Anodic polarization method for inhibiting microbial corrosion of marine oil and gas pipelines

Abstract

The present invention belongs to the field of microbial corrosion protection of metal materials, and in particular provides an anodic polarization method and a special stainless steel material for inhibiting microbial corrosion of marine oil and gas transmission pipelines, adopting an anodic constant potential anodic polarization treatment method, the anodic constant potential selection interval range is: above the middle value of the passivation interval potential range to 0.05V below the pitting potential, and the anodic polarization action time is the actual time required for protection. The present invention forms a positively charged area on the surface of stainless steel, which firmly adsorbs negatively charged bacteria on the surface of the metal material, inhibits the activity of microorganisms adsorbed on the surface, and forms an EPS-Fe film layer for survival, thereby protecting the material. At the same time, the present invention also provides a special stainless steel material, which combines the applied anodic electrical signal with the common advantages of the special stainless steel material, and proposes an effective solution to the problem of inhibiting microbial corrosion of marine oil and gas transmission pipelines.

Description

Technical Field

[0001] The present invention belongs to the field of microbial corrosion protection of metal materials, and specifically is an anodic polarization method for inhibiting microbial corrosion of marine oil and gas stainless steel transmission pipelines. At the same time, a special stainless steel material is provided as a replacement material for the original service pipeline. Background Art

[0002] The phenomenon that the life activities of microorganisms in the ocean and their metabolites directly or indirectly accelerate the corrosion process of metal materials is called microbiologically influenced corrosion (MIC). According to statistics, the corrosion failure and damage of materials related to microorganisms have reached 70%-80% of the total amount of marine materials. Metal materials serving in the marine environment include carbon steel, stainless steel, copper alloy, aluminum alloy and titanium alloy. Microorganisms are everywhere and there are many kinds. The above metal materials are not completely immune to the damage of corrosive microorganisms in the environment. Microorganisms will attach to the surface of the material and then form a biofilm. The microorganisms with different functions in the film affect the corrosion process of the material through metabolic activities. Therefore, the primary purpose of the existing microbial corrosion prevention and control methods is to inhibit the formation of biofilm, including the use of anti-corrosion coatings, bactericides and cathodic polarization, but the above methods have gradually exposed the disadvantages of environmental pollution, increasing costs, enhanced microbial resistance and hydrogen embrittlement fracture of materials.

[0003] The global industry loses billions of dollars every year due to corrosion of pipelines that transport oil and natural gas in the ocean, and has caused large-scale environmental pollution, mining shutdown losses and casualties. The corrosion that occurs in the pipeline includes under-deposit corrosion, microbial corrosion, CO2 / H2S corrosion, scouring corrosion and acid corrosion. Among them, corrosion caused by microorganisms accounts for 40% of related corrosion failures. Corrosive microorganisms can quickly form biofilms in the pipe wall, especially in nutrient-rich seawater, raw water or sewage, so traditional methods of inhibiting microbial corrosion are limited. In addition, in the process of oil and gas production, for the corrosive medium conditions of natural oil and gas fields with high H2S and CO2 content, traditional carbon steel oil well pipes can no longer meet the requirements of oil and gas field production environment. Therefore, high-alloyed martensitic stainless steel and duplex stainless steel are gradually used as alternative products. Although these stainless steel materials avoid the erosion of traditional corrosive media during application, the corrosion caused by microorganisms has become an imminent problem that needs to be solved.

[0004] Therefore, the failure of traditional microbial corrosion prevention and control methods has prompted the development of new materials or methods to inhibit microbial corrosion. Researchers have found that cathodic polarization can form a negatively charged area on the surface of the material. Since most bacteria are electronegative, the bacteria in the area will be repelled by electrostatic repulsion and fall off. However, when cathodic polarization is used to inhibit microbial corrosion, the potential used is too low, which will cause hydrogen embrittlement of the material. It solves the microbial corrosion but causes material damage. Summary of the invention

[0005] To solve the above problems, the present invention has developed an anodic polarization method for inhibiting microbial corrosion of marine oil and gas pipelines. By forming a positively charged area on the surface of stainless steel, negatively charged bacteria are firmly adsorbed on the surface of the metal material, inhibiting the activity of microorganisms adsorbed on the surface or causing their death. At the same time, the present invention also provides a special stainless steel material. The two cooperate with each other to combine the applied anodic electrical signal with the common advantages of the special stainless steel material, and propose an effective solution to inhibit the problem of microbial corrosion of marine oil and gas pipelines. This method can be used in marine oil and gas pipelines to reduce local pitting damage caused by microbial corrosion, extend the service life of the pipeline, and reduce maintenance costs.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] An anodic polarization method for inhibiting microbial corrosion of marine oil and gas transmission pipelines is characterized in that an anodic constant potential anodic polarization treatment method is adopted, and the anodic constant potential selection interval range is: above the middle value of the passivation interval potential range to 0.05V below the pitting potential (further preferably: above the middle value of the passivation interval potential range to 0.1V below the pitting potential), and the anodic polarization action time is the actual protection time required.

[0008] During the application process, in order to further improve the ability to inhibit microbial corrosion, special stainless steel can be selected as a substitute for traditional service stainless steel. The special stainless steel is a new stainless steel formed by adding Cu element to the composition of traditional service stainless steel and increasing the content of Ni element at the same time. According to the weight percentage, the added amount of Cu is 1.0-5.0%, and the increased amount of Ni is 0.5%-2.5%, and the increased amount is the content increased based on the upper limit of the original Ni content.

[0009] As a preferred technical solution: the added amount of Cu is 2.0-4.0%, and the added amount of Ni is 1.0%-2.0%.

[0010] In the present invention, the anodic polarization method is the most important part in inhibiting microbial corrosion of marine oil and gas pipelines, as follows:

[0011] First, the potential selection basis for anodic polarization is based on the passivation range of stainless steel materials in the corresponding service environment. The potential selection should be within the passivation range of critical passivation potential and pitting potential in order to ensure the stability of the corrosion resistance of the protected material. On this basis, the concentration of microorganisms in the marine oil and gas pipeline environment is relatively high, ranging from 10 6 -10 8 CFU / mL, in order to effectively inhibit the microbial corrosion process in the application environment, the setting of the anodic polarization potential is further limited, and the potential value must be above the middle value of the passivation interval potential range and below the pitting potential by 0.05V. Preferably, the potential must be above the middle value of the passivation interval potential range and below the pitting potential by 0.1V.

[0012] Secondly, anodic polarization is the only way to ensure that microorganisms in the environment quickly adhere to the surface of materials. Since most microorganisms in marine oil and gas pipelines are electronegative, anodic polarization can ensure the distribution of positive charges on the surface of materials. Based on the principle of mutual attraction between positive and negative charges, anodic polarization promotes the adsorption of electronegative microorganisms on the surface of materials.

[0013] Finally, the inventors found in their research that microbial cells obtain electrons from outside the cell for their own metabolic activities. In order to survive, they secrete a large amount of extracellular polymeric substance (EPS), which covers the surface of stainless steel. After analyzing the composition of the surface components, the EPS structure formed and the Fe element in stainless steel form a film layer that has never been found on the surface of stainless steel, the EPS-Fe film layer. This film layer protects the material and can inhibit the corrosion of foreign microorganisms on the base material.

[0014] In addition, the special stainless steel described in the present invention is a supplementary option, which is an important material for further improving the microbial corrosion inhibition effect of service materials. The present invention promotes the valence state transformation of the Ni element through anodic polarization, causing oxidative damage to cells during the transformation process, rupturing the cell membrane, and then providing an entrance for the entry of Cu ions, resulting in the loss of bacterial cell replication function until apoptosis.

[0015] The method and special stainless steel of the present invention are particularly suitable for inhibiting microbial corrosion of marine oil and gas pipelines. When the special stainless steel is not used, the microbial corrosion inhibition rate reaches 50%-56% within a 30-day application period. Compared with the original stainless steel material alone, the method of the present invention can reduce the maximum pitting depth by 30%-35%. When the special stainless steel material is used, the microbial corrosion inhibition rate reaches 50%-60%, and the maximum pitting depth is reduced by 30%-40%.

[0016] The beneficial effects of the present invention are:

[0017] 1. Anodic polarization can enable the attachment of microorganisms in the environment to the surface of the material and the subsequent formation of a protective EPS-Fe film layer, as well as inhibit the activity of microorganisms to a certain extent.

[0018] 2. The combined application of special stainless steel materials can further enhance the effect of inhibiting microbial corrosion, thereby achieving a microbial corrosion inhibition rate of 50%-60% and a maximum pitting depth reduction of 30%-40% within a 30-day application period. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Surface morphology of the original in-service marine oil and gas pipeline material after co-cultivation with M. salsuginis for 30 days (Example 5).

[0020] Figure 2 Surface morphology after 30 days of co-cultivation with M. salsuginis using a combination of anodic polarization treatment and dedicated stainless steel material (Example 5).

[0021] Figure 3 The proportion of main elements on the surface of original service material (a) and special stainless steel material (b) (Example 5).

[0022] Image description: Under bacterial conditions, the content of C and N elements on the material surface is significantly increased, which is the result of the presence of bacteria, bacterial biofilm and EPS film layer. After using anodic polarization and combining with special stainless steel materials, the number of bacteria on the material surface is significantly reduced, but the C and N elements on its surface still occupy a high proportion, indicating that its surface is mainly covered by EPS film layer. In addition, the single organic film layer will form an EPS-Fe film layer with the Fe element on the stainless steel surface, thereby forming a close connection and forming a protective effect on the substrate. DETAILED DESCRIPTION

[0023] According to the content of the present invention, the technical scheme of the present invention is further illustrated by specific implementation. The embodiments are only for helping to understand the present invention and are not to be regarded as specific limitations of the present invention. The anodic polarization potential values, passivation intervals, and Cu and Ni contents of the special stainless steel materials used in the embodiments and comparative examples are shown in Table 1.

[0024] Table 1 Anodic polarization potential value parameter selection and special stainless steel composition setting for the embodiments and comparative examples

[0025]

[0026] 1. Immersion experiment

[0027] The immersion test is used to test the pitting behavior changes of the selected experimental materials under the action of anodic polarization. The bacteria selected in this experiment are the Gram-negative bacteria Marinobacter salsuginis (M. salsuginis, 1A01268) commonly found in marine oil and gas pipelines. The bacterial culture medium used is the standard marine bacterial culture medium, 2216E culture medium. The artificial seawater solution is prepared with a concentration of 10 8 CFU / mL of bacterial suspension. M. salsuginis suspension and 2216E medium were mixed to form a bacterial concentration of 10 7 CFU / mL of immersion solution. The experimental materials in the examples and comparative examples are placed in the solution and treated with constant potential at room temperature to form an immersion system for standard testing. The incubation time is set to 30 days. After the incubation, phosphate buffer saline (PBS) is first used to gently rinse and remove the floating bacteria on the surface of the sample, and then the sample is placed in a PBS solution and oscillated for 60 seconds to obtain a solution composed of surface-fixed bacteria, and then a certain amount of liquid is extracted for bacterial counting to obtain the density of fixed bacteria on the surface.

[0028] In addition, according to GB / T 16545-1996 "Removal of Corrosion Products on Corrosion Test Specimens of Metals and Alloys", the surface of the sample that completed the above experiment was cleaned to expose the metallic luster, and the pitting depth change on the material surface was studied by confocal laser scanning microscopy (CLSM), and the maximum pitting depth reduction rate was calculated. A control sample must be set in the experiment, and the control sample is the currently in-service stainless steel material.

[0029] 2. Electrochemical Experiments

[0030] The electrochemical tests for evaluating the microbial corrosion inhibition rate were all completed on an electrochemical instrument (Gamry Reference 600, Gamry Instruments, USA). The electrochemical experiments were conducted to analyze the corrosion resistance of the materials in the embodiments and comparative examples, and to obtain the corrosion current i of the selected materials during their service life. corr , and on this basis, the microbial corrosion inhibition rate (IE%) is calculated, where the calculation formula of IE% is:

[0031]

[0032] Among them, i corr represents the surface current value of the original service pipeline material after being cultured in a bacteria-containing solution for 30 days without anodic polarization treatment, i’ corr It represents the surface current value after 30 days of cultivation in a bacteria-containing solution using anodic polarization treatment technology and special stainless steel materials.

[0033] Table 2 Test results of embodiments and comparative examples

[0034]

[0035]

[0036] From the results in Table 2, it can be seen that in Examples 1-9 of the present invention, after adopting anodic polarization treatment and applying special stainless steel materials, the microbial corrosion resistance of the materials is improved, the number of fixed bacteria on the surface of the materials is reduced, the maximum pitting depth is reduced, and the inhibition rate of microbial corrosion is improved, showing a strong microbial activity inhibition effect. Compared with the comparative example, the selection of a suitable anodic polarization potential and the use of special stainless steel materials to replace the original service stainless steel materials can effectively inhibit the microbial corrosion process in the marine oil and gas transmission pipeline.

[0037] The potential selection of anodic polarization treatment is very important, and the potential selection should be within the passivation range of the critical passivation potential and pitting potential; in addition, the selection of special stainless steel and the copper content of special stainless steel are also important factors in improving the resistance to microbial corrosion. They will affect the inhibition rate of microbial corrosion, the maximum pitting depth reduction rate and the density of fixed bacteria on the material surface.

[0038] First, the potential of the anodic polarization treatment is selected above the passivation interval, including the following two situations: the potential is selected to be higher than the passivation interval and the special stainless steel material is not selected; and the potential is selected to be higher than the passivation interval and the special stainless steel material is selected. Due to the excessively high potential selection, pitting corrosion naturally forms on the surface of the material, thereby accelerating the corrosion process of the material, resulting in the material not having the effect of inhibiting microbial corrosion, making it impossible to calculate the IE% and the maximum pitting depth reduction rate. In addition, due to the excessively high potential and the accelerated corrosion of the material, the density of fixed bacteria on the surface of the material is reduced, but at the same time, it also causes irreversible destructive effects on the material (compared with 1 and comparative example 2).

[0039] Secondly, the potential value is selected within the passivation interval, but it is lower than the middle value of the passivation zone, including the following two situations: the potential is selected to be lower than the middle value of the passivation zone and no special stainless steel material is selected; and the potential is selected to be lower than the middle value of the passivation zone and a special stainless steel material is selected. Since the selected potential is too low, the activity of bacteria cannot be inhibited, resulting in an increase in the amount of bacteria attached to the surface of the material, and a relatively complete EPS-Fe film layer cannot be formed, thereby accelerating the occurrence of pitting corrosion on the surface of the material at the defect; and after adding the special stainless steel material, it can only show the effect of inhibiting microbial corrosion to a certain extent, but the effect is not significant, and the effect of the present invention application cannot be achieved (Comparative Example 3, Comparative Example 4).

[0040] Furthermore, the potential of the anodic polarization treatment is selected within the passivation interval, but the potential value is too close to the pitting potential, including the following two situations: the potential value is too close to the pitting potential and the special stainless steel material is not selected, and the metastable pitting during the service process will form stable pitting, so that the anodic polarization treatment causes the initiation of pitting on the surface of the material or further deepens (Comparative Example 5). The potential value is too close to the pitting potential and the special stainless steel material is selected. Although the introduction of the special stainless steel material can further suppress the density of fixed bacteria and prevent corrosion caused by microorganisms, the metastable pitting is transformed into stable pitting during the service time, thereby still reducing the microbial corrosion inhibition rate and the maximum pitting depth reduction rate as a whole (Comparative Example 6).

[0041] To ensure that the potential value is within the application scope of the present invention, a special stainless steel material is selected, but the Cu content of the special stainless steel is too low, and after the EPS-Fe film layer is detached, the effect of inhibiting bacteria in the detached area is poor, so that regional dissolution will still be formed (Comparative Example 7). Or the Cu content of the special stainless steel is too high, and the corrosion resistance of the material itself is reduced, resulting in a decrease in the microbial corrosion inhibition rate and a weakening of the maximum pitting depth reduction rate (Comparative Example 8).

[0042] To ensure that the potential value is within the application scope of the present invention, a special stainless steel material is selected, but the Ni content of the special stainless steel is too low, and the exit cannot be opened for the process of Cu ions entering the bacterial cells, resulting in reduced antibacterial ability and reduced ability to inhibit microbial corrosion (Comparative Example 9). A special stainless steel material is selected, but the Ni content of the special stainless steel is too high. Since the increase in Ni content cannot further improve the ability to resist microbial corrosion, in order to avoid waste of resources, there is no need to continue to increase the Ni content (Comparative Example 10).

[0043] Without using the anodic polarization constant potential effect, only using special stainless steel materials, although it can show a certain effect of inhibiting microorganisms, the effect is extremely not obvious (Comparative Example 11).

[0044] It can be seen from the above examples and comparative examples that the microbial corrosion inhibition effect can be affected by the potential value setting of the anodic polarization and the chemical composition of the special stainless steel. Only when the parameters are set within this clear range can the effective microbial corrosion resistance be achieved.

[0045] Matters not covered by the present invention are known technologies.

[0046] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. An anodic polarization method for inhibiting microbial corrosion of marine oil and gas pipelines, characterized in that: The special stainless steel is treated by an anodic constant potential anodic polarization method, wherein the anodic constant potential selection interval range is: above the middle value of the passivation interval potential range to 0.05V below the pitting potential, and the anodic polarization action time is the actual protection time required; Special stainless steel is selected as a substitute material for traditional service stainless steel. The special stainless steel is prepared by adding Cu element to the composition of traditional service stainless steel and increasing the content of Ni element at the same time. According to weight percentage, the added amount of Cu is 1.0-5.0%, and the added amount of Ni is 0.5%-2.5%, and the added amount is the content increased based on the upper limit of the original Ni content.

2. The anodic polarization method for inhibiting microbial corrosion of marine oil and gas pipelines according to claim 1, characterized in that: The anode constant potential selection interval range is: above the middle value of the passivation interval potential range to 0.1V below the pitting potential.

3. The anodic polarization method for inhibiting microbial corrosion of marine oil and gas pipelines according to claim 2, characterized in that: The added amount of Cu is 2.0-4.0%, and the added amount of Ni is 1.0%-2.0%.

4. Use of the method according to any one of claims 2 or 3 in inhibiting microbial corrosion of marine oil and gas transmission pipelines.

5. The use according to claim 4, characterized in that: When special stainless steel materials are used, the microbial corrosion inhibition rate reaches 50%-60% within a 30-day application period, and the maximum pitting depth is reduced by 30%-40%.

Images