China’s huge infrastructure scale for the development of stainless steel pipe provides a broad space. With people’s continuous pursuit of a better life, the future market demand of water supply pipeline will transition from price to quality. On August 21st, the 2020 Stainless Steel Application Technology International Forum of Hydraulic Industry, sponsored by International NI Association, School of Environmental Science and Engineering, Donghua University, and Equipment and Materials Working Committee of Zhejiang Municipal Water Conservancy Association. Jiang Wenyuan, Honorary Director of Building Water Supply and Drainage Branch of China Urban Water and Wastewater Association, introduced the application trend of stainless steel in hydraulic industry. At the same time, the application of stainless steel in water supply safety and quality improvement was introduced from local governments, industry associations and related enterprises at home and abroad.
Stainless steel light weight, high strength, environmental hygiene, good corrosion resistance, low thermal conductivity, long service life (can be used more than 70 years), Can save the daily maintenance of the water industry, mainly used in the production of stainless steel water tank, stainless steel valve, stainless pump, stainless accessories, stainless pipe, pipe fittings and other products. China was an early starter in stainless steel pipe production, but in recent years the product has begun to be used in bulk quantities in water and natural gas. At present, the annual usage of thin-walled stainless steel pipe in the field of construction in China is about 100,000 tons, and the annual output value is about 3 billion yuan.
As the state accelerates the construction of new-type urbanization and strengthens the community transformation of old towns, it has issued relevant standards for water supply pipelines. For example, the Ministry of Housing and Urban-Rural Development issued in 2017 “Building and Community Pipeline Direct Drinking Water System Technical Regulations” (CJJ / T110-2017) clearly states that the direct drinking water system pipeline should be selected in line with food-grade stainless steel pipe water supply pipeline; Since August 1, 2019, the Ministry of Housing and Urban-Rural Development has implemented the “Green Building Evaluation Standard” (GB / T50378-2019), which specifically states that indoor water pipelines require stainless steel pipes and fittings. More and more national standards and industry standards have been introduced, stainless steel pipe has also been paid attention to, and gradually become the building water pipe, in Beijing, Shenzhen and other cities in the direct drinking water system has been widely used.
At present, China’s stainless steel pipe is mainly used for manufacturing water industry / 304L and 316 / 316L, 2205 duplex stainless steel tube is also in trial production. Although stainless steel pipes have excellent corrosion resistance, they are also affected by different water, soil and microorganisms. Therefore, different kinds of stainless steel tubes have different service environments. Among them, stainless steel pipes are susceptible to corrosion by chloride ions in water because they are in direct contact with water. Different kinds of stainless steel pipes have different resistance to chloride ion corrosion. In cold water, in order to achieve corrosion resistance, 304 stainless steel tubes can withstand the chloride ion content of 200 ppm (parts per million), 316 stainless steel tube can withstand 1000 ppm of chloride in water; In hot water, 304 stainless steel pipe can withstand chloride ion in water should achieve corrosion resistance. Large content of 50 ppm, 316 stainless steel tube can withstand the water chloride ion, content of 250 ppm. Therefore, 304 stainless steel pipe often served in inland or coastal areas of the buried environment, 316 stainless steel pipes often serve the coastal area of outdoor or buried environment.
Song Quanming, general manager of the International Nickel Association’s Beijing office, said: Stainless steel pipes do not appear large areas of uniform corrosion, but occasionally localized corrosion. From the current application point of view, stainless steel pipe will mainly appear crevice corrosion, pitting corrosion, stress corrosion (cracking), microbial corrosion, galvanic corrosion and other local corrosion.
In addition to the effects of corrosion, accurate installation by workers can also affect the use of stainless steel pipe. Unlike plastic pipes, the installation of stainless steel pipes requires a higher level of operation for workers and also has special requirements for the handling process. For example, thin-walled stainless steel pipes are prone to damage during handling and require careful handling. In addition, there are still some problems to be solved, including the service life of the rubber seal ring and the stainless steel pipe is not synchronous, the influence of the adhesive connection of stainless steel pipes on drinking water, the application prospect of the 2205 duplex stainless pipe and so on.
At present, stainless steel pipe has been widely used in the city drinking water supply system in the international scope. For example, since 2009, Tokyo, Japan, small diameter stainless steel pipes accounted for more than 95% of the water supply pipeline; Since 1980, Germany has made extensive use of stainless steel in tap water systems.
Stainless steel pipe at home and abroad in the six major differences: First, the main use of stainless steel tube brand different. S in foreign US is mainly S, mainly in domestic US 304. 304 stainless steel pipe price below 316 stainless steel tube, but corrosion resistance, poor technical performance, short service life. Second, the wall thickness of stainless steel tube is different, the domestic stainless steel pipe wall thickness was thin wall trend. Stainless steel tube wall can be used in engineering construction, but it will have a certain impact on service life and technical performance. Third, 300 series products are different from 400 series products. The application ratio of 300 series and 400 series is 6: 1. The application ratio of 300 series products to 400 series products is 9 ∶ 1 in China. With the introduction of pure oxygen top blowing process, 400 series of products gradually appear, but there are still some lack of quality and competitiveness. For example, there is no price advantage over imported products. Fourth, compared with foreign countries, the domestic stainless steel pipe connection way has many kinds. Fifth, different types of stainless steel pipe products. China is mostly straight pipe, other types are less. In foreign countries, straight pipe corrugated pipe project cases appeared in spray system. Sixth, the product name is different, known as corrosion-resistant steel pipe abroad, domestic called stainless steel pipe.
We can focus on three development directions of stainless steel pipe:
First, duplex stainless steel pipe, 2205 duplex stainless pipe through austenitic stainless steel and ferritic stainless steel layered interlacing, greatly improving corrosion resistance, can transport chloride in water. The content is up to 10,000 mg / L, which is 10 times that of SUS316 and 50 times of SUS 304. At present, duplex stainless steel pipe products are in trial production, the relevant standards are also in the development.
The second is nano-antibacterial stainless steel tube, the outer layer of the tube is stainless steel, the inner layer is plastic and plastic layer. It’s coated with a nano-antibacterial coating that disinfects and improves water quality. It is a derivative of stainless steel pipe. As the direct contact between water and stainless steel is separated by a plastic layer, the stainless steel does not contact the chloride ion in the water, thereby solving the corrosion problem of the chlorine ion of stainless steel. At the same time, because the plastic layer is a stress layer and the outer stainless steel wall is thin (0). 3 mm), the cost and selling price of the pipe are solved. At present, the pipe has been applied in Shenzhen.
Third, reinforced stainless steel tube (lined stainless steel composite pipe), which is another derivative of stainless steel pipe, but unlike nano-antibacterial stainless steel, it is metal and metal composite pipe. The inner layer of steel pipe is stainless steel pipe, which is in direct contact with water, and the outer layer is carbon steel pipe. The strength and rigidity of the pipe is greater.