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

Abstract

The invention belongs to the field of evaluation of sulfur resistance of welding seams, and particularly relates to a service sulfur resistance evaluation and prediction method for circumferential welding seams of a gathering and transportation pipeline of a sulfur-containing gas field. In order to solve the problems that the sulfur resistance of the circumferential weld of the low-alloy gathering and transportation pipeline serving in the sulfur-containing gas field is reduced and the stress cracking risk of sulfide is improved, four factors (hydrogen sulfide corrosion sensitive environment, material, stress and service time) of the sulfide stress cracking are coupled, and the quantitative evaluation of the sulfur resistance can be effectively realized. Meanwhile, the change of the sulfur resistance of the circumferential weld along with the service time can be predicted, technical and data support is provided for the implementation of pipeline circumferential weld risk assessment and safety guarantee measures, and safe operation of the sulfur-containing gas field low alloy steel gathering and transportation pipeline is guaranteed.

Description

Technical Field

[0001] The invention belongs to the field of evaluation of the anti-sulfur performance of welds, and in particular relates to a method for evaluating and predicting the in-service anti-sulfur performance of girth welds of a gathering and transportation pipeline in a sour gas field. Background Art

[0002] Sour natural gas occupies an important position in my country's reserves and production. The development of such gas fields faces production safety issues such as harsh sulfur-containing corrosion environment, high toxicity, and serious consequences of accidents. Low-alloy pipeline steel is widely used in sour gas field gathering and transportation pipelines due to its good economy, excellent mechanical properties, and excellent weldability, with girth weld butt as the main connection method. Since low-alloy pipeline steel undergoes a series of complex non-equilibrium physical and chemical processes during welding, resulting in uneven joint structure and performance at the girth weld, in a hydrogen sulfide environment, the girth weld becomes the weakest and most accident-prone part of the low-alloy steel gathering and transportation pipeline of sour gas fields, and has an adverse impact on the subsequent service operation safety of the pipeline and various failure risks.

[0003] The failure of the girth welds of the gathering and transportation pipelines in service is essentially because the "failure driving force caused by external factors (including stress and strain, corrosive media, etc.)" exceeds the "failure 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 particle, penetration, 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, and magnetic particle, penetration 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 Method 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 Defective Pressure Vessels in Service" have been widely recognized by the industry. Based on fracture mechanics, they use failure assessment diagrams (FAD) 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 evaluate the suitability of defective girth welds (i.e., fitness for use assessment) and evaluate the safety performance (risk) of girth welds. However, for the evaluation of pipeline welds in a sour service environment, there is no input path for sour environment data in the standard.

[0005] Although there have been some patent reports on pipeline weld performance evaluation and risk assessment, none of them involve hydrogen sulfide working environment. The Chinese invention patent with the announcement number CN 107283083 B discloses a girth weld evaluation method and device, which obtains multiple evaluation data of the girth weld to be evaluated, and 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 the girth weld in a dangerous state. The Chinese invention patent application with the publication number CN 113128807 A discloses a girth weld risk evaluation method, device and storage medium. Since the girth weld to be detected 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. The Chinese invention patent application with publication number CN115689372 A discloses a vulnerability estimation method and system for girth welds of oil and gas pipelines, collects data of each girth weld of the pipe section to be analyzed, obtains vulnerable girth welds according to the sorting results, finds the vulnerable points of girth welds in the pipeline system, and identifies the vulnerability influencing factors. The Chinese invention patent application with publication number CN 114997656 A provides a method, device, processor and storage medium for predicting the risk of pipeline girth welds. For each girth weld, the detection result and failure consequence value of each detection index of the girth weld are obtained, the risk prediction value of each girth weld is determined, and the risk of the girth weld corresponding to each risk prediction value is detected in turn to improve the accuracy of risk prediction. The Chinese invention patent with publication number CN109815981 B provides a method, device and readable storage device for determining the risk level of a girth weld. By obtaining the characteristic parameters of the girth weld from the pipeline radiographic detection data and the in-pipeline detection data, the risk type and risk level of the girth weld are determined, and the reliability of the risk level of the girth weld is further ensured. The Chinese invention patent application with publication number CN 114266493A provides an intelligent method for determining the quality of girth welds in long-distance oil and gas pipelines, which 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] There are some literature and patent reports on pipeline weld prediction (mainly corrosion residual strength, fatigue life, defect failure life prediction, and failure risk prediction), but none of them involve hydrogen sulfide working environment. The literature "Fatigue Properties of Several Oil and Gas Pipeline Materials and Pipeline Life Prediction" (Journal of China Safety Science, Vol. 18, No. 1, January 2008) uses small specimens to test and compare the fatigue crack growth characteristics of three materials commonly used in oil and gas pipelines, namely spiral seam submerged arc welded pipe (SSAW), high-frequency electric resistance welded pipe (ERW) and straight seam submerged arc welded pipe (UOE). The document "Analysis Method of Remaining Life of Weld Defects Based on BS 7910" (Oil and Gas Storage and Transportation, Vol. 35, No. 1, January 2016) studied the propagation mechanism of non-penetrating cracks and the prediction method of weld defect life in order to predict the remaining life of oil and gas pipeline welds. It proposed a dynamic weld remaining life calculation method based on the non-penetrating crack propagation model, combined with the failure assessment diagram (FAD) criterion in BS 7910-2005 and the cumulative method. The document "Research on Failure Risk Prediction System of Girth Weld of Oil and Gas Pipeline Based on BP Neural Network" (Oil and Gas Field Surface Engineering, Vol. 41, No. 4, April 2022) aimed at the problem of accurate prediction of failure pressure of corroded pipelines. According to different corroded pipeline blasting test data, the factors that have a greater impact on pipeline failure pressure were analyzed and screened out, and a girth weld failure prediction BP model was constructed, which is suitable for the prediction of failure pressure of corroded pipelines. The document "Prediction of Failure of Girth Weld Defects in Long-distance Pipelines" (Master's thesis of Xi'an Shiyou University, Feng Xiaoxing, June 2022) combines the highly nonlinear mapping function of artificial neural networks to construct a neural network model for predicting girth weld failures and develops a pipeline girth weld defect failure prediction system. The document "Prediction of Residual Strength of Pipeline Weld Corrosion Based on IWOA PNN Model" (Journal of Safety and Environment, Vol. 23, No. 2, February 2023) aims at the problem of pipeline weld corrosion and constructs a residual strength prediction model based on the improved whale optimization algorithm. Chinese patent document CN 111860993 A discloses a method for predicting fatigue life of welded joints considering residual stress evolution. The base material is subjected to cyclic load fatigue test, and the weld of the welded joint is thermally simulated by sequential coupling method to determine the residual stress field of the welded state during welding, and establish a fatigue life prediction model for welded joints considering residual stress evolution.

[0007] In addition to conventional mechanical properties and safety assessment requirements, there is a special requirement for the girth welds of low-alloy steel gathering and transportation pipelines in sour gas fields - "girth weld anti-sulfur performance", including resistance to sulfide stress cracking (SSC) and resistance to hydrogen-induced cracking (HIC), which are the most critical 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 materials and girth welds) serving in sour gas fields react with hydrogen sulfide (corrosion-sensitive environment) to generate hydrogen, which penetrates into the pipe (including parent materials and girth welds) and migrates and accumulates to strong hydrogen traps (defects such as uneven chemical composition, coarse grains, and segregation of structures in the weld area, which are strong hydrogen trap aggregation areas) under the action of stress (including the pipeline operating pressure borne by the pipeline itself, and residual stress caused by pressure, pressure fluctuations, and external extrusion during the service of the pipeline). When the amount of hydrogen and stress reach the critical value, 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 stage of low-alloy steel gathering and transportation pipelines in sour gas fields, relevant standards have already clarified the technical index requirements from the coupling of three of the four factors required for sulfide stress cracking in welds: hydrogen sulfide corrosion sensitive environment, materials, and stress, ensuring that the sulfur resistance of new girth welds in low-alloy steel gathering and transportation pipelines in 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 High-Sulfur Hydrogen Gas Field Gathering and Transportation Pipelines" stipulate that: (1) The minimum loading stress for girth welds to resist SSC performance is 80% of the yield strength of the parent material (four-point bending method); (2) The HIC resistance of girth welds is the average crack length rate CLR ≤ 10%, the average crack thickness rate CTR ≤ 3%, the average crack sensitivity rate CSR ≤ 1%, and the maximum length of any crack is < 6 mm.

[0009] However, as the service time of pipelines transporting sour natural gas increases (that is, the fourth factor coupling required for sulfide stress cracking of welds: service time), due to hydrogen sulfide, the plasticity and toughness of the welds will decrease, and the anti-sulfur performance will decrease, increasing the risk of weld bursting in gathering and transportation pipelines. The study of the document "Study on Plasticity and Toughness of X52 Gas Pipeline Steel in Service" (Natural Gas Industry, Vol. 26, No. 3, March 2006) shows that as the service time of X52 (L360) gas pipelines transporting H2S increases, its elongation and J integral value will decrease, and the decrease in the weld part is greater than that of the parent material, and the tendency of brittle bursting in the weld part increases. The study of the document "Corrosion Detection and Safety Analysis of Natural Gas Pipelines Transporting Wet Gas" (Oil and Gas Storage and Transportation, Vol. 25, No. 11, November 2006) shows that as the service time of No. 20 steel gas pipelines transporting H2S increases, the weld part will show HIC tendency, and the tendency of brittle bursting in the weld part will increase.

[0010] There are some patent reports on the indoor research of weld anti-sulfur performance. The Chinese invention patent with the announcement number CN 102305761 B provides a set of acid medium pipeline weld and parent material corrosion simulation test equipment and methods for indoor experiments to simulate H2S, CO2 and Cl - The corrosion resistance, SSC, HIC, and welding process evaluation of the parent material and weld of highly acidic natural gas under pipeline transportation conditions. The Chinese invention patent application with publication number CN 104374689 A provides a test device and test judgment method for the suitability of pipes for transportation pipelines. The test pipe ring is cut from the characteristic position of the typical pipe body of the transportation pipeline, and several sections of the test pipe ring are sealed and connected in sequence to obtain a test pipe section, simulating the pipeline operation parameters and the actual service environment. Finally, the characteristic positions such as the pipe body and weld of the test pipe ring are sampled and analyzed in combination with the experimental design, and the suitability of the pipe for the transportation pipeline can be evaluated. The Chinese invention patent application with publication number CN 114754997 A provides a quantitative analysis device for the reliability of the pipeline life cycle based on big data, wherein the pipeline is placed in a simulation box, and prefabricated welds, predetermined defects, and data collection dot matrixes are set on the pipeline wall. A modular design is adopted, and components are replaced as needed to establish a pipeline reliability data information database, 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 sour 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 the girth weld of the low-alloy steel gathering and transportation pipeline in the sour gas field is limited to the new girth weld in the pipeline construction stage (evaluation of welding process), and the influencing factors of the relevant 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. The performance evaluation and risk assessment of in-service welds do not involve the hydrogen sulfide working environment.

[0015] The above situation makes it difficult to effectively evaluate and predict the service anti-sulfur performance of the 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 anti-sulfur performance of girth welds of a sour gas field gathering and transportation pipeline, so as to solve the problem that the effectiveness of the service anti-sulfur 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 anti-sulfur performance of the girth weld of a sour gas field gathering and transportation pipeline, so as to solve the problem that the prior art cannot effectively predict the service anti-sulfur 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 service anti-sulfur performance evaluation method of the girth weld of the gathering and transportation pipeline of the sour gas field 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 the girth weld according to formula (1):

[0022] A(t)=α(t)×β(t)×γ(t) (1)

[0023] In formula (1), t is the service time of the girth weld, A(t) is the sulfur resistance of the girth weld, 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 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 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 surface. The value is 1; D(t) is the average crack thickness rate of the girth weld specimen surface. When D(t)≤3%, The value is 1; E(t) is the average crack sensitivity rate of the girth weld specimen surface. 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 anti-sulfur performance of the girth weld is evaluated based on the calculation result of A(t). A(t) equals 1, indicating that the anti-sulfur performance has not decreased; A(t) greater than 1 indicates that the anti-sulfur performance has decreased. The larger the value, the greater the degree of decrease in the anti-sulfur performance.

[0036] 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 aims to solve the problems of decreased sulfur resistance performance and increased risk of sulfide stress cracking of the girth weld of a low-alloy gathering and transportation pipeline serving in a sour gas field. It couples four factors causing sulfide stress cracking (hydrogen sulfide corrosion sensitive environment, material, stress and service time) to effectively realize quantitative evaluation of the sulfur resistance performance.

[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 the risk assessment of pipeline girth welds and the implementation of safety assurance 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. The evaluation of hardness performance can be achieved by 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) takes the larger calculated value. This method can further improve the effectiveness of hardness evaluation.

[0040] Preferably, the girth weld specimen is a pipe section with girth welds in service on site or an equivalent specimen that can reflect the sulfur resistance of girth welds in service on site. The test form of a pipe section with girth welds in service on site is the most direct, but the sample selection and sampling time are limited to a certain extent: the pipe section can only be removed during inspection and maintenance for analysis and evaluation. The equivalent specimen method is more flexible in sample selection and sampling time.

[0041] Preferably, the equivalent specimen is obtained by keeping the same girth weld sample in a normal working condition, a low-water working condition, and a water-added working condition. The above setting can prepare girth weld specimens under different working conditions, thereby providing improvement suggestions for subsequent operating parameters and other aspects.

[0042] Further preferably, the equivalent specimen is obtained by processing the girth weld sample through the 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 condition environment of the normal service pipe section is the on-site service environment, the water reduction pipe section is connected in series with a separator for separating incoming water, and the water addition pipe section is connected in series with a water addition device. The equivalent specimen is made by the above anti-sulfur evaluation device, which has a high degree of consistency with the actual working conditions, and the authenticity and reliability of the test results are good.

[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 anti-sulfur performance of the girth weld of a gathering and transportation pipeline in a sour gas field comprises the following steps:

[0045] a) Select girth weld samples with different service time to test the SSC resistance and HIC resistance performance;

[0046] b) Quantitatively evaluate the SSC resistance of the girth weld samples 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 the fitting curve of 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 anti-SSC performance meets the requirements, the anti-HIC performance of the girth weld samples 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 anti-sulfur performance of the girth weld of a sour gas field gathering and transportation pipeline of the present invention can predict the change of the anti-sulfur performance of the girth weld with the service time, provide technical and data support for the risk assessment of the pipeline girth weld and the implementation of safety assurance measures, and ensure the safe operation of the low-alloy steel gathering and transportation pipeline of the sour gas field.

[0055] Preferably, the girth weld specimen is a pipe section with girth welds in service on site or an equivalent specimen that can reflect the sulfur resistance of girth welds in service on site. The test form of a pipe section with girth welds in service on site is the most direct, but the sample selection and sampling time are limited to a certain extent: the pipe section can only be removed during inspection and maintenance for analysis and evaluation. The equivalent specimen method is more flexible in sample selection and sampling time.

[0056] Preferably, the equivalent specimen is obtained by keeping the same girth weld sample in a normal working condition, a low-water working condition, and a water-added working condition. The above setting can prepare girth weld specimens under different working conditions, thereby providing improvement suggestions for subsequent operating parameters and other aspects.

[0057] Further preferably, the equivalent specimen is obtained by processing the girth weld sample through the 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 condition environment of the normal service pipe section is the on-site service environment, the water reduction pipe section is connected in series with a separator for separating incoming water, and the water addition pipe section is connected in series with a water addition device. The equivalent specimen is made by the above anti-sulfur evaluation device, which has a high degree of consistency with the actual working conditions, and the authenticity and reliability of the test results are good. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0059] Figure 2 It is a schematic diagram of the distribution of various affected areas on the girth weld;

[0060] Figure 3 is a relationship curve for predicting 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 anti-sulfur 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 of welds: hydrogen sulfide corrosion-sensitive environment, material, stress and service time. This method is more consistent with the actual service 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 anti-sulfur performance of girth welds, and proposes the accuracy and reliability of the quantitative evaluation and prediction results.

[0063] The service anti-sulfur performance evaluation and prediction method of the girth weld of the sour gas field gathering and transportation pipeline of the present invention is based on the anti-SSC performance, anti-HIC performance and hardness test results of the girth weld sample to be evaluated, and quantitative evaluation is performed through the girth weld anti-sulfur performance coupling quantitative evaluation formula. When it is necessary to predict the change of the anti-sulfur performance of the girth weld with the service time, the service time and the anti-SSC performance quantitative evaluation parameters or anti-HIC performance quantitative evaluation parameters established by the present invention are fitted, and the change of the anti-SSC performance and anti-HIC performance can be predicted, thereby providing technical and data support for on-site inspection and maintenance (replacing pipe sections or reinforcing pipe sections, etc.) and optimization of operation parameters (pressure reduction operation, etc.).

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

[0065] 1. Basic parameter collection and analysis

[0066] Including 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 pipes (including steel model, components, mechanical properties, etc.), gathering and transportation pipeline girth weld parameters (including welding process, welding joint performance, etc.), etc.

[0067] 2. Obtaining samples of anti-sulfur performance of girth welds

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

[0069] (1) Method 1: Service Sample

[0070] Remove the girth welded pipe section from the low alloy steel gathering and transportation pipeline serving in the sour gas field, and analyze and evaluate its anti-sulfur performance after service. This method is the most direct, but the sample selection and sampling time are limited to a certain extent: the pipe section can only be removed during inspection and maintenance work to analyze and evaluate.

[0071] (2) Method 2: Equivalent test sample

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

[0073] Specifically, Figure 1 As shown, in the gas gathering station of the sour gas field, a pipe section group connected in series with the gathering and transportation pipeline is set (connected by insulating flanges, with valves in front and behind the pipe section), and each group of pipe sections is divided into several sub-pipe sections connected by insulating flanges (the sub-pipe sections of each group are connected in series, and the sub-pipe sections are connected by insulating flanges, which is conducive to the disassembly of the sub-pipe sections and the placement and installation of the samples), ensuring that the working environment in the pipe section is 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 is installed at the front end of the pipe section to separate the incoming water, so that the free water content in the pipe section can be adjusted, simulating a pipe section with less water or no liquid accumulation. The purpose is 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 is 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. The purpose is to evaluate the anti-sulfur performance 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. Specimens for evaluation of sulfur resistance of girth welds

[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 by an insulating bracket (not in contact with the pipe section) and is divided into the following types:

[0080] ① It is 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 is used to evaluate the anti-sulfur performance 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 specimen for evaluating the sulfur resistance of the girth weld

[0084] ① It is divided into two categories: specimens without stress loading and specimens with stress loading. Specimens with anti-SSC performance and anti-HIC performance generally need to be stressed, so that the anti-SSC performance and anti-HIC performance after being subjected to stress can be reflected.

[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% of the minimum specified yield strength of the parent material to 40% of the minimum specified yield strength.

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

[0087] The tests of SSC resistance and HIC resistance are carried out 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 Pipeline":

[0088] (1) SSC resistance: 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. 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 cracking or cracking 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 Pipeline and Pressure Vessel Steels", the A solution 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℃, and after the test, the average crack length rate CLR of the girth weld specimen surface 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 <6mm.

[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-Sulfide Hydrogen Gas Fields", HV≤248 is required.

[0093] 5. Quantitative evaluation of the anti-sulfur performance of girth welds

[0094] Based on the coupling principle of multi-factor risk assessment, a coupling quantitative calculation formula for evaluating the sulfur resistance of girth welds is 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 parameters of the girth weld for a certain service time

[0099]

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

[0101] Among them, the minimum specified yield strength of the parent material is a basic parameter of the pipe, which represents the yield strength that the pipe must reach. For example, the minimum specified yield strength of the L360 pipe is 360MPa. The highest percentage of the minimum specified yield strength of the parent material is equivalent to the percentage obtained by dividing the "maximum value of the loading stress without cracks and cracks on the surface of the girth weld specimen" by the "minimum specified yield strength of the parent material", specifically the highest value of the loading stress without cracks and cracks on the surface of the girth weld specimen.

[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 other factors are 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 with 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 resistance 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 resistance test for a certain service time. When D(t)≤3%, The value is 1;

[0108] E(t) is the average value CSR of the surface crack sensitivity rate 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 the HIC resistance test for a certain service time. 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] Where HB(t) is the Brinell hardness test for a certain service time. When HB(t)≤200, γ(t) takes the value of 1.

[0113] Vickers Hardness Test Calculation:

[0114] Among them, HV(t) is the Vickers hardness test of a certain service time. When HV(t)≤248, γ(t) takes the value of 1;

[0115] Depending on the hardness test method, either Brinell hardness or Vickers hardness can be used. If both HB(t) and HV(t) are available, the higher value shall be adopted.

[0116] 6. Evaluation steps for sulfur resistance of girth welds

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

[0118] Step 1: Place the girth weld specimens to be evaluated into three groups of pipe sections, including those without loading stress and those with loading stress.

[0119] Step 2: According to a certain service cycle, some girth weld specimens (including those without loading stress and those with loading stress) are taken out, and the remaining specimens continue to serve in the pipe section. At the same time, the vacant positions can also be used to place specimens that need to be evaluated again.

[0120] Step 3: Process into SSC specimens and HIC specimens according to the requirements of SSC specimens and HIC specimens.

[0121] Step 4: Evaluate the SSC and HIC resistance of the girth weld specimens 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".

[0122] Step 5: According to the requirements of the standards "SY / T 0059 Technical Specification for Controlling the Hardness of Steel Equipment Welds to Prevent Sulfide Stress Cracking", "GB / T 27866 Technical Specification for Controlling the Hardness of Steel Pipelines and Equipment Welds to Prevent Sulfide Stress Cracking" and "SY / T0612 Design Specification for Surface Gathering and Transportation Systems of High Hydrogen Sulfide Gas Fields", perform the Brinell hardness HB test; according to the requirements of the standards "GB / T27866 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 for Resistance 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 Engineering" and "SY / T 4117 Technical Specification for Welding of Gathering and Transportation Pipelines of High-Sulfide Gas Fields", perform the Vickers hardness HV test.

[0123] Step 6: Carry out coupled quantitative evaluation calculation and analysis of the sulfur resistance performance of the girth weld.

[0124] When analyzing and evaluating the anti-sulfur performance of a low-alloy steel gathering and transportation pipeline that has been in service for a long time in a sour gas field by removing a girth weld pipe section, the process is as follows: step 3, step 4, step 5, and step 6.

[0125] 7. Prediction of sulfur resistance of girth welds

[0126] The prediction of sulfur resistance of girth welds mainly includes two aspects: SSC performance and HIC resistance. Among them, SSC resistance is the first evaluation factor of veto, and at the same time, it is also the first prediction factor of veto.

[0127] The following are the methods for obtaining samples:

[0128] (1) According to the method 1 of “obtaining the sulfur resistance test sample of the girth weld”:

[0129] ① Sampling and calculation

[0130] Step 1: Take samples according to different service times t1, t2, t3, ... (according to on-site maintenance, pipe replacement and other operations, the corresponding service times t1, t2, t3, ... are analyzed), remove the pipe section containing girth welds from the low-alloy steel gathering and transportation pipeline serving in the sour gas field, and then perform anti-SSC performance and anti-HIC performance tests as required.

[0131] Step 2: Quantitatively calculate the anti-SSC performance parameters of the girth weld for a certain service time t1, t2, t3, ... according to formula (2).

[0132]

[0133] B(t1), B(t2), B(t3), ... are the percentages of the ratio of the maximum loading stress without cracking or cracking on the surface of the girth weld specimen to the minimum specified yield strength of the parent material after the anti-SSC performance test for a certain service time t1, t2, t3, ..., and the actual values ​​of α(t1), α(t2), α(t3), ... are calculated.

[0134] Step 3: According to formula (3), the anti-HIC performance parameters of the girth weld at a certain service time t1, t2, t3, ... are quantitatively calculated.

[0135]

[0136] in,

[0137] C(t1), C(t2), C(t3), ... are the actual values ​​of the average CLR of the surface crack length rate of the girth weld specimen after the HIC resistance test for a certain service time 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 specimen after the HIC resistance test for a certain service time 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 for a certain service time 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 data of the sulfur resistance of the girth weld are fitted by using the curve fitting method to obtain the fitting relationship curve and relationship function:

[0143] Based on the relationship curve and relationship function of "anti-SSC performance of girth welds"-"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 of "anti-HIC performance of girth welds"-"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 the sulfur resistance performance sample of the girth weld”:

[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, a certain welding process, and a certain loading stress is placed in the corresponding evaluation environment.

[0152] According to certain service time t1, t2, t3, ..., the test pieces are taken out for analysis and evaluation of 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 anti-sulfur performance experimental test (including anti-SSC performance and anti-HIC performance test) after service.

[0154] Step 2 and step 3 are carried out according to step 2 and step 3 of "sampling and calculation" in method 1 of "obtaining sulfur resistance test specimens of girth welds".

[0155] ②Data fitting analysis and prediction

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

[0157] Based on the relationship curve and relationship function of "anti-SSC performance of girth welds"-"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 of "anti-HIC performance of girth welds"-"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 gathering and transportation pipeline in China uses L360 low-alloy gathering and transportation seamless pipes, connected by girth welds, and integrates the five elements of "sulfur-resistant pipes + corrosion inhibitors + corrosion monitoring + cathodic protection + intelligent cleaning" in the high-sulfur wet gas gathering and transportation system anti-corrosion technology. The average corrosion rate is kept below 0.076mm / a. The gas field has an on-site laboratory with the test capability to simulate the service conditions of the pipeline.

[0161] 1. Specific embodiments 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 in-service sulfur resistance performance evaluation method of the girth weld of the 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 (in-service sample):

[0164] During the inspection and maintenance, a pipe section with girth weld that had been in service for 13 years (with a strength design factor of 0.6) 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 weld of L360 low alloy steel gathering and transportation pipeline in high sulfur gas field 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 below 248, the γ value is 1.

[0170] According to formula (1), the anti-sulfur performance of girth welds in service for 13 years was quantitatively evaluated:

[0171]

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

[0173] Example 2

[0174] The in-service sulfur resistance performance evaluation method of the girth weld of the 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 specimen for evaluating the sulfur resistance of the girth weld

[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 parent material (L360 low alloy steel).

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

[0180] According to the cycle of taking samples once a year, they are processed into SSC samples and HIC samples according to the requirements of SSC samples and HIC samples; 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 High-Sulfur Hydrogen Gas Field Gathering Pipeline", the anti-SSC performance, anti-HIC performance and hardness of the girth weld samples are evaluated, and the test results are shown in Table 2.

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

[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 below 248, the γ value is 1.

[0186] According to formula (1), the anti-sulfur performance 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 sulfur resistance of the girth weld does not decrease within 5 years of service when the loading stress is 60% of the minimum specified yield strength of the base material (L360 low alloy steel).

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

[0190] Example 3

[0191] The method for predicting the service anti-sulfur performance of the girth weld of the sour gas field gathering and transportation pipeline in this embodiment further performs the prediction of the anti-SSC performance and the anti-HIC performance on the basis of the test data of Example 2, and the specific description is 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 The specific data are shown in Table 3 below.

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

[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 cracking or cracking on the surface of the girth weld specimen and is the highest percentage of the minimum specified yield strength of the parent material, unit: %.

[0200] Substituting 13 years of service time into formula (7), the maximum percentage of the loading stress without cracks and cracks on the surface of the girth weld specimen is 71% of the minimum specified yield strength of the parent material, which is comparable to the 70% measured by 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 the girth weld and the service time was predicted by calculation. From the 10th year, the SSC resistance of the girth weld has declined. The reason for choosing SSC resistance as the first prediction factor is:

[0202] (1) From the mechanism analysis: SSC is the most dangerous because of sudden cracking.

[0203] (2) Analysis from the 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 and obtain 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 weld of L360 low alloy steel gathering and transportation pipeline in long-term service in high sulfur gas field

[0213]

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

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

[0216] Substituting 13 years of service time into formula (8), the HIC resistance performance parameter of the girth weld is 0.000097, which is comparable to the 0.000091 measured by actual sampling in Table 1, indicating that the prediction of HIC resistance performance is relatively accurate.

[0217] The relationship between the HIC resistance of the girth weld and the service time was predicted by calculation. Within 20 years, the quantitative calculated value of the HIC resistance parameter of the girth weld was less than 1, and the HIC resistance of the girth weld did not decrease.

Claims

1. A method for evaluating 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: 1) Conduct SSC resistance, HIC resistance and hardness tests on the girth weld specimen to be evaluated; 2) Quantify the sulfur resistance of the girth weld according to formula (1): A(t)=α(t)×β(t)×γ(t) (1) In formula (1), t is the service time of the girth weld, A(t) is the sulfur resistance of the girth weld, 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 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 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 surface. When C(t)≤10%, The value is 1; D(t) is the average crack thickness rate of the girth weld specimen surface. When D(t)≤3%, The value is 1; E(t) is the average crack sensitivity rate of the girth weld specimen surface. 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) equals 1, indicating 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 service sulfur resistance performance of the girth weld of a sour gas field gathering and transportation pipeline according to claim 1, characterized in that: 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 service sulfur resistance performance of the girth weld of a sour gas field gathering and transportation pipeline according to claim 2, characterized in that: 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 service sulfur resistance performance of the girth weld of a sour gas field gathering and transportation pipeline 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 anti-sulfur performance of the girth weld of a sour gas field gathering and transportation pipeline according to claim 4, characterized in that: The equivalent test 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 service sulfur resistance performance of the girth weld of a sour gas field gathering and transportation pipeline 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 condition 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) Select girth weld samples with different service time to test the SSC resistance and HIC resistance performance; b) Quantitatively evaluate the SSC resistance of the girth weld samples 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 the fitting curve of 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 anti-SSC performance meets the requirements, the anti-HIC performance of the girth weld samples 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 the 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 anti-sulfur performance of the girth weld of the gathering and transportation pipeline of a sour gas field according to claim 8, characterized in that: The equivalent test 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 the gathering and transportation pipeline of a sour gas field 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 condition 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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