Method and system for non-destructive evaluation of the service life of an electrofusion joint for a polyethylene pipe in service

Abstract

The application relates to a kind of in-service polyethylene pipeline electric fusion joint service life nondestructive evaluation methods, comprising: the corresponding relationship between the heat affected zone edge width of polyethylene pipeline electric fusion joint welding area and service life is established in advance in laboratory;Ultrasonic phased array detection is carried out on the in-service polyethylene pipeline electric fusion joint to be evaluated in the field, and the heat affected zone edge width da of the in-service polyethylene pipeline electric fusion joint welding area is obtained;The heat affected zone edge width da is substituted into the corresponding relationship, and the service life tfa of the in-service polyethylene pipeline electric fusion joint is obtained.The application also relates to a corresponding evaluation system, including ultrasonic self-focusing linear array probe and host computer equipped with data analysis software.The method and evaluation system of the application can realize the rapid and nondestructive evaluation of the service life of city buried polyethylene pipeline electric fusion joint.

Description

Technical Field

[0001] This invention relates to the field of pipeline inspection, and in particular to a non-destructive evaluation method and system for the service life of electrofusion joints in in-service polyethylene pipelines. Background Technology

[0002] Electrofusion welded joints for polyethylene pipelines are a crucial component of pipeline systems, playing a vital bridging role in ensuring the safe long-distance transport of flammable and explosive media. However, due to the influence of welding processes and welders' subjective experience, defects (cold welding or over-welding) are prone to occur at the locations of polyethylene pipeline electrofusion joints. This significantly weakens the long-term mechanical properties of the joints, shortens their service life, and can lead to major safety accidents caused by media leakage. Therefore, assessing the service life of in-service polyethylene pipeline electrofusion joints is of vital technical importance for ensuring the safe operation of buried polyethylene pipelines in cities.

[0003] Currently, the main method for predicting the service life of in-service polyethylene pipes is the ISO 9080-2006 international standard (determination of long-term flowing hydrostatic strength of thermoplastic pipe materials by inference method) developed by the Plastics Pipe Association of America, as shown in the following formula:

[0004]

[0005] Among them, t f The failure life is T, the hydrostatic test temperature is T, and A, B, C, and D are regression model parameters related to the specific material grade. σ θ This refers to the circumferential stress applied during compression.

[0006] However, this method has the following limitations: ① It is a destructive test and the evaluation equipment is large, making it impossible to conduct on-site testing. It requires on-site pipe cutting and sampling, and then bringing the samples back to the laboratory for testing. This is not only a large amount of work and a complicated process, but also expensive; ② The evaluation cycle is long. The evaluation cycle of this method is at least one year, which does not meet the actual on-site inspection requirements. Summary of the Invention

[0007] Based on this, the present invention provides a non-destructive evaluation method for the service life of electrofusion joints of in-service polyethylene pipes, which can realize rapid and non-destructive evaluation of the service life of electrofusion joints of buried polyethylene pipes in urban areas.

[0008] The technical solution adopted in this invention is as follows:

[0009] A non-destructive evaluation method for the service life of in-service polyethylene pipe electrofusion joints includes:

[0010] Establish the relationship between the edge width of the heat-affected zone and the service life of the welding area of ​​the electrofusion joint of polyethylene pipe in advance in the laboratory;

[0011] Ultrasonic phased array testing was performed on the in-service polyethylene pipe electrofusion joint to be evaluated on-site to obtain the edge width d of the heat-affected zone of the welded area of ​​the in-service polyethylene pipe electrofusion joint. a ;

[0012] The edge width d of the heat-affected zone a Substituting into the corresponding relationship, the service life t of the in-service polyethylene pipe electrofusion joint is obtained. fa .

[0013] This invention proposes to establish a model in the laboratory beforehand showing the relationship between the edge width of the heat-affected zone (HAZ) of the welded area of ​​an electrofusion joint in polyethylene pipe and its service life. Based on this relationship, it is only necessary to measure the edge width d of the HAZ of the welded area of ​​the electrofusion joint in the in-service polyethylene pipe on-site. a The service life t of the in-service polyethylene pipe electrofusion joint can then be obtained. fa .

[0014] Moreover, the method of the present invention uses ultrasonic phased array non-destructive testing technology for on-site scanning and measurement, which is a non-destructive evaluation method. It does not require on-site destructive sampling of pipe joints, and can intuitively and non-destructively evaluate the service life of buried polyethylene pipe electrofusion joints. It is convenient to implement and overcomes the shortcomings of existing evaluation methods, such as long evaluation cycle, large amount of engineering work, and high cost. It also eliminates the cumbersome operations such as destructive testing required by existing evaluation methods.

[0015] Specifically, establishing the correspondence between the edge width of the heat-affected zone and the service life of the welding area of ​​the polyethylene pipe electrofusion joint in advance in the laboratory includes the following steps:

[0016] S1: Polyethylene pipe electrofusion joint samples were prepared in batches according to different welding times t. Then, each electrofusion joint sample was subjected to ultrasonic phased array testing to obtain the edge width d of the heat-affected zone of the welding area of ​​each electrofusion joint sample. i The different welding times t are set as a series of welding times for the polyethylene pipe electrofusion joint to go from forming a severe cold weld to forming a severe over-weld.

[0017] S2: Using different temperatures T and different aging times t f Thermo-oxidative aging tests were conducted on each electrofusion joint sample obtained in step S1, and the coefficient of change of weldability P of each electrofusion joint sample before and after aging was measured. The aging rate k of each electrofusion joint sample at different temperatures T was calculated. Then, through data fitting processing, the coefficient of change of weldability P of each electrofusion joint sample was obtained in relation to the aging rate k and aging time t. f The relationship between I and II, and the relationship between aging rate k and temperature T for each electrofusion joint sample;

[0018] S3: Calculate the actual operating temperature T based on relationship II obtained in step S2. a Aging rate k of each electrofusion joint sample i Combined with the welding performance variation coefficient P for determining joint failure a Based on the relationship I obtained in step S2, the actual operating temperature T is calculated. a The service life t corresponding to the failure of each electrofusion joint sample below fi Combining the ultrasonic phased array detection results from step S1, the edge width d of the heat-affected zone of the polyethylene pipe electrofusion joint is finally obtained. i With service life t fi The correspondence between them d i ~t fi ;

[0019] In the method, the edge width d of the heat-affected zone of the in-service polyethylene pipe electrofusion joint is... a Substitute the correspondence d from step S3 i ~t fi In this process, the service life t of the in-service polyethylene pipe electrofusion joint is obtained. fa .

[0020] Specifically, in step S1, the material grade of the prepared polyethylene pipe electrofusion joint sample is the same as the material grade of the in-service polyethylene pipe electrofusion joint to be evaluated.

[0021] Specifically, in step S2, the different temperatures T are all set at 80°C or above.

[0022] Specifically, in step S2, the different temperatures T are set to 80℃, 95℃ and 110℃ respectively.

[0023] Specifically, the different aging times t mentioned in step S2 f Set them to 0h, 72h, 216h, 432h, and 720h respectively.

[0024] Specifically, step S2 further includes: performing a crush peel test on each electrofusion joint sample, and measuring the brittle peel percentage C of each electrofusion joint sample. C The coefficient of change P of the welding performance of each electrofusion joint sample before and after aging was calculated. The calculation formula is as follows:

[0025] H C =(1-C C )×100 (1)

[0026] P = H C / H C0 (2)

[0027] In formula (1), C C is the brittle peeling percentage of the electric fusion joint sample, H C is the welding performance of the electric fusion joint sample after aging;

[0028] In formula (2), H C is the welding performance of the electric fusion joint sample after aging, H C0 is the welding performance of the electric fusion joint sample before aging.

[0029] Specifically, in step S2, the relationship I between the welding performance change coefficient P of each electric fusion joint sample, the aging rate k and the aging time tf is obtained by the following formula and data fitting processing:

[0030]

[0031] In formula (3), A and a are material-related constants of the electric fusion joint sample;

[0032] The relationship II between the aging rate k of each electric fusion joint sample and the temperature T is obtained by the following formula and data fitting processing:

[0033] k=Be -(E / RT) (4)

[0034] In formula (4), R is the gas constant, E is the reaction activation energy, and B is a constant.

[0035] Specifically, in step S3, the temperature T of the actual working condition a is room temperature, for example, 20℃, and the welding performance change coefficient P of the identified joint failure a is 0.67.

[0036] The application also provides an evaluation system used in the method, which comprises an ultrasonic self-focusing linear array probe and a host computer. a The ultrasonic self-focusing linear array probe is used to scan the in-service polyethylene pipeline electric fusion joint to be evaluated on site. a The host computer collects the ultrasonic phased array characteristic spectrum measured by the ultrasonic self-focusing linear array probe through a signal transmission line, and then calculates the heat affected zone edge width d fa of the welding area of the in-service polyethylene pipeline electric fusion joint by using data analysis software.

[0037] The application uses the corresponding relationship d i ~t fiThe model is stored into the phased array host analysis software, and the edge width d of the heat affected zone of the welding surface of the actual in-service buried polyethylene pipeline electric fusion joint to be measured on site is measured a The measured d a The data is transmitted to the phased array detection host through the data line, and the data analysis software will automatically calculate the service life t of the pipeline joint fa Therefore, the service life of the in-service buried polyethylene pipeline electric fusion joint can be quickly and non-destructively predicted on site, the defects of the existing evaluation method, such as long evaluation period, large engineering quantity and high cost, are overcome, and the cumbersome operation of the existing evaluation method, such as destructive test, is eliminated.

[0038] In order to better understand and implement, the present application is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 It is a schematic diagram of the non-destructive evaluation system for the service life of the in-service polyethylene pipeline electric fusion joint.

[0040] Figure 2A It is a phased array spectrum measured for the electric fusion joint sample prepared according to a welding time of 87 seconds;

[0041] Figure 2B It is a phased array spectrum measured for the electric fusion joint sample prepared according to a welding time of 30 seconds;

[0042] Figure 2C It is a phased array spectrum measured for the electric fusion joint sample prepared according to a welding time of 135 seconds;

[0043] Figure 3 It is a curve graph of the edge width d of the heat affected zone of the electric fusion joint sample with the change of the welding time t;

[0044] Figure 4 It is a linear fitting relationship graph of the natural logarithm of the welding performance change coefficient P of the electric fusion joint sample and the aging time t f at different temperatures;

[0045] Figure 5 It is a linear fitting relationship graph of the natural logarithm of the aging rate k of the electric fusion joint sample and the reciprocal of the temperature T. DETAILED DESCRIPTION

[0046] The non-destructive evaluation method for the service life of the in-service polyethylene pipeline electric fusion joint provided by the present application comprises:

[0047] The corresponding relationship between the edge width of the heat affected zone of the welding area of the polyethylene pipeline electric fusion joint and the service life is established in advance in the laboratory;

[0048] Ultrasonic phased array testing was performed on the in-service polyethylene pipe electrofusion joint to be evaluated on-site to obtain the edge width d of the heat-affected zone of the welded area of ​​the in-service polyethylene pipe electrofusion joint. a ;

[0049] The edge width d of the heat-affected zone a Substituting into the corresponding relationship, the service life t of the in-service polyethylene pipe electrofusion joint is obtained. fa .

[0050] like Figure 1 As shown, the in-service polyethylene pipe electrofusion joint service life non-destructive evaluation system provided by the present invention includes an ultrasonic self-focusing linear array probe 2, a signal transmission line 3, and a host 4.

[0051] The ultrasonic self-focusing linear array probe 2 is used to scan the in-service polyethylene pipe electrofusion joint 1 to be evaluated on-site. The host 4 is connected to the ultrasonic self-focusing linear array probe 2 via a signal transmission line 3, and is equipped with data analysis software. The correspondence established in advance in the laboratory is stored in the data analysis software.

[0052] The host 4 acquires the ultrasonic phased array characteristic spectrum measured by the ultrasonic self-focusing linear array probe 2 through the signal transmission line 3, and then uses data analysis software to calculate the edge width d of the heat-affected zone of the welding area of ​​the in-service polyethylene pipe electrofusion joint 1. a Finally, the edge width d of the heat-affected zone is... a Substituting the pre-established relationship between the edge width of the heat-affected zone and its service life in the laboratory, the service life T of the in-service polyethylene pipe electrofusion joint 1 is obtained. a .

[0053] The method of the present invention is specifically carried out according to the following steps:

[0054] Step 1: In the laboratory, polyethylene pipe electrofusion joint samples S1, S2, S3... are prepared in batches according to different welding times t. Then, each electrofusion joint sample is subjected to ultrasonic phased array testing to obtain the edge width d of the heat-affected zone of the welding area of ​​each electrofusion joint sample. i (d1, d2, and d3...); the different welding times t are set as a series of welding times for the polyethylene pipe electrofusion joint to go from forming a severe cold weld to forming a severe over-weld.

[0055] In step one, more preferably, the material grade of the prepared polyethylene pipe electrofusion joint sample is the same as the material grade of the in-service polyethylene pipe electrofusion joint to be evaluated.

[0056] A batch of polyethylene pipe electrofusion joint samples S1, S2, S3… of the same brand as the in-service polyethylene pipe electrofusion joint to be evaluated and containing different degrees of process defects are prepared by changing the welding process, i.e. setting different welding time t gradients (t1, t2 and t3…), and the welding time t set must include each welding time period from severe cold welding to severe overwelding, so as to ensure that the unknown state or defect of the in-service polyethylene pipe electrofusion joint to be evaluated is included, thereby improving the accuracy and reliability of the final evaluation result.

[0057] See Figures 2A-2C and Figure 3 , Figures 2A-2C Exemplary phase array maps of the electrofusion joint samples prepared at three different welding times are shown, Figure 3 Exemplary relationship between the heat-affected zone edge width d of the five electrofusion joint samples S1-S5 prepared at different welding times t and the welding time t, and the linear fitting curve are shown. As shown in Figure 2A , the heat-affected zone edge width d1 of the electrofusion joint sample prepared according to the welding time t1 = 87 s is d1 = 2.71 mm; as shown in Figure 2B , the heat-affected zone edge width d2 of the electrofusion joint sample prepared according to the welding time t2 = 30 s is d2 = 1.31 mm, and as shown in Figure 2C , the heat-affected zone edge width d3 of the electrofusion joint sample prepared according to the welding time t3 = 135 s is d3 = 4.27 mm.

[0058] It can be seen that the edge width d of the fusion zone, i.e. the heat-affected zone (HAZ) of the electrofusion joint samples prepared at different welding times t i is different, and the heat-affected zone edge width d i changes with the welding time t.

[0059] Step two: heat and oxygen aging test is performed on each electrofusion joint sample prepared in step one at different temperatures T and different aging times t f , the welding performance change coefficient P of each electrofusion joint sample before and after aging is measured, the aging rate k of each electrofusion joint sample at different temperatures T is calculated, and then through data fitting processing, the relationship I between the welding performance change coefficient P of each electrofusion joint sample and the aging rate k, the aging time t f , and the relationship II between the aging rate k and the temperature T of each electrofusion joint sample is obtained.

[0060] In this step two, specifically, the different temperatures T are set at 80℃ or above to shorten the time required for the aging test; preferably, the different temperatures T are set at 80℃, 95℃ and 110℃, respectively. Specifically, the different aging times t f0h, 72h, 216h, 432h and 720h, respectively.

[0061] The step two specifically further comprises: after the respective aging time tf, each of the electrical fusion joint samples is taken out, respectively, and is subjected to the extrusion peeling test, and the brittle peeling percentage C C of each of the electrical fusion joint samples is measured, and the welding performance change coefficient P of each of the electrical fusion joint samples before and after aging is calculated, and the calculation formula is as follows:

[0062] H C C )×100 (1)

[0063] P=H C / H C0 (2)

[0064] In the formula (1), C C is the brittle peeling percentage of the electrical fusion joint sample, and H C is the welding performance of the electrical fusion joint sample after aging; in the formula (2), H C is the welding performance of the electrical fusion joint sample after aging, and H C0 is the welding performance of the electrical fusion joint sample before aging (i.e. the aging time is 0h).

[0065] The brittle peeling percentage C C is calculated by the following formula:

[0066]

[0067] In the formula, d is the brittle peeling length measured by the extrusion peeling test, and the unit is mm; and s is the wire length measured by the extrusion peeling test, and the unit is mm.

[0068] The relationship I between the welding performance change coefficient P of each of the electrical fusion joint samples and the aging rate k and the aging time t f is specifically taken as the following formula and is obtained by data fitting processing:

[0069]

[0070] In the formula (3), A and a are material-related constants of the electrical fusion joint sample, and are both obtained by linear fitting; and exp represents the exponential function with e as the base.

[0071] The relationship II between the aging rate k of each of the electrical fusion joint samples and the temperature T is specifically taken as the following formula and is obtained by data fitting processing:

[0072] k=Be -(E / RT) (4)

[0073] ​In formula (4), R is a gas constant, E is a reaction activation energy, B is a constant, and are obtained by linear fitting; e is a natural constant.

[0074] Referring to Figure 4 , the figure exemplarily shows the trend of the welding performance variation coefficient P of an electric fusion joint sample prepared at a certain welding time with the increase of aging time tf at 80℃, 95℃ and 110℃, respectively, and it can be seen that the higher the temperature, the faster the welding performance of the joint decreases, which corresponds to the above formula (3).

[0075] Referring to Figure 5 , the figure exemplarily shows the trend of the aging rate k of an electric fusion joint sample prepared at a certain welding time with the change of temperature T, which corresponds to the above formula (4), and the unit of temperature T in the figure is Kelvin (K).

[0076] In step two, the thermal aging test can refer to the standard GB / T 71141-2008 “Plastics - Determination of the effect of heat aging”. The extrusion peeling test can refer to the standard GB / T 19806-2005 “Plastics pipes and fittings - Polyethylene electric fusion joint assembly - Extrusion peeling test”.

[0077] Step three: according to the relationship II obtained in step two, the temperature T of the actual working condition is calculated a The aging rate k of the following electric fusion joint samples i , combined with the welding performance variation coefficient P of the joint failure a , according to the relationship I obtained in step two, the temperature T of the actual working condition is obtained a The aging time t required for the following electric fusion joint samples to reach failure fi , combined with the ultrasonic phased array detection results in step one, the corresponding relationship d i ~t fi between the aging time t and the edge width d of the heat affected zone of the polyethylene pipeline electric fusion joint is finally obtained. i fi .

[0078] In step three, the actual working condition is determined according to the actual common working condition of the in-service polyethylene pipeline electric fusion joint to be evaluated, which is usually room temperature, and preferably, the temperature T of the actual working condition a is selected as 20℃. According to the standard requirements, the welding performance variation coefficient P of the joint failure a = 0.67.

[0079] Step four: using the evaluation system as shown in Figure 1 , the corresponding relationship d i ~t fi ​The model is stored in the data analysis software of the phased array host, and the edge width d of the heat-affected zone of the weld surface of the electrofusion joint of the in-service buried polyethylene pipeline to be evaluated is measured on site. a The tested d a The data is transmitted to the phased array detection host via a data cable. The data analysis software will automatically calculate the corresponding aging time, which is the service life (t) of the in-service polyethylene pipe electrofusion joint. fa .

[0080] In actual operation of polyethylene pipe electrofusion joints, the ambient temperature is generally 20℃. However, in step two of this invention, the test temperature gradient T is set to a relatively high value (e.g., not less than 80℃), which can shorten the joint aging test time. To improve the accuracy of the service life prediction results, in step two of this invention, an aging test with temperature gradient T∈(80℃, 95℃, and 110℃) is established. Using the Arrhenius extrapolation model (see formula (4) above), the relationship between the joint aging rate k and the test temperature T is established. Then, the actual operating temperature T is substituted into the model. a The temperature T can be obtained. a Aging rate k of each electrofusion joint sample i Then the aging rate k i and the coefficient of change of welding performance at failure P a Substituting 0.67 into formula (3) above, we obtain the results for each electrofusion joint sample at temperature T. a The aging time t required to reach failure fi This is equivalent to the service life, thus obtaining the width d of the edge characteristic line of the heat-affected zone of each electrofusion joint specimen prepared by different welding processes (different welding times t). i Its service life t fi The correspondence between them d i ~t fi .

[0081] The method of the present invention can realize rapid and non-destructive prediction of the service life of electrofusion joints of buried polyethylene pipelines in service on site, overcoming the shortcomings of existing evaluation methods such as long evaluation cycle, large amount of engineering and high cost, and eliminating the cumbersome operation of destructive testing required by existing evaluation methods.

[0082] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for evaluating the service life of an electric fusion joint of a polyethylene pipeline in service, comprising: a corresponding relationship between the edge width of a heat-affected zone of a welding area of the electric fusion joint of the polyethylene pipeline and the service life is established in advance in a laboratory, and specifically comprises the following steps: S1: polyethylene pipe electrofusion joint samples are prepared in batches according to different welding times t respectively, and then each electrofusion joint sample prepared is subjected to ultrasonic phased array detection to obtain the heat affected zone edge width d of the welding area of each electrofusion joint sample i ; the different welding times t are set to make the polyethylene pipe electrofusion joint pass through a series of welding times from forming a serious cold weld to forming a serious overweld. S2: heat-aging test is performed on each of the electrical fusion splice samples prepared in step S1 at different temperatures T and different aging times t f , respectively, and the change coefficient P of the welding performance of each of the electrical fusion splice samples before and after aging is measured, the aging rate k of each of the electrical fusion splice samples at different temperatures T is calculated, and then through data fitting processing, the relationship I between the change coefficient P of the welding performance of each of the electrical fusion splice samples and the aging rate k and the aging time t f , and the relationship II between the aging rate k of each of the electrical fusion splice samples and the temperature T is obtained. S3: According to the relationship II obtained in step S2, the temperature T of the actual working condition is calculated a The aging rate k of each electric fusion joint sample i , combined with the welding performance change coefficient P to identify joint failure a , according to the relationship I obtained in step S2, the temperature T of the actual working condition is obtained a The corresponding service life t of each electric fusion joint sample when it fails f i, combined with the ultrasonic phased array detection result of step S1, the edge width d of the heat affected zone of the polyethylene pipeline electric fusion joint is finally obtained i The corresponding relationship d fi ~t i between the service life t fi ; In the method, the edge width d of the heat-affected zone of the in-service polyethylene pipeline electric fusion joint is determined a The corresponding relationship d of step S3 is substituted i ~t fi In the method, the service life t of the in-service polyethylene pipeline electric fusion joint is obtained fa ; The ultrasonic phased array detection is performed on the in-service polyethylene pipeline electric fusion joint to be evaluated on site to obtain the heat affected zone edge width d of the welding area of the in-service polyethylene pipeline electric fusion joint a ; The heat affected zone edge width d a Substituting into the corresponding relationship, the service life t of the in-service polyethylene pipeline electric fusion joint is obtained fa .

2. The method of claim 1, wherein, In step S1, the material grade of the prepared electric fusion joint sample of the polyethylene pipeline is the same as that of the electric fusion joint of the polyethylene pipeline in service to be evaluated.

3. The method of claim 2, wherein, In step S2, the different temperatures T are all set to 80℃ or above.

4. The method of claim 3, wherein, In step S2, the different temperatures T are set to 80℃, 95℃ and 110℃ respectively.

5. The method according to any one of claims 2 to 4, characterized in that, the different aging times t in step S2 f 0h, 72h, 216h, 432h, 720h, respectively.

6. The method according to any one of claims 2-4, characterized in that, The step S2 further comprises: respectively performing an extrusion peeling test on each of the electrical fusion splice samples, and measuring the brittle peeling percentage C of each of the electrical fusion splice samples C The change coefficient P of the welding performance of each of the electrical fusion splice samples before and after aging is calculated, and the calculation formula is as follows: H C = (1 - C C ) x 100 (1) P = H C / H C0 (2) In formula (1), C C is the percentage of brittle flaking of the electrically fused joint sample, H C is the weldability of the electrically fused joint sample after aging; In formula (2), H C H is the welding performance of the electrically fused joint sample after aging C0 H is the welding performance of the electrically fused joint sample before aging 7. The method of claim 6, wherein, In step S2, the coefficient of change of welding performance P of each electrofusion joint sample is related to the aging rate k and aging time t. f The relationship I between them is obtained using the following formula and through data fitting: In formula (3), A and a are material-related constants of the electric fusion joint sample; The relationship II between the aging rate k of each electric fusion joint sample and the temperature T is obtained by data fitting processing according to the following formula: k = Be -(E / RT) (4) In formula (4), R is a gas constant, E is a reaction activation energy, and B is a constant.

8. The method according to any one of claims 2-4, characterized in that, In step S3, the temperature T of the actual working condition a is room temperature, and the welding performance change coefficient P a for identifying the joint failure is 0.

67.

9. An evaluation system used in the method of claim 1, comprising an ultrasonic self-focusing linear array probe and a host computer, wherein the ultrasonic self-focusing linear array probe is used to scan the in-service polyethylene pipeline electric fusion joint to be evaluated on site; the host computer collects the ultrasonic phased array characteristic spectrum measured by the ultrasonic self-focusing linear array probe through a signal transmission line, and then calculates the heat affected zone edge width d of the welding area of the in-service polyethylene pipeline electric fusion joint by using data analysis software. a Finally, the heat affected zone edge width d is substituted into the corresponding relationship between the heat affected zone edge width and the service life previously established in the laboratory to obtain the service life t of the in-service polyethylene pipeline electric fusion joint. a fa Finally, the heat affected zone edge width d is substituted into the corresponding relationship between the heat affected zone edge width and the service life previously established in the laboratory to obtain the service life t of the in-service polyethylene pipeline electric fusion joint.​

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