Permanent solution to corrosion and leakage of water supply system: molybdenum stainless steel corrugated pipe
In today’s world where water resources are increasingly tense, it has become a global consensus to protect and save water resources and reduce leakage rate. The important problem of urban water supply system in China is the leakage of pipe network. According to the statistical data of 654 cities in China, the average leakage rate of tap water in China is about 18%, and the highest is 70% in underdeveloped areas. However, the leakage rate of water supply network in Tokyo, Japan and Seoul, South Korea is below 3%, reaching the world leading level. But do you know that the leakage rate of the pipe network in Tokyo and Seoul was 15% and 27% respectively a few years ago. So what is the secret weapon that makes their water leakage rate drop sharply? Molybdenum Stainless steel corrugated water supply pipe.
Project implementation background
Many cities in the world, rich or poor, are plagued by water system leakage.
The cost loss caused by leakage of water supply system is not only the cost of water loss itself, but also other additional costs, such as lack of water, and need to find, treat and store more water.
Many water companies in North America do not know exactly how much water is leaking from their systems. Tokyo and Taipei have confirmed that about 95% of the total number of leakage repairs occurred in water supply pipes with a diameter of 50 mm (2 inches) or less. In the past, the water supply pipes in these two cities were made of lead, iron or plastic.
Once the water supply pipeline is buried underground, various forces, such as:
- Vibration caused by pedestrian flow, vehicle flow and engineering construction;
- It will lead to deformation, falling off and even fracture of the pipeline.
Poor quality pipes not only have leakage problems, but also cause health problems, so it is necessary to speed up the replacement of these pipes.
How do cities like Tokyo and Taipei reduce water leakage rates?
In 1980, in order to solve the problem of leakage, Tokyo took measures from the following three aspects:
- The existing water supply pipeline was replaced with 316 (UNS S31600) stainless steel pipe and the cast iron main pipe was replaced with ductile iron pipe.
- Improve leak detection.
- Improve response time when leakage is detected.
In 1998, 316 stainless steel bellows were introduced to replace straight pipes and pipe fittings. The pipes are corrugated at regular intervals of length, so it is easy to bend during installation to accommodate changes in direction without the need for additional joints. The pipeline can also absorb the stress caused by vibration, land subsidence and seismic activities. By using a single corrugated pipe, the number of pipe joints is greatly reduced.
316L stainless steel bellows
Tokyo’s successful experience in reducing water leakage rate has attracted the attention of Taipei and Seoul authorities. In 2003, Taipei launched a similar program to Tokyo. Taipei experienced a severe drought in 2002, which caused residents to have only intermittent water supply for 49 days. Of all the 450 measurement areas in Taipei, 40% of the areas have a water yield of less than 50%.
Traditional water pipeline vs flexible water pipeline
The effect of replacing stainless steel corrugated pipe in Tokyo, Taipei and other places is gratifying
Since 1994, Tokyo’s annual water loss has been reduced by nearly 37.5 billion gallons, saving more than $200 million annually. Since 2002, the annual water loss in Taipei has decreased by about 38.6 billion gallons. What’s more, Taipei’s drought in 2014, which led to the start of the stainless steel pipe project, was more severe than that in 2002, when continuous water supply was ensured and there was a surplus.
Implementation results of Tokyo, Seoul and Taipei projects
Relationship between installation of stainless steel pipe in Tokyo and repair times and leakage rate
What are the advantages of stainless steel corrugated water pipe?
Features of stainless steel bellows:
- 1. Good construction performance, reasonable structure and stable performance. This product is a thin-walled hose with light overall weight, which greatly reduces the construction load and construction time.
- 2. High quality material, durable, beautiful appearance, easy installation and disassembly.
- 3. Soft handle, high strength, good elasticity and high fatigue resistance.
- 4. Safety, reliability and quality assurance. The actual working pressure, working environment and service condition of bellows are considered. All parameters are carefully calculated and repeatedly tested to ensure the safety in operation.
- 5. Many kinds, complete specifications and reasonable price.
Why 316 stainless steel?
Buried service environment of water supply pipeline
Due to the buried use of pipelines, the soil has an impact on the corrosion behavior of materials. Buried steel pipes may be corroded by soil.
Stainless steel should be passivated in soil, but the presence of water, corrosive chemicals (chloride ions, sulfate, bacteria) and stray current can cause local corrosion.
The key factors affecting the corrosion of stainless steel in soil are: soil acidity, resistivity, chloride, sulfate and other soluble substances, microbial corrosion, oxygen concentration cell, etc.
1) The acidity of the soil
It is caused by mineral leaching, acid plant decomposition and industrial waste. Soil with high acidity (pH < 5) increases the risk of corrosion.
2) Resistivity of soil
The resistivity is related to the electrochemical reaction. The following are soil corrosivity indexes:
- Strong corrosivity < 100 Ω· cm
- Corrosion 1000 – 5000 Ω· cm
- Medium corrosivity 5000 – 10000 Ω· cm
- Low corrosion 10000 – 20000 Ω· cm
- The corrosivity is gradually weakened > 20000 Ω· cm
- Non corrosive 30000 – 100000 Ω· cm
3) Chloride ions and other soluble substances
Chloride is one of the most important factors. The presence of chloride directly induces pitting corrosion and crevice corrosion of stainless steel and reduces the resistivity of soil. Harmful chlorides may be inherent in the soil or may come from exogenous sources.
4) Microbial corrosion (MIC)
Microbial corrosion refers to the corrosion caused by the activity of microorganisms and their metabolites.
5) Oxygen concentration cell
Different oxygen content may lead to corrosion problems caused by oxygen concentration difference battery. The oxygen concentration of soil determines the redox potential of soil.
Corrosion resistance of 316 stainless steel
Fe, <0.03% C, 16-18.5% Cr, 10-14% Ni, 2-3% Mo, <2% Mn, <1% Si, <0.045% P, <0.03% S
316 stainless steel contains about 2% molybdenum, which significantly improves the local corrosion resistance of stainless steel, such as chloride ion pitting corrosion and crevice corrosion.
Corrosion test results of buried soil in 10 years
The Japanese stainless steel association has carried out soil corrosion tests on stainless steel pipes in 12-15 test sites for 10 years.
10 years test results
- No pitting corrosion occurred in 304 stainless steel tubes at most test points. Some 304 tubes have rust color on the surface, but the corrosion resistance is good. Crevice corrosion was found in some stainless steel pipes at seaside test points.
- 316 stainless steel with molybdenum content of 2% and nickel content of 10% has excellent corrosion resistance in various types of soil environment. The results show that the corrosion resistance of 316 stainless steel pipe is better than that of 304 stainless steel pipe.
- The test results show that some 304 stainless steel pipes have local corrosion. Therefore, the municipal water supply department decided to use 316L stainless steel pipes in the reconstruction project of Tokyo water supply system. The service life of 316 stainless steel pipe is expected to exceed 100 years.
- 316 stainless steel is basically inert in drinking water, and the release of alloy elements is negligible, so it has no impact on water quality.
Stainless steel corrugated water supply pipe has good corrosion resistance, elasticity, durability, and reduces the number of joints, so it plays an important role in preventing leakage.
At present, China’s water resources management is at a high priority. China has 20% of the world’s population and 6% of the world’s freshwater resources. China document No.1 in 2011 defines “three red lines” for water resources management system
- 1. Control the total water consumption of surface water and groundwater.
- 2. Focus on improving water use efficiency and capping with water.
- 3. Control the total discharge of water pollutants.
One of the important problems to be solved in urban water supply system in China is the leakage of pipe network. The successful experience of Tokyo, Seoul and Taipei has proved that stainless steel is suitable for water supply pipes, even for large-scale systems. Although the initial cost may be higher than that of competing materials, the use of stainless steel piping in water supply systems has proven to be a good investment due to extended service life of the piping system, reduced maintenance costs, and significantly reduced leakage and treatment costs per gallon of water.
Source: China Corrugated Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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