Condenser tube replacement renovation
1、 Overview of Condenser Stainless Steel Tube Replacement Technology:
The condenser is an important cooling source equipment for steam turbine generator units. Due to the use of rivers, lakes, seas, or groundwater as cooling water sources and pollution from modern water systems, the corrosion rate of the condenser cooling pipes has increased, resulting in frequent leakage of the condenser. Copper pipes are often used for condenser cooling pipes, which are prone to corrosion and leakage during operation, and are affected by excitation forces and thermal loads. Generally, 2-3 major maintenance periods require partial or complete replacement of the cooling pipes. Serious impact on normal production. Especially copper pipes are susceptible to corrosion by ammonia ions, sulfides, and other substances, which can cause leaks. At the same time, due to the uneven inner wall of copper pipes, microorganisms and various dirt are easily attached, greatly reducing the service life of copper pipes.
Stainless steel pipes have greatly improved service life due to their corrosion resistance and smooth inner walls, with a general lifespan of over 30 years. At the same time, due to the thin wall thickness of thin-walled welded stainless steel pipes, the heat transfer effect is similar to that of copper pipes, and the total investment is almost the same as that of copper pipes.
2、 Characteristics of stainless steel tube replacement for condenser:
Huaneng Power Auxiliary Equipment Company has developed a complete set of advanced processes for replacing stainless steel pipes in condensers through long-term practice. During construction, it is possible to quickly replace all pipes in large quantities, as well as achieve single and partial pipe replacement. The condenser pipe replacement technology is in a leading position in China.
Advantages of stainless steel pipes:
1. The smooth inner wall of the pipe reduces the thickness of the bottom layer of the boundary laminar flow, which not only enhances heat transfer but also improves the anti scaling performance.
2. Not easy to stain or scale, with a lifespan of up to 30-40 years;
3. The heat exchange tubes used by our company can be thin-walled tubes with a diameter of 0.5-0.7mm, which improves the overall heat transfer performance. Under the same heat exchange area, the overall heat transfer coefficient is 2.121-8.408% higher than that of copper tubes.
4. Due to the use of high-quality stainless alloy steel such as American standard AISI304 and 316, the material has a high hardness, and the steel degree of the pipe is significantly improved. Therefore, it has strong resistance to high-temperature steam impact
5. The thermal resistance of the pipe wall only accounts for 3% to 5% of the total thermal resistance. The increase in water velocity, the increase in cleaning coefficient, and the decrease in wall thickness within the pipe result in improved rust resistance and vibration resistance.
3、 Advantages of stainless steel tube replacement technology for condenser:
Before 1995, due to the high cost of stainless steel materials and inadequate production processes for thin-walled tubes, stainless steel tubes were not used in freshwater cooling condensers in China. In recent years, with the significant decrease in stainless steel prices, the production process of welding thin-walled stainless steel pipes for condenser swapping and power auxiliary equipment has become increasingly mature, opening up broad prospects for the application of thin-walled stainless steel pipes in condensers. The replacement of stainless steel pipes for condensers is resistant to water pollution and corrosion, extending their service life. It is an effective means to solve the problem of copper alloy pipes not being resistant to water pollution and corrosion.
In terms of the working conditions for replacing stainless steel pipes with condenser pipes, the significant feature of stainless steel pipes as cooling pipes is their resistance to the impact erosion of water droplet steam flow on the steam side and the corrosion of hydrogen sulfide in cooling water. Therefore, as early as the 1940s, the United States used stainless steel pipes in the selection of condenser pipe cooling pipes, and subsequently, stainless steel pipes were also used in condensers in Western European countries such as France and Germany. Technical transformation and replacement can be carried out on stainless steel pipes, copper pipes, and titanium pipes.
4、 Stainless steel pipe model and technical parameters
The condenser of the power plant produced by Lianyungang Huaneng Electric Power uses stainless steel welded pipes, with specifications of diameter ranging from 14mm to 40mm, wall thickness ranging from 0.5mm to 2.0mm, and materials such as TP304 and TP316.
1. Material and Characteristics Table of Stainless Steel Pipe
2. Common models of stainless steel pipes:
Specification of stainless steel pipes for condenser
3. Comparison table of heat transfer coefficients for commonly used specifications of heat exchange tubes
|
varieties |
wall thickness（㎜） |
texture of material |
Overall heat transfer coefficient |
|
Copper tube |
1 |
H68 |
3682.414 |
|
Stainless steel pipe |
1 |
TP304 |
3460.327 |
|
Stainless steel pipe |
0.7 |
TP304 |
3760.628 |
|
Stainless steel pipe |
0.6 |
TP304 |
3872.607 |
5、 Selection of material for condenser heat exchange tubes:
Refer to the experimental conclusion that 304 pipe is safe in water with chloride ions<500mg/kg, 316 pipe is safe in water with chloride ions<1500mg/kg, and 316L pipe is safe in water with chloride ions<3000mg/kg. However, when the water velocity in the pipe is too low for a long time, it is easy to form pitting, so the circulating water velocity should generally be greater than 1.2m/s; It is best to run at 1.5-2.0m/s, which is both corrosion-resistant and anti scaling.
In practice, when selecting materials, not only should the dissolved solids and chloride ion concentration of the cooling water be considered, but also the ratio of non corrosive ions to corrosive ions, and attention should be paid to the sensitivity of stainless steel to chloride ions. When selecting stainless steel pipes for condenser heat exchange cooling pipes, special attention should be paid to the chloride ion content in the cooling water.
When the chloride ion content is less than 200 mg/L, TP304 should be selected
When the chloride ion content is less than 1000mg/L, TP316 should be selected
When the chloride ion content is less than 2000mg/L, TP316L should be used
6、 Parameters required for condenser tube replacement:
1. Please provide: Unit origin _______ model _______ service life ________;
2. Number of cooling pipes: ____ pieces, diameter: ____, wall thickness: ____, and length: ____;
3. Maintenance plan date: ________ On site construction days: ________;
*Production process of stainless steel welded pipe for condenser:
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| Steel strip forming | welding | Cutting and pressure testing | Manual sampling inspection |
* Photo of the effect after tube replacement
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