Many five-star hotels require copper pipes for water supply system, but more and more hotels also accept stainless steel pipes due to cost and market reasons. This paper mainly makes a technical comparison between copper pipes and stainless steel pipes for reference.
Now, we compare in terms of the physical properties, hygienic properties, corrosion resistance and economic value of the materials.
1. Comparison of physical properties
Comparison of tensile strength:
Taking the 304 thin-walled stainless steel pipe as an example, its tensile strength is 530-750mpa, 2 times of that of galvanized pipe and 3 times of that of copper pipe. Therefore, the wall thickness of the thin-walled stainless steel pipe can be thinner than that of the copper pipe (0.6mm), which conforms to the national industrial policy of saving materials, has the guarantee of strength, and can achieve the purpose of reducing the load-bearing of the building.
Comparison of thermal conductivity:
The thermal conductivity of thin-walled stainless steel pipe is 15 W/m℃(100℃), which is 1/4 of carbon steel pipe and 1/23 of copper pipe. The thin-walled stainless steel pipe is especially suitable for hot water transportation due to its good heat preservation performance. Whether it is the thickness of the insulation layer, or the construction and maintenance costs of the insulation structure, the thin-walled stainless steel pipe has better economical feature.
Comparison of thermal expansion coefficient:
The average thermal expansion coefficient of the thin-walled stainless steel pipe is 0.017mm/（m℃）, which is close to that of the copper pipe.
The inner wall of the thin-walled stainless steel pipe is smooth after internal and external polishing treatment. The equivalent roughness KS of the inner wall of the pipe is 0.00152mm, which is smaller than that of the copper pipe.
Therefore, the water flow of thin-walled stainless steel pipe is larger, the water flow is more smooth, the corrosion resistance is better, and the noise is effectively reduced.
2. Comparison of hygienic performance
Stainless steel water pipes eliminate the problem of "red water, blue-green water and hidden water", and there is no peculiar smell, no scaling, no harmful substances precipitation, which keeps the water pure and is harmless to human body.
It has been used for decades in foreign countries and laboratory tests in different countries, which have shown that the precipitation amount of stainless steel metal elements is lower than 5% of the standard value stipulated by WHO and European drinking water act.
In fact, stainless steel material itself is safe, non-toxic, clean, and has been fully proved by the successful application of stainless steel in various fields involving human health for decades, and has become a well-known fact.
Stainless steel is not only used for a long time in the food industry, including beverage, dairy, brewing, pharmaceutical industry, tableware and cooking utensils and other industries, but also widely used for medical human implants with high requirements for material safety and cleanliness, such as various scaffolds, artificial joints and internal steel nails, and has become the standard material for semiconductor industrial cleanrooms with high requirements for cleanliness.
It is well known that copper tube is easy to corrode and produce copper green.
The copper pipe has the problem of excessive copper, the corrosive bitter smell of blue-green water caused by corrosion, and scaling. The "copper green" in the copper tube is mainly composed of copper carbonate, copper hydroxide compound [cuco3.cu(on)2] and copper sulfate (cuso4). It is easy to be weathered and soluble in water. Although it can inhibit the fungal effect, it has poor effect on bacteria. It is toxic and is also used as insecticide, which has the effect of convergence, stimulation and corrosion on the inner mucous membrane of human body.
It can cause reflex vomiting and has a strong stimulating effect on the intestine. Modern medical research shows that drinking too much water with too much copper is very harmful to health.
3. Comparison of corrosion resistance
Because the thin-walled stainless steel tube can be passivated with oxidant, a tough and dense chromium rich oxide protective film (Cr2O3) is formed on the surface, which can effectively prevent further oxidation reaction. Meanwhile, the passivation ability of copper tube is very small, which is the key reason that the corrosion resistance of copper tube is far less than that of thin-walled stainless steel tube.
When using copper pipes, it is necessary to control the chemical composition and speed of water, otherwise it will cause pipe corrosion. For example, the corrosion of copper pipes in water with pH < 6.5 or residual chlorine content > 70ppm will increase significantly, and the corrosion of soft water will also increase. When using copper pipe, the water speed should not exceed 2 meters every second, otherwise the corrosion rate will increase obviously.
When the flow rate reaches 2 meters per second, the corrosion degree of the copper tube is about 3 times of that of the thin-walled stainless steel tube, and the corrosion degree of the copper tube is 20 times of that of the thin-walled stainless steel tube when the flow rate is more than 6 meters per second. In addition, the copper pipe surface is easy to corrode.
4. Comparison of economic value
Chrysler building is located in New York, USA. It was built from 1926 to 1931, with a total height of 318.9 meters and 77 floors. It is the first building in the world using stainless steel materials in the appearance.
Although it is located in the coastal and polluted environment, the stainless steel on it is still shining after 80 years, and only two cleanings have been carried out.
From Chrysler Building in New York, twin towers in Kuala Lumpur, Disney Concert Hall in Los Angeles and Waterloo railway station in London of England：from 150000 square meters of roof, 452 meters of tower body, to exquisite decorative parts and small structural parts, stainless steel, as the most sustainable green building materials, exudes unique charm that general materials do not have around the world.
These are excellent cases to witness the eternal characteristics of stainless steel materials.
Price comparison of pipe materials: due to the high price of copper raw materials, the price of copper pipe is the highest, and the price of thin-walled stainless steel pipe is about 40% lower than that of copper pipe, so the economic value of thin-walled stainless steel pipe is obviously better than that of copper pipe.
The life cycle cost of thin-walled stainless steel pipe is lower than that of copper pipe.
Once the thin-walled stainless steel pipe is used, it doesn't need to be replaced in the life cycle of 100 years, but other pipes can't reach such a long service life. As long as it is replaced once in the life cycle of 70 years, its comprehensive cost will be at least 2-4 times of the initial investment of the thin-walled stainless steel pipe.
In fact, the initial investment of stainless steel water pipe is not high, and its life cycle cost is very low, which is the biggest advantage of stainless steel material which other materials do not have in economy.
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