Method for evaluating and predicting service sulfur resistance of sulfur-containing gas field gathering pipeline girth weld

Abstract

The present application belongs to the field of evaluation of sulfur resistance of weld, and particularly relates to a method for evaluating and predicting service sulfur resistance of girth weld of sulfur-containing gas field gathering pipeline. In view of the problem that the sulfur resistance of girth weld of low alloy gathering pipeline serving in sulfur-containing gas field decreases and the risk of sulfide stress cracking increases, the present application couples four factors (sulfide stress cracking, material, stress and service time) to effectively realize quantitative evaluation of sulfur resistance. Meanwhile, the present application can predict the change of sulfur resistance of girth weld with service time, provide technical and data support for risk assessment and safety guarantee measures of girth weld, and ensure the safe operation of low alloy steel gathering pipeline in sulfur-containing gas field.

Description

Technical Field

[0001] The invention belongs to the field of evaluation of the sulfur resistance of welds, and particularly relates to a method for evaluating and predicting the sulfur resistance of girth welds of a gathering and transportation pipeline in a sulfur-containing gas field. Background Art

[0002] Sour natural gas holds a significant position in my country's reserves and production. The development of such gas fields presents significant production safety challenges, including harsh sulfur-containing corrosion environments, high toxicity, and severe accident consequences. Low-alloy pipeline steel, due to its economical efficiency, excellent mechanical properties, and weldability, is widely used in gathering and transportation pipelines in sour gas fields, with girth welds being the primary connection method. However, due to the complex, non-equilibrium physical and chemical processes that low-alloy pipeline steel undergoes during welding, resulting in uneven joint structure and performance at the girth weld, the girth weld becomes the weakest and most accident-prone part of low-alloy steel gathering and transportation pipelines in sour gas fields in hydrogen sulfide environments, adversely impacting subsequent pipeline operational safety and various failure risks.

[0003] Essentially, the failure and damage of the girth welds of in-service gathering and transportation pipelines is because the "failure and damage driving force caused by external factors (including stress and strain, corrosive media, etc.)" exceeds the "failure and damage resistance related to the performance of the girth welds of the gathering and transportation pipelines themselves."

[0004] The core work of girth weld performance evaluation and risk assessment is to start with the identification and determination of girth weld defects. Monitoring and detection mainly include ultrasonic, X-ray, magnetic powder, penetrant, eddy current, TOFD and phased array detection technologies. Among them, ultrasonic, X-ray, TOFD and phased array detection technologies are mainly used to detect internal defects, while magnetic powder, penetrant and eddy current detection technologies are mainly used to detect surface or near-surface defects. For the performance evaluation of defective welds, based on the principle of fitness for use, the standards BS7910 "Guide to the Acceptability Assessment of Defects in Metal Structures", API Standard 1104 "Welding of Pipelines and Related Facilities", API 579 "Availability Assessment of In-Service Equipment" and GB / T 19624 "Safety Assessment of Pressure Vessels Containing Defects in Service" are widely recognized in the industry. Based on fracture mechanics, they use failure assessment diagrams (FADs) for assessment, taking into account both brittle fracture failure and plastic instability failure. In fact, it is a combination of fracture mechanics assessment methods and plastic limit load assessment methods to conduct applicability evaluation (i.e., fitness for use evaluation) of defective girth welds and evaluate the safety performance (risk) of girth welds. However, for the evaluation of pipeline welds in sour service environments, the standards do not include an input path for sour environment data.

[0005] Although there have been some patent reports on pipeline weld performance evaluation and risk assessment, none of them involve hydrogen sulfide working conditions. The Chinese invention patent with publication number CN 107283083 B discloses a girth weld evaluation method and device, which obtains multiple evaluation data of the girth weld to be evaluated. The multiple evaluation data include at least one detection data and at least one construction data, which improves the accuracy of the evaluation of the girth weld and can accurately and comprehensively identify girth welds in a dangerous state. The Chinese invention patent application with publication number CN 113128807 A discloses a girth weld risk assessment method, device and storage medium. Since the girth weld to be tested has multiple failure risk factors, it can more accurately reflect the actual failure risk value of the girth weld, and can improve the accuracy of the determined failure risk value of the girth weld. Chinese invention patent application publication number CN115689372 A discloses a vulnerability estimation method and system for girth welds in oil and gas pipelines. The system collects data for each girth weld in the pipeline section to be analyzed, derives vulnerable girth welds based on the sorted data, identifies girth weld vulnerabilities in the pipeline system, and identifies factors influencing vulnerability. Chinese invention patent application publication number CN114997656 A provides a method, device, processor, and storage medium for predicting the risk of girth welds in pipelines. For each girth weld, the system obtains the test results and failure consequence values ​​for each girth weld inspection indicator, determines a risk prediction value for each girth weld, and sequentially inspects the risk of each girth weld corresponding to each risk prediction value, thereby improving the accuracy of risk prediction. Chinese invention patent publication number CN109815981 B provides a method, device, and readable storage device for determining the risk level of a girth weld. By obtaining characteristic parameters of the girth weld from pipeline radiographic inspection data and in-pipeline inspection data, the system determines the risk type and risk level of the girth weld, further ensuring the reliability of the girth weld risk level. The Chinese invention patent application, publication number CN 114266493A, provides an intelligent method for determining the quality of girth welds in long-distance oil and gas pipelines. The method obtains all pipeline data information, obtains a first determination result, collects girth weld excavation data information, constructs a girth weld quality analysis model, and performs near-real-time prediction of the first girth weld excavation data.

[0006] Several papers and patents have reported on the prediction of pipeline welds (primarily corrosion residual strength, fatigue life, defect failure life prediction, and failure risk prediction), but none address hydrogen sulfide environments. The paper "Fatigue Properties and Pipeline Life Prediction of Several Oil and Gas Pipeline Materials" (China Safety Science Journal, Vol. 18, No. 1, January 2008) tested and compared the fatigue crack growth characteristics of three commonly used oil and gas pipeline materials: spiral seam submerged arc welded (SSAW), high-frequency electric resistance welded (ERW), and longitudinal submerged arc welded (UOE). The results were published in the journal SSAW and UOE. The paper "Analysis Method for Remaining Life of Weld Defects Based on BS 7910" (Oil and Gas Storage and Transportation, Vol. 35, No. 1, January 2016) studies the propagation mechanism of non-penetrating cracks and the prediction method for weld defect life to predict the remaining life of oil and gas pipeline welds. It proposes a dynamic weld remaining life calculation method based on a non-penetrating crack propagation model, guided by the cumulative method and combined with the failure assessment diagram (FAD) criteria in BS 7910-2005. The paper "Research on Failure Risk Prediction System for Girth Welds of Oil and Gas Pipelines Based on BP Neural Network" (Oil and Gas Field Surface Engineering, Vol. 41, No. 4, April 2022) addresses the issue of accurately predicting the failure pressure of corroded pipelines. Based on different corroded pipeline blasting test data, it analyzes and selects factors that have a significant impact on pipeline failure pressure, and constructs a BP model for predicting girth weld failure, which is suitable for predicting the failure pressure of corroded pipelines. The document "Prediction of Failure of Girth Welds Due to Defects in Long-Distance Pipelines" (Master's thesis at Xi'an Shiyou University, Feng Xiaoxing, June 2022) combines the highly nonlinear mapping capabilities of artificial neural networks to construct a neural network model for predicting girth weld failures and develop a pipeline girth weld defect failure prediction system. The document "Prediction of Residual Strength of Pipeline Welds Corroded Based on the IWOA PNN Model" (Journal of Safety and Environment, Vol. 23, No. 2, February 2023) addresses the issue of pipeline weld corrosion and constructs a residual strength prediction model based on an improved whale optimization algorithm. Chinese patent document CN 111860993 A discloses a method for predicting the fatigue life of welded joints that considers residual stress evolution. Cyclic load fatigue tests are performed on the parent material, and a sequential coupling method is used to perform thermal simulation on the weld of the welded joint. The residual stress field in the weld state during welding is determined, and a fatigue life prediction model for welded joints that considers residual stress evolution is established.

[0007] In addition to conventional mechanical properties and safety assessment requirements, girth welds in low-alloy steel gathering and transportation pipelines used in sour gas fields also face a specific requirement: "girth weld sulfur resistance." This requirement encompasses resistance to sulfide stress cracking (SSC) and hydrogen-induced cracking (HIC), two key technical indicators for the safe operation of low-alloy steel gathering and transportation pipelines in sour gas fields. Low-alloy gathering and transportation pipelines (including parent metal and girth welds) serving in sour gas fields react with hydrogen sulfide (a corrosion-sensitive environment) to generate hydrogen. This hydrogen permeates the pipe material (including parent metal and girth welds) and, under the influence of stresses (including the operating pressure borne by the pipeline itself, residual stresses caused by pressure, pressure fluctuations, and external extrusion during service), migrate and accumulate in strong hydrogen traps (defects in the weld area, such as uneven chemical composition, coarse grains, and structural segregation, which are areas where strong hydrogen traps accumulate). When the hydrogen content and stress reach critical values, sulfide stress cracking occurs. The occurrence of sulfide stress cracking in welds requires the coupling of four factors: hydrogen sulfide corrosion-sensitive environment, material, stress and service time.

[0008] Regarding the requirements and evaluation of the sulfur resistance of new girth welds in the construction phase of low-alloy steel gathering and transportation pipelines for sour gas fields, relevant standards have already established three of the four factors that require the coupling of hydrogen sulfide corrosion-sensitive environment, materials, and stress, clarifying the technical index requirements and ensuring that the sulfur resistance of new girth welds in low-alloy steel gathering and transportation pipelines for sour gas fields meets the requirements of safe operation in the initial service. The standards "Q / SH 0248-2009 Specification for Welding Construction and Acceptance of High-Sulfur Natural Gas Pipeline Engineering" and "SY / T 4117-2016 Technical Specification for Welding of Gathering and Transportation Pipelines for High-Sulfur Gas Fields" stipulate that: (1) The minimum loading stress for girth weld anti-SSC performance is 80% of the yield strength of the parent material (four-point bending method); (2) The HIC resistance performance of girth welds is the average crack length ratio CLR ≤ 10%, the average crack thickness ratio CTR ≤ 3%, the average crack sensitivity ratio CSR ≤ 1%, and the maximum length of any crack is < 6 mm.

[0009] However, as pipelines transporting sour natural gas age (i.e., the fourth factor required for sulfide stress cracking in welds: age), hydrogen sulfide can cause weld plasticity and toughness to decrease, leading to a decline in sulfur resistance and an increased risk of weld burst in gathering and transportation pipelines. The study "Study on the Plasticity and Toughness of In-Service X52 Gas Pipeline Steel" (Natural Gas Industry, Vol. 26, No. 3, March 2006) shows that the elongation and J-integral values ​​of X52 (L360) gas pipelines transporting H2S decrease with age, with the decrease occurring more significantly in the weld than in the base material, increasing the tendency for welds to experience brittle burst. The study "Corrosion Detection and Safety Analysis of Wet Gas Transmission Natural Gas Pipelines" (Oil and Gas Storage and Transportation, Vol. 25, No. 11, November 2006) also shows that, with age, welds of 20# steel gas pipelines transporting H2S tend to experience HIC, increasing the tendency for welds to experience brittle burst.

[0010] There are some patent reports on the indoor research of the anti-sulfur performance of welds. The Chinese invention patent with the announcement number CN 102305761 B provides a set of simulation test equipment and methods for the corrosion of welds and parent materials in acidic medium pipelines, which are used for indoor experiments to simulate the corrosion of H2S, CO2 and Cl - The corrosion resistance, SSC, HIC, and welding process evaluation of the parent material and welds of highly sour natural gas under pipeline transportation conditions are evaluated. A Chinese invention patent application with publication number CN 104374689 A provides a test device and test judgment method for pipe suitability for transmission pipelines. A test pipe ring is cut from a characteristic location on a typical pipe body of a transmission pipeline, and several sections of the test pipe ring are sealed and connected in sequence to form a test pipe section. The test pipe sections simulate pipeline operating parameters and a real service environment. Finally, the test pipe rings are sampled and analyzed at characteristic locations such as the pipe body and welds, based on an experimental design. This allows for an assessment of the suitability of pipes for transmission pipelines. A Chinese invention patent application with publication number CN 114754997 A provides a big data-based quantitative analysis device for the reliability of pipelines throughout their life cycle. The pipeline is placed in a simulation chamber, and prefabricated welds, predetermined defects, and a data acquisition matrix are provided on the pipeline wall. A modular design is employed, and components are replaced as needed. A pipeline reliability data information database is established, and big data analysis technology is used for mining and processing.

[0011] The girth weld itself is the weakest and most accident-prone part of the low-alloy steel gathering and transportation pipeline in sulfur-containing gas fields. At the same time, as the service time increases, the sulfur resistance of the girth weld decreases, further increasing the risk of the gathering and transportation pipeline.

[0012] The above prior art research still has the following problems:

[0013] (1) The evaluation method for the sulfur resistance of girth welds of low-alloy steel gathering and transportation pipelines in sour gas fields is limited to new girth welds during the pipeline construction phase (evaluation of welding processes). The influencing factors of sulfide stress cracking only involve three of the four factors: hydrogen sulfide corrosion-sensitive environment, material, and stress.

[0014] (2) The risk investigation of girth welds mainly starts with the identification of girth weld defects, and the performance evaluation and risk assessment of service welds do not involve the hydrogen sulfide working environment.

[0015] The above situation makes it difficult to effectively evaluate and predict the service sulfur resistance performance of girth welds of sour gas field gathering and transportation pipelines. Summary of the Invention

[0016] The purpose of the present invention is to provide a method for evaluating the service sulfur resistance performance of girth welds of sour gas field gathering and transportation pipelines, so as to solve the problem that the effectiveness of the service sulfur resistance performance evaluation of girth welds in the prior art needs to be improved.

[0017] The second object of the present invention is to provide a method for predicting the service sulfur resistance performance of the girth weld of a sour gas field gathering and transportation pipeline, so as to solve the problem that the existing technology cannot effectively predict the service sulfur resistance performance of the girth weld.

[0018] In order to achieve the above first purpose, the technical solution adopted by the present invention is:

[0019] The method for evaluating the service sulfur resistance performance of the girth weld of a sour gas field gathering and transportation pipeline comprises the following steps:

[0020] 1) Conduct SSC resistance, HIC resistance and hardness tests on the girth weld specimen to be evaluated;

[0021] 2) Quantify the sulfur resistance of girth welds according to formula (1):

[0022] A(t)=α(t)×β(t)×γ(t) (1)

[0023] In formula (1), t is the service time of girth weld, A(t) is the sulfur resistance of girth weld, which is dimensionless;

[0024] α(t) is a quantitative evaluation parameter for the SSC resistance of girth welds, and is evaluated according to formula (2):

[0025]

[0026] In formula (2), B(t) is the percentage of the ratio of the maximum loading stress without cracks and cracks on the surface of the girth weld specimen after the SSC resistance test to the minimum specified yield strength of the parent material. When B(t) ≥ 80%, α(t) is taken as 1;

[0027] β(t) is a quantitative evaluation parameter for the HIC resistance of girth welds, and is evaluated according to formula (3):

[0028]

[0029] In formula (3), C(t) is the average crack length rate of the girth weld specimen. The value is 1; D(t) is the average crack thickness rate of the girth weld specimen. When D(t)≤3%, The value is 1; E(t) is the average value of the surface crack sensitivity of the girth weld specimen. When E(t)≤1%, The value is 1; F(t) is the maximum length of any crack on the surface of the girth weld specimen. When F(t) is less than 6mm, The value is 1;

[0030] γ(t) is a quantitative evaluation parameter for girth weld hardness, which is evaluated according to formula (4):

[0031]

[0032] In formula (4), H(t) is the hardness test value, H(0) is the specified hardness value, and when H(t)≤H(0), γ(t) takes the value of 1;

[0033] 3) Evaluate the sulfur resistance of the girth weld in the following manner:

[0034] α(t) is the first evaluation factor that vetoes the sulfur resistance performance of the girth weld. If α(t) = 1, the SSC resistance performance has not decreased. If α(t) > 1, the SSC resistance performance has decreased, and the sulfur resistance performance evaluation result of the girth weld is unqualified.

[0035] When α(t)=1, the sulfur resistance of the girth weld is evaluated based on the calculation result of A(t). A(t) equal to 1 indicates that the sulfur resistance has not decreased; A(t) greater than 1 indicates that the sulfur resistance has decreased. The larger the value, the greater the degree of decrease in sulfur resistance.

[0036] The method for evaluating the service sulfur resistance of girth welds of sour gas field gathering and transportation pipelines of the present invention addresses the problems of decreased sulfur resistance and increased risk of sulfide stress cracking in girth welds of low-alloy gathering and transportation pipelines serving in sour gas fields. By coupling four factors causing sulfide stress cracking (hydrogen sulfide corrosion-sensitive environment, material, stress, and service time), the method can effectively achieve quantitative evaluation of sulfur resistance.

[0037] The present invention can evaluate the severity of sulfide stress cracking and the effectiveness of anti-corrosion process measures in the working environment of the gathering and transportation system, provide technical and data support for pipeline girth weld risk assessment and the implementation of safety measures, and ensure the safe operation of low-alloy steel gathering and transportation pipelines in sour gas fields.

[0038] Preferably, H(t) is the Brinell hardness or the Vickers hardness. When H(t) is the Brinell hardness, H(0) is 200; when H(t) is the Vickers hardness, H(0) is 248. Hardness performance can be evaluated using either the Brinell hardness or the Vickers hardness.

[0039] Further preferably, when both Brinell hardness and Vickers hardness test data are available, γ(t) is calculated to have the larger value. This approach can further improve the effectiveness of hardness evaluation.

[0040] Preferably, the girth weld specimen is a field-service pipe section containing girth welds, or an equivalent specimen that can reflect the sulfur resistance of field-service girth welds. Using field-service pipe sections containing girth welds is the most direct testing method, but it limits sample selection and sampling time to a certain extent: analysis and evaluation can only be performed when the pipe section is removed during inspection or maintenance. Using an equivalent specimen method provides greater flexibility in sample selection and sampling time.

[0041] Preferably, the equivalent specimens are obtained by subjecting the same girth weld sample to normal operating conditions, low-water operating conditions, and water-added operating conditions. The above-described configuration allows girth weld specimens to be prepared under different operating conditions, thereby providing suggestions for improvement in subsequent operating parameters and other aspects.

[0042] Further preferably, the equivalent specimen is obtained by processing a girth weld sample using a sulfur resistance evaluation device. The device comprises a gathering pipeline and a test pipe assembly connected in series to the gathering pipeline. The test pipe assembly comprises a water reduction section, a water addition section, and a normal service section arranged in parallel. The normal service section operates under the on-site service environment. The water reduction section is connected in series with a separator for separating incoming water, and the water addition section is connected in series with a water addition device. Equivalent specimens produced using the aforementioned sulfur resistance evaluation device closely match actual operating conditions, ensuring the authenticity and reliability of the test results.

[0043] In order to achieve the above second purpose, the technical solution adopted by the present invention is:

[0044] The method for predicting the service sulfur resistance performance of the girth weld of a sour gas field gathering and transportation pipeline includes the following steps:

[0045] a) Girth weld specimens with different service times were selected to conduct SSC and HIC resistance tests;

[0046] b) Quantitatively evaluate the SSC resistance of the girth weld specimens with different service times according to formula (2):

[0047]

[0048] In formula (2), α(t) is the quantitative evaluation parameter of the SSC resistance of the girth weld, and B(t) is the percentage of the maximum loading stress without cracks and cracks on the surface of the girth weld specimen after the SSC resistance test to the minimum specified yield strength of the parent material;

[0049] Establish a fitting curve between α(t) or B(t) and service time to predict the SSC resistance of girth welds with longer service time;

[0050] c) On the basis that the SSC resistance performance meets the requirements, the HIC resistance of the girth weld specimens with different service times is quantitatively evaluated according to formula (3):

[0051]

[0052] In formula (3), β(t) is the quantitative evaluation parameter of the HIC resistance of the girth weld, C(t) is the average crack length rate of the girth weld specimen surface; D(t) is the average crack thickness rate of the girth weld specimen surface; E(t) is the average crack sensitivity rate of the girth weld specimen surface; F(t) is the maximum length of any crack on the girth weld specimen surface;

[0053] A fitting curve of β(t) and service time is established to predict the HIC resistance of girth welds with longer service time.

[0054] The method for predicting the service sulfur resistance performance of girth welds of sour gas field gathering and transportation pipelines of the present invention can predict the changes in the sulfur resistance performance of girth welds over service time, provide technical and data support for pipeline girth weld risk assessment and the implementation of safety assurance measures, and ensure the safe operation of low-alloy steel gathering and transportation pipelines in sour gas fields.

[0055] Preferably, the girth weld specimen is a field-service pipe section containing girth welds, or an equivalent specimen that can reflect the sulfur resistance of field-service girth welds. Using field-service pipe sections containing girth welds is the most direct testing method, but it limits sample selection and sampling time to a certain extent: analysis and evaluation can only be performed when the pipe section is removed during inspection or maintenance. Using an equivalent specimen method provides greater flexibility in sample selection and sampling time.

[0056] Preferably, the equivalent specimens are obtained by subjecting the same girth weld sample to normal operating conditions, low-water operating conditions, and water-added operating conditions. The above-described configuration allows girth weld specimens to be prepared under different operating conditions, thereby providing suggestions for improvement in subsequent operating parameters and other aspects.

[0057] Further preferably, the equivalent specimen is obtained by processing a girth weld sample using a sulfur resistance evaluation device. The device comprises a gathering pipeline and a test pipe assembly connected in series to the gathering pipeline. The test pipe assembly comprises a water reduction section, a water addition section, and a normal service section arranged in parallel. The normal service section operates under the on-site service environment. The water reduction section is connected in series with a separator for separating incoming water, and the water addition section is connected in series with a water addition device. Equivalent specimens produced using the aforementioned sulfur resistance evaluation device closely match actual operating conditions, ensuring the authenticity and reliability of the test results. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 is a schematic diagram of a pipe section group connected in series with a gathering pipeline;

[0059] Figure 2 Schematic diagram of the distribution of various affected areas on the girth weld;

[0060] Figure 3 This is the relationship curve for the prediction of the anti-SSC performance in Example 3 of the present invention;

[0061] Figure 4 This is the relationship curve for predicting the anti-HIC performance in Example 3 of the present invention. DETAILED DESCRIPTION

[0062] The method for evaluating and predicting the service sulfur resistance performance of girth welds of sour gas field gathering and transportation pipelines proposed in the present invention proposes for the first time the coupling of four factors that lead to sulfide stress cracking in welds: hydrogen sulfide corrosion-sensitive environment, material, stress, and service time. This method is more consistent with the actual service experience of girth welds of sour gas field gathering and transportation pipelines, and can therefore serve as a basis for quantitative evaluation and prediction of the sulfur resistance performance of girth welds, and proposes the accuracy and reliability of the quantitative evaluation and prediction results.

[0063] The present invention's method for evaluating and predicting the in-service sulfur resistance performance of girth welds in sour gas field gathering and transportation pipelines utilizes a quantitative evaluation formula coupled with the sulfur resistance performance of the girth welds, based on the SSC resistance, HIC resistance, and hardness test results of the girth weld specimens to be evaluated. When it is necessary to predict how the sulfur resistance of the girth welds changes with service time, the service time and the quantitative evaluation parameters for SSC resistance or HIC resistance established in the present invention are fitted to predict changes in SSC and HIC resistance performance, thereby providing technical and data support for on-site inspection and maintenance (such as pipe section replacement or pipe section reinforcement) and optimization of operating parameters (such as reduced pressure operation).

[0064] The evaluation and prediction process of the service sulfur resistance performance of the girth weld of the sour gas field gathering and transportation pipeline can generally be achieved through the following steps:

[0065] 1. Basic parameter collection and analysis

[0066] Including the natural gas components of high-sulfur gas fields (including hydrogen sulfide content, carbon dioxide content, etc.), natural gas water content (including water components, etc.), gathering and transportation pipeline operating parameters (including temperature, pressure, flow rate, service time, etc.), gathering and transportation pipeline pipe materials (including steel model, composition, mechanical properties, etc.), gathering and transportation pipeline girth weld parameters (including welding process, welding joint performance, etc.), etc.

[0067] 2. Obtaining sulfur resistance test samples of girth welds

[0068] The sulfur resistance performance samples of girth welds are mainly obtained through the following two methods:

[0069] (1) Method 1: Service Sample

[0070] Removing girth-welded sections of low-alloy steel gathering and transportation pipelines serving sour gas fields to analyze and evaluate their post-service sulfur resistance is the most direct approach, but sample selection and sampling time are somewhat limited: analysis and evaluation can only be performed when the pipe sections are removed during inspections and maintenance.

[0071] (2) Method 2: Equivalent sample

[0072] The equivalent specimen is not an on-site service specimen, but can be made through on-site gathering and transportation pipeline modification so that the separately manufactured specimen is placed under the actual operating conditions of the girth weld. Therefore, it can truly reflect the changes in the sulfur resistance performance of the actual service girth weld and is called an equivalent specimen.

[0073] Specifically, if Figure 1 As shown in the figure, at the gas gathering station of the sour gas field, a pipe section group connected in series with the gathering and transmission pipeline is set up (using insulating flanges, with valves before and after the pipe section). Each group of pipe sections is divided into several sub-pipe sections connected with insulating flanges (the sub-pipe sections of each group are connected in series, and the sub-pipe sections are connected with insulating flanges. This facilitates the disassembly of the sub-pipe sections and the placement and installation of samples). The working environment within the pipe section is guaranteed to be the on-site service environment. The pipe sections are divided into three parallel groups:

[0074] ① The first group is exactly the same as that in the gathering and transportation pipeline. The purpose is to evaluate the sulfur resistance of the girth weld in the working environment exactly the same as that in the gathering and transportation pipeline.

[0075] ② In the second group, a separator was installed at the front end of the pipe section to separate the incoming water, so that the free water content in the pipe section could be adjusted, simulating a pipe section with less water or no liquid accumulation. The purpose was to evaluate the sulfur resistance of the girth weld in the working environment of a pipe section with less water or no liquid accumulation in the gathering and transportation pipeline;

[0076] ③ In the third group, a water adding device was installed at the front end of the pipe section to adjust the water content in the pipe section, simulating a pipe section with high water content or liquid accumulation. The purpose was to evaluate the sulfur resistance of the girth weld in the working environment of a pipe section with high water content or liquid accumulation in the gathering and transportation pipeline.

[0077] A bypass pipe section is set in parallel with the pipe section group, a nitrogen purge system and other safety monitoring systems are installed, and connected to the safety monitoring system of the gas gathering station to achieve safety linkage.

[0078] 3. Evaluation specimen of sulfur resistance of girth weld

[0079] (1) The size of a single specimen meets the requirements of SSC specimens and HIC specimens after processing. The specimen is supported and fixed with an insulating bracket (not in contact with the pipe section) and is divided into the following types:

[0080] ① The material should be consistent with the girth welds of low-alloy steel gathering and transportation pipelines serving in sour gas fields (including pipe materials, welding process, surface conditions, etc.), and used to evaluate the sulfur resistance of the serving girth welds;

[0081] ② Girth welds of different types of low alloy steel gathering and transportation pipelines, used to evaluate the sulfur resistance of girth welds of different types of low alloy steel gathering and transportation pipelines;

[0082] ③ The sulfur resistance of girth welds of low alloy steel gathering and transportation pipelines with different welding processes.

[0083] (2) Stress of the specimens used to evaluate the sulfur resistance of girth welds

[0084] ① There are two categories: specimens without stress loading and specimens with stress loading. Specimens for SSC and HIC resistance generally require stress loading to reflect the SSC and HIC resistance after being stressed.

[0085] ② Loading stress specimen: The stress loading method for the girth weld specimen (the weld is located in the center) is the four-point bending method, and the loading stress is 100% to 40% of the minimum specified yield strength of the parent material.

[0086] 4. Evaluation benchmark indicators for sulfur resistance of girth welds

[0087] The SSC and HIC resistance tests are conducted in accordance with the standards "2009-Q / SH 0248-2009 Specification for Welding Construction and Acceptance of High-Sulfur Natural Gas Pipeline Engineering" and "SY / T 4117-2016 Technical Specification for Welding of High-Sulfur Hydrogen Gas Field Gathering and Transportation Pipelines":

[0088] (1) Anti-SSC performance: According to the standard "NACE TM 0177 Standard Test Method for Laboratory Testing of Metals for Resistance to Sulfide Stress Cracking and Stress Corrosion Cracking in H2S Environments", solution A was used, and the girth weld specimen (weld located in the center) was loaded with stress by the four-point bending method. The loading stress was 80% of the minimum specified yield strength of the parent material. The test period was 720 hours and the test temperature was 24±3℃. After the test, there was no crack or fissure on the surface of the girth weld specimen.

[0089] (2) HIC resistance: in accordance with the standard “NACE TM 0284 Test Method for Evaluation of Hydrogen-Induced Cracking Resistance of Steel for Pipelines and Pressure Vessels”, solution A of the standard “NACE TM 0177 Standard Test Method for Laboratory Testing of Metals for Resistance to Sulfide Stress Cracking and Stress Corrosion Cracking in H2S Environments” was used. The test period was 96 hours, the test temperature was 25±3°C, and after the test, the average crack length rate CLR of the girth weld specimens was ≤10%, the average crack thickness rate CTR was ≤3%, the average crack sensitivity rate CSR was ≤1%, and the maximum length of any crack was <6 mm.

[0090] (3) Hardness value is an essential attribute indicator for the SSC sensitivity of girth welds:

[0091] According to the standards "SY / T 0059 Technical Specification for Controlling the Hardness of Steel Equipment Welds to Prevent Sulfide Stress Cracking", "GB / T27866 Technical Specification for Controlling the Hardness of Steel Pipelines and Equipment Welds to Prevent Sulfide Stress Cracking" and "SY / T 0612 Design Specification for Surface Gathering and Transportation Systems of High Hydrogen Sulfide Gas Fields", HB≤200;

[0092] According to the standards "GB / T 27866 Technical Specification for Controlling the Hardness of Steel Pipelines and Equipment Welds to Prevent Sulfide Stress Cracking", "SY / T 0599 Technical Specification for Metal Materials Resistant to Sulfide Stress Cracking and Stress Corrosion Cracking of Natural Gas Surface Facilities", "Q / SH 0248 Specification for Welding Construction and Acceptance of High-Sulfur Natural Gas Pipeline Projects" and "SY / T 4117 Technical Specification for Welding of Gathering and Transportation Pipelines of High-Sulfur Hydrogen Gas Fields", HV≤248 is required.

[0093] 5. Coupling quantitative evaluation of sulfur resistance of girth welds

[0094] Based on the coupling principle of multi-factor risk assessment, a coupled quantitative calculation formula for evaluating the sulfur resistance of girth welds was established:

[0095] A(t)=α(t)×β(t)×γ(t) (1)

[0096] Where:

[0097] (1) A(t): Anti-sulfur performance of girth welds after a certain service time, dimensionless. A value equal to 1 indicates that the anti-sulfur performance has not decreased; a value greater than 1 indicates that the anti-sulfur performance has decreased. The larger the value, the worse the anti-sulfur performance and the greater the degree of decrease.

[0098] (2)α(t): Quantitative calculation of the SSC resistance performance parameter of the girth weld for a certain service time

[0099]

[0100] B(t) is the percentage of the ratio of the maximum loading stress without cracks on the surface of the girth weld specimen to the minimum specified yield strength of the parent material after the SSC resistance test for a certain service time. When B(t) ≥ 80%, α(t) is taken as 1.

[0101] The minimum specified yield strength of the parent material is a fundamental parameter of the pipe, representing the yield strength it must achieve. For example, the minimum specified yield strength of L360 pipe is 360 MPa. The highest percentage of the minimum specified yield strength of the parent material is calculated by dividing the "maximum loading stress at which no cracks or crazing occurs on the girth weld specimen surface" by the "minimum specified yield strength of the parent material." Specifically, this percentage is the maximum loading stress at which no cracks or crazing occurs on the girth weld specimen surface.

[0102] α(t) is the first evaluation factor that vetoes the sulfur resistance performance of the girth weld; α(t) = 1 means that the anti-SSC performance has not decreased, and α(t) > 1 means that the anti-SSC performance has decreased; if the anti-SSC performance has not decreased, a comprehensive evaluation of other factors will be performed; if the anti-SSC performance has decreased, even if the evaluation of other factors is qualified, the sulfur resistance performance of the girth weld is still unqualified.

[0103] (3)β(t): Quantitative calculation of HIC resistance performance parameters of girth welds for a certain service time

[0104]

[0105] in,

[0106] C(t) is the average CLR of the surface crack length rate of the girth weld specimen after the HIC performance test for a certain service time. When C(t)≤10%, The value is 1;

[0107] D(t) is the average value of the surface crack thickness rate CTR of the girth weld specimen after the HIC performance test for a certain service time. When D(t)≤3%, The value is 1;

[0108] E(t) is the average value of the surface crack sensitivity rate CSR of the girth weld specimen after the HIC resistance test for a certain service time. When E(t)≤1%, E1(%t) takes the value of 1;

[0109] F(t) is the maximum length of any crack on the surface of the girth weld specimen after a certain service time HIC resistance test. When F(t) is less than 6mm, The value is 1.

[0110] (4)γ(t): Quantitative calculation of the hardness parameter of the girth weld at a certain service time

[0111] Brinell hardness test calculation:

[0112] Wherein, HB(t) is the Brinell hardness test at a certain service time, when HB(t)≤200, γ(t) takes the value of 1;

[0113] Vickers hardness test calculation:

[0114] Wherein, HV(t) is the Vickers hardness test at a certain service time, when HV(t)≤248, γ(t) takes the value of 1;

[0115] According to the hardness test method, both Brinell hardness and Vickers hardness can be used, if both HB(t) and HV(t) exist, the value of the higher one is used.

[0116] 6. Evaluation steps of girth weld sulfur resistance performance

[0117] For equivalent sample method, the evaluation steps are as follows:

[0118] Step 1: Put the girth weld sample to be evaluated into three groups of pipe sections, including no load stress and load stress.

[0119] Step 2: According to a certain service period, take out part of the girth weld sample (including no load stress and load stress), the remaining sample continues to serve in the pipe section, at the same time, the vacant position can also be put into the sample to be evaluated again.

[0120] Step 3: According to the requirements of SSC sample and HIC sample, process into SSC sample and HIC sample.

[0121] Step 4: According to the provisions of the standard “2009-Q / SH 0248-2009 High Sulfur Natural Gas Pipeline Engineering Welding Construction and Acceptance Specification” and “SY / T 4117-2016 High Hydrogen Sulfide Gas Field Gathering Pipeline Welding Technical Specification”, evaluate the SSC resistance performance and HIC resistance performance of the girth weld sample.

[0122] Step 5: According to the requirements of the standard "SY / T 0059 Technical Specification for Controlling Hardness of Welds of Steel Equipment to Prevent Sulfide Stress Cracking", "GB / T 27866 Technical Specification for Controlling Hardness of Welds of Steel Pipes and Equipment to Prevent Sulfide Stress Cracking", and "SY / T 0612 Design Specification for High Hydrogen Sulfide Gas Field Surface Gathering System", Brinell hardness HB test is carried out; according to the requirements of the standard "GB / T 27866 Technical Specification for Controlling Hardness of Welds of Steel Pipes and Equipment to Prevent Sulfide Stress Cracking", "SY / T 0599 Technical Specification for Sulfide Stress Cracking and Stress Corrosion Cracking Resistant Metal Materials for Natural Gas Surface Facilities", "Q / SH 0248 Welding Construction and Acceptance Specification for High Sulfur Natural Gas Pipeline Engineering", and "SY / T 4117 Welding Technical Specification for High Hydrogen Sulfide Gas Field Gathering Pipeline", Vickers hardness HV test is carried out.

[0123] Step 6: Perform coupling quantitative evaluation calculation and analysis of the girth weld sulfur resistance performance.

[0124] For the way of taking down the girth weld pipe section of the low alloy steel gathering pipeline serving in the sulfur-containing gas field for a long time, when analyzing and evaluating its sulfur resistance performance after long-term service, steps 3, 4, 5 and 6 are performed.

[0125] 7. Girth weld sulfur resistance performance prediction

[0126] Girth weld sulfur resistance performance prediction mainly includes SSC performance and HIC resistance performance, among which, SSC resistance performance is the first evaluation factor of one vote veto, and also as the first prediction factor of one vote veto.

[0127] According to the sample acquisition method, it is described as follows:

[0128] (1) According to the "girth weld sulfur resistance performance sample acquisition" method one:

[0129] ① Sampling and calculation

[0130] Step 1: According to different service times t1, t2, t3, … (according to the site maintenance, pipe replacement and other operation conditions, corresponding different service times t1, t2, t3, …, sampling is carried out, and then analysis is carried out), the girth weld pipe section is taken down from the low alloy steel gathering pipeline serving in the sulfur-containing gas field, and then the SSC resistance performance and HIC resistance performance test is carried out according to the provisions.

[0131] Step 2: According to formula (2), the SSC resistance performance parameters of the girth weld with certain service time t1, t2, t3, … are quantitatively calculated.

[0132]

[0133] B(t1), B(t2), B(t3), ... are the percentages of the ratio of the maximum loading stress without cracks or cracks on the surface of the girth weld specimen to the minimum specified yield strength of the parent material after the SSC resistance test for certain service times t1, t2, t3, .... Calculate the actual values ​​of α(t1), α(t2), α(t3), ...

[0134] Step 3: Quantitatively calculate the HIC resistance performance parameters of the girth weld for a certain service time t1, t2, t3, ... according to formula (3).

[0135]

[0136] in,

[0137] C(t1), C(t2), C(t3), ... are the actual values ​​of the average surface crack length rate CLR of the girth weld specimen after the HIC resistance test at certain service times t1, t2, t3, ...;

[0138] D(t1), D(t2), D(t3), ... are the actual values ​​of the average surface crack thickness rate CTR of the girth weld specimens after the HIC resistance test at certain service times t1, t2, t3, ...;

[0139] E(t1), E(t2), E(t3), ... are the actual values ​​of the average surface crack sensitivity rate CSR of the girth weld specimen after the HIC resistance test at certain service times t1, t2, t3, ...;

[0140] F(t1), F(t2), F(t3), ... are the actual values ​​of the maximum length of any crack on the surface of the girth weld specimen after the HIC resistance test for certain service times t1, t2, t3, ...

[0141] ②Data fitting analysis and prediction

[0142] The calculated sulfur resistance evaluation data of the girth weld are fitted using a curve fitting method to obtain the fitting relationship curve and relationship function:

[0143] Based on the relationship curve and relationship function between "anti-SSC performance of girth welds" and "service time", the "anti-SSC performance of girth welds" with longer service times α(tI), α(tII), α(tIII), ... are predicted, providing technical and data support for on-site inspection and maintenance (replacing pipe sections or reinforcing pipe sections, etc.) and optimization of operating parameters (pressure reduction operation, etc.).

[0144] Based on the relationship curve and relationship function between "anti-HIC performance of girth welds" and "service time", the "anti-HIC performance of girth welds" with longer service times β(tI), β(tII), β(tIII), ... are predicted, providing technical and data support for on-site inspection and maintenance (replacing pipe sections or reinforcing pipe sections, etc.) and optimization of operating parameters (pressure reduction operation, etc.).

[0145] (2) According to the second method of “obtaining sulfur resistance test samples of girth welds”:

[0146] Divided into three groups:

[0147] The first group is exactly the same as that in the gathering and transportation pipeline;

[0148] In the second group, a separator was installed at the front end of the pipe section to separate the incoming water, so that the free water content in the pipe section could be adjusted, simulating a pipe section with less water or no liquid accumulation;

[0149] In the third group, a water adding device was installed at the front end of the pipe section to make the water content in the pipe section adjustable, simulating a pipe section with high water content or liquid accumulation.

[0150] ① Sampling and calculation

[0151] A girth weld specimen of a certain gathering and transportation pipe material, a certain welding process, and a certain loading stress is placed in the corresponding evaluation environment.

[0152] According to certain service times t1, t2, t3, ..., the test pieces are taken out to analyze and evaluate their anti-sulfur performance after service.

[0153] Step 1: According to certain service times t1, t2, t3, ..., take out the pipe section containing girth weld from the corresponding evaluation environment, and conduct analysis and evaluation of its sulfur resistance performance test after service (including anti-SSC performance and anti-HIC performance test).

[0154] Steps 2 and 3 are carried out in accordance with steps 2 and 3 of "Sampling and Calculation" in Method 1 of "Obtaining Sulfur Resistance Test Samples for Girth Welds".

[0155] ②Data fitting analysis and prediction

[0156] The calculated sulfur resistance evaluation data of the girth weld are fitted using a curve fitting method to obtain the fitting relationship curve and relationship function:

[0157] Based on the relationship curve and relationship function between "anti-SSC performance of girth welds" and "service time", the "anti-SSC performance of girth welds" with longer service times α(tI), α(tII), α(tIII), ... are predicted, providing technical and data support for on-site inspection and maintenance (replacing pipe sections or reinforcing pipe sections, etc.) and optimization of operating parameters (pressure reduction operation, etc.).

[0158] Based on the relationship curve and relationship function between "anti-HIC performance of girth welds" and "service time", the "anti-HIC performance of girth welds" with longer service times β(tI), β(tII), β(tIII), ... are predicted, providing technical and data support for on-site inspection and maintenance (replacing pipe sections or reinforcing pipe sections, etc.) and optimization of operating parameters (pressure reduction operation, etc.).

[0159] The implementation process of the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0160] A high-sulfur gas field in China utilizes L360 low-alloy seamless gathering and transportation pipes, connected by girth welds. This high-sulfur wet gas gathering and transportation system anti-corrosion technology integrates five key elements: sulfur-resistant pipes, corrosion inhibitors, corrosion monitoring, cathodic protection, and intelligent pigging. The average corrosion rate is maintained below 0.076 mm / year. The gas field has an on-site laboratory capable of simulating pipeline service conditions.

[0161] 1. Specific embodiment of the method for evaluating the service sulfur resistance performance of the girth weld of a sour gas field gathering and transportation pipeline of the present invention

[0162] Example 1

[0163] The method for evaluating the service sulfur resistance performance of the girth weld of a sour gas field gathering and transportation pipeline in this embodiment is specifically described as follows for the first method for obtaining the sulfur resistance performance sample of the girth weld (service sample):

[0164] During the inspection and maintenance, a pipe section with girth welds (strength design factor of 0.6) that had been in service for 13 years was removed and tested for SSC resistance, HIC resistance and hardness according to regulations. The results are shown in Table 1. Figure 2 shown.

[0165] Table 1 Test results of sulfur resistance of girth welds of L360 low alloy steel gathering and transportation pipelines in high sulfur gas fields after 13 years of service

[0166]

[0167] The value of B(13) is 70%, so the value of α(13) is

[0168] Anti-HIC performance test, due to The value is 1, D(13)<3%, The value is 1, E(13)<1%, The value is 1, F(13)<6mm, The value is 1, so the value of β is β=1×1×1×1=1.

[0169] Since all Vickers hardness values ​​in the weld zone are lower than 248, the value of γ is 1.

[0170] According to formula (1), the coupled quantitative evaluation of the sulfur resistance of girth welds with 13 years of service is carried out:

[0171]

[0172] A>1, indicating that the sulfur resistance of the girth weld has declined after 13 years of service. Among them, the HIC resistance and hardness have not declined, but the SSC resistance has declined.

[0173] Example 2

[0174] The method for evaluating the service sulfur resistance performance of the girth weld of a sour gas field gathering and transportation pipeline in this embodiment is specifically described as follows for the first method for obtaining the sulfur resistance performance sample of the girth weld (equivalent sample):

[0175] (1) Specifications of test specimens for evaluation of sulfur resistance of girth welds

[0176] It is consistent with the girth weld of the low-alloy steel gathering and transportation pipeline serving in the sour gas field, including pipe material, welding process, surface condition, L360 low-alloy gathering and transportation pipe material, welding process of combination of gas shielded welding and arc welding, and post-weld heat treatment.

[0177] (2) Stress of the specimens used to evaluate the sulfur resistance of girth welds

[0178] The stress loading specimen adopts the girth weld specimen (the weld is located in the center) and the stress loading method is the four-point bending method. The loading stress is 60% of the minimum specified yield strength of the base material (L360 low alloy steel).

[0179] (3) Evaluation of sulfur resistance of girth welds

[0180] According to the annual sampling cycle and the requirements of SSC and HIC specimens, the specimens were processed into SSC and HIC specimens. According to the standards "2009-Q / SH 0248-2009 Specification for Welding Construction and Acceptance of High-Sulfur Natural Gas Pipeline Engineering" and "SY / T 4117-2016 Technical Specification for Welding of Gathering and Transportation Pipelines of High-Sulfur Hydrogen Gas Fields", the SSC resistance, HIC resistance and hardness of the girth weld specimens were evaluated. The test results are shown in Table 2.

[0181] Table 2 Test results of sulfur resistance of girth welds of L360 low alloy steel gathering and transportation pipelines in long-term service in high sulfur gas fields

[0182]

[0183] The values ​​of B(1), B(2), B(3), B(4), and B(5) are all ≥80%, so the value of α is taken as 1.

[0184] In the HIC resistance test, the values ​​of C(1), C(2), C(3), C(4), and C(5) are all less than 10%. The value is 1, and the values ​​of D(1), D(2), D(3), D(4), and D(5) are all less than 3%. The value is 1, and the values ​​of E(1), E(2), E(3), E(4), and E(5) are all less than 1%. The value is 1, and the values ​​of F(1), F(2), F(3), F(4), and F(5) are all less than 6 mm. The value is 1, so the value of β is β=1×1×1×1=1.

[0185] Since all Vickers hardness values ​​in the weld zone are lower than 248, the value of γ is 1.

[0186] According to formula (1), the sulfur resistance of girth welds within 5 years of service is quantitatively evaluated:

[0187] A=α×β×γ=1×1×1=1

[0188] A=1, indicating that the girth weld with a loading stress of 60% of the minimum specified yield strength of the base material (L360 low alloy steel) has no degradation in sulfur resistance within 5 years of service.

[0189] 2. Specific embodiments of the method for predicting the service sulfur resistance performance of the girth weld of a sulfur-containing gas field gathering and transportation pipeline of the present invention

[0190] Example 3

[0191] The method for predicting the service sulfur resistance performance of the girth weld of the sour gas field gathering and transportation pipeline in this embodiment further performs the SSC resistance performance prediction and the HIC resistance performance prediction based on the test data of Example 2, as described in detail as follows:

[0192] ①Prediction of anti-SSC performance

[0193]

[0194] The curve fitting method is used to fit the relationship curve between "the loading stress without cracks on the surface of the girth weld specimen and the highest percentage of the minimum specified yield strength of the parent material" and "service time" (such as Figure 3 ), and the relationship function, the specific data are shown in Table 3 below.

[0195] Table 3 Prediction of SSC resistance of girth welds of L360 low alloy steel gathering and transportation pipelines in long-term service in high-sulfur gas fields

[0196]

[0197]

[0198] The relationship function is: y = -2.5x + 103.5 (7)

[0199] Where: x is the service time, unit: year; y is the loading stress at which there is no crack on the surface of the girth weld specimen and the crack is the highest percentage of the minimum specified yield strength of the base material, unit: %.

[0200] Substituting 13 years of service time into formula (7), the maximum percentage of the loading stress at which the girth weld specimen has no cracks or cracks on its surface and the minimum specified yield strength of the parent material is 71%, which is comparable to the 70% measured in the actual sampling in Table 1, indicating that the prediction of the anti-SSC performance is relatively accurate.

[0201] The relationship between the SSC resistance of girth welds and service time was predicted by calculation. Starting from the 10th year, the SSC resistance of girth welds has declined. The reason for choosing SSC resistance as the first prediction factor is:

[0202] (1) Analysis from the mechanism aspect: SSC is the most dangerous because of sudden cracking.

[0203] (2) Analysis from experimental data: The anti-SSC performance is the first to decline.

[0204] (3) From the perspective of preventive measures: Since the occurrence of SSC requires the combined effects of pipe materials, force, and environment, preventive measures can be implemented from the force perspective (pressure reduction or pipeline reinforcement measures need to be taken on site) to ensure the safe operation of the gathering and transportation pipeline.

[0205] ②Prediction of anti-HIC performance

[0206]

[0207]

[0208]

[0209]

[0210]

[0211] The curve fitting method is used to fit the relationship curve of "girth weld anti-HIC performance parameters"-"service time" (such as Figure 4 The specific data results and prediction results are shown in Table 4 below.

[0212] Table 4 Prediction of HIC resistance of girth welds of L360 low alloy steel gathering and transportation pipelines in long-term service in high-sulfur gas fields

[0213]

[0214] The relationship function is: y=0.000009x-0.00002 (8)

[0215] Wherein: x is the service time, unit: year; y is the HIC resistance performance parameter of the girth weld, dimensionless.

[0216] The HIC resistance performance parameter of the girth weld is 0.000097 obtained by bringing the service time of 13 years into the formula (8), which is equivalent to the actual sampling measured value of 0.000091 in Table 1, so the prediction of the HIC resistance performance is relatively accurate.

[0217] The change relationship of the HIC resistance performance of the girth weld with the service time is predicted by calculation, and the quantitative calculation value of the HIC resistance performance parameter of the girth weld is less than 1 within 20 years, and the HIC resistance performance of the girth weld does not decrease.

Claims

1. A method for evaluating the sulfur resistance of girth welds in a sour gas field gathering and transportation pipeline, characterized in that: The following steps are involved: 1) Conduct SSC resistance, HIC resistance and hardness tests on the girth weld specimen to be evaluated; 2) Quantify the sulfur resistance of girth welds according to formula (1): A(t)=α(t)×β(t)×γ(t) (1) In formula (1), t is the service time of girth weld, A(t) is the sulfur resistance of girth weld, which is dimensionless; α(t) is a quantitative evaluation parameter for the SSC resistance of girth welds, and is evaluated according to formula (2): In formula (2), B(t) is the percentage of the ratio of the maximum loading stress without cracks and cracks on the surface of the girth weld specimen after the SSC resistance test to the minimum specified yield strength of the parent material. When B(t) ≥ 80%, α(t) is taken as 1; β(t) is a quantitative evaluation parameter for the HIC resistance of girth welds, and is evaluated according to formula (3): In formula (3), C(t) is the average crack length rate of the girth weld specimen. When C(t)≤10%, The value is 1; D(t) is the average crack thickness rate of the girth weld specimen. When D(t)≤3%, The value is 1; E(t) is the average value of the surface crack sensitivity of the girth weld specimen. When E(t)≤1%, The value is 1; F(t) is the maximum length of any crack on the surface of the girth weld specimen. When F(t) is less than 6mm, The value is 1; γ(t) is a quantitative evaluation parameter for girth weld hardness, which is evaluated according to formula (4): In formula (4), H(t) is the hardness test value, H(0) is the specified hardness value, and when H(t)≤H(0), γ(t) takes the value of 1; 3) Evaluate the sulfur resistance of the girth weld in the following manner: α(t) is the first evaluation factor that vetoes the sulfur resistance performance of the girth weld. If α(t) = 1, the SSC resistance performance has not decreased. If α(t) > 1, the SSC resistance performance has decreased, and the sulfur resistance performance evaluation result of the girth weld is unqualified. When α(t)=1, the sulfur resistance of the girth weld is evaluated based on the calculation result of A(t). A(t) equal to 1 indicates that the sulfur resistance has not decreased; A(t) greater than 1 indicates that the sulfur resistance has decreased. The larger the value, the greater the degree of decrease in sulfur resistance.

2. The method for evaluating the sulfur resistance performance of the girth weld of a sour gas field gathering and transportation pipeline according to claim 1, wherein: H(t) is the Brinell hardness or Vickers hardness. When H(t) is the Brinell hardness, H(0) is 200; when H(t) is the Vickers hardness, H(0) is 248.

3. The method for evaluating the sulfur resistance performance of the girth weld of a sour gas field gathering and transportation pipeline according to claim 2, wherein: When both Brinell hardness and Vickers hardness test data are available, γ(t) shall be the larger calculated value.

4. The method for evaluating the sulfur resistance performance of the girth weld of a sour gas field gathering and transportation pipeline in service according to any one of claims 1 to 3, characterized in that: The girth weld specimen is a pipe section containing a girth weld in field service or an equivalent specimen that can reflect the sulfur resistance of the girth weld in field service.

5. The method for evaluating the sulfur resistance performance of the girth weld of a sour gas field gathering and transportation pipeline according to claim 4, characterized in that: The equivalent specimens are obtained by respectively maintaining the same girth weld sample in a normal working environment, a water-scarce working environment, and a water-added working environment.

6. The method for evaluating the sulfur resistance performance of the girth weld of a sour gas field gathering and transportation pipeline in service according to claim 5, characterized in that: The equivalent test specimen is obtained by processing a girth weld sample through an anti-sulfur evaluation device. The anti-sulfur evaluation device includes a gathering pipeline and a test pipe group connected in series on the gathering pipeline. The test pipe group includes a water reduction pipe section, a water addition pipe section and a normal service pipe section arranged in parallel. The working environment of the normal service pipe section is the on-site service environment. A separator for separating incoming water is connected in series on the water reduction pipe section, and a water addition device is connected in series on the water addition pipe section.

7. A method for predicting the service sulfur resistance performance of the girth weld of a sour gas field gathering and transportation pipeline, characterized in that: The following steps are involved: a) Girth weld specimens with different service times were selected to conduct SSC and HIC resistance tests; b) Quantitatively evaluate the SSC resistance of the girth weld specimens with different service times according to formula (2): In formula (2), α(t) is the quantitative evaluation parameter of the SSC resistance of the girth weld, and B(t) is the percentage of the maximum loading stress without cracks and cracks on the surface of the girth weld specimen after the SSC resistance test to the minimum specified yield strength of the parent material; Establish a fitting curve between α(t) or B(t) and service time to predict the SSC resistance of girth welds with longer service time; c) On the basis that the SSC resistance performance meets the requirements, the HIC resistance of the girth weld specimens with different service times is quantitatively evaluated according to formula (3): In formula (3), β(t) is the quantitative evaluation parameter of the HIC resistance of the girth weld, C(t) is the average crack length rate of the girth weld specimen surface; D(t) is the average crack thickness rate of the girth weld specimen surface; E(t) is the average crack sensitivity rate of the girth weld specimen surface; F(t) is the maximum length of any crack on the girth weld specimen surface; A fitting curve of β(t) and service time is established to predict the HIC resistance of girth welds with longer service time.

8. The method for predicting the service sulfur resistance performance of the girth weld of a sour gas field gathering and transportation pipeline according to claim 7, characterized in that: The girth weld specimen is a pipe section containing a girth weld in field service or an equivalent specimen that can reflect the sulfur resistance of the girth weld in field service.

9. The method for predicting the service sulfur resistance performance of the girth weld of a sour gas field gathering and transportation pipeline according to claim 8, characterized in that: The equivalent specimens are obtained by respectively maintaining the same girth weld sample in a normal working environment, a water-scarce working environment, and a water-added working environment.

10. The method for predicting the service sulfur resistance performance of the girth weld of a sour gas field gathering and transportation pipeline according to claim 9, characterized in that: The equivalent test specimen is obtained by processing a girth weld sample through an anti-sulfur evaluation device. The anti-sulfur evaluation device includes a gathering pipeline and a test pipe group connected in series on the gathering pipeline. The test pipe group includes a water reduction pipe section, a water addition pipe section and a normal service pipe section arranged in parallel. The working environment of the normal service pipe section is the on-site service environment. A separator for separating incoming water is connected in series on the water reduction pipe section, and a water addition device is connected in series on the water addition pipe section.

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