CN1257848C - A method for inhibiting chloride ion corrosion in circulating cooling water - Google Patents

Abstract

The present invention relates to a method for inhibiting the corrosion of chloride ions in circulation cooling water. Sulfate with the concentration which is 0.5 to 1.8 times of that of the concentration of chloride ions is added into water to lead the surface of stainless steel to be completely inactivated, and antiscale dispersant is added into the mixture to prevent the surface of the stainless steel from scaling. The sulphate is the mixture of one of sodium sulfate, potassium sulfate and magnesium sulfate, or two or more than two of the sodium sulfate, the potassium sulfate and the magnesium sulfate. The addition amount of the sulphate is 0.5 to 1.8 times of the concentration of the chloride ions. The antiscale dispersant is polyacrylic acid, or the binary copolymer of salt, polymaleic anhydride, acrylic acid and acrylate, or the terpolymer of the acrylic acid, the binary copolymer of AMPS, or the terpolymer acrylic acid and the maleic anhydride, etc. The method provided by the present invention converts the problem that the corrosion of the chloride ions to holes of the stainless steel is difficult to process into the problem the corrosion of sulfate radical to carbon steel is easy to process, and has the advantages of good effect, simple operation, low price and no secondary pollution to circulation water.

Description

A method for inhibiting chloride ion corrosion in circulating cooling water

technical field

The invention relates to industrial water treatment technology, in particular to a method for inhibiting chloride ion corrosion in circulating cooling water.

technical background

Chloride ion, present in industrial water, is an ion that promotes corrosion of metals. It has a small radius and strong penetrating ability, and it is easy to damage the protective film on the steel surface. It shows comprehensive corrosion on carbon steel, and pitting corrosion and stress corrosion on stainless steel. Pitting corrosion is a hidden and destructive localized corrosion. Chloride ions are one of the main causes of pitting or localized corrosion in circulating cooling water systems. Although stainless steel has a very low overall corrosion rate in various industrial cooling waters, under actual industrial production conditions, stainless steel equipment, especially various industrial water coolers, have corrosion and perforation accidents until the entire equipment fails. These corrosion damages (including localized corrosion such as stress corrosion cracking and crevice corrosion) are initially caused by pitting corrosion.

With the shortage of water resources and the increasingly serious water pollution, it is imminent to rationally use water and increase the reuse rate of water. Since the maximum allowable amount of chloride ions in circulating cooling water is closely related to the concentration ratio and operating conditions, the important reason for the low concentration ratio of some large petrochemical enterprises in my country is the limitation of the concentration of chloride ions. In the operation plan of the circulating water system, there are strict restrictions on the concentration of Cl ^- . The "Code for Design of Industrial Circulating Cooling Water Treatment" (GB50050-95) stipulates that Cl ^- in water should be ≤300mg/L for circulating water systems with stainless steel heat exchangers. , but for the circulating water system or sewage reuse system where seawater backflow often occurs in some coastal areas, the concentration of Cl ^- in the replenishment water often reaches hundreds or even thousands of mg/L, although the concentration factor is kept at a low level in actual operation level, but corrosion damage accidents still occur from time to time.

From the literature reports, most of the research on the pitting corrosion behavior of stainless steel in high-concentration chloride ion solution only stays in the mechanism research stage, and the research on the localized corrosion of stainless steel in actual production, especially pitting corrosion and stress corrosion is still very limited. Perfection is a topic yet to be further studied.

US 5320779 provides a corrosion inhibitor that can prevent uniform corrosion and localized corrosion of carbon steel, stainless steel and copper alloys in circulating cooling water systems. The corrosion inhibitor provided to inhibit uniform corrosion is organic phosphonate+zinc salt, provided Corrosion inhibitors that inhibit localized corrosion are molybdates, tungstates and vanadium compounds. The preferred corrosion inhibitor for the formulation to inhibit localized corrosion is molybdate, with a concentration of 5-10mg/L. However, this patent does not provide the chloride ion resistance of the formula and the reasons for local corrosion of the circulating cooling water system. The water quality of the provided examples is all chlorine ion-free or low chloride ion-containing water, so the water quality is less corrosive.

US 5330683 provides an environmentally friendly, economical water treatment agent capable of localized corrosion or scaling, which can treat salt water containing 10-35% CaCl ₂ , with a corrosion rate of 0.0408mm/a. The formulation consists of at least 2000mg/L gluconate, 2000mg/L sorbitol, and 400mg/L sodium borate.

US 604272 provides a method for inhibiting uniform corrosion and pitting corrosion of carbon steel and austenitic stainless steel in high chloride ion and high hardness solution, the formula is composed of C ₃ -C ₈ polymeric organic dicarboxylic acid or tricarboxylic acid ( Preferable citric acid) and its salts or alkali metal composition for adjusting pH, such as: citric acid 70%, _NaCO 30% or citric acid 40%, trisodium citrate 60% or citric acid 75%, NaOH 25%. The use concentration is 2000mg/L.

The biggest disadvantage of the above two patents is that the concentration of the medicament is too high, which is suitable as a pickling agent for chemical cleaning, and is not suitable for dosing when the circulating water is in normal operation.

CA13685A provides a method for reducing pitting corrosion and stress corrosion caused by chloride ions on the surface of stainless steel heat exchangers in the water system of thermal power plants: add a certain concentration of octadecylamine, ethanol, etc. to the water. However, octadecylamine has low solubility in neutral or alkaline solutions, and is generally used as a corrosion inhibitor for metals in acidic media. For neutral or alkaline circulating cooling water systems, a large amount of ethanol must be added as a solvent to make the water Processing costs are too high.

At present, the commonly used deposited film corrosion inhibitors in circulating water are organic phosphine + zinc salts. After being added to water, this kind of corrosion inhibitors can form chelates with metal ions and deposit in the cathode area, which is very effective in inhibiting neutral chlorine-containing circulating water. The corrosion effect of carbon steel is excellent, but this type of formula will increase the area ratio of the large cathode and small anode of the passivation metal for stainless steel that relies on the formation of a passivation film to inhibit corrosion, and cannot prevent the formation of stainless steel pitting corrosion, nor can it be repaired and repaired immediately. The exposed metal surface caused by passivation pitting corrosion has basically no corrosion inhibition effect.

For the suppression of pitting corrosion of stainless steel in high-concentration chloride ion water, the method often used on site is 1. Select stainless steel with higher grade and better corrosion resistance, such as: high-chromium-nickel stainless steel, with increased chromium and nickel content, stainless steel is resistant to chloride ion pitting corrosion Enhanced capabilities. However, the cost of this method is too high and there is still the possibility of pitting corrosion on harsh heat exchangers. 2. Maintaining the operation of circulating water at a low concentration ratio will result in waste of water resources and greatly increase the investment in pharmaceutical fees, water fees and sewage discharge fees.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the prior art and provide a simple, efficient and inexpensive method for inhibiting the corrosion of high-concentration chloride ions in circulating cooling water.

The treatment method provided by the invention is to add sulfate 0.5-1.8 times the chloride ion concentration (mass concentration) in circulating water containing chloride ions to completely passivate the surface of the stainless steel, and add scale inhibitor and dispersant to control scaling.

Said sulfate can be one of sodium sulfate, potassium sulfate, magnesium sulfate or a mixture of two or more thereof, preferably sodium sulfate and potassium sulfate. The amount of sulfate added is 0.5-1.8 times, preferably 1.0-1.4 times, the chloride ion concentration.

Said scale inhibitor dispersant can be polyacrylic acid or salt, polymaleic anhydride, binary copolymer of acrylic acid and acrylate, binary copolymer of acrylic acid and AMPS (2-acrylamido-2-methylpropanesulfonic acid). Copolymers, terpolymers of acrylic acid, AMPS and maleic anhydride, etc., or mixtures of two or more of them, preferably binary copolymers of acrylic acid and AMPS, ternary copolymers of acrylic acid, AMPS and maleic anhydride copolymer. The dosage of scale inhibitor and dispersant can be 1-300 mg/L, preferably 5-60 mg/L.

If the circulating water system contains carbon steel, a corrosion inhibitor should also be added to the circulating water. Said corrosion inhibitor can be hydroxyethylidene diphosphonic acid, hydroxyphosphinoacetic acid, amino trimethylene phosphonic acid, ethylenediamine tetramethylene phosphonic acid, polyol phosphonate, zinc salt and benzotriazole Copper-like corrosion inhibitors can also be a mixture of two or more of them, preferably hydroxyethylidene diphosphonic acid, hydroxyphosphinoacetic acid, polyol phosphonate and zinc salt. The dosage of the corrosion inhibitor can be 0-300 mg/L, preferably 2-60 mg/L.

According to the number of microorganisms in the circulating water, a bactericide can also be added. Said bactericide can be chlorine gas, sodium hypochlorite, potassium hypochlorite, calcium hypochlorite, dichloroisocyanuric acid, trichloroisocyanuric acid, chlorine dioxide, bromine, sodium hypobromite, potassium hypobromite, calcium hypobromite , one of quaternary ammonium salts and quaternary phosphorus salts or a mixture of two or more of them. Sodium hypochlorite, dichloroisocyanuric acid, and trichloroisocyanuric acid are preferred, and the dosing concentration is 0-300 mg/L, preferably 1-50 mg/L.

Sulfate ion, which is common in circulating water, is a good corrosion-inhibiting anion for stainless steel, but it is a strong corrosive ion next to chloride ion for carbon steel, which can easily cause localized corrosion on the surface of carbon steel , because the circulating water system usually contains stainless steel and carbon steel, so the prior art has never considered adding sulfate to the circulating water system when dealing with high chlorine-containing circulating water. However, the present invention successfully solves the problem of corrosion of stainless steel by chloride ions by adding sulfate to the high chlorine-containing circulating water system. First, sulfates can passivate the surface of stainless steel. The test shows (see Figure 1) that after adding 1200mg/L sulfate to circulating water containing 1000mg/L of chloride ions, the turning-back section of the anodic polarization curve of the electrochemical test cycle is almost reversed along the original curve, which is indicative of pitting corrosion of metal materials. The sensitive electrochemical parameters E _b and E _p are equal, indicating that after the passive film on the surface of stainless steel is destroyed in the local area of anodic polarization, it can be quickly repaired in the process of negative potential shift, maintain the original passivation state, and inhibit The occurrence and development of stainless steel pitting corrosion. Secondly, with the development of water treatment technology, water treatment agents such as corrosion inhibitors, scale inhibitors and dispersants, and bactericides in the prior art can effectively solve the corrosion problem of high-concentration sulfate ions on carbon steel. For example, under harsh water quality conditions with a Cl ^- concentration of 6000mg/L and a SO ₄ ^2- concentration of 8000mg/L, adding a suitable water treatment agent can reduce the corrosion rate of carbon steel coupons to 0.0653mm/a. Therefore, by adding a certain amount of sulfate ions to the circulating water system, the difficult problem of inhibiting the pitting corrosion of stainless steel by chloride ions can be successfully transformed into the easy-to-handle problem of preventing the corrosion of carbon steel by sulfate ions.

Since the inhibitory effect of SO ₄ ^2- ions on stainless steel pitting corrosion increases with its concentration, the pitting corrosion breakdown potential will also increase with the increase of SO ₄ ^2- ions concentration, so even if SO ₄ ^2- ions are added The ratio is low, and the occurrence of pitting corrosion is also suppressed to a certain extent.

The advantages of the present invention are:

1. Overcoming the prejudice in this field and adopting a unique idea to transform the difficult-to-handle chloride ion pitting corrosion problem on stainless steel into the easy-to-handle sulfuric acid root corrosion problem on carbon steel. The effect is excellent, the operation is simple, the price is low, and it will not damage Circulating water produces secondary pollution.

2. By adding sulfate to the circulating water, the surface of the stainless steel is passivated, which reduces the water quality requirements for the stainless steel material and greatly reduces the cost of the material.

Description of drawings

Figure 1 is the cycle anodic polarization curve of the stainless steel electrode when the concentration of Cl ^- is 1000mg/L and the concentration of SO ₄ ^2- is 1200mg/L.

Figure 2 shows the change of E _b and E _p after adding different concentrations of SO _{4 2} ^- when the concentration of Cl ^- is 800mg/L.

Detailed ways

Instance 1

In this example, 18-8 stainless steel was used for corrosion test.

Test instrument: American EG&G PARC M352 comprehensive corrosion tester. The working electrode is the sample, the reference electrode is the saturated calomel electrode, and the auxiliary electrode is the platinum electrode.

Test sample: 18-8 stainless steel. Seal the sample with epoxy resin, expose 1cm ² of the test surface, polish it step by step with metallographic sandpaper to 600 ^# , wash with water, and wash with ethanol. The polished sample was passivated in 25% HNO ₃ at 50°C for 1 hour.

Test conditions: temperature 30±2°C; scanning speed 1mv/s; retrace current density 0.1mA/cm ² , solution does not deoxygenate.

Test water quality: 1/2 Beijing tap water + 1/2 deionized water was used as the basic water quality of the test. The main water quality is shown in Table 1. The test results are shown in Figure 2.

Table 1 Test basic water quality project value Total hardness, mg/L 121.0 Ca ²⁺ (calculated as CaCO ₃ ), mg/L 104.0 Alkalinity (CaCO ₃ meter), mg/L 72.2 Cl ^- , mg/L 9.2 SO ₄ ^2- , mg/L 8.1 Conductivity, μS/cm 175

Figure 2 shows the change of E _b and E _p after adding different concentrations of SO ₄ ^2- when the concentration of Cl ^- is 800mg/L. It can be seen from Figure 2 that E _b and E _p increase significantly with the increase of SO ₄ ^2- concentration. And it has shown a good corrosion inhibition effect at a lower concentration: only adding 100mg/L SO ₄ ^2- to the solution, _Eb increased from 380.5mV to 530mV, which is higher than the oxygen evolution equilibrium potential of 513mV under the test conditions . When 1200 mg/L SO ₄ ^2- is added to the solution, E _b =E _p , the metal surface is completely passivated and pitting corrosion does not occur anymore.

Example 2

In this example, 18-8 stainless steel was used for corrosion test.

Test condition and water quality are the same as example 1, and the results are shown in Table 2.

Table 2 Change of E _b with Cl ^- in 600mg/L SO ₄ ^2- solution serial number 1 2 3 4 5 6 7 8 SO ₄ ^2- (mg/L) 600 600 600 600 600 600 600 0 Cl ^- (mg/L) 0 100 200 300 400 600 800 100 _Eb (mV SCE) 1270 1270 1270 1266 1247 923 575 556

Table 2 shows that the presence of SO ₄ ^2- greatly improves the corrosion resistance of stainless steel. Adding chloride ions below 400 mg/L to the experimental water with SO ₄ ^2- 600 mg/L, the pitting potential of 18-8 stainless steel is at Above 1247mV, no pitting occurs. But when there is no SO ₄ ^2- , even if only 100mg/L chloride ion is added to the water, the pitting potential of 18-8 stainless steel will drop to 556mV.

Example 3

In this example, 20 ^# carbon steel is used for corrosion test.

The test water quality is the same as Example 1, the test conditions refer to HG/T215991, the test temperature is 50°C, the speed is 75 rpm, the operation is 72 hours, and the pH is 7.5-7.6.

Add 20 mg/L of hydroxyethylidene diphosphonic acid, 30 mg/L of polyol phosphonate, 50 mg/L of terpolymer of acrylic acid, AMPS and maleic anhydride, 15 mg/L of zinc salt and Different concentrations of SO ₄ ^2- and Cl ^- (prepared with analytically pure Na ₂ SO ₄ and NaCl, respectively). The test results are shown in Table 3.

Table 3 Corrosion test results of carbon steel after adding SO ₄ ^2- and Cl ^- serial number 1 2 3 4 5 6 7 8 Cl ^- (mg/L) / 1000 2000 3000 4000 5000 6000 6000 SO ₄ ^2- (mg/L) / 1500 3000 4000 5000 6000 8000 8000 Corrosion rate (mm/a) 0.0086 0.0131 0.0182 0.0150 0.0240 0.0546 0.0653 1.4320

The results in Table 3 show that when no water treatment agent is added, the 20 ^# carbon steel is seriously corroded in the presence of high concentrations of Cl ^- and SO ₄ ^2- , and the corrosion rate is as high as 1.4320mm/a. After adding the water treatment agent, the corrosion rate is below 0.0653mm/a, which shows that the water treatment agent has an excellent effect on inhibiting the corrosion of 20 ^# carbon steel in the presence of high concentration Cl ^- and SO ₄ ^2- .

Example 4

In this example, 20 ^# carbon steel and 18-8 stainless steel are used for corrosion test.

The test water quality simulates the circulating water of an oil refinery, and the specific water quality is shown in Table 4. After sequentially adding 10 mg/L of hydroxyphosphinoacetic acid, 20 mg/L of acrylic acid and AMPS binary copolymer, 10 mg/L of zinc salt and 150 mg/LSO ₄ ^2- into the test water, the results of the rotary coupon and electrochemical tests are shown in Table 5.

Table 4 Main water quality data of circulating water in a refinery project value Calcium hardness (calculated as CaCO ₃ ), mg/L 304.0 Total alkali (calculated as CaCO ₃ ), mg/L 128.6 Cl ^- , mg/L 352.8 SO ₄ ^2- , mg/L 327.3 pH 8.3 Turbidity, mg/L 16.6

Table 5 Carbon steel and stainless steel test results carbon steel Stainless steel Corrosion rate mm/a blank 0.8868 / dosing 0.0610 / E _b , mV SCE / 1267 E _p , mVSCE / 1267

The results show that the corrosion rate of carbon steel is only 0.0610mm/a after adding sulfate and water treatment agent; the E _b and E _p of stainless steel are equal, and no pitting corrosion occurs.

Example 5

In this example, 20 ^# carbon steel and 18-8 stainless steel are used for corrosion test.

The test water quality is the circulating water of a coastal petrochemical enterprise, and the specific water quality is shown in Table 6. Add 40 mg/L of hydroxyphosphinoacetic acid, 20 mg/L of polyol phosphonate, 40 mg/L of acrylic acid and AMPS binary copolymer, 20 mg/L of zinc salt and 250 mg/L of SO ₄ ^2- into the test water in sequence, and rotate The sheet and electrochemical test results are shown in Table 7.

Table 6 Main water quality data of circulating water in a coastal petrochemical enterprise project value Calcium hardness (calculated as CaCO ₃ ), mg/L 44.0 Total alkali (calculated as CaCO ₃ ), mg/L 66.7 Cl ^- , mg/L 268.1 SO ₄ ^2- , mg/L 78.9 pH 7.3 Turbidity, mg/L 4.5

Table 7 Carbon steel and stainless steel test results carbon steel Stainless steel Corrosion rate mm/a blank 1.0021 / dosing 0.0668 / E _b , mV SCE / 1247 E _p , mVSCE / 1247

The experimental results in Table 7 show that the corrosion of carbon steel and stainless steel is well controlled after adding sulfate and water treatment agent.

Claims (10)

1. method that suppresses chloride ion corrosion in the recirculated cooling water, comprise: the 0.5-1.8 vitriol doubly that in the recirculated water of chloride ion-containing, adds the chlorion mass concentration, make the stainless steel surface passivation, and add dirt dispersion agent control fouling, wherein the mass concentration of vitriol is in sulfate radical.

2. in accordance with the method for claim 1, it is characterized in that said sulfate radical is from one of sodium sulfate, vitriolate of tartar, sal epsom or two or more mixture wherein.

3. in accordance with the method for claim 1, it is characterized in that the vitriol add-on is 1.0-1.4 a times of chlorion mass concentration.

4. in accordance with the method for claim 1, it is characterized in that said dirt dispersion agent is the terpolymer or two or more the mixture wherein of copolymer, vinylformic acid and 2-acrylamido-2-methyl propane sulfonic acid and maleic anhydride of copolymer, vinylformic acid and the 2-acrylamido-2-methyl propane sulfonic acid of polyacrylic acid or salt, polymaleic anhydride, vinylformic acid and acrylate.

5. in accordance with the method for claim 1, it is characterized in that the dirt dispersion agent consumption is 1～300mg/L.

6. in accordance with the method for claim 1, it is characterized in that, said dirt dispersion agent is the terpolymer of copolymer, vinylformic acid and the 2-acrylamido-2-methyl propane sulfonic acid or the maleic anhydride of vinylformic acid and 2-acrylamido-2-methyl propane sulfonic acid, and the dirt dispersion agent consumption is 5～60mg/L.

7. in accordance with the method for claim 1, it is characterized in that, in recirculated water, also add the inhibition profit, said inhibiter is 1-Hydroxy Ethylidene-1,1-Diphosphonic Acid, hydroxyl phosphino-acetate, amido three methene phosphonic acids, ethylene diamine tetra methylene phosphonic acid, polyvalent alcohol phosphonic acid ester, zinc salt and benzotriazole copper inhibitor or two or more mixture wherein

8. in accordance with the method for claim 7, it is characterized in that the inhibiter consumption is 0～300mg/L.

9. in accordance with the method for claim 7, it is characterized in that said inhibiter is 1-Hydroxy Ethylidene-1,1-Diphosphonic Acid, hydroxyl phosphino-acetate, polyvalent alcohol phosphonic acid ester or zinc salt, the inhibiter consumption is 2～60mg/L.

10. in accordance with the method for claim 1, it is characterized in that, also add sterilant in the recirculated water, said sterilant is selected from one of chlorine, clorox, potassium hypochlorite, Losantin, DICHLOROISOCYANURIC ACID, trichloroisocyanuric acid, dioxide peroxide, bromine, sodium hypobromite, potassium hypobromite, hypobromous acid calcium, quaternary ammonium salt and quaternary alkylphosphonium salt or two or more mixture wherein, and adding concentration is 0～300mg/L.

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