A method for establishing a multi-factor synergistic local rapid corrosion rate prediction model

Abstract

The application discloses a multi-factor synergistic local rapid corrosion rate prediction model, considers charge transfer and mass transfer in a dissolution oxygen, SRB and CO2 corrosion process, respectively calculates corrosion current of each factor, calculates total corrosion current, converts the total corrosion current into a corrosion rate based on Faraday's law, comprehensively considers acceleration effects of the dissolution oxygen, SRB, CO2 and Cl ‑ , and flow rate on corrosion, combines with an orthogonal experiment, establishes the multi-factor synergistic local rapid corrosion rate prediction model of an oil and gas pipeline, can perform corrosion rate prediction of the oil and gas pipeline, and has wide application value.

Description

Technical Field

[0001] This invention relates to a method for establishing a multi-factor collaborative local rapid corrosion rate prediction model, which relates to the field of multi-factor local corrosion prediction for oil and gas pipelines. Background Technology

[0002] Against the backdrop of continuously growing energy demand, the development of oil and gas resources is advancing, and the scale of oil and gas pipeline transportation systems is expanding. However, as pipelines age, the potential risk of internal corrosion failure increases daily. Once a pipeline leaks, the consequences are extremely serious, causing not only huge economic losses but also widespread pollution and damage to the surrounding environment. Therefore, in-depth research into the corrosion behavior inside oil and gas pipelines and the achievement of accurate corrosion prediction are of irreplaceable and crucial significance for effectively reducing the risk of corrosion-induced failure and ensuring the stable and safe operation of oil and gas transportation systems.

[0003] The corrosion condition inside oil and gas pipelines is primarily influenced by a series of factors, including the transported medium and operating conditions. These factors are broad, encompassing temperature, pressure, fluid velocity, and various corrosive media. In real pipeline operating environments, the situation is even more complex, with multiple corrosive media often coexisting, such as common H2S, CO2, and Cl-. Of particular note is the frequent presence of dissolved oxygen, SRB (sulfate-reducing bacteria), and CO2, whose interactions make the corrosion mechanism under the synergistic influence of multiple factors intricate and difficult to accurately assess.

[0004] In the field of microbial corrosion, numerous studies have shown that microorganisms can accelerate the localized corrosion process of pipelines and may even lead to pipeline perforation accidents. In oil and gas field production systems, the types of microorganisms are diverse and complex. For example, at various stages of Marcellus shale gas well development, 31 species of microorganisms, including sulfate-reducing bacteria (SRB), have been detected. Among them, SRB are widely distributed and numerous, posing the most serious threat to pipelines. During their metabolism, SRB secrete biofilm matrix, building a microbial film on the pipeline surface. Their metabolic products corrode the pipeline, and their corrosion mechanism has undergone developmental stages such as the "cathodic depolarization theory" and the "extracellular electron transfer kinetics theory." Furthermore, research has found that SRB are not entirely anaerobic bacteria. Under specific conditions, they can coexist with other microorganisms such as iron bacteria (IOB). This coexistence significantly affects the pipeline corrosion process. Their oxygen tolerance is not only closely related to their own species characteristics but also to the other microorganisms they coexist with. In practice, adjusting the dissolved oxygen concentration in the pipeline can purify the biofilm on the pipeline wall and slow down pipe wall corrosion, but at the same time, it also introduces the potential risk of oxygen corrosion.

[0005] CO2 corrosion is extremely common in oil and gas field corrosion. While CO2 is not corrosive in dry environments, its corrosiveness becomes apparent in condensate or solution environments. The mechanism of CO2 corrosion of carbon steel is complex; even in the dissolution process of anolyte, there are two main viewpoints: a "continuous mechanism" and a "catalytic mechanism." CO2 corrosion is controlled by numerous factors, including pH, temperature, CO2 partial pressure, and the structure of corrosion products. Under different pH conditions, the morphology of the corrosion product film varies significantly; temperature has a significant impact on the formation rate of the corrosion product film; and increasing the CO2 partial pressure accelerates the corrosion mass transfer process. It is noteworthy that the protective performance of the CO2 corrosion product film is closely related to its structure and formation process; different types of corrosion product films exhibit different formation processes and evolution mechanisms.

[0006] O2, due to its strong oxidizing properties, can act as a cathodic depolarizer in neutral or alkaline solutions, participating in the corrosion reaction of carbon steel. Taking an environment of 80℃ as an example, if the pH value changes at this temperature, Fe... 2+ Different types of corrosion products will be generated accordingly. The films formed by these different corrosion products have different effects on inhibiting further corrosion of carbon steel surfaces. That is, changes in pH value affect the formation of corrosion products, which in turn affects the protective effect of the corrosion product film and thus affects the subsequent corrosion process.

[0007] In the oil and gas sector, the extremely complex extraction conditions and the coexistence of multiple corrosive media lead to prominent multi-factor synergistic corrosion problems, greatly increasing the difficulty of corrosion protection. For example, in offshore oilfield production water treatment systems, there is a phenomenon of synergistic corrosion by carbon dioxide, oxygen, and sulfate-reducing bacteria. In a CO2 and O2 coexisting system, O2 accelerates the corrosion process of CO2, inhibits the formation of FeCO3 films, damages the integrity of product films, and thus induces localized corrosion. In the CO2-O2-H2O corrosion system, water containing dissolved oxygen and CO2 is more corrosive, while in oil and gas pipelines, SRB can react with Cl... - The combined effects of CO2 and other factors accelerate pipeline corrosion, seriously threatening the safe operation of oil and gas pipelines.

[0008] Currently, most corrosion failures in oil and gas pipelines originate from localized corrosion. In actual operating conditions, the combined effects of multiple factors such as dissolved oxygen, SRB, and CO2 can lead to rapid localized corrosion of pipelines. However, to date, there is no mature and reliable prediction model for this complex multi-factor synergistic rapid localized corrosion scenario. This invention, based on multi-condition parameters obtained from numerous related experiments, constructs a method for establishing a prediction model for the rate of rapid localized corrosion caused by the combined effects of dissolved oxygen, SRB, and CO2 in oil and gas pipelines. This model aims to accurately solve the problem of predicting rapid localized corrosion in oil and gas pipelines under the combined effects of dissolved oxygen, SRB, and CO2, thereby providing a solid guarantee for the integrity of oil and gas pipelines. Summary of the Invention

[0009] To identify pipeline corrosion under the synergistic effect of multiple factors and reduce pipeline perforation accidents caused by corrosion, this invention proposes a method for establishing a multi-factor synergistic local rapid corrosion rate prediction model.

[0010] To achieve the above objectives, the present invention employs the following technical solution:

[0011] S1: Dissolved oxygen, SRB, and CO2 corrosion all take charge transfer and mass transfer into account, and the corrosion current for each factor is calculated.

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

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

[0014] 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.

[0015] S5: In the corrosion reaction, Fe at the anolyte loses electrons and dissolves, becoming Fe2+. 2+ Its dissolution process is related to SRB, CO2 and O2 corrosion, and the total corrosion current is calculated;

[0016] 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 CO2 are calculated.

[0017] S7: Considering dissolved oxygen synergistically corrodes SRB and CO2, as well as Cl... - The accelerating effect of flow velocity on corrosion was investigated, and a multi-factor collaborative local rapid corrosion rate prediction model for oil and gas pipelines was established.

[0018] Furthermore, the formula for calculating the corrosion current in step S1 is as follows:

[0019]

[0020] In the formula, i c(i) Let i be the cathode current density caused by the material, in A / m. 2 i lim(i) Let i be the current density for mass transfer control, in A / m. 2 i ct(i) Let i be the current density controlled by charge transfer of matter, in A / m. 2 .

[0021] Furthermore, the formula for calculating the dissolved oxygen corrosion current density in step S2 is as follows:

[0022]

[0023] In the formula, Oxygen corrosion current density, A / m 2 ; The current density controlled by charge transfer in oxygen corrosion, A / m 2 ; Current density for oxygen corrosion mass transfer control, A / m 2 .

[0024] Furthermore, the formula for calculating the SRB corrosion current density in step S3 is as follows:

[0025]

[0026] In the formula, The current density for sulfate reduction is A / m. 2 ; The current density for sulfate reduction mass transfer control, A / m 2 ; The current density controlled by charge transfer during sulfate reduction, in A / m 2 .

[0027] Furthermore, the formula for calculating the CO2 corrosion current density in step S4 is as follows:

[0028]

[0029] In the formula, CO2 corrosion current density, A / m 2 ; The current density for CO2 mass transfer control, in A / m 2 ; The current density controlled by CO2 charge transfer, A / m 2 .

[0030] Furthermore, the formula for calculating the total corrosion current density in step S5 is as follows:

[0031]

[0032] Furthermore, the formulas for calculating the corrosion rates of dissolved oxygen, SRB, and CO2 in step S6 are as follows:

[0033]

[0034] In the formula, 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 The molecular weight of Fe is 56 kg / mol; ρ Fe The density of Fe is 7.8 kg / m³. 3 i α The total corrosion current density is expressed in A / m. 2 n is 2;

[0035] Furthermore, in step S7, a prediction model for the localized rapid corrosion rate of oil and gas pipelines based on multiple factors is provided:

[0036] ln(CR-CR(SRB)-CR(CO2)-CR(DO))=Eln(ν+1) 2 +Fln(ν+1)+Mln(C α +1)+N

[0037] In the formula: v is the liquid flow velocity, m / s; C Cl - For Cl - Concentration, mg / L; E / F / M / N are constants that can be determined experimentally. Attached Figure Description

[0038] Figure 1 The prediction results and error diagram of the multi-factor synergistic local rapid corrosion mechanism model of the present invention. Detailed Implementation

[0039] A method for establishing a multi-factor synergistic local rapid corrosion rate prediction model, the specific calculation method includes the following steps:

[0040] S1: Dissolved oxygen, SRB, and CO2 corrosion all take charge transfer and mass transfer into account, and the corrosion current for each factor is calculated.

[0041] S2: Considering dissolved oxygen mass transfer and electron transfer, calculate the current density for dissolved oxygen corrosion.

[0042] S3: In SRB corrosion, due to the formation of corrosion products and biofilm, the influence of mass transfer on corrosion must be considered, and the corrosion current density caused by SRB must be calculated.

[0043] 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.

[0044] S5: In the corrosion reaction, Fe at the anolyte loses electrons and dissolves, becoming Fe2+. 2+ Its dissolution process is related to SRB, CO2 and O2 corrosion, and the total corrosion current is calculated;

[0045] 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 CO2 are calculated.

[0046] S7: Considering dissolved oxygen synergistically corrodes SRB and CO2, as well as Cl... - The accelerating effect of flow velocity on corrosion was investigated, and a multi-factor collaborative local rapid corrosion rate prediction model for oil and gas pipelines was established.

[0047] The formula for calculating corrosion current in step S1 is as follows:

[0048]

[0049] In the formula, i c(i) Let i be the cathode current density caused by the material, in A / m. 2 i lim(i) Let i be the current density for mass transfer control, in A / m. 2 i ct(i) Let i be the current density controlled by charge transfer of matter, in A / m. 2 .

[0050] The formula for calculating dissolved oxygen corrosion current density in step S2 is as follows:

[0051]

[0052] In the formula, Oxygen corrosion current density, A / m 2 ; The current density controlled by charge transfer in oxygen corrosion, A / m 2 ; Current density for oxygen corrosion mass transfer control, A / m 2 .

[0053] The formula for calculating the SRB corrosion current density in step S3 is as follows:

[0054]

[0055] In the formula, The current density for sulfate reduction is A / m. 2 ; The current density for sulfate reduction mass transfer control, A / m 2 ; The current density controlled by charge transfer during sulfate reduction, in A / m 2 .

[0056] The formula for calculating the CO2 corrosion current density in step S4 is as follows:

[0057]

[0058] In the formula, CO2 corrosion current density, A / m 2 ; The current density for CO2 mass transfer control, in A / m 2 ; The current density controlled by CO2 charge transfer, A / m 2 .

[0059] The formula for calculating the total corrosion current density in step S5 is as follows:

[0060]

[0061] The formulas for calculating the corrosion rates of dissolved oxygen, SRB, and CO2 in step S6 are as follows:

[0062]

[0063] In the formula, 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 The molecular weight of Fe is 56 kg / mol; ρ Fe The density of Fe is 7.8 kg / m³. 3 i α The total corrosion current density is expressed in A / m. 2 n is 2.

[0064] The prediction model for the local rapid corrosion rate of oil and gas pipelines based on multiple factors in step S7 is as follows:

[0065] ln(CR-CR(SRB)-CR(CO2)-CR(DO))=Eln(ν+1) 2 +Fln(ν+1)+Mln(C α +1)+N

[0066] In the formula: v is the liquid flow velocity, m / s; CCl - For Cl - Concentration, mg / L; E / F / M / N are constants that can be determined experimentally.

[0067] The orthogonal experimental data are shown in Table 1.

[0068] Table 1. Charge transfer and mass transfer current density of O2 / SRB / CO2 under orthogonal experimental conditions.

[0069]

[0070]

[0071] The model was validated using the results of orthogonal experiments on local corrosion rates. The linear fitting error in a multi-factor synergistic local rapid corrosion rate prediction model is shown in [the table]. Figure 1 The absolute value of the relative error in corrosion prediction ranges from 0.18% to 9.67%, with an average absolute value of 2.92%.

Claims

1. A method for establishing a multi-factor synergistic local rapid corrosion rate prediction model, characterized in that, Includes the following steps: S1: Dissolved oxygen, SRB, and CO2 corrosion all take charge transfer and mass transfer into account, and the corrosion current density of each factor is calculated. S2: Considering dissolved oxygen mass transfer and electron transfer, calculate the current density for dissolved oxygen corrosion. S3: In SRB corrosion, due to the formation of corrosion products and biofilm, the influence of mass transfer on corrosion must be considered, and the corrosion current density caused by SRB must be calculated. 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, Fe at the anolyte loses electrons and dissolves, becoming Fe2+. 2+ Its dissolution process is related to SRB, CO2 and O2 corrosion, and the total corrosion current density is calculated. 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 CO2 are calculated. S7: Considering dissolved oxygen synergistically corrodes SRB and CO2, as well as Cl... - The accelerating effect of flow velocity on corrosion was investigated, and a multi-factor collaborative local rapid corrosion rate prediction model for oil and gas pipelines was established. Formula for calculating corrosion current density: In the formula, i c(i) Let i be the cathode current density caused by the material, in A / m. 2 ; i lim(i) Let i be the current density for mass transfer control, in A / m. 2 ; i ct(i) Let i be the current density controlled by charge transfer of matter, in A / m. 2 ; Formula for calculating total corrosion current density: In the formula, i α The total corrosion current density is expressed in A / m. 2 ; Oxygen corrosion current density, A / m 2 ; The current density for sulfate reduction is A / m. 2 ; CO2 corrosion current density, A / m 2 ; Formulas for calculating corrosion rates of dissolved oxygen, SRB, and CO2: In the formula, 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; MW Fe The molecular weight of Fe is 56 kg / mol; ρ Fe The density of Fe is 7.8 kg / m³. 3 i α The total corrosion current density is expressed in A / m. 2 n is 2; A predictive model for the rate of rapid local corrosion in oil and gas pipelines, based on the combined effects of multiple factors: ln(CR-CR(SRB)-CR(CO2)-CR(DO))=Eln(ν+1) 2 +Fln(ν+1)+Mln(C α +1)+N In the formula: CR is the corrosion rate, mm / a; v is the liquid flow rate, m / s; C α The total concentration is expressed in mg / L; E / F / M / N are constants, determined experimentally.

2. The method for establishing a multi-factor synergistic local rapid corrosion rate prediction model as described in claim 1, characterized in that, The formula for calculating dissolved oxygen corrosion current density in step S2 is as follows: In the formula, Oxygen corrosion current density, A / m 2 ; The current density controlled by charge transfer in oxygen corrosion, A / m 2 ; Current density for oxygen corrosion mass transfer control, A / m 2 .

3. The method for establishing a multi-factor synergistic local rapid corrosion rate prediction model as described in claim 1, characterized in that, The formula for calculating the SRB corrosion current density in step S3 is as follows: In the formula, The current density for sulfate reduction is A / m. 2 ; The current density for sulfate reduction mass transfer control, A / m 2 ; The current density controlled by charge transfer during sulfate reduction, in A / m 2 .

4. The method for establishing a multi-factor synergistic local rapid corrosion rate prediction model as described in claim 1, characterized in that, The formula for calculating the CO2 corrosion current density in step S4 is as follows: In the formula, CO2 corrosion current density, A / m 2 ; The current density for CO2 mass transfer control, in A / m 2 ; The current density controlled by CO2 charge transfer, A / m 2 .

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