CN112195489A

CN112195489A - Protective coating of pipe wall, electroplating method and application

Info

Publication number: CN112195489A
Application number: CN202011015440.6A
Authority: CN
Inventors: 张志超; 李代强; 郇承武; 邱桃; 倪小龙; 白杨; 刘红林; 孟祥伟
Original assignee: Xinjiang Defeng Yisheng Petroleum Anticorrosion Engineering Co Ltd
Current assignee: Xinjiang Defeng Yisheng Petroleum Anticorrosion Engineering Co Ltd
Priority date: 2020-09-24
Filing date: 2020-09-24
Publication date: 2021-01-08

Abstract

The invention provides a protective coating for sulfate reducing bacteria corrosion, an electroplating method and application. The protective coating is a three-layer composite coating; the composite plating layer is bottom semi-bright nickel, middle bright copper and outer bright nickel; the potential of the bottom layer semi-bright nickel is 120mV or more higher than that of the middle layer bright copper, and the potential of the middle layer bright copper is 60-100 mV higher than that of the outer layer bright nickel; the electroplating method adopts a flow electroplating mode, and the additive of the electroplating solution is added at a liquid outlet of the electroplating tank by taking the electroplating current as a metering reference. The invention has perfect process flow, reasonable matching and use of the additives, and multilayer corrosion prevention on the inner wall of the oil pipe and the sleeve, and can effectively reduce the corrosion of sulfate reducing bacteria on the pipe matrix.

Description

Protective coating of pipe wall, electroplating method and application

Technical Field

The invention relates to the field of petroleum and mechanical engineering surface treatment, in particular to a protective coating of a pipe wall, an electroplating method and application.

Background

The understanding of microbial corrosion is that the corrosion of oil wells, mines, harbors and lakes to pipes is related to microbial activities, Sulfate Reducing Bacteria (SRB) are the most common strains causing microbial corrosion, and because of the large amount of sulfate reducing bacteria, oil wells not only corrode equipment, but also reduce the treatment efficiency of water treatment equipment and the like. Sulfate reducing bacteria cause economic losses of up to several billion dollars per year. The sulfate reducing bacteria can accelerate anaerobic corrosion of carbon steel, and hydrogen ions released by metabolite hydrogen sulfide under a humid condition are strong depolarizers to accelerate metal depolarization. The corrosion of the steel can be accelerated by a factor of 15 due to the action of sulfate-reducing bacteria.

Aiming at the corrosion action of sulfate reducing bacteria, the protection mode commonly used in the field generally adopts comprehensive measures such as electrochemical protection, sterilization, bacteriostasis, biological control, covering layer and the like. For buried steel pipes, coatings are commonly used which are barriers between the steel and the corrosive environment and protect the steel against corrosion, and cathodic protection. Electrodeposition is widely used to make metal matrix composites over its low cost, low operating temperature, low energy requirements, and ability to handle complex geometry coatings.

The oil pipe protective material is generally selected from nickel and its alloy. Under acidic and neutral conditions, the potential of nickel drops below-0.4V, cathodic protection can be easily achieved, the corrosion of nickel is much slower than that of iron, and nickel and its alloys can be passivated in most media to resist corrosion of the media.

In the surface single-layer nickel alloy plating technology, the porosity of nickel is high, the thickness reaches 40-50 microns, the effect is better, and the investment on cost is high. The most important point is that the corrosion action of sulfate reducing bacteria cannot be completely resisted, sulfide can cause the change of an oxide layer of the sulfide to cause the fracture of the sulfide, local corrosion can be caused, corrosion points can easily permeate into an oil pipe matrix, and under the corrosion mechanism action of the sulfate reducing bacteria, the corrosion rate of the oil pipe matrix can be accelerated. The problems of short service cycle, high maintenance cost and the like of the surface single-layer common nickel plating still exist.

Liu hong Fang et al in material protection, 1999,32(11) reported that the microbial corrosion resistance of Q235 steel can be improved by chemically plating Ni-P and Ni-Mo-P, wherein the P content of the Ni-P plating layer is 8.56 wt%, the P content of the Ni-Mo-P plating layer is 4.59 wt%, and the Mo content is 17.19 wt%. The test piece was subjected to a corrosion test in a medium containing SRB, and it was found that the corrosion rate of Q235 steel in the medium of SRB was 0.0339mm/a, that of Ni-P was 0.0145mm/a, and that of Ni-Mo-P was 0.0438 mm/a. Although the material has certain microbial corrosion resistance, the effect is not good.

In summary, the research of the prior art is of great significance in developing a plating material capable of effectively preventing the corrosion of sulfate reducing bacteria aiming at the unsatisfactory corrosion effect of microorganisms, especially sulfate reducing bacteria.

Disclosure of Invention

Aiming at the problem of anaerobic corrosion of sulfate reducing bacteria to carbon steel and metal for producing oil wells, the invention provides a protective coating of a pipe wall, an electroplating method and application, and aims to solve the corrosion problem of sulfate reducing bacteria from a protective material, so that the effect of protecting against microbial corrosion tends to be green, ecological and efficient. The harmonious development of materials and environment is realized, and the corrosion of sulfate reducing bacteria to metals is economically and effectively prevented.

The invention provides a protective coating of a pipe wall, which is a three-layer composite coating; the composite plating layer is bottom semi-bright nickel, middle bright copper and outer bright nickel;

the potential of the bottom semi-bright nickel is higher than that of the middle bright copper by 120mV or more, preferably 120-130 mV; the potential of the middle bright copper layer is 60-100 mV higher than that of the outer bright nickel layer.

The thickness of the bottom layer of the composite coating is 10-15 mu m, the thickness of the middle layer is 20-25 mu m, and the thickness of the outer layer is 10-15 mu m; the outer plating layer contains phosphorus and sulfur, the phosphorus content accounts for 3-5% of the mass of the outer plating layer, and the sulfur content accounts for 0.05-0.08% of the mass of the outer plating layer.

The invention provides a method for electroplating a protective coating on a pipe wall, wherein the electroplating process is divided into three stages, the first stage is to electroplate bottom semi-bright nickel, the second stage is to electroplate middle bright copper, and the third stage is to electroplate outer bright nickel;

the first stage electroplating solution comprises the following components: 200-350 g/L of nickel sulfate, 20-50 g/L of boric acid, 0.05-0.1 g/L of sodium dodecyl sulfate and 3.0-4.8 of pH; the second stage electroplating solution comprises the following components: 150-260 g/L of copper sulfate solution, 50-100 g/L of sulfuric acid, 0.05-0.1 g/L of polyethylene glycol and 0.01-0.02 g/L of sodium polydithio dipropyl sulfonate; the third stage plating solution consists of: 200-400 g/L nickel sulfate, 20-50 g/L boric acid, and saccharin (C)₆H₅COSO₂NH) 0.6-1.0 g/L, 1, 4-butynediol 0.4-0.5 g/L, coumarin 0.1-0.2 g/L, sodium hypophosphite 1.2-6 g/L, and pH 4.0-4.8;

the protective coating is an inner coating of the oil pipe or the sleeve; the electroplating method adopts a flow electroplating mode and comprises the following steps: the electroplating solution continuously circulates and flows through the inner wall of the pipe at a flow speed of 0.2-0.5 m/s for flow electroplating.

In the electroplating process, additives need to be added along with the consumption of the effective components of the plating solution. The additive of the electroplating solution is added at the liquid outlet of the plating bath, and flows into the liquid inlet after being circularly stirred uniformly; the addition amount is based on the current of electroplating.

Furthermore, the additives are added in a mode that the additives in the first stage are 2.5-2.7 g/kAh of nickel sulfate, 2.5-2.7 kg/kAh of nickel carbonate and 2-6 g/kAh of sodium dodecyl sulfate; the second stage additive is 2.2-2.4 kg/kAh copper sulfate, 2.0-2.2 kg/kAh copper carbonate, 1.4-2.2 g/kAh polyethylene glycol, 0.5-0.8 g/kAh sodium polydithio dipropyl sulfonate; the third stage additive is 4-4.4 kg/kAh of nickel sulfate, 1.9-2.4 kg/kAh of nickel carbonate, 37-115 g/kAh of sodium hypophosphite, 22-24 g/kAh of saccharin, 10-14 g/kAh of 1, 4-butynediol and 10-14 g/kAh of coumarin.

In the electroplating method, the electroplating condition of the first stage is that the current density is 2.0-5.5A/dm²The electroplating temperature is 45-60 ℃, and the electroplating time is 20-30 min; plating conditions of the second stage: the current density is 1.9-4.6A/dm²The electroplating temperature is 18-28 ℃, and the electroplating time is 20-30 min; plating conditions of the third stage: the current density is 1.5 to 4.5A/dm²The electroplating temperature is 45-60 ℃, and the electroplating time is 15-20 min.

The electroplating method comprises one or more steps of degreasing, derusting, acid cleaning, neutralizing and activating before flow electroplating.

The oil removal is divided into high-temperature oil removal and flow oil removal. The high-temperature oil removal temperature is 350-450 ℃; the flowing oil removal is that the oil removal liquid circularly flows through the inner wall of the sleeve at the flow speed of 0.5-1 m/s, the temperature of the oil removal liquid is 40-60 ℃, and the oil removal time is 10-30 min. The deoiling liquid comprises the following components: 30-60 g/L of sodium hydroxide, 20-40 g/L of sodium carbonate and the balance of water.

The acid washing adopts a flowing acid washing mode: namely, the pickling solution circularly flows through the inner wall of the sleeve at the flow speed of 0.5-1 m/s; the pickling time is 5-10 min; the pickling solution comprises 92-184 g/L sulfuric acid, 118-236 g/L hydrogen chloride and the balance of water;

the neutralization adopts a flow neutralization mode: namely, the neutralization solution circularly flows through the inner wall of the sleeve at the flow speed of 0.5-1 m/s; the neutralization time is 2-8 min; the neutralization solution comprises 30-80 g/L trisodium phosphate and 20-60 g/L potassium sodium tartrate, and the pH value is greater than 12.

The activation adopts a flow activation mode: namely, the activating solution circularly flows through the inner wall of the sleeve at the flow speed of 0.2-0.5 m/s; the activation time is 3 min-6 min. The activating solution comprises 92-184 g/L sulfuric acid and the balance of water.

The anode installation mode in the electroplating method is that an insoluble cylindrical anode with uniform conductivity is designed and used according to the size of the pipe and penetrates into the pipe.

The electroplating method also comprises a dehydrogenation treatment process after electroplating: the dehydrogenation treatment temperature is 180-250 ℃, and the dehydrogenation treatment time is 2 h. The total thickness of the coating after hydrogen removal is not less than 40 μm.

The invention also provides a protective application of the protective coating of the pipe wall in a sulfate reducing bacteria corrosion environment.

Compared with the prior art, the invention has the following advantages:

(1) the electroplating method adopts a flow electroplating mode, and the easily consumed main salt and the auxiliary agent are added at the liquid outlet of the plating tank in the form of additive supplement, and are circularly refluxed to the bottom of the liquid outlet after being uniformly mixed. The additive amount is based on the current of electroplating. The method optimizes the adding mode and dosage of the additive, and particularly optimizes the brightener which consumes less quantity in the electroplating process. Compared with the traditional electroplating method, the additive amount is more accurate, the circulation is sufficient, the sufficient supply of the additive can be ensured, the ionic components and the content of the plating solution in the plating tank are stable, and the produced plating layer is not easy to generate plating layer defects.

(2) In the nickel-copper-nickel composite coating prepared by the electroplating method, the bright nickel on the outer layer is high-dispersion bright nickel, the thickness of the coating is uniform, and the error of the thickness of the coating is within 5% of a target value; the outer bright nickel layer has high chemical stability in air, the passivation characteristic can avoid the depolarization under the aerobic condition, and the thickness and the corrosion resistance of the plating layer can not be reduced due to corrosion after long-term use. The bright nickel contains a small amount of phosphorus, so that the preservative effect on the sulfate reducing bacteria can be improved. The thickness of the plating layer is ensured by the bright copper plating layer in the middle layer, the porosity of the plating layer is further reduced, and the porosity of the tight combination of the copper layer and the nickel layer is less than that of the combination of the nickel layer and the nickel layer. The potential of the semi-bright nickel of the bottom layer is higher than that of the copper layer and bright nickel, the potential of the semi-bright nickel of the bottom layer is higher than that of the bright copper by at least 120mV, the potential of the bright copper layer is higher than that of the bright nickel layer by 60-100 mV, and once galvanic cell reaction occurs, the outer layer is preferentially corroded transversely. And the semi-bright nickel is firmly combined with the tube substrate and the bright copper, so that the binding force of the coating is ensured. The composite plating layer of nickel, copper and nickel can make the pores of every metal plating layer dislocate, so that the pores of the plating layer can be optimized, and the corrosion of sulfate reducing bacteria to the pipe substrate can be avoided. Therefore, the composite plating layer has better stability and effectiveness on the anticorrosion effect of sulfate reducing bacteria.

(3) The process flow is complete, the additives are reasonably matched and used, and multilayer corrosion prevention is performed on the oil pipe and the inner wall of the casing pipe. The type and proportion of the primary brightener and the secondary brightener are reasonably added in the bright nickel plating solution in a matched manner, so that the potential of the plating layer is slightly shifted negatively, the corrosion potential of the bright nickel layer can be lower than that of the bright copper layer by 60-100 mV, the passivation of the nickel plating layer is ensured, the cathode is protected, and the corrosion rate is reduced.

Detailed Description

In order to make the technical solutions of the present invention better understood by those skilled in the art, the solutions of the present invention are further described below with reference to the following examples. And (4) detecting the thickness of the coating by adopting a metallographic test method. The plating layer potential difference detection instrument is an electrolytic thickness gauge, carries out electrochemical corrosion on the plating layer according to the difference of plating layer potential differences, obtains the potential of the corresponding plating layer according to the stable corrosion potential of each layer and calculates the potential difference value between each layer. The alloy content in the coating is tested by adopting a scanning electron microscope.

Example 1

The embodiment provides an electroplating method of a protective coating corroded by sulfate reducing bacteria. The coating is an inner coating of the oil pipe; the electroplating comprises the steps of adopting a flow electroplating mode, and sequentially carrying out rust removal, oil removal, acid washing, neutralization and activation before the flow electroplating.

The specific flow of the electroplating process in this embodiment is as follows:

high-temperature degreasing → inner wall rust removal → replacement tooling → flowing degreasing → flowing water washing → flowing acid washing → flowing water washing → flowing neutralization → anode installation → flowing water washing → flowing activation → flowing pure water washing → semi-bright nickel plating → flowing pure water washing → bright copper plating → flowing pure water washing → high dispersion bright nickel plating → flowing water washing → lower hanging → dehydrogenation treatment → packaging.

The main scheme and steps of the electroplating process of the embodiment are as follows:

1. high-temperature oil removal: the oil pipe is treated at 400 ℃ to carbonize oil stains, so that the binding capacity of the coating is improved.

2. Flow degreasing: the oil pipe is placed in a sodium hydroxide solution with the concentration of 40g/L and a sodium carbonate solution with the concentration of 30g/L for internal circulation flow, the flow rate is 1m/s, the temperature is 60 ℃, and the time is 20 min.

3. Flow pickling: the oil pipe after oil removal is placed in acid liquor (104g/L sulfuric acid, 150g/L hydrogen chloride and the balance of water) to circularly flow, the flow rate is 1m/s, and the time is 8 min.

4. Flow neutralization: and (3) placing the acid-washed oil pipe in a solution of trisodium phosphate with the concentration of 40g/L and potassium sodium tartrate with the pH value of 13 for internal circulation flow, wherein the flow rate is 1m/s, and the time is 5 min.

5. Loading an anode: insoluble cylindrical anodes with uniform conductivity are used according to the pipe size design. Penetrating into the pipe.

6. Flow activation: adopting a flow activation mode, namely circulating the activation liquid through the inner wall of the sleeve at the flow speed of 0.3 m/s; the activation time was 5 min. The composition of the activating solution is 150g/L sulfuric acid solution.

7. Electroplating bottom semi-bright nickel in the first stage: the bottom layer coating is a semi-bright nickel coating, and the composition of the plating solution is 250g/L of nickel sulfate; 30g/L of boric acid; sodium dodecyl sulfate 0.08g/L, pH 4.0, electroplating temperature 50 deg.C, electroplating time 30min, and current density 3A/dm²。

8. Bright copper electroplating in the second stage: the middle layer coating is a bright copper coating, and the plating solution comprises 180g/L of copper sulfate solution and 80g/L of sulfuric acid; 0.08g/L of polyethylene glycol; 0.02g/L of sodium polydithio-dipropyl sulfonate. At 2.0A/dm²Electroplating at 25 deg.C for 30 min.

9. And bright nickel electroplating at the third stage: the outer layer plating layer is a bright nickel plating layer, and the plating solution consists of 300g/L nickel sulfate; boric acid 40 g/L; saccharin (C)₆H₅COSO₂NH)0.8 g/L; 0.5g/L of 1, 4-butynediol; 0.2g/L of coumarin; sodium hypophosphite of 4g/L, pH of 4.5 and current density of 1.5A/dm²Electric powerThe plating temperature is 60 ℃ and the plating time is 20 min.

10. And (3) dehydrogenation treatment: the dehydrogenation treatment is carried out at the temperature of 200 ℃ for 2 h.

The composite plating layer A is obtained. The plating layer is uniform, and the thickness error is 3%. The coating properties are shown in Table 1.

Example 2

The difference from the embodiment 1 is that the additive is added in the electroplating process, and the additive is 2.6kg/kAh nickel sulfate, 2.6kg/kAh nickel carbonate and 4g/kAh lauryl sodium sulfate in the first stage; the second stage additive is copper sulfate 2.3kg/kAh, copper carbonate 2.1kg/kAh, polyethylene glycol 1.8g/kAh, and sodium polydithio dipropyl sulfonate 0.7 g/kAh; the third stage additive is 4.2kg/kAh nickel sulfate, 2.2kg/kAh nickel carbonate, 80g/kAh sodium hypophosphite, 23g/kAh saccharin, 12g/kAh 1, 4-butynediol and 12g/kAh coumarin;

after 1 addition, a composite plating layer B was prepared. The plating layer is uniform, and the thickness error is 2%. The coating properties are shown in Table 1.

Example 3

After 5 additions of the same example 1 as the addition of example 2, a composite coating C was prepared. The plating layer is uniform, and the thickness error is 3%. The coating properties are shown in Table 1.

Comparative example 1

Steps 1 to 7 are the same as in example 1. The difference lies in that the middle layer and the outer layer of the high-sulfur nickel three-layer nickel composite plating layer are electroplated according to the following steps:

8. high-sulfur nickel electroplating: the middle layer coating is a high-sulfur nickel coating, and the composition of the plating solution is 300g/L of nickel sulfate; 40g/L of nickel chloride; boric acid 40 g/L; 0.2g/L sodium benzene sulfinate, the electroplating temperature of 50 ℃, and the current density of 4A/dm²Electroplating time 3 min. At 2.0A/dm²Electroplating at 25 deg.C for 30 min.

9. Bright nickel plating: the outer layer plating layer is a bright nickel plating layer, and the plating solution consists of 300g/L nickel sulfate; 40g/L of nickel chloride; 38g/L of boric acid; saccharin 0.8 g/L; 0.4g/L of 1, 4-butynediol; coumarin 0.2g/L, and current density of 3A/dm²The electroplating temperature is 50 ℃ and the electroplating time is 20 min.

The composite coating D is prepared. The coating properties are shown in Table 1.

Comparative example 2

Steps 1 to 6 the pretreatment steps were the same as in example 1. The difference lies in that the coating is a single-layer nickel-tungsten-phosphorus alloy coating, and the electroplating method comprises the following steps:

7. long anode electroplating: placing the oil pipe in 250g/L nickel sulfate; 20g/L of citric acid; phosphorous acid 22 g/L; 300g/L of sodium tungstate; the long anode electroplating is carried out in 40g/L active micro powder, the length of the anode is 1.3m of the oil pipe, the temperature is 72 ℃, and the current density is 6A/dm²Time 40min, pH 2.5.

8. Short anode electroplating: the long anode is replaced by a short anode with the length of 2m, and the short anode repeatedly walks and electroplates in the oil pipe at the speed of 0.6m/s in the whole length. The time is 7 h.

9. And (3) dehydrogenation treatment: the dehydrogenation treatment is carried out at the temperature of 200 ℃ for 2 h.

The composite coating E is prepared. The coating properties are shown in Table 1.

TABLE 1 composite coating Properties

Test example 1

A well in an oil field in Xinjiang has severe microbial corrosion. Extracting oil field layer water containing desulfurization vibrio, culturing and keeping SRB in a growth vigorous period. The composite plating A, C, D sample in table 1 was selected for testing. The test conditions were a temperature of 28 ℃ for a period of 50 days for corrosion coupon testing. In the test process, the bacterial quantity of the SRB is measured by a spectrophotometer, and the bacterial quantity is kept at 3 multiplied by 10⁵～1×10⁶Between one and one ml. The composition of the SRB desulfurization vibrio devulcani culture medium is shown in Table 2. And observing the appearance contrast of the sample by using a scanning electron microscope after the coupon corrosion test is finished. The thickness of the coating was measured electrolytically and is shown in Table 3.

TABLE 2 SRB desulfurization Desulfuromicrobia medium composition

Composition of matter	Sodium lactate (60%)	Yeast powder	MgSO₄·7H₂O	NaCl
					Content of ingredients	4.0ml	1g	0.5g	5.0g

Note: the pH of the culture system was 7.2.

TABLE 3 thickness of each coating after corrosion of static coupon of composite coating

Composite coating	Bottom layer	Middle layer	Outer layer
				A	11μm	21μm	12.5μm
C	13μm	22μm	12.4μm
				D	15μm	0μm	15.5μm

The appearance of the composite plating layer A, C, D was relatively intact, but the thickness of the middle layer in the D composite plating layer, as determined by metallographic experiments, was already approximately 0, indicating that the high-sulfur nickel plating layer was completely corroded. Therefore, the lasting corrosion resistance of the high-sulfur nickel three-layer nickel composite coating is lower than that of the embodiment of the application. The plating sample A, C has no obvious difference, which shows that the additive parameter value of the application keeps the stability of the plating solution formula, and the plating layers produced in different periods have consistent anti-corrosion property.

The traditional electroplated nickel corrosion prevention has good corrosion resistance in dilute acid, dilute alkali and organic acid, because nickel and oxygen interact to form an oxide film to play a role in corrosion prevention. However, nickel has a high porosity and once the corrosive medium contacts the tube matrix through the pores, the galvanic cell increases the corrosion rate of the inner layer. In the comparative example 1, the outer layer nickel is difficult to form an oxidation film in the anaerobic environment, so that a corrosive medium contacts the middle layer high-sulfur nickel layer through pores, the middle layer and the outer layer form a primary battery, and the potential of the middle layer high-sulfur nickel is most negative, so that the middle layer is corroded, and the inner layer substrate cannot be protected. Therefore, the traditional composite three-layer nickel layer containing high-sulfur nickel is not suitable for protecting SRB sulfate reducing bacteria.

The high-dispersion bright nickel-bright copper-semi-bright nickel in the embodiment of the application has better performance in coping with sulfate reducing bacteria, and the outer layer of the plating layer is protected from corrosion by the passivation effect of the high-dispersion bright nickel-bright copper-semi-bright nickel. The inner layer has good low potential and plays a role in electrochemical corrosion protection. The semi-bright nickel is firmly combined with the tube base body and the bright copper, so that the binding force of the plating layer is ensured. The bright copper is used as the middle layer plating layer, the porosity number of the tight combination of the copper layer and the nickel layer is smaller than that of the combination of the nickel layer and the nickel layer, and the composite plating layer of the nickel, the copper and the nickel ensures the dislocation of the pores of each metal plating layer, so that the pores of the plating layer are optimal, and the direct corrosion of sulfate reducing bacteria to the pipe substrate is avoided. The adding modes and the adding amounts of the primary brightener saccharin, the secondary brightener coumarin and the 1, 4-butynediol are adjusted in the bright nickel layer, and the obtained coating has relatively good corrosion resistance.

Test example 2

The composite plating layer A, E sample in Table 1 is selected for testing, and the sample is placed in oil well produced liquid with sulfide concentration of 30mg/L for soaking for 60 days. The laminated corrosion of the composite plating layer A sample appears. And pits of the composite coating E sample appear. The thickness of the thinnest plating layer was measured after sanding the corroded A, E coupon. The thickness of the composite plating layer A in the embodiment 1 is 11 μm, 20 μm and 11.5 μm from the inside to the outside. Comparative example 2 the thickness of the test specimen was measured to be 49 μm after sanding the most severe portions of the pits in the test specimen of composite coating E. The composite plated samples of example 1 and comparative example 2 each suffered different levels of corrosion. Whereas the plating thickness of comparative example 2 was significantly reduced by about 11 μm due to the corrosion plating thickness. The thickness of the innermost layer of the coating in the embodiment 1 of the application is unchanged, which indicates that the coating is not corroded or is lighter. The thickness of the middle layer and the outer layer are respectively corroded by about 1-2 μm. Therefore, the corrosion resistance effect of the composite plating layer of the embodiment 1 is better than that of the nickel-tungsten-phosphorus alloy plating layer of the comparative example 3, the nickel-tungsten-phosphorus electroplating time is long, the cost is high, and the production cost of the nickel-copper-nickel is lower than that of the nickel-tungsten-phosphorus alloy plating layer.

Claims

1. The protective coating of the pipe wall is characterized in that the protective coating is a three-layer composite coating; the composite plating layer is bottom semi-bright nickel, middle bright copper and outer bright nickel;

the potential of the bottom layer semi-bright nickel is higher than that of the middle layer bright copper by 120mV or more, preferably 120-130 mV, and the potential of the middle layer bright copper is higher than that of the outer layer bright nickel by 60-100 mV.

2. The protective coating for the tube wall as claimed in claim 1, wherein the composite coating has a bottom layer thickness of 10-15 μm, a middle layer thickness of 20-25 μm, and an outer layer thickness of 10-15 μm; the outer plating layer contains phosphorus and sulfur, the phosphorus content accounts for 3-5% of the mass of the outer plating layer, and the sulfur content accounts for 0.05-0.08% of the mass of the outer plating layer.

3. A method of electroplating a protective coating on a pipe wall as claimed in claim 1 or claim 2, wherein the electroplating process is divided into three stages, a first stage of electroplating a bottom layer of semi-bright nickel, a second stage of electroplating a middle layer of bright copper, and a third stage of electroplating an outer layer of bright nickel;

the first stage electroplating solution comprises the following components: 200-350 g/L of nickel sulfate, 20-50 g/L of boric acid, 0.05-0.1 g/L of sodium dodecyl sulfate and 3.0-4.8 of pH;

the second stage electroplating solution comprises the following components: 150-260 g/L of copper sulfate solution, 50-100 g/L of sulfuric acid, 0.05-0.1 g/L of polyethylene glycol and 0.01-0.02 g/L of sodium polydithio dipropyl sulfonate;

the third stage plating solution consists of: 200-400 g/L of nickel sulfate, 20-50 g/L of boric acid, 0.6-1.0 g/L of saccharin, 0.4-0.5 g/L of 1, 4-butynediol, 0.1-0.2 g/L of coumarin, 1.2-6 g/L of sodium hypophosphite and pH of 4.0-4.8;

the electroplating method adopts a flow electroplating mode and comprises the following steps: the electroplating solution continuously circulates and flows through the inner wall of the pipe at a flow speed of 0.2-0.5 m/s for flow electroplating.

4. The electroplating method as claimed in claim 3, wherein additives are added to the electroplating solution during the electroplating process, wherein the additives are added from a liquid outlet of the electroplating solution and are circularly and uniformly stirred and then flow into a liquid inlet; the additive is added in a metered basis based on the current of electroplating.

5. The electroplating method according to claim 4, wherein the additives are added in an amount such that the first-stage additives comprise 2.5-2.7 kg/kAh of nickel sulfate, 2.5-2.7 kg/kAh of nickel carbonate, and 2-6 g/kAh of sodium dodecyl sulfate; the second stage additive is 2.2-2.4 kg/kAh copper sulfate, 2.0-2.2 kg/kAh copper carbonate, 1.4-2.2 g/kAh polyethylene glycol, 0.5-0.8 g/kAh sodium polydithio dipropyl sulfonate; the third stage additive is 4-4.4 kg/kAh of nickel sulfate, 1.9-2.4 kg/kAh of nickel carbonate, 37-115 g/kAh of sodium hypophosphite, 22-24 g/kAh of saccharin, 10-14 g/kAh of 1, 4-butynediol and 10-14 g/kAh of coumarin.

6. The plating method according to claim 3, wherein the plating condition in the first stage is a current density of 2.0 to 5.5A/dm²The electroplating temperature is 45-60 ℃, and the electroplating time is 20-30 min; plating conditions of the second stage: the current density is 1.9-4.6A/dm²The electroplating temperature is 18-28 ℃, and the electroplating time is 20-30 min; plating conditions of the third stage: the current density is 1.5 to 4.5A/dm²The electroplating temperature is 45-60 ℃, and the electroplating time is 15-20 min.

7. The plating method as recited in claim 3, wherein the flow plating is preceded by one or more of degreasing, descaling, pickling, neutralization, and activation.

8. The plating method as recited in claim 7, wherein said degreasing is divided into high-temperature degreasing and flow degreasing; the high-temperature oil removal temperature is 350-450 ℃; the flowing oil removal is that the oil removal liquid circularly flows through the inner wall of the sleeve at the flow speed of 0.5-1 m/s, the temperature of the oil removal liquid is 40-60 ℃, and the oil removal time is 10-30 min; the deoiling liquid comprises the following components: 30-60 g/L of sodium hydroxide, 20-40 g/L of sodium carbonate and the balance of water;

the neutralization adopts a flow neutralization mode: namely, the neutralization solution circularly flows through the inner wall of the sleeve at the flow speed of 0.5-1 m/s; the neutralization time is 2-8 min; the neutralization solution consists of 30-80 g/L trisodium phosphate and 20-60 g/L potassium sodium tartrate, and the pH value is greater than 12;

the activation adopts a flow activation mode: namely, the activating solution circularly flows through the inner wall of the sleeve at the flow speed of 0.2-0.5 m/s; the activation time is 3min to 6 min; the activating solution comprises 92-184 g/L sulfuric acid and the balance of water.

9. The plating method according to claim 3, further comprising a hydrogen removal treatment process after the plating: the dehydrogenation treatment temperature is 180-250 ℃, and the dehydrogenation treatment time is 2 h; the total thickness of the coating after hydrogen removal is not less than 40 μm.

10. Use of the protective coating according to claim 1 or 2 for protection against the corrosive environment of sulfate-reducing bacteria.