A structure and evaluation method suitable for creep supervision of P91 pipeline containing soft zone

Abstract

The application discloses a structure suitable for creep supervision of P91 pipeline containing a soft area, which comprises a plurality of creep supervision measuring points fixedly installed on the outer wall of the P91 pipeline containing the soft area, wherein the creep supervision measuring points comprise a creep supervision measuring point upper layer and a creep supervision measuring point lower layer which are stacked together, and at least one of the creep supervision measuring points is located on the soft area of the P91 pipeline. The structure suitable for the creep supervision of the P91 pipeline containing the soft area can carry out the creep supervision on the soft area with the worst creep performance, the supervision object is more targeted, the creep strain law of the soft area of the pipeline can be accurately reflected, lossy detection such as hardness detection and metallographic detection does not need to be frequently carried out, no damage is caused to the pipeline, and more data support can be provided for the supervision and evaluation and life assessment of the pipeline. The application also discloses an evaluation method suitable for the creep supervision of the P91 pipeline containing the soft area, which has the same advantages as the structure suitable for the creep supervision of the P91 pipeline containing the soft area.

Description

Technical Field

[0001] This invention belongs to the field of creep monitoring technology for power plant pipelines with soft P91 zones, and in particular relates to a structure and evaluation method suitable for creep monitoring of pipelines with soft P91 zones. Background Technology

[0002] With the rapid development of my country's thermal power generation industry, large-capacity, high-parameter, and high-efficiency ultra-supercritical thermal power units have gradually become the mainstream of thermal power equipment development. This places more stringent requirements on the performance of power plant metal materials (high-temperature creep resistance, endurance performance, and oxidation resistance). Among them, P91 steel has excellent high-temperature performance, with an endurance strength of up to 100 MPa at 593℃ / 100,000h. It is currently widely used in high-temperature components such as main steam pipes, reheat steam pipes and their bypasses, and high-temperature headers at temperatures above 566℃.

[0003] However, during the inspection of P91 materials, it was found that many power plants' P91 pipelines had not yet reached the end of their service life. Some units had only been in operation for a few thousand hours or even before operation, yet low hardness had already appeared. It was also found that this low hardness phenomenon was divided into two types: overall low circumferential hardness and local low circumferential hardness. For pipelines with overall low circumferential hardness, life assessment can be carried out in accordance with DL / T654 and DL / T940, which is a simple and easy method. However, for pipelines with local low circumferential hardness, the stress distribution is more complex due to factors such as the size and shape of the low hardness area, making it difficult to conduct accurate safety evaluation and life assessment.

[0004] As early as 2011, the Electric Power Research Institute (EPRI) conducted an in-depth analysis of the local low hardness phenomenon in P91 pipes in its technical report "Effect of Soft-Zone on the Creep Performance of Grade 91" and proposed the concept of a soft zone. As the name suggests, a soft zone is a low-hardness area. Through finite element analysis of the stress redistribution in local soft zones, it can be seen that the steady-state stress level of the soft zone is always lower than that of the surrounding normal area. The relatively low creep stress in the soft zone is the result of the redistribution of creep stress from the soft zone to the surrounding normal material. Moreover, local soft zones do not directly lead to pipe failure. The size, shape, and orientation of the soft zone, as well as the stress conditions in the pipe, should be considered. Local soft zones may be constrained by the surrounding normal Grade 91 material, and their creep performance can still provide a long service life. Pipes containing some soft zones have a longer service life than pipes with all soft zones, but a much shorter service life than pipes with all normal hardness. Pipes with a large number of soft zones will have a shorter creep life than pipes with a small number of soft zone areas. In recent years, some domestic scholars have also conducted extensive research on the local low hardness phenomenon of P91 pipes and obtained similar conclusions.

[0005] In existing technologies, power plants generally follow DL / T441 "Supervision Procedure for Creep of High-Temperature and High-Pressure Steam Pipelines in Thermal Power Plants" to obtain creep strain data during pipeline service by uniformly setting creep measuring points on the pipeline, thereby conducting creep supervision and evaluation. However, the measurement results represent the average creep strain of the entire circumferential cross-section of the pipeline, and cannot reflect the creep strain of the softest areas with the worst creep performance. Therefore, this existing supervision and measurement method lacks specificity. Currently, when many power plants discover local soft areas in P91 pipelines during inspection and testing, they often struggle to make a decision. Some power plants directly cut and replace the pipe, while others adopt a more intensive monitoring approach. Based on the research conclusions on low-hardness P91, pipe cutting and replacement may not be the best option, potentially leading to waste of pipe materials and power generation losses. In many cases, intensive monitoring may be more suitable. Currently, the measures and plans adopted by power plants for intensive monitoring are relatively fixed, namely, using maintenance opportunities to inspect the hardness and metallographic structure of the soft areas and observe the changing trends of their hardness and microstructure. In reality, using hardness testing and metallographic examination for supervision still has certain limitations, which are reflected in two aspects. First, although hardness testing and metallographic examination are non-destructive testing in a narrow sense, they still fall under the category of destructive testing because each test will cause a reduction in the pipe wall thickness, at least about 2 mm. Especially at the same location, the wall thickness reduction effect is more obvious with the increase of the number of tests. This will greatly affect the safety performance and remaining life of the supervised components. Second, it is difficult to determine the safe operating status of the pipeline based solely on the results of on-site hardness testing and metallographic examination, let alone carry out life prediction, as the supporting data is too weak.

[0006] In summary, for P91 pipelines with localized soft areas, the soft area, being an arc-shaped region of the pipeline, is difficult to measure for creep strain using traditional creep measuring points. Therefore, how to achieve creep monitoring and evaluation or life prediction of the soft area through creep strain measurement is an urgent problem to be solved. Summary of the Invention

[0007] To address the aforementioned issues, this invention provides a structure and evaluation method suitable for creep monitoring of pipelines containing soft P91 zones. This method enables creep monitoring in the soft zones with the worst creep performance, making the monitoring more targeted and accurately reflecting the creep strain patterns in the pipeline's soft zones. It eliminates the need for frequent destructive testing such as hardness and metallographic examinations, and does not cause any damage to the pipeline. Furthermore, it provides more data support for pipeline monitoring, evaluation, and life assessment.

[0008] The present invention provides a structure for creep monitoring of P91 pipelines containing soft areas, comprising multiple creep monitoring points fixedly installed on the outer wall of the P91 pipeline containing soft areas. The creep monitoring points include an upper layer and a lower layer of creep monitoring points stacked together, wherein at least one of the creep monitoring points is located in the soft area of ​​the P91 pipeline.

[0009] Preferably, in the above-mentioned structure applicable to creep monitoring of pipelines containing soft P91, the upper layer of the creep monitoring measuring point is made of stainless steel, and the lower layer of the creep monitoring measuring point is made of P91.

[0010] Preferably, in the above-mentioned structure applicable to creep monitoring of pipelines with soft P91, the upper layer of the creep monitoring measuring point and the lower layer of the creep monitoring measuring point are connected and fixed by welding.

[0011] Preferably, in the above-described structure applicable to creep monitoring of pipelines containing soft P91, the lower layer of the creep monitoring measuring point is fixedly installed on the outer wall of the pipeline containing soft P91 by welding.

[0012] Preferably, in the above-mentioned structure applicable to creep monitoring of pipelines containing soft areas (P91), the overall shape of the creep monitoring measuring point is a cuboid.

[0013] Preferably, in the above-described structure applicable to creep monitoring of pipelines containing soft P91, the creep monitoring points are distributed on two cross sections of the pipeline containing soft P91.

[0014] The first cross section is located in the soft zone and is provided with 6 creep monitoring points. One creep monitoring point is provided at the center of the soft zone and one creep monitoring point is provided at each of the two sides of the soft zone. Three creep monitoring points are provided in the normal zone of the first cross section.

[0015] The second section is entirely located in the normal zone and has six creep monitoring points. The lines connecting the corresponding creep monitoring points on the first section to the points on the circumference are parallel to the axial direction of the pipe containing the soft zone P91.

[0016] Preferably, in the above-described structure applicable to creep monitoring of pipelines containing soft zones (P91), the positions of the three creep monitoring points in the normal zone of the first cross section and the three creep monitoring points in the soft zone are centrally symmetrical with respect to the center of the pipeline containing soft zones (P91).

[0017] Preferably, in the above-described structure applicable to creep monitoring of pipelines containing soft P91, the vertical distance between the first cross-section and the second cross-section ranges from 1000 mm to 1500 mm.

[0018] This invention provides an evaluation method for monitoring creep in pipelines with soft P91 zones, utilizing the structure described above for monitoring creep in pipelines with soft P91 zones, comprising:

[0019] The creep monitoring points are fixedly installed on the outer wall of the P91 pipe containing the soft zone, wherein at least one creep monitoring point is fixedly installed on the soft zone section of the P91 pipe, and at least one creep monitoring point is fixed on the normal zone section of the P91 pipe.

[0020] When the unit is shut down, the first creep strain value of the creep monitoring point located on the soft zone section and the second creep strain value of the creep monitoring point located on the normal zone section are measured.

[0021] After the unit has been running for a preset time, the third creep strain value of the creep monitoring point located on the soft zone section and the fourth creep strain value of the creep monitoring point located on the normal zone section are measured.

[0022] The first relative creep strain and the first relative creep strain rate of the soft zone, as well as the second relative creep strain and the second relative creep strain rate of the normal zone, are calculated based on the first creep strain value, the second creep strain value, the third creep strain value, the fourth creep strain value, and the preset time.

[0023] The creep monitoring and evaluation of the soft area of ​​the pipeline is carried out based on the first relative creep strain and the first relative creep strain rate of the soft area.

[0024] Preferably, the evaluation method applicable to creep monitoring of pipelines containing soft P91 areas further includes:

[0025] The creep lifetime remaining rate and creep lifetime loss rate of the soft zone are calculated based on the first relative creep strain rate and the second relative creep strain rate.

[0026] The lifespan of the P91 pipeline containing the soft zone is assessed based on the creep life remaining rate and creep life loss rate of the soft zone.

[0027] As described above, the structure for creep monitoring of P91 pipelines with soft areas provided by this invention includes multiple creep monitoring points fixedly installed on the outer wall of the P91 pipeline. These creep monitoring points consist of an upper layer and a lower layer of stacked creep monitoring points, with at least one point located in the soft area of ​​the P91 pipeline. Therefore, creep monitoring can be carried out in the soft area with the worst creep performance, making the monitoring more targeted and accurately reflecting the creep strain law of the pipeline's soft area. It eliminates the need for frequent destructive testing such as hardness testing and metallographic examination, and does not cause any damage to the pipeline. Furthermore, it provides more data support for pipeline monitoring, evaluation, and life assessment. The method for creep monitoring of P91 pipelines with soft areas provided by this invention has the same advantages as the structure described above. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the creep strain curves in the soft zone and normal zone of the P91 main steam pipeline.

[0030] Figure 2 A front view of the overall creep monitoring measurement point layout of an embodiment of the present invention, applicable to creep monitoring of pipelines containing soft zone P91;

[0031] Figure 3 A schematic diagram of the creep monitoring measurement point arrangement of a cross section containing a soft zone, provided by the present invention, for an embodiment of a structure applicable to creep monitoring of a pipeline containing a soft zone P91.

[0032] Figure 4 A schematic diagram of the creep monitoring measurement point arrangement of a cross section without soft zone, provided by the present invention, for a structure applicable to creep monitoring of a pipeline containing a soft zone P91.

[0033] Figure 5 A schematic diagram of the composition of the creep monitoring measuring point itself, which is an embodiment of the present invention applicable to creep monitoring of pipelines containing soft zone P91;

[0034] Figure 6 A schematic diagram of a preferred installation method for creep monitoring points on the first cross section;

[0035] Figure 7This is a schematic diagram of an embodiment of an evaluation method for monitoring creep in pipelines containing soft P91, provided by the present invention. Detailed Implementation

[0036] The core of this invention is to provide a structure and evaluation method suitable for creep monitoring of pipelines with soft P91 soft zones. It can carry out creep monitoring in the soft zones with the worst creep performance, making the monitoring objects more targeted and accurately reflecting the creep strain law of the pipeline soft zones. It eliminates the need for frequent destructive testing such as hardness testing and metallographic testing, and will not cause any damage to the pipeline. At the same time, it can provide more data support for pipeline monitoring, evaluation and life assessment.

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] For normal P91 pipelines, the creep strain can be considered circumferentially uniform. Creep strain measurement and creep strain rate calculation according to DL / T441-2004 "Regulations for Creep Supervision of High-Temperature and High-Pressure Steam Pipelines in Thermal Power Plants" can achieve creep monitoring and evaluation or life prediction of the pipeline. However, for P91 pipelines containing localized soft zones, the creep strain curves of different regions will differ significantly due to the different creep properties of the soft zones and normal zones. (Refer to...) Figure 1 , Figure 1 This diagram illustrates the creep strain curves of the soft zone and normal zone in the P91 main steam pipeline. Curve I represents the creep strain curve of the normal zone in the P91 pipeline, and curve II represents the creep strain curve of the soft zone. Due to the decreased creep performance in the soft zone, it exhibits a higher creep strain rate. This is reflected in the larger slope of the second stage of the creep strain curve. It can be seen that the soft zone reaches the ultimate creep strain first, and its creep life t... r1 It is also shorter than the creep life t in the normal region. r Therefore, for P91 pipelines containing soft zones, the soft zone, as the area with the worst creep performance in the entire pipeline, should be considered the primary focus area for creep monitoring. Since the soft zone is an arc-shaped area of ​​the pipeline, it is difficult to measure creep strain using traditional creep measurement methods. Therefore, how to achieve creep monitoring evaluation or life prediction of the soft zone through creep strain measurement is a challenge. Therefore, based on the principle of "double-sided arrangement and simultaneous measurement," this invention designs the following structure for creep monitoring of the soft zone.

[0039] This invention provides an embodiment of a structure suitable for creep monitoring of pipelines containing soft P91 areas, for example. Figure 2 , Figure 3 , Figure 4 and Figure 5 As shown, Figure 2 This is a front view of the overall creep monitoring point layout of an embodiment of the present invention, applicable to creep monitoring of pipelines containing soft zones (P91). Figure 3 This is a schematic diagram of the creep monitoring measurement point arrangement for a cross-section containing a soft zone, according to an embodiment of the present invention, applicable to creep monitoring of a pipeline containing a soft zone (P91). Figure 4 This is a schematic diagram of the creep monitoring measurement point arrangement for a cross-section without soft regions, according to an embodiment of the present invention, applicable to creep monitoring of pipelines with soft regions (P91). Figure 5 This is a schematic diagram illustrating the composition of a creep monitoring point in an embodiment of a structure for creep monitoring of a pipeline containing a soft P91 zone, provided by the present invention. The pipeline 1 containing the soft P91 zone includes three regions: a soft zone 11, a transition zone 12, and a normal zone 13 (unfilled white area). The soft zone 11 has the lowest hardness value, the transition zone 12 has the next highest, and the normal zone 13 meets the hardness requirements of P91. The structure may include multiple creep monitoring points 2 fixedly installed on the outer wall of the pipeline 1 containing the soft P91 zone. These creep monitoring points 2 can be configured as follows: Figure 5 Thus, including the upper layer 21 and lower layer 22 of the creep monitoring points stacked together, the overall shape of the creep monitoring points 2 can preferably be a cuboid, which is more conducive to measuring deformation. Furthermore, they can be made of two different materials. For example, the upper layer 21 of the creep monitoring points can preferably be made of stainless steel, which has sufficiently high strength and hardness, resulting in a longer service life. The lower layer 22 of the creep monitoring points can preferably be made of P91, which provides better compatibility with pipe materials and more accurate characterization of deformation in P91 pipes. Moreover, the upper layer 21 and lower layer 22 of the creep monitoring points can be connected and fixed by welding. 2. Alternatively, it can be fixed to the outer wall of the P91 pipe 1 containing the soft zone by welding. This welding method can ensure a more secure connection and prevent detachment, thereby ensuring the safety of the monitoring and measurement process. Of course, other types of connection methods, such as bonding, can also be selected according to actual needs. There are no restrictions here. At least one creep monitoring point 2 is located in the soft zone 11 on the P91 pipe 1. That is to say, there are other creep monitoring points 2 located in the normal zone. In other words, at least one measurement section is located in the soft zone and at least one measurement section is located in the normal zone. In this way, creep monitoring of the P91 pipe containing the soft zone can be achieved by simultaneously measuring the creep strain of the measurement sections in the soft zone and the normal zone.

[0040] As described above, the embodiment of the structure for creep monitoring of P91 pipelines with soft areas provided by the present invention includes multiple creep monitoring points fixedly installed on the outer wall of the P91 pipeline with soft areas. The creep monitoring points include an upper layer and a lower layer of creep monitoring points stacked together. At least one creep monitoring point is located in the soft area of ​​the P91 pipeline. Therefore, creep monitoring can be carried out in the soft area with the worst creep performance. The monitoring object is more targeted and can accurately reflect the creep strain law of the pipeline's soft area. It does not require frequent destructive testing such as hardness testing and metallographic testing, and will not cause any damage to the pipeline. At the same time, it can also provide more data support for the monitoring evaluation and life assessment of the pipeline.

[0041] In a specific embodiment of the above-described structure applicable to creep monitoring of pipelines containing soft zones (P91), reference continues to... Figure 2 , Figure 3 and Figure 4 Creep monitoring points 2 can preferably be distributed on two cross sections of pipe 1 containing the soft zone P91;

[0042] The first section 3 is located in the soft zone and is equipped with 6 creep monitoring points 2. One creep monitoring point 2 is set at the center (top) of the soft zone and one creep monitoring point 2 is set at each of the two sides of the soft zone. Three creep monitoring points 2 are set in the normal zone (bottom) of the first section 3.

[0043] The second section 4 is entirely located in the normal zone and has six creep monitoring points 2. The lines connecting these points on the circumference to the corresponding creep monitoring points 2 on the first section 3 are parallel to the axial direction of the pipe 1 containing the soft zone P91. This arrangement eliminates other inconsistencies, ensuring that the difference in deformation is solely due to the different creep patterns in the soft and normal zones, thus better guaranteeing the accuracy of the measurement results from this monitoring structure. Furthermore, the vertical distance between the first section 3 and the second section 4 is preferably between 1000mm and 1500mm. It should be noted that this distance should not be too large to ensure strong comparability, nor too small to avoid insufficient creep difference leading to inaccurate results.

[0044] Further reference Figure 6 , Figure 6This diagram illustrates a preferred installation method for creep monitoring points on the first cross-section. The positions of the three creep monitoring points a, b, and c in the normal zone of the first cross-section 3, and the three creep monitoring points A, B, and C in the soft zone, are centrally symmetrical with respect to the center O of the P91 pipeline containing the soft zone. In actual operation, through circumferential and radial multi-point "grid-like" hardness testing of the P91 main steam pipeline 1, it was found that within a certain radial distance, the hardness value of the top arc DE region of the P91 main steam pipeline 1 was below 180 HB, with a hardness range of approximately 140–180 HB, indicating localized low hardness. The arc FG region had the lowest hardness value, approximately 140–160 HB, defined as soft zone 11. The arc DF and arc EG regions had the next lowest hardness values, approximately 160–180 HB, defined as transition zone 12. The remaining areas had normal hardness values, defined as normal zone 13. In other words... Figure 6 The area between E and G is a transition zone, as is the area between F and D. Of course, the hardness range for each region can be adjusted according to actual needs; this is not a restriction. Creep monitoring point C is placed near point G, and creep monitoring point B is placed near point F. This eliminates other factors that may affect deformation, thus ensuring better accuracy of the creep monitoring results. This is a preferred solution; other distribution methods can be chosen according to actual needs; this is not a restriction.

[0045] An example implementation of the evaluation method for monitoring creep in pipelines containing soft P91 zones provided by this invention. Figure 7 As shown, Figure 7 This is a schematic diagram of an embodiment of an evaluation method for monitoring creep in pipelines with soft P91 areas provided by the present invention. Utilizing the structure described above for monitoring creep in pipelines with soft P91 areas, the method includes the following steps:

[0046] S1: The creep monitoring point is fixedly installed on the outer wall of the P91 pipe containing the soft zone, wherein at least one creep monitoring point is fixedly installed on the soft zone section of the P91 pipe, and at least one creep monitoring point is fixed on the normal zone section of the P91 pipe.

[0047] It should be noted that the above-mentioned methods can be preferred. Figure 2 , Figure 3 and Figure 4 The arrangement shown uses a total of 12 creep monitoring points, but it can be adjusted according to actual needs; there are no restrictions here.

[0048] S2: When the unit is shut down, measure the first creep strain value of the creep monitoring point located on the soft zone section and the second creep strain value of the creep monitoring point located on the normal zone section;

[0049] Among these methods, a micrometer can be used to measure the creep strain value, and the measurement result of the first creep strain value can be denoted as ε. 10 The measurement result of the second creep strain value can be denoted as ε. 20 The time at this point is denoted as t0.

[0050] S3: After the unit has been running for a preset time, measure the third creep strain value of the creep monitoring point located on the soft zone section and the fourth creep strain value of the creep monitoring point located on the normal zone section.

[0051] Among these methods, a micrometer can be used to measure the creep strain value. The measurement result of the third creep strain value at the creep monitoring point can be denoted as ε. 11 The measurement result of the fourth creep strain value at the creep monitoring point can be denoted as ε. 21 The time at this point is denoted as t1.

[0052] S4: Calculate the first relative creep strain and the first relative creep strain rate of the soft zone, as well as the second relative creep strain and the second relative creep strain rate of the normal zone, based on the first creep strain value, the second creep strain value, the third creep strain value, the fourth creep strain value and the preset time.

[0053] Among them, the first relative creep strain ε1 and the first relative creep strain velocity of the soft region The second relative creep strain ε2 and the second relative creep strain rate in the normal region The formula for calculating can be as follows:

[0054]

[0055] S5: Based on the first relative creep strain ε1 and the first relative creep strain rate of the soft region. Creep monitoring and evaluation were conducted on the soft areas of the pipeline.

[0056] It should be noted that the criteria for conducting this creep monitoring and evaluation can be, but is not limited to, the first relative creep strain rate during the constant-rate phase in the soft region. It must not exceed 0.5 × 10 -5 When the total first relative creep strain ε1 reaches 0.5%, a test should be conducted. When the total first relative creep strain ε1 reaches 1%, the tube should be replaced. Of course, this criterion can be adjusted according to actual needs, and no restrictions are imposed here.

[0057] As can be seen, the above method can provide creep strain data for both soft and normal zones simultaneously, providing more evidence for monitoring operation and life assessment while effectively reducing the number of field tests.

[0058] In a specific embodiment of the evaluation method applicable to creep monitoring of pipelines containing soft P91, the following steps may also be included:

[0059] Based on the first relative creep strain rate Second relative creep strain rate Calculate the creep lifetime remaining rate t of the soft zone r1 / t r and creep life loss rate 1-t r1 / t r , ;

[0060] The lifespan of P91 pipelines containing soft zones is assessed based on the remaining creep life rate and creep life loss rate of the soft zone.

[0061] It should be noted that the calculation formula can be:

[0062]

[0063] It should also be noted that the creep life remaining rate of the soft zone can characterize the creep life status of the soft zone compared to the normal zone, while the creep life loss rate of the soft zone can characterize the proportion of life loss caused by the decline in creep performance in the soft zone. Relevant expressions can be found in [reference needed]. Figure 1 Solve for the creep strain curve.

[0064] refer to Figure 1 The creep strain relationship between the soft zone and the normal zone is as follows:

[0065]

[0066] According to the above formula, we have:

[0067]

[0068] In the above formula, and t represents the relative creep strain rate of the soft zone and the normal zone, respectively. r1 / t r The creep lifetime remaining rate of the soft zone, 1-t r1 / t r This represents the creep life loss rate in the soft zone. Creep monitoring points are set on two measurement sections, one in the soft zone and the other in the normal zone. The creep strain of both sections is measured simultaneously. The creep strain measurement result of the section in the soft zone is recorded as ε1, and the creep strain measurement result of the section in the normal zone is recorded as ε2. Then the creep strain of the soft zone can be represented by ε1-ε2 / 2.

[0069] In summary, the aforementioned structure and evaluation method for pipeline creep monitoring are based on creep strain theory. Creep monitoring is conducted in the soft zone with the worst creep performance, making the monitoring target more targeted and able to more accurately reflect the creep strain law of the pipeline's soft zone. Moreover, based on the concepts of creep life remaining rate and creep life loss rate, the creep life status of the soft zone can be characterized without the need for frequent destructive testing such as hardness testing and metallographic testing, thus avoiding any damage to the pipeline. At the same time, it can provide more data support for pipeline monitoring, evaluation, and life assessment. Furthermore, the aforementioned structure and evaluation method are also applicable to high-temperature and high-pressure steam pipelines made of other materials, such as P22 material pipelines in subcritical or supercritical units or P92 material pipelines in ultra-supercritical units.

[0070] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An evaluation method for monitoring creep in pipelines containing soft P91 areas, characterized in that, A structure suitable for creep monitoring of P91 pipelines containing soft areas includes: The creep monitoring points are fixedly installed on the outer wall of the P91 pipe containing the soft zone, wherein at least one creep monitoring point is fixedly installed on the soft zone section of the P91 pipe, and at least one creep monitoring point is fixed on the normal zone section of the P91 pipe. When the unit is shut down, the first creep strain value of the creep monitoring point located on the soft zone section is measured. and the second creep strain value of the creep monitoring point located on the normal zone section. The time at this moment is recorded as ; After the unit has been running for a preset time, the third creep strain value of the creep monitoring point located on the soft zone cross section is measured. and the fourth creep strain value of the creep monitoring point located on the cross section of the normal zone. The time at this moment is recorded as ; The first relative creep strain and the first relative creep strain rate of the soft region, and the second relative creep strain and the second relative creep strain rate of the normal region are calculated based on the first creep strain value, the second creep strain value, the third creep strain value, the fourth creep strain value, and the preset time. The first relative creep strain of the soft region... and the first relative creep strain rate The second relative creep strain in the normal region and the second relative creep strain rate The calculation formula is as follows: ； The creep monitoring and evaluation of the soft area of ​​the pipeline is carried out based on the first relative creep strain and the first relative creep strain rate of the soft area.

2. The evaluation method for creep monitoring of pipelines containing soft P91 as described in claim 1, characterized in that, Also includes: The creep lifetime remaining rate and creep lifetime loss rate of the soft zone are calculated based on the first relative creep strain rate and the second relative creep strain rate. The lifespan of the P91 pipeline containing the soft zone is assessed based on the creep life remaining rate and creep life loss rate of the soft zone.

3. The evaluation method for creep monitoring of pipelines containing soft P91 as described in claim 1, characterized in that, The structure applicable to creep monitoring of P91 pipelines with soft areas includes multiple creep monitoring points fixedly installed on the outer wall of the P91 pipeline with soft areas. The creep monitoring points include an upper layer and a lower layer of creep monitoring points stacked together, wherein at least one of the creep monitoring points is located in a soft area on the P91 pipeline.

4. The evaluation method for creep monitoring of pipelines containing soft P91 as described in claim 3, characterized in that, The upper layer of the creep monitoring point is made of stainless steel, and the lower layer of the creep monitoring point is made of P91.

5. The evaluation method for creep monitoring of pipelines containing soft P91 as described in claim 3, characterized in that, The upper layer and the lower layer of the creep monitoring point are connected and fixed by welding.

6. The evaluation method for creep monitoring of pipelines containing soft P91 as described in claim 3, characterized in that, The creep monitoring points are fixedly installed on the outer wall of the P91 pipeline containing the soft zone by welding.

7. The evaluation method for creep monitoring of pipelines containing soft P91 as described in claim 3, characterized in that, The overall shape of the creep monitoring point is a cuboid.

8. An evaluation method for monitoring creep in pipelines containing soft P91 zones according to any one of claims 3-7, characterized in that, The creep monitoring points are distributed on two cross sections of the P91 pipe containing the soft zone. The first cross section is located in the soft zone and is provided with 6 creep monitoring points. One creep monitoring point is provided at the center of the soft zone and one creep monitoring point is provided at each of the two sides of the soft zone. Three creep monitoring points are provided in the normal zone of the first cross section. The second section is entirely located in the normal zone and has six creep monitoring points. The lines connecting the corresponding creep monitoring points on the first section to the points on the circumference are parallel to the axial direction of the pipe containing the soft zone P91.

9. The evaluation method for creep monitoring of pipelines containing soft P91 as described in claim 8, characterized in that, The positions of the three creep monitoring points in the normal zone of the first cross section and the three creep monitoring points in the soft zone are centrally symmetrical with respect to the center of the P91 pipeline containing the soft zone.

10. The evaluation method for monitoring creep in pipelines containing soft P91 as described in claim 8, characterized in that, The vertical distance between the first section and the second section ranges from 1000mm to 1500mm.

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