How to avoid leakage and scale buildup when installing sanitary pipe fittings for pure water equipment?

In pure water, ultrapure water, and purified water systems, sanitary pipe fittings are the core transport carriers of the entire water treatment system, widely used in key stages such as RO reverse osmosis, EDI ultrapure water, sterile water storage, and circulation transport. Pure water systems have much higher requirements for the cleanliness, sealing, and smoothness of pipelines than ordinary fluid pipelines. If pipe fittings are not installed correctly, problems such as interface leakage, pipe wall scale buildup, and microbial growth are very likely to occur.

Leaks can lead to unstable pipeline pressure, pure water loss, and equipment shutdown; scale buildup can breed bacteria and form biofilms, directly causing substandard pure water quality, decreased resistivity, and unqualified end-use water, seriously affecting precision water applications such as pharmaceutical companies, electronics manufacturers, food and beverage companies, and laboratories. Many pure water systems experience frequent bacterial outbreaks and substandard water quality later on, and the root cause is not filter failure, but rather improper installation details of the pipe fittings in the early stages. This article details the key points for avoiding pitfalls in the installation of pure water equipment pipe fittings, covering aspects such as material matching, installation process, sealing specifications, and pipeline layout, to eliminate the potential for leakage and scale buildup from the source.

I. Optimize Pipe Fitting Materials Suitable for Pure Water Conditions to Reduce Scale and Corrosion at the Source
Pure and ultrapure water media are free of impurities but have extremely high permeability. Ordinary inferior pipe fittings are prone to scaling, rusting, and impurity precipitation. No matter how standard the installation process, substandard materials will ultimately lead to malfunctions. Ordinary carbon steel and inferior stainless steel pipe fittings are strictly prohibited in pure water equipment; high-cleanliness, hygienic materials must be selected. For conventional pure water systems, 304 stainless steel hygienic pipe fittings are preferred, suitable for ordinary reverse osmosis pure water transportation, rust-proof, corrosion-resistant, and not prone to scaling, meeting conventional water standards.

For ultrapure water, pharmaceutical purified water, and electronic high-purity water systems, 316L stainless steel pipe fittings must be upgraded. 316L material contains molybdenum, resists chloride ion corrosion, does not release metal ions, has better surface passivation, and is less prone to oxide layer formation and scale adhesion. Meanwhile, the surface roughness of the inner and outer surfaces of the pipe fittings must be ≤0.8μm. Mirror polishing significantly reduces the adhesion between water and the pipe wall, making it difficult for scale and biofilm to adhere and accumulate, thus effectively preventing scale buildup from a material perspective.

For both pure water and ultrapure water applications, food-grade EPDM or PTFE gaskets are uniformly recommended. These are water-resistant, aging-resistant, do not leach, and do not mold, making them suitable for long-term pure water circulation. When installing gaskets, ensure they are intact, without deformation, scratches, or gaps. The use of aged, hardened, or cracked old gaskets is strictly prohibited. Simultaneously, it is essential to ensure uniform clamp tightening force, with both sides of the interface aligned and centered, avoiding uneven tilting or stress to prevent loosening and leakage after pipeline vibration during operation. Improper operation such as mixing, under-installing, or misaligning gaskets is strictly prohibited.

Pipeline installation must follow the principle of slope-following layout, maintaining a reasonable slope, avoiding horizontal depressions and local subsidence, and ensuring no residual water remains in the pipeline after shutdown. All branch pipes and diversion pipes should be shortened as much as possible to reduce the number of blind pipes. The length of blind pipes must strictly adhere to industry standards to avoid stagnant water accumulation. Meanwhile, the pipeline layout should be as simple and neat as possible, reducing unnecessary bends and joints. The fewer the pipe splices, the fewer the potential for leaks and scale buildup. For end points prone to water accumulation, drain valves and empty valves can be added to regularly drain residual water and completely eliminate stagnant water and scale buildup.

Welded pipelines must use a sterile automatic argon arc welding process with nitrogen purging throughout the welding process to prevent oxidation and blackening of the weld. Improper welding can result in pinholes and incomplete welds, causing micro-leaks. Rough welds and oxidized peeling create uneven surfaces that easily attract impurities from the water, gradually forming stubborn scale that cannot be removed by conventional cleaning, becoming a permanent hygiene hazard. After installation, each section must be pressure tested for leaks to identify and prevent micro-leaks from occurring later.

Many new projects directly run water after equipment installation, neglecting pipe cleaning and passivation. This results in welding slag, dust, and metal oxide residue remaining in the pipes, which quickly solidify into scale after water flow, causing initial water quality to fail to meet standards.

After pipe installation, a complete process of pipe flushing, acid washing, passivation, and disinfection must be performed to thoroughly remove impurities, welding residues, and metal floats from the pipe walls, allowing a dense passivation layer to form, improving resistance to scale formation and corrosion. Continuous circulation flushing is required during the initial water flow. Only after the water quality stabilizes and is free of impurities can the system be officially put into operation, preventing initial scale buildup from the source.

In summary, the key to preventing leaks and scale buildup in sanitary pipe fittings for pure water equipment in the long term lies in "material compatibility, compliant sealing, seamless layout, standardized processes, and post-treatment pre-cleaning." Leaks are solved by standardized sealing and installation processes, while scale buildup is prevented by seamless layout, high-cleanliness materials, and standardized post-treatment. When installing equipment and modifying pipelines, companies should not only focus on the main equipment configuration but also pay attention to the details of pipe fitting installation. Standardized pipe fitting installation processes can effectively ensure the long-term stability of pure water system quality, reduce downtime due to malfunctions, pipeline cleaning, and parts replacement costs, and achieve long-term stable and compliant operation of the equipment.