Applications and Technological Advantages of Stainless Steel Pipes in Water Treatment and Water Supply

I. Introduction

The water treatment and supply industry, as a fundamental project ensuring people's livelihood, encompasses core aspects such as municipal drinking water transmission and distribution, wastewater treatment and reuse, industrial pure water preparation, and seawater desalination. The requirements for pipeline materials are "multi-dimensionally stringent"—they must resist corrosion from acidic and alkaline wastewater, chloride ions, disinfectants, and other media; prevent secondary pollution such as heavy metal migration; and withstand different water pressure conditions (0.6-10MPa) to ensure long-term stable fluid transmission. Stainless steel pipes (based on 304, 316L, and 2205 duplex steel, containing Cr≥16%, Ni≥8%, and some with added Mo and N elements) have become the preferred pipeline material for the entire water treatment chain due to their excellent corrosion resistance, hygiene safety, and pressure-bearing reliability. With the advancement of the "water conservation first, green and low-carbon" policy, stainless steel pipes are continuously empowering the efficient, safe, and sustainable development of the water treatment industry through material upgrades and innovative connection processes.

II. Core Characteristics of Stainless Steel Pipes for Water Treatment Needs

Broad-spectrum corrosion resistance: The dense passivation film formed by the chromium-nickel alloy resists corrosion from acidic and alkaline substances (pH 2-12) in municipal sewage, drinking water disinfectants (chlorine, chlorine dioxide), and chloride ions in seawater and industrial wastewater. The 316L model has three times the chlorine resistance of 304, and the 2205 duplex stainless steel can withstand high chlorine environments above 5000ppm, making it suitable for complex water quality conditions.

Hygienic, safe, and pollution-free: The smooth, non-porous surface (roughness Ra≤0.8μm) does not adsorb microorganisms, scale, or pollutants, eliminating the risk of heavy metal migration. It complies with GB/T 17219 "Safety Evaluation Standard for Drinking Water Transmission and Distribution Equipment and Protective Materials" and NSF/ANSI 61 certification, ensuring that drinking water quality meets standards.

Pressure Resistance and Structural Stability: Yield strength ranges from 205-550MPa, and can be manufactured into seamless pipes (pressure resistance ≤10MPa) and welded pipes (pressure resistance ≤6MPa). Pipe deformation rate ≤0.2%, no leakage or rupture risk during long-term operation, and service life of 30-50 years, far exceeding that of plastic pipes (10-15 years) and cast iron pipes (15-20 years).

High Fluid Transmission Efficiency: Smooth inner wall with low resistance (friction coefficient λ≤0.012), improving transmission efficiency by more than 20% compared to traditional cast iron pipes. It is also less prone to scaling, eliminating the need for frequent cleaning and reducing maintenance costs.

Installation and Environmental Compatibility: Lightweight (only 1/3 the weight of steel pipes), it can be quickly connected through various methods such as crimping, welding, and flanges, resulting in high construction efficiency. It is also 100% recyclable, with no waste pollution, meeting the requirements of green water treatment projects.

III. Typical Application Scenarios in Water Treatment and Water Supply

(I) Municipal Drinking Water Transmission and Distribution: Ensuring the Safety of the "Lifeline"

Urban Main Pipeline Network: Utilizes 304/316L stainless steel seamless pipes (diameter DN50-DN600), suitable for municipal water supply working pressures of 0.6-1.6MPa, resistant to chlorine disinfection corrosion, with no risk of rust and detachment, ensuring that the water quality at the end of the pipeline is consistent with the water leaving the treatment plant.

Secondary Water Supply System: 304 stainless steel press-fit water pipes (diameter DN15-DN100) are used for pressurized water supply pipelines in residential areas and high-rise buildings. They are easy to install and have good sealing properties, avoiding water pollution during secondary pressurization and solving the "last mile" drinking water safety problem.

Direct Drinking Water Pipelines: Direct drinking water systems in hospitals, schools, and high-end communities use 316L stainless steel thin-walled pipes (wall thickness 0.8-2.0mm), with electrolytic polishing treatment of the inner wall (Ra≤0.4μm), preventing bacterial growth and meeting the high hygiene requirements for direct drinking water quality.

(II) Wastewater Treatment and Reuse: Resistant to Complex Media Corrosion

Wastewater Treatment Plant Process Pipelines:

Aeration Pipelines: 316L stainless steel welded pipes are used, resistant to acid and alkaline wastewater and hydrogen sulfide corrosion in the aeration tank, ensuring aeration efficiency and extending service life by 5 times compared to carbon steel pipes;

Sludge Transport Pipelines: 2205 duplex stainless steel pipes are selected, resistant to abrasion from solid particles in sludge and chloride ion corrosion, preventing pipe blockage and leakage.

Reclaimed Water System: Pipelines for wastewater treatment and reuse in industrial cooling and greening irrigation are made of 304 stainless steel, resistant to corrosion from residual disinfectants and organic matter in the reclaimed water, achieving water resource recycling.

(III) Industrial Pure Water and Ultrapure Water Preparation: Adapted to High-Precision Water Quality Requirements

Electronics and Semiconductor Industry: Ultrapure water (resistivity ≥ 18.2 MΩ・cm) preparation and delivery pipelines use 316L stainless steel electrolytically polished pipes with an inner wall roughness Ra ≤ 0.2 μm, preventing particle shedding and contaminant adsorption, meeting the ultrapure water standards for chip manufacturing.

Pharmaceutical and Food Industry: Purified water and water for injection pipelines use 316L stainless steel sanitary pipes with quick-connect clamps, eliminating sanitary dead corners, and are resistant to high-temperature steam sterilization (121℃), meeting GMP certification requirements.

Chemical Industry: High-purity process water pipelines use 2205 duplex stainless steel pipes, resistant to strong acids, strong alkalis, and high-chlorine media corrosion in chemical wastewater, ensuring the purity of process water and safe pipeline operation.

(IV) Seawater Desalination Project: Resisting High-Salt Corrosion

Seawater Pretreatment Pipelines: Use 316L stainless steel pipes, resistant to seawater corrosion (chloride ion content approximately 19000ppm), suitable for the transmission requirements of seawater filtration and sedimentation processes, preventing premature corrosion of pipelines.

Reverse Osmosis (RO) System Pipelines: High-pressure seawater pipelines before and after the RO membrane use 2205 duplex stainless steel seamless pipes, with a yield strength ≥450MPa, resistant to high pressure (≤8MPa) and high-chlorine corrosion, ensuring stable operation of the reverse osmosis system.

Desalinated water transmission pipeline: The desalinated water pipeline is made of 304 stainless steel, which prevents secondary pollution, is suitable for long-distance transmission, and meets the drinking water and industrial water needs of coastal cities.

IV. Key Processing Technologies and Adaptation

Forming and Connection Processes:

Seamless Forming: Seamless stainless steel pipes are manufactured through hot extrusion and cold drawing processes, resulting in no weld defects and suitability for high-pressure conditions (such as RO systems);

Welded Forming: Welded stainless steel pipes are manufactured using argon arc welding (TIG). The weld seams are pickled and passivated, resulting in corrosion resistance close to that of the base material, suitable for medium and low-pressure pipe networks;

Connection Methods:

Press-fit Connection: Suitable for thin-walled stainless steel pipes (DN15-DN100), with fast construction speed (single joint ≤3 minutes) and an IP68 sealing rating;

argon Arc Welding Connection: Suitable for high-pressure pipelines and sanitary pipelines, producing smooth and even weld seams with no risk of leakage;

Flange Connection: Suitable for large-diameter pipelines (DN300) (Above), easy to assemble and disassemble, suitable for frequent maintenance scenarios such as sewage treatment plants. Surface Treatment Process: Electropolishing: Sanitary and ultrapure water pipes undergo electropolishing to remove the surface oxide layer and microburrs, achieving a roughness Ra≤0.2μm, reducing bacterial adsorption and scaling; Passivation Treatment: All stainless steel pipes are immersed in nitric acid passivation solution before leaving the factory to form a dense passivation film with a thickness ≥0.006mm, achieving a salt spray corrosion resistance of ≥2000 hours; Acid Pickling Treatment: Welded pipe welds are acid-pickled to remove oxide scale, restore the integrity of the passivation film, and improve corrosion resistance.

Testing and Quality Control Processes:

Material Testing: Spectroscopic analysis verifies that the content of Cr, Ni, Mo, and N elements meets standards, preventing material adulteration;

Pressure Resistance Testing: Water pressure test (test pressure is 1.5 times the working pressure), holding pressure for 30 minutes without leakage;

Non-destructive Testing: Welded pipes undergo ultrasonic testing and X-ray inspection to ensure that welds are free of defects such as porosity and cracks;

Hygiene Testing: Drinking water pipes pass heavy metal migration tests and bacterial culture tests, meeting the safety standards for food contact materials.

V. Application Cases and Development Trends Typical Cases A coastal city's municipal water supply network renovation: DN300 316L stainless steel welded pipes, 15km in length, suitable for a working pressure of 1.2MPa, resistant to seawater backflow corrosion. After commissioning, the network leakage rate decreased from 18% to 5%, and the water quality compliance rate reached 100%. A large-scale sewage treatment plant: Aeration pipelines were constructed using DN100 2205 duplex stainless steel pipes, 8km in length, resistant to high-chlorine wastewater corrosion. After 8 years of use, there was no rust or leakage, and maintenance costs were reduced by 70% compared to carbon steel pipes. A semiconductor company's ultrapure water system: DN50 316L electrolytically polished stainless steel pipes were used, with an inner wall Ra=0.15μm, suitable for ultrapure water transportation. The pipeline has been operating for 5 years... Zero particulate pollution annually, meeting the water quality requirements for chip manufacturing. Future Trends Upgraded Corrosion Resistance: Developing super duplex steels (such as 2507) with higher Mo and N content and acid-resistant stainless steel pipes to adapt to extreme water treatment conditions with high chlorine and high acid content, extending service life; Thinner Walls and Lighter Weight: Promoting ultra-thin-walled stainless steel pipes (0.5-1.5mm wall thickness), combined with precision forming processes, reducing pipe usage and transportation and installation costs, adapting to municipal small-diameter pipe networks; Intelligent Monitoring Integration: Embedding corrosion sensors and flow sensors on the inner wall of the pipes, combined with IoT technology to achieve real-time monitoring of pipe corrosion levels and water flow status, improving operation and maintenance efficiency; Green Manufacturing and Recycling: Adopting short-process smelting technology to produce stainless steel pipes, reducing carbon emissions, and establishing a recycling system for waste stainless steel pipes (recycling rate of over 99%), aligning with the "dual carbon" principle. Objectives; Standardization and Modularization: Develop selection standards for stainless steel pipes under different water quality conditions, promote modular connection systems, and improve construction efficiency and project quality. VI. Conclusion With its core advantages of "corrosion resistance, reliability, hygiene and safety, long-term durability, and environmental friendliness," stainless steel pipes have constructed a complete application system for water treatment, from raw water transportation and treatment processes to finished water supply, becoming a core material support for ensuring the safe utilization and recycling of water resources. As the water treatment industry transforms towards high quality, low energy consumption, and green development, highly corrosion-resistant, lightweight, and intelligent stainless steel pipes will continue to break through application boundaries, providing key guarantees for municipal water supply safety, sewage treatment and reuse, seawater desalination, and other fields, helping to achieve the development goal of "sustainable utilization of water resources."