Multi-factor collaborative local rapid corrosion rate prediction model

Abstract

The invention discloses a multi-factor collaborative local rapid corrosion rate prediction model, which considers charge transfer and mass transfer conditions in the corrosion process of dissolved oxygen, SRB and CO2, respectively calculates the corrosion current of each factor so as to calculate the total corrosion current, converts the total corrosion current into the corrosion rate based on the Faraday's law, and predicts the local rapid corrosion rate based on the total corrosion current. The acceleration effect of dissolved oxygen cooperating with SRB, CO2, Cl <-> and flow velocity on corrosion is comprehensively considered, an orthogonal experiment is combined, an oil and gas pipeline multi-factor cooperating local rapid corrosion rate prediction model is established, the corrosion rate of the oil and gas pipeline can be predicted, and the method has wide application value.

Description

Technical Field

[0001] The present invention relates to a multi-factor collaborative local rapid corrosion rate prediction model, and relates to the field of multi-factor local corrosion prediction of oil and gas pipelines. Background Art

[0002] In the context of the continuous growth of energy demand today, the development process of oil and gas resources is constantly advancing, and the scale of the oil and gas pipeline transportation system is also continuously expanding. However, as the time of pipeline operation gradually extends, the potential risk of internal failure due to corrosion increases day by day. Once the pipeline leaks, the consequences are extremely serious, not only causing huge economic losses, but also causing large-scale pollution and damage to the surrounding environment. Based on this, in-depth exploration of the corrosion behavior inside the oil and gas pipeline and accurate corrosion prediction are of irreplaceable key significance for effectively reducing the failure risk caused by corrosion and ensuring the stable and safe operation of the oil and gas transportation system.

[0003] The corrosion condition inside the oil and gas pipeline is mainly affected by a series of factors such as the internal transportation medium and operating conditions. These factors cover a wide range, including temperature, pressure, fluid velocity, and various corrosive media in multiple dimensions. In the real pipeline operation environment, the situation is more complex, and multiple corrosive media often coexist, such as common H 2 S, CO 2 2 - -, Cl 2 -, etc. In particular, corrosion factors such as dissolved oxygen, SRB (sulfate-reducing bacteria), and CO

[0004] In the field of microbial corrosion, numerous studies have shown that microorganisms can accelerate the process of local corrosion of pipelines and may even lead to pipeline perforation accidents. In the oil and gas field production system, the types of microorganisms are diverse and complex. For example, during various stages of Marcellus shale gas well exploitation, 31 types of microorganisms, including sulfate-reducing bacteria (SRB), have been detected. Among them, SRB is widely distributed and has a large number, causing the most serious harm to pipelines. During the metabolism process, SRB secretes biofilm matrix to build a microbial film on the pipeline surface. Its metabolites can corrode the pipeline, and its corrosion mechanism has gone through development stages such as the "cathodic depolarization theory" and the "extracellular electron transfer kinetics theory". In addition, studies have found that SRB is not a complete anaerobe. Under specific conditions, it can coexist with other microorganisms such as iron-oxidizing bacteria (IOB). This coexistence state will have a significant impact on the pipeline corrosion process. Its oxygen tolerance characteristics are not only closely related to its own species characteristics but also closely related to other coexisting microorganisms. In actual operation, adjusting the dissolved oxygen concentration in the pipeline can purify the biofilm on the pipeline wall and slow down the pipeline wall corrosion, but at the same time, it also introduces the potential risk of oxygen corrosion.

[0005] CO 2 Corrosion is extremely common among the corrosion types in oil and gas fields. When in a dry environment, CO 2 does not have corrosiveness, but once in a condensate water or solution environment, its corrosiveness will be revealed. For the CO 2 corrosion of carbon steel, its mechanism is relatively complex. Just for the dissolution process of anodic iron, there are two viewpoints: the "continuous mechanism" and the "catalytic mechanism". CO 2 corrosion is jointly controlled by many factors, including pH value, temperature, CO 2 partial pressure, and the structure of corrosion products, etc. Under different pH value conditions, the product films generated by CO 2 corrosion show great differences in morphology; temperature has a very significant impact on the formation rate of the corrosion product film layer, and the increase of CO 2 partial pressure can accelerate the corrosion mass transfer process. It should be noted that the protective performance of the CO 2 corrosion product film is closely related to the film layer structure and the formation process. For different types of corrosion product films, their formation processes and evolution mechanisms are different.

[0006] O 2 Due to its strong oxidizing property, in a neutral or alkaline solution environment, it can act as a cathodic depolarizer and participate in the corrosion reaction of carbon steel. Taking the environmental conditions of 80 °C as an example, when the pH value changes at this time, Fe 2+Different types of corrosion products will be generated accordingly. The film layers composed of these different corrosion products have differences in the retardation effect on the further corrosion of the carbon steel surface, that is, the change in pH value indirectly affects the protective effect of the corrosion product film by affecting the generation of corrosion products, thereby affecting the subsequent corrosion process.

[0007] In the oil and gas field, due to the extremely complex mining conditions and the coexistence of multiple corrosion media, the problem of multi-factor synergistic corrosion is prominent, greatly increasing the difficulty of corrosion protection. For example, in the production water treatment system of offshore oilfields, there is a phenomenon of synergistic corrosion of carbon dioxide, oxygen and sulfate-reducing bacteria. In the CO 2 and O 2 coexistence system, O 2 will accelerate the corrosion process of CO 2 , inhibit the formation of the FeCO 3 film, destroy the integrity of the product film, and then induce local corrosion. In the CO 2 -O 2 -H 2 O corrosion system, water containing dissolved oxygen and CO 2 is more corrosive. And in oil and gas pipelines, SRB can act synergistically with other factors such as Cl - and CO 2 to accelerate the corrosion of pipelines, seriously threatening the safe operation of oil and gas pipelines.

[0008] Currently, most of the corrosion failure accidents of oil and gas pipelines are caused by local corrosion. In actual working conditions, the synergistic action of multiple factors such as dissolved oxygen, SRB and CO 2 will cause local rapid corrosion of pipelines. However, up to now, there is no mature and reliable prediction model for this complex multi-factor synergistic local rapid corrosion situation. Based on a large number of multi-condition parameters obtained from relevant experiments, the present invention constructs a multi-factor synergistic local rapid corrosion rate prediction model. This model aims to accurately solve the problem of local rapid corrosion prediction of oil and gas pipelines under the synergistic action of multiple factors such as dissolved oxygen, SRB and CO 2 so as to provide a strong guarantee for the integrity of oil and gas pipelines. Summary of the Invention

[0009] The present invention proposes a multi-factor synergistic local rapid corrosion rate prediction model to identify the corrosion situation of pipelines under the synergistic action of multiple factors and reduce pipeline perforation accidents caused by corrosion.

[0010] To achieve the above object, the present invention adopts the following technical solutions to be realized:

[0011] S1: For the corrosion of dissolved oxygen, SRB and CO 2 , both charge transfer and mass transfer are considered, and the corrosion current of each factor is calculated;

[0012] S2: Considering the mass transfer of dissolved oxygen and electron transfer, calculate the current density of dissolved oxygen corrosion;

[0013] S3: In SRB corrosion, due to the formation of corrosion products and biofilms, the influence of mass transfer on corrosion must be considered, and calculate the corrosion current density caused by SRB;

[0014] S4: CO 2 Corrosion is controlled by mass transfer and electrochemical electron transfer. From the perspective of reaction kinetics, calculate the corrosion current density of CO 2 corrosion;

[0015] S5: In the corrosion reaction, the anode is the dissolution of Fe losing electrons and becoming Fe 2+ , and its dissolution process is related to SRB, CO 2 and O 2 corrosion. Calculate the total corrosion current;

[0016] S6: According to Faraday's law, convert the total corrosion current into the corrosion rate, and calculate the corrosion rates of dissolved oxygen, SRB and CO 2 ;

[0017] S7: Considering the synergistic corrosion of dissolved oxygen with SRB and CO 2 corrosion, as well as the accelerating effects of Cl - , flow rate on corrosion, establish a prediction model for the multi-factor synergistic local rapid corrosion rate of oil and gas pipelines.

[0018] Furthermore, the corrosion current calculation formula in step S1: In the formula, i c(i) is the cathodic current density caused by substance i, A / m 2 ; i lim(i) is the current density controlled by mass transfer of substance i, A / m 2 ; i ct(i) is the current density controlled by charge transfer of substance i, A / m 2 .

[0019] Furthermore, the calculation formula for the dissolved oxygen corrosion current density in step S2: In the formula, is the oxygen corrosion current density, A / m 2 ; is the current density controlled by charge transfer of oxygen corrosion, A / m 2 ; is the current density controlled by mass transfer of oxygen corrosion, A / m 2 .

[0020] Furthermore, the calculation formula for the corrosion current density of SRB in step S3 is: In the formula, is the sulfate reduction current density, A / m 2 ; is the current density controlled by mass transfer of sulfate reduction, A / m 2 ; is the current density controlled by charge transfer of sulfate reduction, A / m 2 .

[0021] Furthermore, the calculation formula for the corrosion current density of CO 2 in step S4 is: In the formula, is the corrosion current density of CO 2 , A / m 2 ; is the current density controlled by mass transfer of CO 2 , A / m 2 ; is the current density controlled by charge transfer of CO 2 , A / m 2 .

[0022] Furthermore, the calculation formula for the total corrosion current density in step S5 is:

[0023] Furthermore, the calculation formula for the corrosion rates of dissolved oxygen, SRB, and CO 2 in step S6 is: In the formula, CR(SRB) is the corrosion rate caused by SRB, mm / a; CR(CO 2 ) is the corrosion rate caused by CO 2 , mm / a; CR(DO) is the corrosion rate caused by dissolved oxygen, mm / a; F is the Faraday constant, C / V; MW Fe is the molecular weight of Fe, 56 kg / mol; ρ Fe is the density of Fe, 7.8 kg / m 3 ; i α is the total corrosion current density, A / m 2 ; n is 2;

[0024] Furthermore, the prediction model for the multi-factor collaborative local rapid corrosion rate of oil and gas pipelines in step S7 is: ln(CR - CR(SRB) - CR(CO 2 ) - CR(DO)) = Eln(ν + 1) 2 + Fln(ν + 1) + Mln(C α + 1) + N Where: ν is the liquid flow rate, m / s; is the concentration of Cl - , mg / L; E / F / M / N are constants and can be measured through experiments. Description of the Drawings

[0025] Figure 1 This is the prediction result and error graph of the multi - factor synergistic local rapid corrosion mechanism model of the present invention Detailed Embodiment

[0026] A method for establishing a multi - factor synergistic local rapid corrosion rate prediction model, and the specific calculation method includes the following steps:

[0027] S1: For the corrosion of dissolved oxygen with SRB and CO 2 , both charge transfer and mass transfer are considered, and the corrosion current of each factor is calculated;

[0028] S2: Considering the mass transfer of dissolved oxygen and electron transfer, the current density of dissolved oxygen corrosion is calculated;

[0029] S3: In the corrosion of SRB, due to the formation of corrosion products and biofilms, the influence of mass transfer on corrosion must be considered, and the corrosion current density caused by SRB is calculated;

[0030] S4: The corrosion of CO 2 is controlled by mass transfer and electrochemical electron transfer. From the perspective of reaction kinetics, the corrosion current density of CO 2 corrosion is calculated;

[0031] S5: In the corrosion reaction, the anode is Fe losing electrons and dissolving to become Fe 2+ , and its dissolution process is related to the corrosion of SRB, CO 2 and O 2 , and the total corrosion current is calculated;

[0032] S6: According to Faraday's law, the total corrosion current is converted into the corrosion rate, and the corrosion rates of dissolved oxygen, SRB, and CO 2 are calculated;

[0033] S7: Considering the synergistic corrosion of dissolved oxygen with SRB and CO 2 , as well as the accelerating effect of Cl - and flow rate on corrosion, a multi - factor synergistic local rapid corrosion rate prediction model for oil and gas pipelines is established.

[0034] The corrosion current calculation formula in step S1:

[0035] In the formula, i c(i) is the cathodic current density caused by substance i, A / m 2 ; i lim(i) is the current density controlled by mass transfer of substance i, A / m 2 ; i ct(i) is the current density controlled by charge transfer of substance i, A / m 2 .

[0036] The dissolved oxygen corrosion current density calculation formula in step S2:

[0037] In the formula, is the oxygen corrosion current density, A / m 2 ; is the current density controlled by charge transfer of oxygen corrosion, A / m 2 ; is the current density controlled by mass transfer of oxygen corrosion, A / m 2 .

[0038] The SRB corrosion current density calculation formula in step S3:

[0039] In the formula, is the sulfate reduction current density, A / m 2 ; is the current density controlled by mass transfer of sulfate reduction, A / m 2 ; is the current density controlled by charge transfer of sulfate reduction, A / m 2 .

[0040] The CO 2 corrosion current density calculation formula in step S4:

[0041] In the formula, is the CO 2 corrosion current density, A / m 2 ; is the current density controlled by mass transfer of CO 2 , A / m 2 ; is the current density controlled by charge transfer of CO 2 , A / m 2 .

[0042] The total corrosion current density calculation formula in step S5 is as follows:

[0043] In step S6, the corrosion rate calculation formula for dissolved oxygen, SRB, and CO 2 is as follows:

[0044] In the formula, CR(SRB) is the corrosion rate caused by SRB, mm / a; CR(CO 2 ) is the corrosion rate caused by CO 2 , mm / a; CR(DO) is the corrosion rate caused by dissolved oxygen, mm / a; F is the Faraday constant, C / V; MW Fe is the molecular weight of Fe, 56 kg / mol; ρ Fe is the density of Fe, 7.8 kg / m 3 ; i α is the total corrosion current density, A / m 2 ; n is 2.

[0045] The prediction model for the multi-factor synergistic local rapid corrosion rate of oil and gas pipelines in step S7 is as follows: ln(CR - CR(SRB) - CR(CO 2 ) - CR(DO)) = Eln(ν + 1) 2 + Fln(ν + 1) + Mln(C α + 1) + N

[0046] In the formula: v is the liquid flow velocity, m / s; is the Cl - concentration, mg / L; E / F / M / N are constants, which can be measured through experiments.

[0047] The orthogonal experiment data is shown in Table 1. Table 1 Charge transfer and mass transfer current density under orthogonal experiment conditions for O 2 / SRB / CO 2

[0048] Using the orthogonal experiment local corrosion rate results for model verification, the linear fitting error in a multi-factor synergistic local rapid corrosion rate prediction model is shown in Figure 1 . The absolute value range of the relative error of corrosion prediction is 0.18% - 9.67%, and the average absolute value of the relative error is 2.92%.

Claims

1. A multi-factor synergistic local rapid corrosion rate prediction model, characterized in that: The following steps are involved: S1: Charge transfer and mass transfer are considered for dissolved oxygen, SRB and CO2 corrosion, and the corrosion current of each factor is calculated; S2: Considering dissolved oxygen mass transfer and electron transfer, calculate the current density of dissolved oxygen corrosion; S3: In SRB corrosion, due to the formation of corrosion products and biofilm, the effect of mass transfer on corrosion must be considered to calculate the corrosion current density caused by SRB; S4: CO2 corrosion is controlled by mass transfer and electrochemical electron transfer. From the perspective of reaction kinetics, the corrosion current density of CO2 corrosion is calculated; S5: In the corrosion reaction, the anode is Fe, which loses electrons and dissolves into Fe 2+ , whose dissolution process is related to SRB, CO2 and O2 corrosion, and the total corrosion current is calculated; S6: According to Faraday's law, the total corrosion current is converted into corrosion rate, and the corrosion rates of dissolved oxygen, SRB and CO2 are calculated; S7: Consider dissolved oxygen synergistic with SRB and CO2 corrosion, as well as Cl - , and the accelerating effect of flow velocity on corrosion, and establish a multi-factor coordinated local rapid corrosion rate prediction model for oil and gas pipelines.

2. A method for establishing a multi-factor collaborative local rapid corrosion rate prediction model as claimed in claim 1, characterized in that: The corrosion current calculation formula in step S1 is: In the formula, i c(i) is the cathode current density caused by substance i, A / m 2 ; i lim(i) is the current density controlled by mass transfer of substance i, A / m 2 ; i ct(i) is the current density controlled by the charge transfer of material i, A / m 2 .

3. The method for establishing a multi-factor collaborative local rapid corrosion rate prediction model according to claim 1, characterized in that: The calculation formula of dissolved oxygen corrosion current density in step S2 is: In the formula, is the oxygen corrosion current density, A / m 2 ; Current density controlled by oxygen corrosion charge transfer, A / m 2 ; The current density controlled by oxygen corrosion mass transfer, A / m 2 .

4. The method for establishing a multi-factor coordinated local rapid corrosion rate prediction model according to claim 1, characterized in that: The calculation formula of SRB corrosion current density in step S3 is: In the formula, is the sulfate reduction current density, A / m 2 ; is the current density for sulfate reduction mass transfer control, A / m 2 ; is the current density controlled by the charge transfer for sulfate reduction, A / m 2 .

5. The method for establishing a multi-factor coordinated local rapid corrosion rate prediction model according to claim 1, characterized in that: The calculation formula of CO2 corrosion current density in step S4 is: In the formula, is the CO2 corrosion current density, A / m 2 ; is the current density for CO2 mass transfer control, A / m 2 ; is the current density controlled by CO2 charge transfer, A / m 2 .

6. The method for establishing a multi-factor coordinated local rapid corrosion rate prediction model according to claim 1, characterized in that: The total corrosion current density calculation formula in step S5 is:

7. The method for establishing a multi-factor coordinated local rapid corrosion rate prediction model according to claim 1, characterized in that: The corrosion rate calculation formula of dissolved oxygen, SRB and CO2 in step S6 is: Where, CR(SRB) is the corrosion rate caused by SRB, mm / a; CR(CO2) is the corrosion rate caused by CO2, mm / a; CR(DO) is the corrosion rate caused by dissolved oxygen, mm / a; F is the Faraday constant, C / V; MW Fe is the molecular weight of Fe, 56 kg / mol; ρ Fe is the density of Fe, 7.8kg / m 3 ;i α is the total corrosion current density, A / m 2 ; n is 2.

8. The method for establishing a multi-factor coordinated local rapid corrosion rate prediction model according to claim 1, characterized in that: The prediction model of the local rapid corrosion rate of oil and gas pipelines in step S7 is: ln(CR-CR(SRB)-CR(CO2)-CR(DO))=Eln(ν+1) 2 +Fln(ν+1)+Mln(C α +1)+N Where: v is the liquid flow rate, m / s; C Cl - Cl - Concentration, mg / L; E / F / M / N are constants and can be measured experimentally.

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