Special anti-corrosion technology for desulfurization pipelines

Boiler anti-corrosion - anti-wear and high-efficiency new technology
Nano silicon crystal adhesive material

1、 Reality Overview
Hainan Yisheng Petrochemical Co., Ltd. uses gas as fuel. When it was first put into operation, there was very little corrosion, but over the years, it was found that the corrosion was quite severe, especially in recent years, with several consecutive pipe bursts occurring within a year. This is mainly reflected in the flame breaking zone at the upper part of the furnace, which is about 70 square meters. If not dealt with in a timely manner, there is a possibility of replacing a large number of furnace tubes in a short period of time. Therefore, it is recommended that Hainan Yisheng Petrochemical Co., Ltd. take effective anti-corrosion measures as soon as possible to eliminate unnecessary losses. Otherwise, this not only increases the maintenance intensity but also incurs significant costs. Therefore, it is recommended to adopt the nano silicon crystal adhesive anti-corrosion technology invented by Lianyungang Shengyuan Technology. This technology has been used in boilers of all sizes across the country, achieving good economic benefits.

Attachment: Corrosion Example of Water Wall Tubes in Hainan Yisheng Petrochemical Co., Ltd

2、 Reasons for Corrosion of Boiler Water Wall

From the current pictures and combined with the feedback from the manufacturer's technical personnel, corrosion prevention of gas furnaces has been a common phenomenon for many years. There are many reasons for this, mainly due to the oxidation of the combustion medium with the metal surface at high temperatures, which causes some mobile ions to "crack" and lead to corrosion. The reason why it occurs at the bend angle is that the furnace flue gas burns from bottom to top, with high density, strong flushing force, long residence time, and even the formation of a certain vortex shape at the bend angle.

3、 Anti corrosion principle of nano silicon crystal adhesive

The main factors affecting boiler corrosion are ① medium characteristics ② furnace temperature ③ air flow ratio ④ influence of aerodynamic field characteristics

To prevent furnace corrosion, the main focus is on improving aerodynamic conditions and enhancing the corrosion resistance of water-cooled wall surfaces during operation; Preventing corrosion in the upper part of the furnace mainly relies on reducing the flue gas temperature or improving the anti-corrosion properties of the water-cooled wall surface.

1. After using nano silicon crystal adhesive material on the water-cooled wall of the furnace, the heat absorption capacity of the furnace water-cooled wall will be appropriately increased. Analysis shows that the heat absorption capacity of the metal tube wall after using nano silicon crystal adhesive material is 7.89% higher than that of the metal tube wall without nano silicon crystal adhesive material. Therefore, the use of nano silicon crystal adhesive material on the water-cooled wall enhances the anti-corrosion margin of the furnace.

2. Using nano silicon crystal adhesive material on the water-cooled wall of the furnace, due to its smooth surface, greatly reduces the erosion of the medium on the tube wall.

3. Nano silicon crystal adhesive materials are processed through nanomaterialization, thus possessing the common characteristic of nanomaterials - low specific surface energy. Preventing contamination of the water-cooled wall, thereby avoiding or reducing corrosion.

                      Figure 1. Materials for Layer B of Nano Silicon Crystal Adhesive      Figure 2. Materials for Layer A of Nano Silicon Crystal Adhesive

4、 Construction Plan for Nano Silicon Crystal Adhesive

1. Surface pretreatment:

1.1 Firstly, inspect the pipes at the construction site and discover defects such as pits, wear, and hard damage on the surface of the pipes. The bidding party shall treat the pipe defects and then sandblasting the surface of the steel pipe to remove surface coke, slag, hard ash, rust layer, and oxide layer until a metallic luster is exposed. The sandblasting pressure shall be 0.6-0.8MPa.

1.2 The sandblasting range should be larger than the coating area of the pipe construction to ensure sufficient coverage for the next step of construction.

2. Surface sandblasting:

① Surface cleaning: Remove various pollutants from the sprayed surface, especially grease, dirt, scale, rust, and corrosive substances. The cleanliness of the working surface meets the Sa3.0 level specified in GB8923-88 "Rust grades and removal grades of steel surfaces before painting".

② Surface roughness: The bonding between the coating and the substrate is mainly mechanical bonding, which requires the substrate pre-treatment not only to remove oil and rust, but also to roughen the surface, and the surface should have a certain roughness when used. The surface roughness reaches the Rz60-90 μ m specified in GB11373-89, and will not cause any damage to the thickness of the pipe wall.

The purpose of sandblasting treatment

a、 Increase the contact area between the coating layer and the substrate to improve the adhesion of the coating.

b、 Increase the mutual embedding and interlocking between the coating material and the substrate surface, playing the role of an "anchor hook" and improving the adhesion between the coating and the substrate.

3. Activated surface:

Sandblasting provides active surface capabilities to coatings, such as lattice defects and plastic deformation, generating certain stress states to increase the adhesion between coating particles and substrate surfaces, and improving the micro metallurgical bonding ability between coating particles and substrate. The analysis of activation effect is as follows:

① Sandblasting creates a certain residual compressive stress on the surface of the workpiece after repeated impact by sand particles. Although the stress value is extremely small, it is beneficial for relaxing the thermal stress of the coating during the coating process, improving the bonding strength of the coating, and also increasing the fatigue strength of the workpiece.

② Coatings can remove organic pollutants and oxide layers on the surface of workpieces, and can increase the plastic deformation of metal surface grains and cause lattice defects, making the substrate surface in a state prone to chemical reactions, which helps to enhance the physical and chemical bonding strength between coating particles and the substrate surface.

③ Explanation of damage to pipe wall thickness caused by sandblasting: Sandblasting only removes surface dirt and debris, with a pipe wall thickness of ≤ 15 μ m. This thickness is thin and will not affect the entire pipe wall thickness. Secondly, sandblasting operations will not cause tearing or blowing damage to the pipe wall. Thirdly, sandblasting operations are carried out uniformly, and the thickness reduction of the entire surface is consistent. In summary, sandblasting operations are only an effective method for achieving drying, cleaning, and activating the surface of the furnace tube, improving the bonding strength of the coating, and will not damage the pipe wall thickness.

Therefore, sandblasting treatment is extremely necessary before coating the workpiece. And the sandblasted workpiece should be coated as soon as possible, the shorter the time, the better the surface activation effect, and the higher the coating quality.

A Sandblasting Requirements: First, use 12-20 mesh quartz sand for rough spraying on the surface of the workpiece to achieve a surface cleanliness level of Sa3.0. Then, use 12-20 mesh quartz sand for surface roughening treatment again, with a surface roughness of Rz60-90 μ m. The sand particles used must be clean and dry, and the sandblasting area should be enclosed and other recycling measures should be taken to ensure that it does not pollute the surrounding environment. Sandblasting can only be carried out after confirmation by the on-site engineer. Parts that do not meet the pre-treatment requirements need to be re sandblasted, and attention should be paid to protecting qualified parts during re sandblasting.

B Sandblasting machine selection: TS9015 high-efficiency sandblasting equipment

Quality requirements for compressed air: Use on-site air source or self provided air compressor, exhaust flow rate ≥ 6m3/min, working pressure 0.55-0.8Mpa.

D Operation method: Sandblasting distance is 150-200 millimeters, and the sandblasting angle is 50-70 ℃ from the substrate.

E Operation sequence and inspection requirements: First, spray a coarse layer of quartz sand to completely remove surface coke and slag, then coat it with quartz sand to remove the surface oxide layer, and then spray a fine layer of quartz sand to remove debris from cracks on the surface of the furnace tube. The effect of spraying quartz sand and iron sand is only to roughen the surface of the substrate to achieve the required surface roughness for the coating, without causing any damage to the thickness of the pipe wall. After sandblasting, the surface of the pipe wall should be dry, free of dust, oil stains, oxygen scale, rust spots and other debris, and the substrate surface should present a homogeneous gray white metallic appearance.

Before coating, the pre treated surface should be inspected. If rust or any non-conforming parts are found, they should be reprocessed. After passing the inspection, a thickness gauge should be used to measure the thickness of the pipe wall, δ 1. If serious thinning or cracking is found, please request Party A to replace the pipe or reinforce it. The pipes that have undergone sandblasting treatment must be coated within 4-6 hours. Before coating, it is necessary to check whether there is still any residual dust on the coated pipes. Compressed air can be used to remove the residual dust before coating.

F coating method: To prevent local overheating during the coating process, the interlayer temperature should not exceed 800C in actual operation. A transition layer should be designed at the junction of each construction area or daily construction area, and the coating thickness at the transition layer should be from thick to thin and clearly marked. In the specific construction, our company has decided to conduct sandblasting at night and coating work during the day. Adopting the cross shaped coating method, layer by layer and zone by zone operation, the coating in some areas reaches the process design thickness before being moved to other areas to ensure uniform thickness and adhesion of the coating layers, and prevent missed spraying. After the coating is completed, a coating quality inspection should be carried out, and the thickness δ 2 should be measured. If δ 2- δ 1 is ≥ 0.7 millimeters, it is judged to be qualified and can proceed to the next process. Otherwise, the non-conforming parts should be coated again.

Example of Cold Wall Construction with Nano Silicon Crystal Adhesive

G process:

Precautions for H operation:

A block operation, where the coating in a local area reaches the design thickness before being moved to other areas, and identification marks are set at the overlapping parts. During operation, the interlayer temperature should not exceed 80 ℃.

Before coating, a trial spray should be conducted on the test panel to adjust the voltage, current, wire feeding speed, and compressed air flow rate. The flexible joints and hose joints of the air circuit should be checked for any air leakage. If unstable wire feeding, unstable arc combustion, severe gas leakage and other special situations are found on site, they should be checked and adjusted in a timely manner. When adjusting the voltage, the main circuit should be disconnected to avoid damaging the coating power supply.

Note: Conductive tips burned during the coating process should be replaced in a timely manner, and conductive tips with unqualified processing accuracy are prohibited from use.

4. Quality Description

A、 Sandblasting quality:

Select 12-20 mesh high-quality quartz sand to remove the oxide scale on the surface of the pipe wall until the metal luster is exposed on the pipe surface, so that the surface cleanliness meets the Sa3.0 level specified in GB8923-88 "Rust Grades and Preparation Grades of Steel Surfaces before Coating".

B、 Coating quality:

① Coating appearance: The coating layer should be uniform, smooth, dense, and free of abnormal phenomena such as peeling, cracking, and peeling. The surface should be smooth, shiny, dense, dust-free, and non foaming. The substrate should not deform, expand freely, and not produce cracks.

② The abrasive used for sandblasting must be clean, dry, free of oil stains, and have uniform particle size.

③ After sandblasting, the wear of the pipe should not exceed 0.08mm, and there should be no obvious pitting, rust, slag or other adhesion on the surface. The pipe must be completely exposed to metallic luster.

④ Coating thickness: The following measures are taken to control the thickness of the coating for defects in use: firstly, it is required to supervise the construction personnel to strictly follow the operating specifications during the operation process; The second is to control the coating thickness through the consumption of coating materials; The third is to operate according to the preset parameters before construction, and measure and inspect the coating sample or on-site sample with a caliper; Fourthly, after sandblasting the metal surface, a portable coating thickness gauge is first used to measure the thickness δ 1 at a large number of points. Then, after the hot coating is completed and before sealing the hole, the thickness δ 2 of the pipe wall is measured at points, and the numbers are slightly corrected. The difference between the two average values is the coating thickness.

⑤ Coating adhesion strength (coating and substrate): Use a special puller to inspect the coating layer, and make longitudinal and transverse stripe marks in the shape of "#" on the coating layer to observe whether there is chip like peeling. During installation, friction with the bracket must not cause detachment or peeling.

⑥ After sales service: Arrive at the scene within 48 hours of discovering problems, and perform maintenance work at any time during minor repairs.

5、 The effect of nano silicon crystal adhesive after use

1. Improved the anti-corrosion, wear and oxidation life of the boiler;

2. Enhanced the operational capability of the boiler;

3. Due to the decrease in furnace temperature and the lower surface energy of nano silicon gel, large-scale corrosion of boiler water-cooled walls is prevented;

4. Avoiding the occurrence rate of boiler pipe deformation and rupture caused by the alternating cold and hot conditions during the operation of hydraulic soot blowing, and improving the safety and reliability of boiler operation;

5. Increased the adaptability of the boiler to the medium, improved the economic efficiency of boiler operation, and reduced the production cost of boiler operation.

6. Effectively reduce the generation of thermal NOx (about 5%).

7. The increase in heat absorption of the boiler after coating can improve boiler efficiency by more than 1%.

8. The decrease in flue gas temperature of the boiler leads to a corresponding reduction in power consumption of equipment such as the boiler induced draft fan.