar is reserved, and when the difference of the hardness results on the same cross section is more than 10%, the P91 square bar is discarded.
In the step 3), the reserved P91 square bars are respectively divided into a 160HB hardness group, a 165HB hardness group, a 170HB hardness group and a 175HB hardness group, wherein the number of the P91 square bars in each group is more than or equal to 20.
And (3) respectively carrying out normal-temperature short-time stretching and high-temperature short-time stretching test and room-temperature impact test on three P91 square bars in different hardness groups.
In step 7), 10 is calculated according to formula (1) 5 The endurance strength of the sample at h time;
σ＝k(t r ) m (1)
wherein sigma is the stress level of the sample loading, t r For break time, k, m are the material constants determined by the test.
In step 8), the residual life of the original sample to be detected is as follows:
is->Respectively at a certain temperature of 10 4 h and 10 5 h, endurance strength.
The invention has the following beneficial effects:
according to the method for evaluating the material state of the low-hardness P91 pipe fitting based on the partition, in the specific operation, the hardness divides all the P91 square strips into a plurality of hardness groups, and metallographic examination, normal-temperature short-time stretching, high-temperature short-time stretching, room-temperature impact test and high-temperature endurance strength test are respectively carried out on each hardness group to evaluate the material state of the low-hardness P91 pipe fitting in different hardness states, so that the defects of large discreteness of examination data, limited examination positions, large hardness distribution difference of the pipe fitting and the like in the evaluation process are avoided, and the evaluation accuracy is higher.
Drawings
FIG. 1 is a pattern diagram of a P91 hardness square bar according to the present invention;
FIG. 2a is a photograph of a typical metallographic structure of a 160HB hardness group;
FIG. 2b is a photograph of a typical metallographic structure of a 170HB hardness group;
FIG. 3a is a graph of 160HB hardness group isotherms push-out;
FIG. 3b is a graph of 170HB hardness group isotherms push-out;
fig. 4 is a flow chart of the present invention.
Detailed Description
The invention is described in further detail below with reference to the attached drawing figures:
the invention relates to a material state evaluation method of a low-hardness P91 pipe fitting based on partition, which comprises the following steps:
1) Selecting an original sample to be detected;
2) Processing an original sample to be detected into a plurality of P91 square strips;
3) Carrying out Brinell hardness test on each P91 material square bar, wherein a plurality of measuring points are selected on each cross section of the P91 material square bar for hardness test, when the difference of hardness results on the same cross section is smaller than or equal to a preset value, the hardness results are recorded, the P91 material square bar is reserved, when the difference of hardness results on the same cross section is larger than the preset value, the P91 material square bar is discarded, and finally, the reserved P91 material square bars are respectively divided into a plurality of different hardness groups;
4) Carrying out normal-temperature short-time tensile test, test high-temperature short-time tensile test and room-temperature impact test on the P91 square strips with different hardness groups;
5) Performing metallographic examination on the P91 square strips with different hardness groups;
6) Carrying out high-temperature endurance strength test on the P91 square strips in each hardness group;
7) Drawing isothermal extrapolation endurance strength curves of different hardness groups according to high-temperature endurance strength test results, and calculating 10 according to the isothermal extrapolation endurance strength curves 5 The endurance strength of the sample at h time;
8) Determining the maximum stress position and the maximum stress sigma max under the working condition of the sample and combining 10 5 Calculating the residual life of the original sample to be detected by the lasting strength of the sample in h time;
9) And evaluating the material state of the low-hardness P91 pipe fitting based on the partition according to the residual life of the original sample to be detected, the result of the normal-temperature short-time tensile test, the result of the high-temperature short-time tensile test and the result of the room-temperature impact test.
The length, width and height of the square strips made of the P91 material are respectively 20mm, 20mm and 200mm, and the number of the square strips made of the P91 material is more than or equal to 100.
And 2) processing the original sample to be detected into a plurality of P91 square strips by using oxyacetylene flame and linear cutting.
In the step 3), when the difference of the hardness results on the same cross section is less than or equal to 10%, the hardness results are recorded, the P91 square bar is reserved, and when the difference of the hardness results on the same cross section is more than 10%, the P91 square bar is discarded.
In the step 3), the reserved P91 square bars are respectively divided into a 160HB hardness group, a 165HB hardness group, a 170HB hardness group and a 175 hardness group, wherein the number of the P91 square bars in each group is more than or equal to 20.
And (3) respectively carrying out normal-temperature short-time stretching and high-temperature short-time stretching test and room-temperature impact test on three P91 square bars in different hardness groups.
In step 7), 10 is calculated according to formula (1) 5 The endurance strength of the sample at h time;
σ＝k(t r ) m (1)
wherein sigma is the stress level of the sample loading, t r For break time, k, m are the material constants determined by the test.
In step 8), the residual life of the original sample to be detected is as follows:
is->Respectively at a certain temperature of 10 4 h and 10 5 h, endurance strength.
Example 1
The specific process of the embodiment is as follows:
1) Selecting a P91 pipe fitting with low hardness and uneven hardness found in field inspection as an original sample to be detected;
2) Processing a large-size pipe fitting into at least 100 square P91 material strips with the diameter of 20mm being 200mm by using oxyacetylene flame and wire cutting, wherein the square P91 material strips are used as test units of the invention, and refer to FIG. 1;
3) Carrying out Brinell hardness test on the P91 square bars, wherein each section of each P91 square bar is subjected to equidistant 3 hardness tests, when the hardness results are within 10%, recording the hardness results and reserving the P91 square bars, when the hardness results are greater than 10%, discarding the P91 square bars, and finally dividing the reserved P91 square bars into 160HB hardness groups, 165HB hardness groups, 170HB hardness groups and 175HB hardness groups, wherein each group comprises 20 or more P91 square bars;
4) Performing normal-temperature short-time stretching, high-temperature short-time stretching test and room-temperature impact test on the P91 square bars with different hardness groups, wherein each test item selects one P91 square bar, and is shown by taking 160HB hardness groups and 170HB hardness groups as examples, and referring to tables 1 and 2, it is seen that the room-temperature tensile strength, room-temperature specified plastic elongation strength and high Wen Guiding plastic elongation strength of samples with 160HB hardness and 170HB hardness groups are lower than the standard requirements, and each test index of 160HB hardness is lower than 170 HB;
TABLE 1
TABLE 2
5) Carrying out metallographic examination on P91 square bars of different hardness groups, wherein each hardness group selects one P91 square bar, and is shown by taking 160HB hardness group and 170HB hardness group as examples, as shown in fig. 2a and 2b, the metallographic structures of the two groups of samples are aged to a certain extent, the martensite orientation of the metallographic structures of the 160HB hardness group samples is seriously dispersed, carbide size coarsens and obviously gathers at a crystal boundary, the martensite orientation of the metallographic structures of the 170HB hardness group samples is dispersed to a certain extent, part of lath structures can still be seen to exist under 500 times of view field, the number of carbide particles at the crystal boundary is increased, and the size coarsens;
6) High temperature endurance strength tests were performed on square bars of P91 material in each hardness group, shown by way of example in the 160HB hardness group and the 170HB hardness group, with reference to table 3;
TABLE 3 Table 3
7) Drawing isothermal extrapolation endurance strength curves of different hardness groups according to the high-temperature endurance strength test result, and then calculating 10 according to formula (1) 5 The lasting strength of the sample in h time, wherein the high-temperature lasting test temperature is 550 ℃;
σ＝k(t r ) m (1)
wherein sigma is the stress level of the sample loading, t r For break time, k, m are the material constants determined by the test.
8) Determining the maximum stress position and the maximum stress sigma max under the working condition of the sample, calculating the residual life of the sample according to the formula (2),
is->Respectively at a certain temperature of 10 4 h and 10 5 h, a permanent strength;
fig. 3a and 3b are isotherm push-out curves for the 160HB hardness group and the 170HB hardness group, wherein k=230.1 for the 160HB hardness group, k=271.4 for the m= 0.07,170HB hardness, m=0.07;
calculating the remaining life of the 160HB hardness group and the 170HB hardness group according to formula (2), wherein the remaining life of the 160HB hardness group is about 27000h and the remaining life of the 170HB hardness group is about 360000h;
according to the comprehensive analysis of the test results, taking the 160HB hardness group and the 170HB hardness group as examples, when the hardness of the material is lower than the lower limit value (180 HB) required by the standard, the structure of the material is aged to different degrees, the room temperature mechanical property test is in an abnormal state lower than the standard requirement, the accurate life assessment is carried out by adopting an isotherm extrapolation method, the residual life of the 160HB hardness group is about 27000h, less than one overhaul period is achieved, the power plant is recommended to replace a pipe fitting with the 160HB hardness as a test result, the residual life of the 170HB hardness is about 360000h, and the replacement is not recommended in a short period, but because the short-time mechanical property of a sample of the hardness group is abnormal, the supervision is recommended, and if the material degradation and the hardness reduction phenomenon occur, the replacement is performed as soon as possible.

Claims (6)

1. The material state evaluation method of the low-hardness P91 pipe fitting based on the partition is characterized by comprising the following steps of:
1) Selecting an original sample to be detected;
2) Processing an original sample to be detected into a plurality of P91 square strips;
3) Carrying out Brinell hardness test on each P91 material square bar, wherein a plurality of measuring points are selected on each cross section of the P91 material square bar for hardness test, when the difference of hardness results on the same cross section is smaller than or equal to a preset value, the hardness results are recorded, the P91 material square bar is reserved, when the difference of hardness results on the same cross section is larger than the preset value, the P91 material square bar is discarded, and finally, the reserved P91 material square bars are respectively divided into a plurality of different hardness groups;
4) Carrying out normal-temperature short-time tensile test, test high-temperature short-time tensile test and room-temperature impact test on the P91 square strips with different hardness groups;
5) Performing metallographic examination on the P91 square strips with different hardness groups;
6) Carrying out high-temperature endurance strength test on the P91 square strips in each hardness group;
7) Drawing isothermal extrapolation endurance strength curves of different hardness groups according to high-temperature endurance strength test results, and calculating 10 according to the isothermal extrapolation endurance strength curves 5 The endurance strength of the sample at h time;
8) Determining the maximum stress position and the maximum stress sigma max under the working condition of the sample and combining 10 5 Calculating the residual life of the original sample to be detected by the lasting strength of the sample in h time;
9) Evaluating the material state of the low-hardness P91 pipe fitting based on the partition according to the residual life of the original sample to be detected, the result of the normal-temperature short-time tensile test, the result of the high-temperature short-time tensile test and the result of the room-temperature impact test;
in step 7), 10 is calculated according to formula (1) 5 The endurance strength of the sample at h time;
σ＝k(t r ) m (1)
wherein sigma is the stress level of the sample loading, t r K and m are material constants determined by experiments for breaking time;
in step 8), the residual life of the original sample to be detected is as follows:
is->Respectively at a certain temperature of 10 4 h and 10 5 h, endurance strength.
2. The method for evaluating the material state of the P91 pipe fitting with low hardness based on the partition according to claim 1, wherein the length, width and height of the square strips made of the P91 material are respectively 20mm, 20mm and 200mm, and the number of the square strips made of the P91 material is more than or equal to 100.
3. The method for evaluating the material state of a P91 pipe fitting with low hardness based on partition according to claim 1, wherein in step 2), the original sample to be inspected is processed into a plurality of square strips of P91 material by using oxyacetylene flame and wire cutting.
4. The method for evaluating the texture of a low-hardness P91 pipe based on partition according to claim 1, wherein in step 3), when the hardness results on the same cross section differ by 10% or less, the hardness results are recorded and the P91 square is retained, and when the hardness results on the same cross section differ by more than 10%, the P91 square is discarded.
5. The method for evaluating the texture state of a low-hardness P91 pipe fitting according to claim 1, wherein in step 3), the reserved P91 square bars are respectively divided into 160HB hardness group, 165HB hardness group, 170HB hardness group and 175HB hardness group, wherein the number of the P91 square bars in each group is 20 or more.
6. The method for evaluating the material state of the low-hardness P91 pipe fitting based on the partition section according to claim 1, wherein the three P91 square bars in different hardness groups are subjected to normal temperature short time tensile test, test high temperature short time tensile test and room temperature impact test respectively.
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