A protection method for suppressing the influence of in-ground current on natural gas pipelines

Abstract

The present invention relates to the field of natural gas pipeline protection, and discloses a protection method for suppressing the influence of in-ground current on natural gas pipelines, comprising the following steps: formulating an optimization order for various protection measures according to their protection effects and scope of action, where the optimization order is that cathodic protection is Class A with the highest priority, insulating joints are Class B with the second highest priority, and connecting grounding devices are Class C with the lowest priority; setting the parameters of the entire pipeline; calculating the results without protection measures, and if the requirements are met, outputting the results, and if not, adding measures; and determining whether to continue optimization. Selecting the optimization order according to the priority, conventional single direct current interference suppression measures such as pipeline segment insulation method and cathodic current protection method, etc., are difficult to reduce the potential at the pipeline valve chamber to within the safety limit; while the comprehensive pipeline protection measures of the present invention can effectively reduce the pipe-to-soil potential difference at the valve chamber, and can ensure the safety of pipeline equipment and operating personnel.

Description

Technical Field

[0001] The present invention relates to the field of natural gas pipeline protection, and specifically to a protection method for suppressing the influence of in-ground current on natural gas pipelines. Background Art

[0002] The DC transmission system will affect pipelines through the in-ground current of the grounding electrode, and will also affect pipeline safety through electromagnetic coupling, short circuits, lightning strikes and other transient in-ground currents in space. When metal pipelines are buried in the nearby soil, the in-ground current of the DC grounding electrode will generate an induced potential on the pipeline, causing a potential difference between the pipeline and the near-surface soil, resulting in an excessive pipeline-to-soil potential difference. The excessive pipeline-to-soil potential difference will pose a hazard to pipeline equipment and operating personnel at the gas distribution station or valve chamber on the pipeline. Currently, the measures to suppress the influence of in-ground current on natural gas pipelines mainly include: insulating joints, local grounding devices, sacrificial anodes, and cathodic protection. Each protection measure has its own advantages, disadvantages and protection effects. For some pipelines that intersect each other and are close to the grounding electrode, using a single protection measure cannot well solve the problem of high pipeline-to-soil potential. Generally, comprehensive protection measures need to be adopted to limit the pipeline-to-soil potential. Currently, when designing protection measures, usually a certain measure is taken for simulation first. If the calculation result is overprotection or underprotection, the application intensity of the protection measure is modified and the simulation is continued repeatedly until a satisfactory effect is achieved. Although this method can finally complete the design, it is time-consuming and laborious. In short, the current design process of the protection measures applied to prevent interference of buried metal pipelines lacks scientific and standardized optimization processes.

[0003] Combined with Figure 1 , refer to the following existing solutions, the content is as follows:

[0004] The metal pipe body inside the pipeline can effectively bear pressure, and the external insulation layer can effectively protect the metal pipe body, preventing or slowing down its natural corrosion rate, thus constructing a safe and stable gas transmission system. However, when the DC grounding electrode is close to the natural gas pipeline, the in-ground current of the DC grounding electrode will cause great harm to the natural gas pipeline.

[0005] The in-ground current of the DC grounding electrode has two main effects on natural gas pipelines:

[0006] (1) Pipeline-to-soil potential difference

[0007] The in - ground short - circuit current will cause the soil potential to rise, resulting in a large potential gradient in the soil near the grounding electrode and affecting the voltage of the metal pipeline to the ground through resistive coupling. A relatively high pipeline - to - ground potential difference will interfere with the normal operation of the equipment on the pipeline and even cause damage to the equipment on the pipeline. At this time, if an operator happens to touch the metal part of the pipeline, under the influence of resistive coupling, the touch voltage suffered by the operator may be very high, and in severe cases, it may endanger personal safety.

[0008] A long - distance equipotential natural gas pipeline in soil with large potential changes will inevitably be affected by the soil potential change, resulting in an excessive pipeline - to - ground potential difference of the pipeline and posing certain risks to the operation of the natural gas pipeline:

[0009] 1) Risk of insulation bushing breakdown. The influence of the in - ground current will generate a large potential difference at both ends of the insulation bushing on the pressure - guiding pipeline of the gas - liquid linkage ball valve (at both ends of the insulation bushing, one end is the pipeline potential and the other end is the ground potential), causing spark discharge, which poses a great threat to the safety of the natural gas pipeline and may lead to fire or explosion accidents.

[0010] 2) Risk of personal safety. Maintenance personnel of natural gas pipelines are at risk. It is easy to cause electric shock accidents without wearing insulating gloves (shoes).

[0011] 3) Risk of pipeline equipment safety. It will damage the original impressed current cathodic protection system or other pipeline protection equipment of the natural gas pipeline.

[0012] (2) Pipeline leakage current

[0013] When there are metal components near the grounding electrode, due to the current - collecting effect of the metal, the in - ground current will become a stray interference source for buried metals. When the buried pipeline is affected by the stray current electric field, the pipeline potential will shift positively or negatively at the places where the current leaves or enters the metal surface. When the stray DC current leaves the pipeline, an anodic corrosion reaction will occur at the metal / electrolyte interface, resulting in metal oxidation (dissolution); when the stray DC current enters the pipeline, the cathodic part of the corrosion reaction occurs at the metal / electrolyte interface. The cathodic reaction causes cathodic polarization (negative potential shift) on the metal surface of the pipeline. Excessive cathodic current density (such as > 0.1 A / m2) or lack of oxygen will cause the decomposition of water, leading to the formation of hydrogen and the generation of hydroxide ions. The generation of hydroxide ions will increase the pH value on the pipeline surface, cause cathodic disbonding, and reduce the adhesion between the organic anti - corrosion coating and the metal surface at the damaged part of the anti - corrosion coating. Before the formation of hydrogen, atomic hydrogen is formed. If atomic hydrogen dissolves into the steel, in a certain environment, it will cause hydrogen embrittlement of high - strength steel.

[0014] The influence of the DC grounding electrode's in-ground current on natural gas pipelines has the following characteristics: the time is uncertain (occurring during faults or maintenance), the action time is short (several hours), the in-ground current amplitude is large (thousands of amperes), the positive and negative polarities are uncertain, resulting in a drastic shift in pipeline potential, etc. At present, some units in the domestic power and petroleum industries have realized the severity of the influence of the DC grounding electrode's in-ground current on buried metal pipelines. However, it is difficult to reduce the potential at the pipeline valve chamber to within the safety limit by taking measures such as the pipeline section insulation method and the cathode current protection method according to conventional DC interference; for the pipeline drainage protection method, such as the pipeline grounding and draining through a strip-shaped zinc alloy anode, the pipe-to-soil potential difference at the grounding point can be reduced to within the safety limit. However, the long-term grounding and draining method will cause long-term stray currents to flow into and out of the pipeline, resulting in an exacerbation of pipeline electrochemical corrosion.

[0015] Therefore, we propose a protection method to suppress the influence of in-ground current on natural gas pipelines. Summary of the Invention

[0016] (I) Technical Problems to be Solved

[0017] In view of the deficiencies of the prior art, the present invention provides a protection method to suppress the influence of in-ground current on natural gas pipelines, solving the above problems.

[0018] (II) Technical Solutions

[0019] To achieve the above object, the present invention provides the following technical solutions: A protection method to suppress the influence of in-ground current on natural gas pipelines, including the following steps:

[0020] The first step: Draw up an optimization order for various protection measures according to their protection effects and scopes of action. The optimization order is that the cathodic protection is Class A with the highest priority, the insulating joint is Class B with the second highest priority, and the connecting grounding device is Class C with the lowest priority;

[0021] The second step: Set the parameters of the whole pipeline;

[0022] The third step: Calculate the result without protection measures. If the requirements are met, output the result; if not, add measures;

[0023] The fourth step: Judge whether further optimization is needed;

[0024] The fifth step: Select the optimization order according to the priority.

[0025] Preferably, the selection of the optimization order in the seventh step includes the following content:

[0026] Measures with lower priorities are all based on the optimized results of the previous higher-priority optimization;

[0027] If the result obtained by optimization meets the requirements, the calculation of low-priority measures will no longer be carried out;

[0028] If the obtained result does not meet the requirements, continue with the next-level optimization based on the previous-level optimization;

[0029] For measures at the same priority level, that is, sacrificial anode protection and forced cathode drainage protection in cathodic protection, both cathodic protection measures are usually not used simultaneously in engineering. Therefore, one of the measures is selectively used according to the characteristics of the two measures and the on-site conditions.

[0030] Preferably, the parameters in the second step are the maximum allowable pipe-to-soil potential of the pipeline or the pipe-to-soil potential allowed at the target location, grounding electrode parameters, soil parameters, and pipeline parameters.

[0031] Preferably, the judgment on whether to continue optimization in the fourth step includes the following:

[0032] If cathodic protection is allowed, use the number of cathodic protection devices up to the maximum value. If the pipe-to-soil potential value is less than the target value after use, gradually reduce the number of cathodic protection devices used until the pipe-to-soil potential value just meets the requirements, output the details and cost of the measures used, and the calculation ends. If the pipe-to-soil potential value is greater than the target value, ask whether other measures are needed. If so, continue with the optimization.

[0033] If insulated joints are allowed, use the number of insulated joints up to the maximum value. If the pipe-to-soil potential value is less than the target value after use, gradually reduce the number of insulated joints used until the pipe-to-soil potential value just meets the requirements, output the details and cost of the measures used, and the calculation ends. If the pipe-to-soil potential value is greater than the target value, select whether other measures are needed. If so, continue with the optimization;

[0034] If local grounding devices are allowed, use the number of grounding devices up to the maximum value. If the pipe-to-soil potential value is less than the target value after use, gradually reduce the number of grounding devices used until the pipe-to-soil potential value just meets the requirements. If the pipe-to-soil potential value is greater than the target value, select whether other measures are needed. If so, continue with the optimization.

[0035] (III) Beneficial effects

[0036] Compared with the prior art, the present invention provides a protection method for suppressing the influence of in-ground current on natural gas pipelines, having the following beneficial effects:

[0037] 1. Conventional single DC interference suppression measures, such as pipeline sectional insulation method and cathodic current protection method, etc., are difficult to reduce the potential at the pipeline valve chamber to within the safety limit; while this comprehensive pipeline protection measure can effectively reduce the pipe-to-soil potential difference at the valve chamber, ensuring the safety of pipeline equipment and operating personnel.

[0038] 2. Other methods do not consider the coupling effects of various protection measures. In fact, while a certain protection measure improves the indicators of a certain section of the pipeline, it may deteriorate the indicators of another section of the pipeline.

[0039] 3. This measure is easy to implement and basically does not change the normal operating conditions of the pipeline. It only needs to be constructed around the pipeline, which is easy to be accepted by the natural gas pipeline company.

[0040] 4. In actual engineering, the types and quantities of pipeline protection measures for the influence of grounding electrode current mainly rely on engineering experience and repeated calculations to determine. This method is not only time-consuming and laborious, but also has great uncertainty. The optimization process proposed in this paper can facilitate and quickly design protection measures, taking into account both calculation efficiency and accuracy, simplifying the repeated and unproductive calculation process, and making the use of pipeline protection measures more economical and effective. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 FIG. is a schematic diagram of the influence of DC grounding electrode current on buried metal pipelines;

[0042] Figure 2 FIG. is a schematic diagram of the optimization process of a single measure;

[0043] Figure 3 FIG. is a schematic diagram of the overall optimization calculation process. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0044] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0045] Please refer to Figure 2-3 , a protection method for suppressing the influence of grounding current on natural gas pipelines, including the following content:

[0046] First, an optimization order is drawn up for various protection measures according to their protection effects and scopes of action: cathodic protection is Class A with the highest priority; insulating joints are Class B with the second highest priority; connecting grounding devices are Class C with the lowest priority.

[0047] Measures with lower priorities are all based on the optimized results of the previous higher-priority optimization; if the results obtained from the optimization meet the requirements, the calculation of lower-priority measures will not be carried out; if the results do not meet the requirements, the next-level optimization will continue based on the previous-level optimization; for measures at the same priority level, that is, sacrificial anode protection and forced cathode drainage protection in cathodic protection, usually both cathodic protection measures will not be used simultaneously in engineering, so one of the measures will be selectively used according to the characteristics of the two measures and the on-site conditions.

[0048] The intelligent optimization algorithms mentioned above can adopt but are not limited to genetic algorithms, simulated annealing algorithms, ant colony algorithms, neural network algorithms, tabu search algorithms, etc.

[0049] The specific steps of the design are as follows:

[0050] (1) Set the maximum allowable pipe-to-soil potential for the entire pipeline or the pipe-to-soil potential allowed at the target location, grounding electrode parameters, soil parameters, and pipeline parameters.

[0051] (2) Calculate the results without protective measures. If the requirements are met, output the results; if not, add measures.

[0052] (3) If cathodic protection is allowed to be used, use the number of cathodic protection devices up to the maximum value. If the pipe-to-soil potential value is less than the target value after use, gradually reduce the number of cathodic protection devices used until the pipe-to-soil potential value just meets the requirements, output the details and cost of the measures used, and the calculation ends. If the pipe-to-soil potential value is greater than the target value, ask whether other measures need to be used. If so, continue the optimization.

[0053] (4) If insulating joints are allowed to be used, use the number of insulating joints up to the maximum value. If the pipe-to-soil potential value is less than the target value after use, gradually reduce the number of insulating joints used until the pipe-to-soil potential value just meets the requirements, output the details and cost of the measures used, and the calculation ends. If the pipe-to-soil potential value is greater than the target value, choose whether other measures need to be used. If so, continue the optimization.

[0054] (5) If local grounding devices are allowed to be used, use the number of grounding devices up to the maximum value. If the pipe-to-soil potential value is less than the target value after use, gradually reduce the number of grounding devices used until the pipe-to-soil potential value just meets the requirements. If the pipe-to-soil potential value is greater than the target value, choose whether other measures need to be used. If so, continue the optimization.

[0055] Taking the insulating joint as an example, the flow chart of single-measure optimization is as Figure 2 shown, and the overall optimization calculation process is as Figure 3As shown above. The optimization process proposed above can facilitate and quickly design protection measures, taking into account both computational efficiency and accuracy, simplifying the repeated and unproductive calculation process, and making the use of pipeline protection measures more economical and effective.

[0056] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A protection method for suppressing the influence of in-ground current on natural gas pipelines, characterized in that, It includes the following steps: Step 1: Draw up an optimization order for various protective measures according to their protection effects and scope of action. The optimization order is that the cathodic protection is Class A with the highest priority, the insulating joint is Class B with the second highest priority, and the connecting grounding device is Class C with the lowest priority; Step 2: Set the parameters of the whole pipeline; Step 3: Calculate the result without protective measures. If the requirements are met, output the result. If not, add measures; Step 4: Judge whether further optimization is needed; If cathodic protection is allowed to be used, use the number of cathodic protection devices up to the maximum value. If the pipe-to-soil potential value is less than the target value after use, gradually reduce the number of cathodic protection devices used until the pipe-to-soil potential value just meets the requirements, output the details and cost of the measures used, and the calculation ends. If the pipe-to-soil potential value is greater than the target value, ask whether other measures need to be used. If so, continue the optimization; If insulating joints are allowed to be used, use the number of insulating joints up to the maximum value. If the pipe-to-soil potential value is less than the target value after use, gradually reduce the number of insulating joints used until the pipe-to-soil potential value just meets the requirements, output the details and cost of the measures used, and the calculation ends. If the pipe-to-soil potential value is greater than the target value, choose whether other measures need to be used. If so, continue the optimization; If local grounding devices are allowed to be used, use the number of grounding devices up to the maximum value. If the pipe-to-soil potential value is less than the target value after use, gradually reduce the number of grounding devices used until the pipe-to-soil potential value just meets the requirements. If the pipe-to-soil potential value is greater than the target value, choose whether other measures need to be used. If so, continue the optimization; Step 5: Select the optimization order according to the priority; 2. The protection method for suppressing the influence of in-ground current on a natural gas pipeline according to claim 1, characterized in that: The selection of the optimization order in the fifth step includes the following: Measures with lower priorities are all based on the optimized results of the previous higher-priority ones; If the optimized result meets the requirements, no further calculation of measures with lower priorities is carried out; If the obtained result does not meet the requirements, continue the next-level optimization on the basis of the previous-level optimization; For measures at the same priority level, that is, sacrificial anode protection and forced cathodic drainage protection in cathodic protection, usually both cathodic protection measures are not used simultaneously in engineering, so one of the measures is selectively used according to the characteristics of the two measures and the on-site conditions.

3. A protection method for suppressing the influence of in-ground current on a natural gas pipeline according to claim 1, characterized in that: The parameters in the second step are the maximum allowable pipe-to-soil potential of the pipeline or the allowable pipe-to-soil potential at the target location, grounding electrode parameters, soil parameters, and pipeline parameters.

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