What is the difference between pure water, purified water and ultrapure water?

1. The difficulty of manufacturing is different.

At present, the pure water used in the market is basically prepared by reverse osmosis, distillation and other methods. Purified water is pharmaceutical water prepared by distillation, ion exchange, reverse osmosis or other suitable methods. Ultra-pure water is prepared on the basis of pure water through a series of complex purification technologies, such as photooxidation technology, polishing and polishing treatment. Such water is difficult to achieve by ordinary processes. Ultra-pure water can be prepared by double-stage reverse osmosis water treatment equipment supplemented by EDI equipment.

2. Heavy metals, bacteria, particle number and other indicators are also very different.

The impurity content of pure water is ppm, while that of ultra-pure water is ppb. Except for water molecules, this water has almost no impurities, no bacteria, viruses, chlorinated dioxins and other organic substances, and of course, no mineral trace elements required by human body. It is close to theoretical water, that is, water with almost all atoms except oxygen and hydrogen.

3. The requirements for the material of the transmission pipeline are also different.

Ultra-pure water and purified water have more strict requirements on the material of transmission pipeline than pure water.

4. Conductivity is different.

The conductivity of pure water is 2-10us/cm, the conductivity of purified water is ≤ 0.2us/cm, and the conductivity of ultra-pure water is 0.056us/cm.

5. Different uses.

Pure water is mainly used in biological, chemical, metallurgical, aerospace, electric and other fields.

Purified water is generally used as water for medicine.

Ultra-pure water is generally used in the fields of electronics, electricity, electroplating, lighting appliances, laboratories, food, paper making, daily chemicals, building materials, paint making, battery, laboratory, biology, pharmacy, petroleum, chemical, steel, glass, etc.

Description of UPVC/PVC pipe material and brief analysis of process cooling water and pure water pipe selection

1、 Material properties:

PVC is polymerized from vinyl chloride monomer (VCM). PVC material is non-toxic, anti-aging, acid and alkali resistant, so it is very suitable for use in chemical pipelines. The mixture of PVC raw materials and a certain amount of solid additives (without plasticizer) is called rigid polyvinyl chloride (UPVC).

CPVC is a high polymer material made from chlorinated polyvinyl chloride (PVC). After chlorination, the chlorine content of PVC resin increases from 56.7% to 63-69%, which increases the chemical stability, thus improving the heat resistance, acid resistance, alkali resistance, salt resistance, oxidant resistance, etc. of the material; Its thermal deformation temperature and mechanical properties are much higher than UPVC. Therefore, CPVC is one of the best engineering materials for industrial pipelines.

2、 Pipeline system introduction:

UPVC and CPVC pipe systems are corrosion resistant, impact resistant, not easy to deform, smooth inner wall, not easy to scale, good thermal insulation, non-conductive, convenient adhesion, long service life and other characteristics. Therefore, UPVC and CPVC pipe systems are gradually replacing other metal pipe systems on the advantages of high cost performance and low construction costs. Besides, UPVC and CPVC pipe systems are convenient and fast for maintenance, and do not require long downtime to cause huge losses. Therefore, UPVC and CPVC pipe systems are the first choice for current industrial pipe design.

The maximum allowable operating temperature of UPVC pipe system is 60 ℃, and the long-term operating temperature is 45 ℃. It is suitable for transporting some corrosive media with temperature lower than 45 ℃; It can also be used for the transmission of ordinary pressure fluid, generally used for water supply and drainage pipes, agricultural irrigation pipes, environmental engineering pipes, air conditioning pipes, etc.

The maximum allowable operating temperature of CPVC pipe system is 110 ℃, and the long-term operating temperature is 95 ℃. It is suitable for transporting hot water and corrosive media within the pressure range allowed by the standard. It is generally used in petroleum, chemical, electronics, electricity, metallurgy, paper, food and beverage, medicine, electroplating and other industrial fields.

3、 Physical performance: 1. UPVC physical performance table:

4、 Comparison table of operating temperature and operating pressure of UPVC/PVC pipes:

The process water supply of the electronic cleaning plant mainly includes process cooling water and pure water.

Process cooling water is mainly used for cooling various process equipment. Since many of the cooling pipes in the process equipment are capillary pipes with very fine diameter, in order to avoid scaling of the capillary pipes, corresponding requirements are also put forward for the quality of the process cooling water.

Pure water is mainly used for cleaning various electronic products. The use of pure water can avoid the pollution of impurities in the water to electronic products. The main characteristics of pure water used in electronic plants are not only high water resistivity, but also different requirements for particle size, total organic carbon (TOC), total silicon, dissolved oxygen (DO), and the content of various ions.

1. Selection of process cooling water pipeline

Process cooling water systems in semiconductor, TFT-LCD and other industries put forward requirements for process cooling water quality in order to avoid scaling and blocking of cooling coils of process equipment.

Take the design water quality of process cooling water in a semiconductor factory as an example: resistivity>30 k Ω · cm hardness<0.5 Germany, so the selection of process cooling water pipeline mainly considers two requirements, on the one hand, the requirements for water quality; The other is the requirement for pipeline corrosion.

Process cooling water pipes mainly include stainless steel pipes and plastic pipes.

(1) Stainless steel pipe

According to the water quality requirements of process cooling water, SS304 stainless steel pipe can meet the requirements, but the semiconductor and TFT industries usually use the reverse osmosis (RO) effluent produced in the process of pure water preparation as the supplementary water source of process cooling water, and the pH of RO effluent varies according to the process of pure water preparation. When the pH value of water is neutral or weakly alkaline, SS304 stainless steel can be used. When the pH value of water is acidic (RO effluent is usually acidic without alkali), SS304L stainless steel with good acid resistance should be used.

According to the investigation of different projects, the corrosion of stainless steel pipeline occurs at the interface and the bottom of the pipeline. The main reason is that the interface corrosion is mainly caused by the damage of the oxide layer caused by the failure of argon arc welding during the welding process, which causes the corrosion of the stainless steel metal chromium complex under the oxide layer. The corrosion at the bottom of the pipeline is mainly due to the use of tap water during pipeline flushing, which contains a lot of residual chlorine. The water in the pipeline after flushing is not drained in time, resulting in water collection in local pipe sections. When the system is not put into operation for a long time after the completion of pipeline construction and acceptance, it is easy to cause chlorine corrosion of stainless steel. The chloride ion corrosion in stainless steel is stress corrosion, in "austenitic stainless steel-CL", The existence of oxygen in the solution promotes the passivation of metal, while chloride ion destroys the passivation of metal, and enters the crack tip to form hydrochloric acid, which intensifies the corrosion.

Therefore, certain corrosion allowance should be taken into consideration when selecting stainless steel pipes. At least products with wall thickness grade of Sch-10S should be selected, and the correct welding method should be adopted, and the water in the pipe should be drained and dried after the pipe is washed.

(2) Plastic pipe

According to the quality requirements of process cooling water, PVC pipes can meet the requirements. There are two kinds of PVC commonly used. Rigid polyvinyl chloride (PVC-U) is a thermoplastic polymer compound polymerized from polyethylene monomer; Chlorinated polyvinyl chloride (PVC-C) is a unique polymer obtained by chlorination of polyvinyl chloride resin. Because PVC pipes have strong corrosion resistance, even if the water quality is weak acid or alkali, it will not cause corrosion of pipes.