Method for coating inner coating of nodular cast iron pipe

Abstract

The invention discloses a method for coating an inner coating of a nodular cast iron pipe, which adopts the working procedures of shot blasting treatment, acid cleaning, weak base neutralization, clean water cleaning and nitrogen blow-drying on the surface of a pipe wall, and adopts a pipeline heating high-speed rotating centrifugal measure during coating. According to the invention, sharp bulges, scrap iron, rust, dust, sundries, oil stains and the like on the surface of the inner wall of the cast iron pipe can be effectively removed while the surface roughness is increased to facilitate adhesion; nitrogen is used as inert gas, so that oxygen in common air can be effectively prevented from generating oxidation reaction with the treated pipe wall surface; the surface of the pipe wall treated by the method is high in cleanliness, and the coating is high in adhesive force, few in pinholes and bubbles and high in surface flatness after being coated.

Description

Technical Field

[0001] The invention belongs to the technical field of pipeline inner coatings and relates to a method for coating the inner coating of a ductile iron pipe. Background Art

[0002] Ductile iron pipes have excellent corrosion resistance, heat resistance and mechanical properties, and are easy to use and have high construction efficiency. They are widely used in the field of liquid and gas transportation in engineering construction, playing an increasingly important role. During production, the inner wall of ductile iron pipes is usually coated with a layer of cement mortar or ester coating as an anti-corrosion and drag-reducing coating, which has an important impact on the flow of fluid in the pipe and the life of the cast pipe itself. However, the current coating process has problems such as incomplete cleaning of the inner wall and poor adhesion of the inner coating after coating, easy appearance of pinholes, bubbles, and uneven surface, which have a series of negative impacts on product quality. Summary of the invention

[0003] The technical problem solved by the present invention is to provide a method for coating the inner coating of a ductile iron pipe. After coating, the coating has strong adhesion and high cleanliness of the pipe wall surface.

[0004] The present invention is achieved through the following technical solutions:

[0005] A method for coating the inner coating of a ductile iron pipe comprises the following operations:

[0006] For the ductile iron pipe to be coated on the inner wall, the inner wall is subjected to pre-treatment including shot blasting, acid cleaning, alkali neutralization cleaning, water cleaning, continuous nitrogen purging until dry, heating, and then high-speed centrifugal coating is carried out.

[0007] Further, the method specifically includes the following steps:

[0008] 1) Shot blast the inner surface of the ductile iron pipe to remove surface protrusions, rust and dust. After treatment, the surface is uniform and burr-free;

[0009] 2) Clean the inner surface of the ductile iron pipe with dilute hydrochloric acid solution to dissolve surface oil and rust;

[0010] 3) Clean the inner surface of the ductile iron pipe with sodium carbonate solution, neutralize the residual hydrochloric acid and clean it;

[0011] 4) Clean the inner surface of the ductile iron pipe with clean water;

[0012] 5) Continuously purge the inner surface of the ductile iron pipe with nitrogen until the surface is dry and free of moisture;

[0013] 6) Heat the ductile iron pipe to 45-55°C;

[0014] 7) Place the ductile iron pipe on the coating machine, rotate it at high speed, and then apply the coating.

[0015] After the shot blasting, the inner surface reaches Sa2.5.

[0016] The dilute hydrochloric acid solution cleaning is to use a dilute hydrochloric acid solution with a mass concentration of 10-15% for cleaning 1-2 times.

[0017] The sodium carbonate solution cleaning is performed by using a sodium carbonate solution with a mass concentration of 5 to 15% for 1 to 2 times.

[0018] When the nitrogen is continuously purged, the purity of the nitrogen is ≥99.9%.

[0019] When the ductile iron pipe is coated with the coating, its rotation speed is 1000-1500r / min.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects:

[0021] The invention provides a method for coating the inner coating of a ductile iron pipe.

[0022] The present invention adopts the processes of shot blasting, acid cleaning, weak alkali neutralization, water cleaning, and nitrogen drying on the pipe wall surface, and adopts the pipe heating high-speed rotation centrifugal measures when coating, which can effectively remove the sharp protrusions, iron filings, rust, dust, debris, oil stains, etc. on the inner wall surface of the cast iron pipe while increasing the surface roughness to facilitate adhesion. In addition, nitrogen as an inert gas can effectively prevent the oxygen in ordinary air from producing an oxidation reaction with the treated pipe wall surface; the pipe wall surface treated by the present invention has high cleanliness, strong adhesion, few pinholes, few bubbles, and high surface flatness after coating; it solves the problems of incomplete inner wall cleaning, poor adhesion of the inner coating, easy generation of pinholes, bubbles, and uneven surface when coating in the existing coating process.

[0023] The invention can be used for the pretreatment and coating process during the centrifugal coating of the cement mortar inner coating of the ductile iron pipe, and can also be used for further coating of the anti-corrosion functional coating on the surface of the cement mortar layer. DETAILED DESCRIPTION

[0024] The present invention is further described in detail below in conjunction with the embodiments, which are intended to explain the present invention rather than to limit it.

[0025] The method for coating the inner surface of ductile iron pipes provided by the present invention places the pipes that need to be coated with an inner coating on a bracket, and successively performs shot blasting (surface Sa≥2.5), low-concentration acid cleaning (1-2 times with a 10-15% mass concentration dilute hydrochloric acid solution), weak base neutralization (1-2 times with a 5-15% mass concentration sodium carbonate solution), water cleaning (2-3 times), nitrogen drying (nitrogen purity≥99.9%), heating (50±5°C), high-speed centrifugal coating (rotation speed 1000-1500r / min) and other processes.

[0026] Its specific processing method includes the following steps:

[0027] 1) Shot blast the inner surface of the ductile iron pipe that needs to be coated with a coating to remove surface protrusions, debris, rust, and dust. The treated surface is uniform and free of burrs.

[0028] 2) Clean the inner surface of the ductile iron pipe with a dilute hydrochloric acid solution to dissolve surface oil stains, iron filings, and rust.

[0029] 3) Clean the inner surface of the ductile iron pipe with a sodium carbonate solution to neutralize and clean the hydrochloric acid and dissolved impurity solutions remaining from the previous process.

[0030] 4) Clean the inner surface of the ductile iron pipe with water to wash away the residual liquid from the previous process.

[0031] 5) Continuously blow the inner surface of the ductile iron pipe with nitrogen until the surface is dry and free of moisture.

[0032] 6) Heat the ductile iron pipe.

[0033] 7) Rotate the ductile iron pipe at high speed on a coating machine to generate centrifugal force for coating application.

[0034] Now, the following three example formulations are used for the inner coating application process of the ductile iron pipes of the present invention, and performance testing and comparison are carried out:

[0035] Example 1

[0036] 1) Shot blast the inner surface of the ductile iron pipe that needs to be coated with a coating to remove surface protrusions, debris, rust, and dust. The treated surface is uniform and free of burrs, and the inner surface reaches Sa2.5.

[0037] 2) Clean the inner surface of the ductile iron pipe twice with a 10% dilute hydrochloric acid solution to dissolve surface oil stains, iron filings, and rust.

[0038] 3) Clean the inner surface of the ductile iron pipe twice with a 5-15% concentration sodium carbonate solution to neutralize and clean the hydrochloric acid and dissolved impurity solutions remaining from the previous process.

[0039] 4) Clean the inner surface of the ductile iron pipe with clean water to remove the liquid from the previous process.

[0040] 5) Continuously purge the inner surface of the ductile iron pipe with nitrogen until the surface is dry and free of moisture.

[0041] 6) Heat the ductile iron pipe to 45°C.

[0042] 7) The ductile iron pipe is rotated at a speed of 1000r / min on a coating machine to generate centrifugal force for coating.

[0043] Example 2

[0044] 1) Shot blast the inner surface of the ductile iron pipe that needs to be coated to remove surface protrusions, debris, rust, and dust. The treated surface is uniform and burr-free, and the surface reaches Sa2.5.

[0045] 2) Clean the inner surface of the ductile iron pipe twice with 12% dilute hydrochloric acid solution to dissolve surface oil, iron filings and rust.

[0046] 3) The inner surface of the ductile iron pipe is cleaned twice with a 5-15% concentration sodium carbonate solution to neutralize and clean the residual hydrochloric acid and dissolved impurity solution from the previous process.

[0047] 4) Wash the inner surface of the ductile iron pipe twice with clean water to clean the liquid from the previous process.

[0048] 5) Continuously purge the inner surface of the ductile iron pipe with nitrogen until the surface is dry and free of moisture.

[0049] 6) Heat the ductile iron pipe to 50°C.

[0050] 7) The ductile iron pipe coating machine is rotated at a speed of 1250r / min to generate centrifugal force for coating.

[0051] Example 3

[0052] 1) Shot blast the inner surface of the ductile iron pipe that needs to be coated to remove surface protrusions, debris, rust, and dust. The treated surface is uniform and burr-free, and the surface reaches Sa2.5.

[0053] 2) Clean the inner surface of the ductile iron pipe twice with 12.5% ​​dilute hydrochloric acid solution to dissolve surface oil, iron filings and rust.

[0054] 3) The inner surface of the ductile iron pipe is cleaned twice with a 5-15% concentration sodium carbonate solution to neutralize and clean the residual hydrochloric acid and dissolved impurity solution from the previous process.

[0055] 4) Wash the inner surface of the ductile iron pipe twice with clean water to clean the liquid from the previous process.

[0056] 5) Continuously purge the inner surface of the ductile iron pipe with nitrogen until the surface is dry and free of moisture.

[0057] 6) Heat the ductile iron pipe to 55°C.

[0058] 7) The ductile iron pipe is rotated at a speed of 1500r / min on a coating machine to generate centrifugal force for coating.

[0059] The cement mortar lining coatings obtained by the corresponding processing techniques of the above three embodiments were tested for adhesion, roughness and porosity according to GB / T1031-2009 and JGJ / T 70-2009 standards. The test comparison data are shown in Table 1.

[0060] Table 1 Detection of coating effect of ductile iron pipe inner coating

[0061] Serial number Test items Technical indicators Existing coating process Example 1 Example 2 Example 3 1 Roughness k≦0.05mm 0.04mm 0.02mm 0.02mm 0.01mm 2 Porosity / 5.3％ 2.3％ 2.1％ 1.9％ 3 Adhesion / 7.3MPa 10.9MPa 11.5MPa 12.8MPa

[0062] The present invention optimizes and improves the existing ductile iron pipe inner coating coating process, adopts low-concentration pickling, high-purity nitrogen protection drying and heating centrifugal coating process, which can effectively solve the problems of incomplete cleaning, poor adhesion of the inner coating, easy generation of pinholes, bubbles, uneven surface, etc. in the existing coating process. The performance is greatly improved compared with the existing ductile iron pipe inner coating coating process, which is of great significance.

[0063] The above embodiments are preferred examples for implementing the present invention, and the present invention is not limited to the above embodiments. Any non-essential additions and substitutions made by those skilled in the art based on the technical features of the technical solution of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for coating the inner coating of a ductile iron pipe, characterized in that: The following operations are included: For the ductile iron pipe to be coated on the inner wall, the inner wall is subjected to pre-treatment including shot blasting, acid cleaning, alkali neutralization cleaning, water cleaning, continuous nitrogen purging until dry, heating, and then high-speed centrifugal coating is carried out.

2. The method for coating the inner coating of a ductile iron pipe according to claim 1, characterized in that: The specific steps include: 1) Shot blast the inner surface of the ductile iron pipe to remove surface protrusions, rust and dust. After treatment, the surface is uniform and burr-free; 2) Clean the inner surface of the ductile iron pipe with dilute hydrochloric acid solution to dissolve surface oil and rust; 3) Clean the inner surface of the ductile iron pipe with sodium carbonate solution, neutralize the residual hydrochloric acid and clean it; 4) Clean the inner surface of the ductile iron pipe with clean water; 5) Continuously purge the inner surface of the ductile iron pipe with nitrogen until the surface is dry and free of moisture; 6) Heat the ductile iron pipe to 45-55°C; 7) Place the ductile iron pipe on the coating machine, rotate it at high speed, and then apply the coating.

3. The method for coating the inner coating of a ductile iron pipe according to claim 2, characterized in that: After the shot blasting, the inner surface reaches Sa2.

5.

4. The method for coating the inner coating of a ductile iron pipe according to claim 2, characterized in that: The dilute hydrochloric acid solution cleaning is to use a dilute hydrochloric acid solution with a mass concentration of 10-15% for cleaning 1-2 times.

5. The method for coating the inner coating of a ductile iron pipe according to claim 2, characterized in that: The sodium carbonate solution cleaning is performed by using a sodium carbonate solution with a mass concentration of 5 to 15% for 1 to 2 times.

6. The method for coating the inner coating of a ductile iron pipe according to claim 2, characterized in that: When the nitrogen is continuously purged, the purity of the nitrogen is ≥99.9%.

7. The method for coating the inner coating of a ductile iron pipe according to claim 2, characterized in that: When the ductile iron pipe is coated with the coating, its rotation speed is 1000-1500r / min.