Preparation method of anti-corrosion coating lining of nodular cast iron sewage pipe

Abstract

The invention discloses a preparation method of a nodular cast iron sewage pipe anti-corrosion coating lining, and belongs to the technical field of pipeline corrosion prevention. The method comprises the steps that 40-80-mesh sand blasting roughening treatment is conducted on the inner surface of a pipe blank, anticorrosive mortar coating lining with the thickness of 2-12 mm is centrifugally coated at the speed of 300-900 rpm, and mortar is composed of high-alumina cement, fly ash, quartz sand-chromite sand composite aggregate and a nanometer silicon compound; performing steam curing for 6-8 hours at the temperature of 30-70 DEG C and the humidity of more than or equal to 95%, and then polishing; and the super-hydrophobic material permeates into the micropores of the coating lining under the pressure of 0.8-1.2 MPa, the pressure is maintained for 30-60 minutes, and the gradient hydrophobic layer with the contact angle larger than or equal to 150 degrees is formed. Through the triple synergistic effect of composite aggregate filling, nano silicon modification and super-hydrophobic permeation, the porosity of a mortar coating lining is smaller than or equal to 5%, the compressive strength is larger than or equal to 50 MPa, the corrosion current density is reduced by 75%, the service life is longer than 15 years in the strong corrosion environment with the pH being 1-13 and the Cl <-> being larger than or equal to 5000 mg / L, and the technical problems that traditional cement mortar is high in porosity and poor in corrosion resistance are solved.

Description

Technical Field

[0001] This invention relates to the field of sewage pipeline corrosion protection technology, specifically to a method for preparing an anti-corrosion coating for ductile iron sewage pipes. Background Technology

[0002] Ductile iron pipes are widely used in municipal water supply and drainage systems due to their excellent mechanical properties, corrosion resistance, and ease of construction. Cement mortar lining, as a traditional protective technology, is widely applied to the inner wall of ductile iron pipes to enhance their corrosion resistance and service life. Cement mortar lining forms a protective film, effectively isolating the transported medium from direct contact with the pipe body, thereby reducing the risk of corrosion. Its good hydraulic properties reduce water resistance and improve water delivery efficiency, while exhibiting strong adaptability in various environments, including the transport of raw water, drinking water, and sewage. Furthermore, cement mortar lining is relatively easy to repair, further reducing maintenance costs. However, traditional cement mortar linings have high porosity, allowing corrosive media to easily penetrate, thus affecting the pipe's service life.

[0003] In environments involving high-velocity, high-scouring, and highly corrosive liquids, ordinary cement mortar linings may not meet the requirements. With the continuous advancement of urbanization in China, the renovation and application of urban underground sewage pipe networks are becoming increasingly widespread, with urban sewage pipe networks increasing by approximately 20% annually. Against this backdrop, traditional cement mortar lining processes can no longer fully meet the needs of modern municipal drainage projects. To overcome these shortcomings, researchers are constantly exploring new processes and materials. For example, using aluminate cement as a lining material offers better corrosion resistance and strength, effectively resisting chemical corrosion from sewage. Furthermore, by optimizing the lining process and curing conditions, such as adjusting the sand-cement ratio, water-cement ratio, curing time, and temperature, the quality and performance of the lining can be significantly improved. These improvements not only extend the service life of ductile iron pipes but also reduce production costs and increase production efficiency.

[0004] However, although these improvements have addressed some of the shortcomings of traditional processes, some problems still exist in practical applications, such as high porosity, insufficient lining strength, and poor corrosion resistance. In particular, the lining that is not in contact with water in the semi-winter state is prone to falling off. These problems seriously affect the service life of the pipeline.

[0005] Therefore, developing a post-treatment process that can effectively solve these problems has significant practical importance and market value. Based on this background, this invention proposes a method for preparing an anti-corrosion lining for ductile iron sewage pipes. By selecting specific superhydrophobic post-treatment materials and processes, the structural density, interfacial bonding strength, and corrosion resistance of the mortar lining layer are enhanced, thereby extending the service life of the pipeline and meeting the stringent requirements of modern municipal drainage projects. Summary of the Invention

[0006] The purpose of this invention is to address the problems existing in the prior art by providing a preparation method that can effectively improve the corrosion resistance of ductile iron sewage pipes. This method optimizes the process parameters and material composition of each step to form a stable and long-lasting superhydrophobic lining layer, which significantly enhances the service life of the pipe in highly corrosive environments.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a method for preparing an anti-corrosion lining for ductile iron sewage pipes, comprising the following steps:

[0008] S1. The molten iron is heated, tempered, and spheroidized, and then centrifugally cast to obtain ductile iron pipe blanks. Subsequently, the pipe blanks are annealed, and the outer surface of the pipe blanks is subjected to anti-corrosion treatment and water pressure testing.

[0009] S2. The inner surface of the tube blank is pretreated by sandblasting, coated with anti-corrosion mortar by centrifugation, and then steam cured. After curing, the inner surface is polished.

[0010] S3. Superhydrophobic materials are infiltrated into the micropores of the pipe wall through pressure permeation to form a superhydrophobic inner lining layer with a contact angle ≥150°.

[0011] Furthermore, in the sand roughening pretreatment, the abrasive particle size of the sandblasting is 40-80 mesh, and the inner surface roughness Ra after sandblasting is ≥30 μm.

[0012] Furthermore, the steam curing conditions are: temperature 30-70℃, relative humidity ≥95%, and curing time 6-8 hours.

[0013] Furthermore, the superhydrophobic material includes at least one of methyl nano silica, fluorosilane, and silazane.

[0014] Furthermore, the pressure for the pressure infiltration is 0.8-1.2 MPa, and the infiltration time is 30-60 minutes.

[0015] Furthermore, the centrifugal coating speed is 300-900 rpm, and the coating thickness is 2-12 mm.

[0016] Furthermore, the annealing process includes two-stage temperature control: the first stage is to hold at 900-950℃ for 10-30 minutes, and the second stage is to hold at 730-780℃ for 10-35 minutes, followed by slow cooling to 680℃.

[0017] Furthermore, the anti-corrosion mortar is composed of the following raw materials in parts by weight: 1000-1200 parts of high-alumina cement, 150-200 parts of fly ash, 2000-2500 parts of fine aggregate, 1.5-3 parts of water-reducing agent, 8-12 parts of nano-silicon composite and water.

[0018] Furthermore, the Al2O3 content in the high-alumina cement is 50%-60%.

[0019] Furthermore, the fly ash is selected from calcium fly ash, wherein the CaO content is ≤10%.

[0020] Furthermore, the particle size of the fine aggregate is 0.15-4.5 mm.

[0021] Furthermore, the fine aggregate is a composite aggregate of quartz sand and chromite sand.

[0022] Furthermore, the mass ratio of the quartz sand to the chromite sand is (3-5):1.

[0023] Furthermore, the SiO2 content in the quartz sand is ≥95%.

[0024] Furthermore, the Cr2O3 content of the chromite sand is ≥45%.

[0025] Furthermore, the water-reducing agent is selected from polycarboxylate water-reducing agents.

[0026] Furthermore, the nano-silicon composite is composed of the following components in parts by weight: 100-150 parts silica sol, 30-50 parts lithium silicate solution, 0.5-1.2 parts rheology modifier, and 0.3-0.8 parts surfactant;

[0027] The silica sol is an alkaline silica sol with a pH of 9-11, a SiO2 content of 25-30%, and a particle size of 10-30 nm; the lithium silicate solution has a modulus (SiO2 / Li2O molar ratio) of 4.5-5.5 and a Li2O content of 1.9-2.6%.

[0028] Furthermore, the rheology modifier is a compound system of hydroxypropyl methylcellulose (HPMC) and polycarboxylic acid ether (PCE) with a compound mass ratio of (2-3):1, wherein the viscosity of HPMC is 40000-60000 mPa·s and the solid content of PCE is 40-45%.

[0029] Furthermore, the surfactant is a compound system of nonionic surfactant and anionic surfactant, with a compound mass ratio of (1-1.5):0.3, wherein the nonionic surfactant is Pluronic® F127 and the anionic surfactant is sodium dodecylbenzenesulfonate (SDBS).

[0030] Furthermore, the nano-silicon composite also includes a silane coupling agent, the amount of which is 2-3% of the mass of SiO2 in the silica sol, and the silane coupling agent is selected from at least one of KH-550, KH-560 or KH-570.

[0031] Furthermore, the preparation method of the nano-silicon composite includes the following steps:

[0032] P1. Pre-reaction: Mix silica sol and lithium silicate solution at a mass ratio of (2.5-3.5):1, adjust the pH to 4-5, and stir the reaction at 50-70℃ for 1-3 hours to form a silicon-lithium gel precursor;

[0033] P2. Additive compounding: Add rheology modifier and surfactant, and ultrasonically disperse for 20-40 minutes. The ultrasonic power is 500-800W and the frequency is 35-45kHz.

[0034] P3. In-situ modification: Add silane coupling agent, heat to 70-90℃ and react for 3-5 hours to generate an organic-inorganic hybrid structure;

[0035] Furthermore, the pH adjustment in P1 uses hydrochloric acid or nitric acid with a concentration of 0.3-0.7 mol / L, and the adjustment rate is 0.5-1.0 mL per minute.

[0036] Furthermore, the silane coupling agent and silica sol in P3 are added in batches, with each batch added 30-60 minutes apart, and the total reaction time is 4-6 hours.

[0037] Furthermore, the total mass of the nano-silicon composite and water is 0.35-0.45 times the mass of the high-alumina cement.

[0038] Furthermore, the preparation method of the anti-corrosion mortar is as follows: high-alumina cement, fly ash, fine aggregate and water-reducing agent are mixed evenly to obtain a dry mixture; nano-silicon composite is added to water and stirred to form a nano-silicon composite solution; the nano-silicon composite solution is added to the dry mixture to obtain cement mortar for ductile iron pipe lining.

[0039] High-alumina cement, acting as the main binder, hydrates to form a dense, corrosion-resistant CAH gel, creating an acid- and alkali-resistant framework. Low-calcium fly ash (CaO≤10%) undergoes a secondary hydration reaction to generate nanoscale gel, which synergistically fills the pores with quartz sand-chromite sand composite aggregate (3-5:1), resulting in a mortar porosity ≤5% and compressive strength ≥50MPa. Nano-silicon composites further block the nanoscale pores, while water-reducing agents optimize particle dispersion, collectively achieving high mortar density.

[0040] Al in high-alumina cement 3+In an acidic environment, an Al(OH)3 passivation film is formed. Chromite sand (Cr2O3≥45%) generates a Cr(OH)3 layer in an alkaline medium, synergistically blocking the migration of corrosion ions. Quartz sand (SiO2≥95%) reacts with cement to form an acid-resistant mullite phase. The high density and hardness of the composite aggregate resist media erosion. Nano-silicon and superhydrophobic materials form a gradient hydrophobic layer (contact angle≥150°) through pressure permeation, achieving zero droplet permeation.

[0041] Multi-scale synergy (material-structure-interface) enables the corrosion protection system to possess structural density, chemical stability, and superhydrophobicity, operating at pH values ​​between 1-13 and Cl... - In extreme corrosive environments with a concentration ≥5000 mg / L, the corrosion current density is reduced by 75%, and the design life is ≥15 years.

[0042] A method for preparing an anti-corrosion coating for ductile iron sewage pipes, and its application in highly corrosive industrial sewage transport pipelines.

[0043] Furthermore, the pH of the medium transported in the pipeline is ≤3 or ≥11, and Cl - With a concentration ≥5000mg / L, the superhydrophobic lining layer with a contact angle ≥150° works synergistically with the composite structure of the anti-corrosion mortar to ensure that the pipeline has a corrosion resistance life ≥15 years under continuous transportation conditions.

[0044] Compared with the prior art, the beneficial effects of the present invention are:

[0045] 1. Through a 0.8-1.2MPa pressure infiltration process, superhydrophobic materials are deeply penetrated into micropores of 50-200μm, forming a gradient hydrophobic layer with a contact angle ≥150°. This structure effectively blocks the penetration paths of moisture and corrosive media. Combined with a high-density mortar layer (compressive strength ≥50MPa), the design life of the pipeline under continuous flushing conditions is extended to more than 15 years.

[0046] 2. By combining two-stage steam curing (30-70℃ / ≥95% humidity) with centrifugal coating (0-900rpm) process, the curing time is reduced to within 8 hours while ensuring the uniformity of the 2-12mm coating layer, achieving the strength of conventional 28-day natural curing, increasing efficiency by 23 times and significantly reducing production costs.

[0047] 3. The mortar utilizes a composite aggregate of quartz sand and chromite sand (3-5:1) in synergistic filling with nano-silicon composites, ensuring the corrosion-resistant mortar operates at pH 1-13 and Cl... - It maintains structural stability even in strong acid / strong alkali and high salt corrosive media with a concentration of ≥5000mg / L, and the corrosion current density is reduced by 75%, breaking through the limitation of traditional cement mortar being only suitable for neutral media.

[0048] 4. Through a triple protective structure consisting of a high-alumina cement matrix, a composite aggregate layer, and a superhydrophobic permeable layer, a synergistic effect is achieved at the material-structure-interface level. The CAH gel generated during the hydration of the high-alumina cement, together with the chromite sand passivation layer, resists chemical corrosion. The nano-silicon composite and the gradient hydrophobic layer achieve pore closure, resulting in an overall porosity of ≤5%, which is more than 60% lower than that of traditional mortars. Attached Figure Description

[0049] Figure 1 This is a flowchart illustrating the preparation method of an anti-corrosion coating for ductile iron sewage pipes according to the present invention. Detailed Implementation

[0050] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0051] Example 1-1

[0052] The preparation method of the nano-silicon composite provided in this embodiment includes the following specific steps:

[0053] P1. Pre-reaction:

[0054] Weigh 250g of silica sol and 100g of lithium silicate solution and mix them at a mass ratio of 2.5:1. Adjust the pH of the mixture to 4 using 0.3mol / L hydrochloric acid at a rate of 0.5mL per minute. Place the mixture in a 50℃ water bath and stir at an appropriate speed for 1 hour to form a homogeneous silicon-lithium gel precursor.

[0055] P2. Additive compound:

[0056] Add appropriate amounts of the compound system of hydroxypropyl methylcellulose (HPMC) and polycarboxylate ether (PCE) and the compound system of Pluronic® F127 and SDBS to the silicon-lithium gel precursor. Turn on the ultrasonic equipment, set the ultrasonic power to 500W and the frequency to 35kHz, and ultrasonically disperse the mixture for 20 minutes to ensure that the additives are fully dispersed and incorporated into the system.

[0057] P3. In-situ modification:

[0058] A certain amount of silane coupling agent was accurately weighed and added in batches at 30-minute intervals. KH-550 was added to the mixture, the temperature of the system was raised to 70°C, and the reaction was continued at this temperature for 3 hours to form a nano-silicon composite with an organic-inorganic hybrid structure.

[0059] Examples 1-2

[0060] The preparation method of anti-corrosion mortar provided in this embodiment includes the following specific steps:

[0061] 1100 parts of high-alumina cement (Al2O3 content 55%), 180 parts of fly ash (CaO content 8%), 2100 parts of quartz sand (SiO2 content 97%), 700 parts of chromite sand (Cr2O3 content 48%), and 2.5 parts of polycarboxylate superplasticizer were mixed evenly to obtain a dry mixture. 10 parts of nano-silicon composite (prepared in Example 1-1) were added to water (the total mass of nano-silicon composite and water was 0.4 times the mass of cement) and stirred to form a nano-silicon composite solution. The nano-silicon composite solution was added to the dry mixture to obtain cement mortar for ductile iron pipe lining.

[0062] Example 1

[0063] The method for preparing the anti-corrosion coating for ductile iron sewage pipes provided in this embodiment is as follows: Figure 1 As shown, the specific steps are as follows:

[0064] Tube blank preparation: Molten iron is heated to 1450-1520℃ for spheroidization treatment, and then centrifugally cast to obtain ductile iron tube blanks, followed by annealing. The annealing process includes two-stage temperature control: the first stage is held at 930℃ for 10 minutes, and the second stage is held at 740℃ for 10 minutes, followed by slow cooling to 680℃ before unloading from the furnace;

[0065] After being cooled by water spraying, the outer surface of the tube blank is subjected to anti-corrosion treatment and water pressure test.

[0066] Inner surface pretreatment: The inner surface of the tube blank is roughened by sandblasting. The abrasive particle size is 60 mesh, and the roughness of the inner surface after sandblasting is Ra≥35μm.

[0067] Centrifugal coating: The anti-corrosion mortar prepared above (prepared in Examples 1-2) is coated on the inner surface of the tube blank by centrifugal coating. The centrifugal coating speed is 500 rpm and the coating thickness is 4 mm.

[0068] Steam curing: The coated tube blank is placed in a steam curing environment. The curing conditions are: temperature 40℃, relative humidity ≥98%, and curing time 6 hours.

[0069] Inner surface polishing: After the curing process is completed, the inner surface is polished.

[0070] Superhydrophobic material infiltration: Superhydrophobic material (superhydrophobic material is fluorosilane + nano SiO2 (mass ratio 3:1)) is infiltrated into the micropores of the tube wall by pressure infiltration at a pressure of 1.0 MPa and an infiltration time of 45 minutes to form a superhydrophobic inner lining layer with a contact angle ≥150°.

[0071] Example 2

[0072] In the preparation method of the anti-corrosion coating for ductile iron sewage pipes provided in this embodiment, the permeation pressure is 0.8 MPa, the permeation time is 60 min, and other parameters are the same as in Embodiment 1.

[0073] Example 3

[0074] In the preparation of the anti-corrosion coating for ductile iron sewage pipes provided in this embodiment, the ratio of quartz sand to chromite sand is 3:1, 12 parts of nano-silicon composite are added, and other parameters are the same as in Example 1.

[0075] Comparative Example 1

[0076] In the preparation of the anti-corrosion coating for the sewage pipe provided in this comparative example, conventional cement mortar (42.5 ordinary Portland cement) was used for coating, and other parameters were the same as in Example 1.

[0077] Comparative Example 2

[0078] In the preparation of the anti-corrosion coating for sewage pipes provided in this comparative example, the sandblasting parameters were changed, and 100-mesh quartz sand was used, while other parameters were the same as in Example 1.

[0079] Comparative Example 3

[0080] In the preparation of the anti-corrosion coating for sewage pipes provided in this comparative example, the curing conditions were changed to 20°C and 60% humidity, while other parameters were the same as in Example 1.

[0081] Performance testing:

[0082] Contact angle test: The test was performed using a contact angle measuring instrument (model DSA100) in accordance with GB / T 30693-2014 standard.

[0083] Compressive strength test: conducted in accordance with GB / T 17671-2021 "Test Method for Strength of Cement Mortar".

[0084] Corrosion current density test: Performed using an electrochemical workstation (PARSTAT 4000) according to ASTM G59 standard. See Table 1 below.

[0085] Table 1

[0086]

[0087] As can be seen from Table 1, the contact angles of Examples 1-3 are all ≥150°, indicating that they have good superhydrophobic properties. Among them, Example 1 has the largest contact angle of 158°, and the best anti-corrosion effect. The contact angle of Comparative Example 1 is only 82°, which is much lower than that of the Examples, indicating that the hydrophobicity of conventional cement mortar is poor.

[0088] Regarding compressive strength, Example 3 exhibited the highest compressive strength at 63 MPa. This was due to the different proportions of quartz sand and chromite sand, as well as the varying amounts of nano-silicon composite added, which resulted in a denser mortar structure and higher strength. Comparative Example 1 showed the lowest compressive strength at 38 MPa, indicating that the nano-silicon composite significantly improves mortar strength.

[0089] Regarding porosity, Example 3 exhibited the lowest porosity at 3.8%, indicating that its anti-corrosion mortar had the best density and could effectively prevent the intrusion of corrosive media. Comparative Example 1, with a porosity as high as 12.5%, was more prone to corrosive media penetration. In the corrosion current density test, Example 3 showed the lowest corrosion current density at 0.12 μA / cm². 2 This indicates that it has the best anti-corrosion performance; Comparative Example 1 has the highest corrosion current density, at 0.62 μA / cm. 2 The results show that the preparation process and material ratio used in the examples can effectively reduce the corrosion risk of the pipes.

[0090] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an anti-corrosion coating for ductile iron sewage pipes, characterized in that, Includes the following steps: The molten iron is heated, tempered, and spheroidized, and then centrifugally cast to obtain ductile iron pipe blanks. Subsequently, the pipe blanks are annealed, and the outer surface of the pipe blanks is subjected to anti-corrosion treatment and water pressure testing. The inner surface of the tube blank is pretreated by sandblasting, then coated with anti-corrosion mortar by centrifugation and steam cured. After curing, the inner surface is polished. Superhydrophobic materials are infiltrated into the micropores of the pipe wall through pressure osmosis to form a superhydrophobic liner with a contact angle ≥150°.

2. The method for preparing an anti-corrosion coating for ductile iron sewage pipes according to claim 1, characterized in that, In the sand roughening pretreatment, the abrasive particle size of the sandblasting is 40-80 mesh, and the inner surface roughness Ra after sandblasting is ≥30 μm.

3. The method for preparing an anti-corrosion coating for ductile iron sewage pipes according to claim 1, characterized in that, The steam curing conditions are: temperature 30-70℃, relative humidity ≥95%, and curing time 6-8 hours.

4. The method for preparing an anti-corrosion coating for ductile iron sewage pipes according to claim 1, characterized in that, The superhydrophobic material includes at least one of methyl nano silica, fluorosilane, and silazane.

5. The method for preparing an anti-corrosion coating for ductile iron sewage pipes according to claim 1, characterized in that, The pressure for the pressure infiltration is 0.8-1.2 MPa, and the infiltration time is 30-60 minutes.

6. The method for preparing an anti-corrosion coating for ductile iron sewage pipes according to claim 1, characterized in that, The centrifugal coating is performed at a speed of 300-900 rpm, and the coating thickness is 2-12 mm.

7. The method for preparing an anti-corrosion coating for ductile iron sewage pipes according to claim 1, characterized in that, The anti-corrosion mortar is composed of the following raw materials in parts by weight: 1000-1200 parts high-alumina cement, 150-200 parts fly ash, 2000-2500 parts fine aggregate, 1.5-3 parts water-reducing agent, 8-12 parts nano-silicon composite and water.

8. The method for preparing an anti-corrosion coating for ductile iron sewage pipes according to claim 7, characterized in that, The particle size of the fine aggregate is 0.15-4.5 mm.

9. The method for preparing an anti-corrosion coating for ductile iron sewage pipes according to claim 7, characterized in that, The total mass of the nano-silicon composite and water is 0.35-0.45 times the mass of the high-alumina cement.

10. The method for preparing an anti-corrosion lining for ductile iron sewage pipes according to any one of claims 1-9, and its application in highly corrosive industrial sewage conveying pipelines.

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