CN111504846A - A rapid indoor evaluation method of corrosion inhibitor for crude oil production and transportation pipeline - Google Patents

Abstract

The invention discloses an indoor rapid evaluation method for a corrosion inhibitor of a crude oil production and transportation pipeline, and relates to the field of corrosion and protection of crude oil pipelines. Aiming at the problem that the evaluation speed of the corrosion inhibitor for crude oil production and transportation pipelines is slow at present, the invention provides an indoor rapid evaluation method for the corrosion inhibitor of crude oil production and transportation pipelines. And designed the loop test device used in the dynamic coupon test, combined the three experimental results to determine the mechanism of action of different corrosion inhibitors, comprehensively evaluate the effect of corrosion inhibitors, and can quickly screen out the corrosion inhibitor suitable for crude oil production and transportation. etchant.

Description

A rapid indoor evaluation method of corrosion inhibitor for crude oil production and transportation pipeline

technical field

The invention relates to the technical field of material corrosion and protection, in particular to an indoor rapid evaluation method of a corrosion inhibitor for crude oil production and transportation pipes, which mainly screens and evaluates the corrosion inhibitors used for the corrosion protection of crude oil production and transportation pipes.

Background technique

Crude oil pipeline transportation plays an extremely important role in the economic development of my country and the world. Therefore, maintaining the safe and healthy operation of crude oil pipelines is an important and arduous long-term task for pipeline workers. Most of the crude oil pipelines are in complex soil environment, and the transported medium is also corrosive, so the inner and outer walls of the pipeline may be corroded. Once the pipeline is corroded and perforated, the leakage of oil and gas will not only interrupt the transportation, but also pollute the environment and even cause fire hazards. The production and transportation pipeline in the crude oil pipeline has the most complex transportation medium, the most impurities, and the worst transportation environment. A type of pipe that is prone to corrosion.

In recent years, due to the high water content, salinity and chloride ion content of the produced fluid in some old oil wells, as well as the emergence of corrosive gases such as CO ₂ , the phenomenon of serious corrosion of some production and transportation pipes has begun to emerge, while the corrosion inhibition As an efficient and low-cost chemical preservative, it is gradually becoming a mainstream anti-corrosion measure in oil and gas fields. However, there are many types of corrosion inhibitors, and different production and transportation pipelines require different corrosion inhibitors, resulting in abnormal selection of corrosion inhibitors. Complicated and time-consuming. Therefore, it has broad prospects and practical significance to find a method for rapid screening and evaluation of corrosion inhibitors for crude oil production and transportation pipelines.

SUMMARY OF THE INVENTION

Aiming at the problem that the evaluation speed of the corrosion inhibitor for crude oil production and transportation pipelines is slow in the prior art, the invention provides a method for evaluating the indoor effect of the corrosion inhibitor for crude oil production and transportation pipelines. Experiments, combined with three experimental results to comprehensively evaluate the effect of corrosion inhibitors, can quickly screen out corrosion inhibitors suitable for crude oil production and transportation pipelines.

In order to achieve the above purpose, the concrete technical scheme of a method for evaluating the indoor effect of a crude oil production pipeline corrosion inhibitor of the present invention is:

Static slide test solution:

(1) Treatment of the test piece before the test

①Degreasing and decontamination: take out the coupons, wipe off the oil stains with coarse filter paper, remove the dirt on the surface of the test piece with absorbent cotton, and clean it continuously for 2 to 3 times;

②Dehydration: The degreased specimens are soaked in absolute ethanol for further degreasing and dehydration;

③Drying: Take out the test piece and wipe it with dry filter paper, and dry it with cold air at the same time;

④Weighing: Pack the wiped and blow-dried test piece with filter paper according to the test piece number, and weigh it after placing it in a desiccator for 4 hours.

(2) Test operation process

①Use a vernier caliper to measure the size of the processed coupons, and weigh them at the same time. Do not touch the coupons directly with your hands during the process;

② Prepare the solution according to the corrosion inhibitor concentration required for the test;

③After that, hang it in the sample with a rope and let it stand for 168 hours, then take it out for processing and calculate the weight loss.

(3) The processing method after the test coupon is taken out

①Configure the cleaning solution: Weigh hydrochloric acid and add distilled water to dissolve it to form a solution;

②Degreasing and decontamination: Take out the test piece, gently wipe off the oil stain with filter paper, wash the oil with acetone and put it in the cleaning solution for 1-5min (you can use a brush to gently brush it when cleaning), and then use sodium hydroxide after cleaning the test piece. The solution is acid-base neutralized;

③Dehydration: soak the specimen in absolute ethanol for about 5 minutes to further degreasing and dehydration;

④Drying and weighing; dry the surface of the test piece with filter paper, and dry it with cold air at the same time, then store it in a desiccator for 4 hours and weigh it.

Dynamic hanging test plan:

①The metal coupons are polished with sandpaper, rinsed with water, and soaked in absolute ethanol;

② Take out the coupons and dry them with cold air, take pictures, weigh, and record the data;

③Open the hose (1), hang the hanging piece (3) in the hose with a thin nylon thread (2), make the hanging piece (3) lie flat on the bottom of the hose, and add different kinds of water into the produced water. and concentration of corrosion inhibitor, using micro DC brushless water pump (4) to make the produced water wash the coupons repeatedly at different flow rates; the cycle is about 168h;

④Using hydrochloric acid (100mL) and hexamethylenetetramine (5g) to configure acid cleaning solution;

⑤ After completing one cycle, take out the coupons and soak them in the above solution, rinse them with clean water and dry them with cold air, then weigh them and record the data;

⑥Use the tee to change the flow rate and repeat the test, the test process and the test material.

The corrosion rate is calculated as follows:

where V _corr —average corrosion rate, mm/a; m ₀ —mass of test piece before test, g; m1 _— mass of test piece after test, g; S—total area of test piece, cm ² ; ρ—test piece Density of sheet material, g/cm ³ ; t—test time, h.

where R _L —local corrosion rate, mm/a; h—pitting depth, μm; t—corrosion time, d.

Electrochemical test scheme:

In the electrochemical reaction, a three-electrode system was used to measure the Tafel polarization curve. The electrochemical electrodes were first prepared. The reference electrode was Ag/AgCl electrode, the crude oil production and transportation pipe was processed as the working electrode, and the auxiliary electrode was Pt wire. Cut a PVC pipe into thousands of sections of appropriate length, and use sandpaper of different thickness to smooth the front and rear ends of the shortened PVC pipe; prepare several sections of copper wires with insulating sheaths of appropriate length, and cut off each section. The insulating sheath of the front and rear sections of the metal wire, if the exposed copper wire is embroidered, it needs to be polished with sandpaper until it is bright; place the polished and cleaned steel sheet on the glass surface, and use an electric soldering iron to melt it on the surface of the steel sheet Quickly insert one side of the metal wire into the molten solder wire on the surface of the steel sheet to fix it for 30 seconds, fix the other side of the steel sheet on the double-sided tape, and use the prepared curing agent to fill and seal the PVC pipe. , let stand for seven days, the curing agent used is epoxy resin system curing agent, first put the prepared working electrode, saturated electrode, Ganlai electrode and uranium electrode into the electrolytic cell, and then put the electrolytic cell, electrochemical workstation and gas cylinder three connection. When the applied polarization potential is large, the logarithm of the current density has a linear relationship with the overpotential. By extrapolating the polarization curve, kinetic parameters such as Tafel slope, corrosion current density, and corrosion potential can be obtained. A comparative experiment was carried out with the agent group, and the action mechanism of the corrosion inhibitor was determined by the moving direction of the electrochemical polarization curve.

Description of drawings

Fig. 1 is the indoor effect evaluation steps of the corrosion inhibitor for crude oil production and transportation;

Fig. 2 is a schematic diagram of a dynamic coupon test loop experimental device;

Figure 3 is the electrochemical test curve of X210-LSJW;

Figure 4 is the electrochemical test curve of X210-2-GTW-400;

Figure 5 is the electrochemical test curve of X210-5-DLO-300.

Detailed ways

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, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Table 1 is the crude oil density of the measured crude oil samples:

Table 1 Density of oil samples at 20℃

Hashtag X210 X210-2 X210-5 X216-2 X275 X275-1 H132 H131-5 Density/(g/cm³) 0.851 0.846 0.846 0.848 0.852 0.852 0.851 0.844

Step 1: Perform a static corrosion coupon test,

1) Test plan

In order to further verify the effect of adding corrosion inhibitor on site, an indoor supplementary test of the field test is planned. The test steps include the processing of the test piece before the test, the test operation process, the processing method after the test coupon is taken out, etc. The specific operations are as follows:

(1) Treatment of the test piece before the test

①Degreasing and decontamination: take out the coupons, wipe off the oil stains with coarse filter paper, remove the dirt on the surface of the test piece with absorbent cotton, and clean it continuously for 2 to 3 times;

②Dehydration: The degreased specimens were soaked in absolute ethanol for about 5 minutes for further degreasing and dehydration;

③Drying: Take out the test piece and wipe it with dry filter paper, and dry it with cold air at the same time;

④Weighing: Pack the wiped and blow-dried test piece with filter paper according to the test piece number, place it in a desiccator for 4 hours, and weigh it to the nearest 0.1 mg for use.

(2) Test operation process

①Use a vernier caliper to measure the size of the processed coupons, and weigh them at the same time. Do not touch the coupons directly with your hands during the process;

② Prepare the solution according to the corrosion inhibitor concentration (1000mg/L) required for the test;

③After that, hang it in the sample with a rope and let it stand for 168 hours, then take it out for processing and calculate the weight loss.

(3) The processing method after the test coupon is taken out

①Configure the cleaning solution: Weigh 50mL of hydrochloric acid, add distilled water to dissolve it, and prepare a solution of 500mL;

②Degreasing and decontamination: Take out the test piece, gently wipe off the oil stain with filter paper, wash the oil with acetone and put it in the cleaning solution for 1-5min (you can use a brush to gently brush it when cleaning), and then use sodium hydroxide after cleaning the test piece. The solution is acid-base neutralized;

③Dehydration: soak the specimen in absolute ethanol for about 5 minutes to further degreasing and dehydration;

④Drying and weighing; dry the surface of the test piece with filter paper, and dry it with cold air at the same time, then store it in a desiccator for 4 hours and weigh it to the nearest 0.1 mg.

(4) The corrosion rate is calculated according to formula (1-1).

2) Corrosion inhibition effect of different corrosion inhibitors at the same concentration

Table 2 shows the corrosion inhibition effect of five corrosion inhibitors on N80 steel coupons at a concentration of 1000 mg/L. It can be seen that under the same concentration (1000mg/L), the corrosion inhibitor GTW-400 has better corrosion inhibition effect in H131-5, X210-5 and X210, and the lowest corrosion inhibition rate reaches 58.24%; Corrosion inhibitor DLO-300 has better corrosion inhibition effect in H131-5 and X210, with a minimum corrosion inhibition rate of more than 51%; corrosion inhibitor DLW-300 in X210-5 and X210-2 The corrosion inhibition rate of more than 79%; The corrosion inhibition rate of GTO-180 is only 84.62% in X210, and the corrosion inhibition rate in other samples is lower than 30%; LSJW-500 has poor corrosion inhibition effect in all four samples, and the highest corrosion inhibition rate rates are below 40%.

Table 2 Corrosion Inhibition Effect of Five Corrosion Inhibitors on N80 Steel

When the corrosion inhibition effect of the added corrosion inhibitor is good, the corresponding coupons will naturally have less rust spots, while when the corrosion inhibition effect is poor, the corresponding coupons will corrode more seriously and the rust spots will increase.

Table 3 Corresponding immersion solutions for coupons

3) The effect of different inhibitor concentrations

The two corrosion inhibitors DLW-300 and GTW-400 with the best corrosion inhibition effect in the previous test were selected, and N80 steel was used to make coupons. Static coupon weight loss method, observe the coupon corrosion after a period of time (one week) and calculate the corrosion rate.

The corrosion inhibition effect of the corrosion inhibitor DLW-300 is obviously better than that of GTW-400. With the increase of the concentration of the two corrosion inhibitors, the corrosion inhibition effect does not increase significantly, and the corrosion inhibition effect of the two corrosion inhibitors at 500 mg/L is better than that at 1500 mg/L.

Step 2: Dynamic Corrosion Coupon Test

1) Test plan

①The metal coupons are polished with sandpaper, rinsed with water, and soaked in absolute ethanol;

② Take out the coupons and dry them with cold air, take pictures, weigh, and record the data;

③ Open the hose, hang the coupon in the hose with a thin nylon thread, and make the coupon lie flat on the bottom of the hose, add corrosion inhibitors of different types and concentrations to the produced water, and use a submersible pump to make the produced water The coupons are washed repeatedly under different flow rates, and the cycle is about 168h;

④Using hydrochloric acid (100mL) and hexamethylenetetramine (5g) to configure acid cleaning solution;

⑤ After completing one cycle, take out the coupons and soak them in the above solution, rinse them with clean water and dry them with cold air, then weigh them and record the data;

⑥Use the tee to change the flow rate and repeat the test. The test process is different from the test material.

2) Dynamic corrosion inhibition effect of corrosion inhibitor LSJW-500

The dynamically corroded coupons of X210 produced water corrode more seriously than the statically corroded coupons, which may also be due to erosion corrosion.

It can be seen from Table 4 that with the increase of the concentration of corrosion inhibitor LSJW-500, the corrosion rate first decreased and then increased. When the dosage of corrosion inhibitor LSJW-500 reached 112.2 mg/L, the quality of the coupons The loss is the lowest, and the slow release effect is the best.

Table 4 Corrosion inhibition effect of corrosion inhibitor LSJW-500

3) Evaluation of corrosion inhibition effect of corrosion inhibitor DLW-300

The dynamic coupon test results of X210-5 produced water show that the dynamic coupon corrosion degree is obviously more serious than the static coupon corrosion. It can be seen from Table 5 that for the corrosion inhibitor DLW-300, compared with the first cycle, the corrosion inhibition rate of the second cycle decreased significantly. With the further increase of the concentration, the corrosion inhibition rate rises to the state of the first cycle again. When the dosage of DLW-300 is 148.2mg/L, the corrosion inhibition effect is the best.

Table 5 Corrosion inhibition effect of corrosion inhibitor DLW-300

Step 3: Electrochemical evaluation, add corrosion inhibitor LSJW-500 to X210 sample to prepare a solution with a corrosion inhibitor concentration of 1000 mg/L; add corrosion inhibitor GTW-400 to X210-2 sample to prepare a corrosion inhibitor The solution with a concentration of 1000mg/L; the corrosion inhibitor DLO-300 was added to the X210-5 sample to prepare a solution with a corrosion inhibitor concentration of 1000mg/L; DLO-300, GTO-180 and LSJW were added to the H131-5 sample respectively -500 three kinds of corrosion inhibitors, respectively prepare 1000mg/L solution.

Fig. 3, Fig. 4, Fig. 5 are the poles after adding corrosion inhibitor LSJW-500, GTW-400 and DLW-300 to the produced water of X210, X210-2 and X210-5, respectively, of N80 steel for production and transportation. Chemical curve, the concentration of the additive is 1000mg/L. It can be seen that the corrosion potential increases and the polarization curves move to the upper left after adding the corrosion inhibitor, which indicates that the corrosion current densities of the cathode and the anode are reduced after the addition of the corrosion inhibitor, so the corrosion rate is reduced. It was also observed that the addition of the agent had little effect on the cathodic polarization curve, which basically coincided with the cathodic polarization curve of the blank group, which indicated that the added corrosion inhibitor mainly controlled the corrosion process of the metal anode. In addition, according to the principle of the anodic desorption process of the corrosion inhibitor: when the potential increases, the adsorption coverage decreases, and the anodic polarization increases, so that the anodic dissolution rate of the metal surface not covered by the corrosion inhibitor increases, and the anodic dissolution rate increases. The stability of the metal surface covered by the corrosion inhibitor is weakened, and finally the anodic desorption process occurs, and the coverage of the corrosion inhibitor is reduced. Cycling like this will cause the coverage to go to zero, and the metal surface will behave as if it were in a solution without corrosion inhibitor. Therefore, on the anodic polarization curve of the corrosion metal in the solution with corrosion inhibitor, when the potential reaches a relatively positive electrode potential, there will be a "platform" in which the anode current density increases rapidly. "After continuing the anodic polarization, the polarization curve will nearly coincide with the metal anodic polarization curve in the blank solution. This shows that the added corrosion inhibitor conforms to the principle of anodic desorption.

Three corrosion inhibitors DLO-300, GTO-180 and LSJW-500 were added to the produced water of H131-5 at 1000 mg/L each. It can be seen that after adding the three kinds of corrosion inhibitors, the corrosion potential increases and the corrosion is controlled. Among them, the cathodic polarization curve of LSJW-500 overlapped with the blank group, and there was an anodic desorption process. After the anodic desorption process, the anodic polarization curve completely overlapped with the anodic polarization curve in the blank solution. After adding the three corrosion inhibitors, the corrosion potential of DLO-300 moved the most to the positive direction, indicating that the corrosion inhibition effect was the best.

Claims (5)

1. a crude oil production pipeline corrosion inhibitor indoor rapid evaluation method, is characterized in that, comprises following process: The first step: take the liquid in the crude oil production pipeline on site for static coupon test, and calculate the average corrosion rate and local corrosion rate; The second step: take the liquid in the crude oil production pipeline on site, use the loop test device to carry out dynamic coupon test, and calculate the average corrosion rate and local corrosion rate; The third step: carry out electrochemical experimental evaluation to determine the mechanism of corrosion inhibitor; The fourth step: comprehensively compare the results of the electrochemical experiment with the static coupon test and the dynamic coupon test, and complete the evaluation of the corrosion inhibitor effect. 2. a kind of crude oil production pipeline corrosion inhibitor indoor rapid evaluation method according to claim 1, is characterized in that, described static coupon experiment concrete operation: Firstly, the experimental solution is prepared according to the required concentration of corrosion inhibitor, and then the coupons are subjected to pre-test treatment, including (1) degreasing and decontamination: take out the coupons, wipe off the oil stains with coarse filter paper, and use absorbent cotton to remove the surface contamination of the test piece; (2) Dehydration: degreased specimens, soaked in absolute ethanol; ③Drying: Take out the specimens, wipe them with dry filter paper, and blow dry with cold air at the same time; ④Weighing: Weigh the wiped and dried specimens and measure their length , width and height. After the coupons are processed, hang the coupons in the solution with a rope and let them stand for a period of time, then take them out, and then test the coupons after treatment, including: ① Prepare cleaning solution: prepare hydrochloric acid solution; ② degrease to remove Contamination: Take out the test piece, gently wipe off the oil stain with filter paper, wash the oil with acetone and put it in the cleaning solution. After cleaning the test piece, use sodium hydroxide solution for acid-base neutralization; ③Dehydration: soak in absolute ethanol; ④Drying and weighing: Dry the surface of the test piece with filter paper, and dry it with cold air at the same time and weigh it. 3. a kind of crude oil production pipeline corrosion inhibitor indoor rapid evaluation method according to claim 1, is characterized in that, the loop experiment device that described dynamic coupon experiment adopts: Open the hose (1), hang the coupon (3) in the hose (1) with a thin nylon thread (2), and make the coupon (3) lie flat on the bottom of the hose (1). The corrosion inhibitor solution is added to the tank (6), the produced water is circulated by the miniature DC brushless water pump (4), and the flow rate is changed by the flow rate regulating valve (5), so that the produced water repeatedly washes the coupons at different flow rates. 4. a kind of crude oil production pipeline corrosion inhibitor indoor rapid evaluation method according to claim 1, is characterized in that, described dynamic coupon test step is: ①The metal coupons are polished with sandpaper, rinsed with water, and soaked in absolute ethanol; ② Take out the coupons and dry them with cold air, take pictures, weigh, and record the data; ③Open the hose (1), hang the hanging piece (3) in the hose with a thin nylon thread (2), make the hanging piece (3) lie flat on the bottom of the hose, and add different kinds of water into the produced water. and concentration of corrosion inhibitor, the produced water is repeatedly washed with the coupons at different flow rates by using the micro DC brushless water pump (4); ④Using hydrochloric acid and hexamethylenetetramine to configure acid cleaning solution; ⑤ After completing one cycle, take out the coupons and soak them in the above solution, rinse them with clean water and dry them with cold air, then weigh them and record the data; ⑥Use the flow rate control valve (5) to change the flow rate and repeat the test. 5. a kind of crude oil production pipeline corrosion inhibitor indoor quick evaluation method according to claim 1, is characterized in that, in electrochemical reaction, adopts three-electrode system to measure Tafel polarization curve, wherein, reference electrode is Ag /AgCl electrode, the crude oil production and transportation pipeline is processed as the working electrode, and the auxiliary electrode is Pt wire. When the external polarization potential is large, the logarithm of the current density and the overpotential have a linear relationship. By extrapolating the polarization curve, we can get The kinetic parameters such as Tafel slope, corrosion current density, corrosion potential, etc., were compared with the blank group and the corrosion inhibitor group, and the action mechanism of the corrosion inhibitor was determined by the moving direction of the electrochemical polarization curve.

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