Pipelines Used in the Refrigeration System

According to the regulations on pressure pipelines in the "Safety Technical Regulations for Pressure Pipelines": "The maximum working pressure is greater than or equal to 0.1MPa; the nominal diameter is greater than 25mm; the conveyed medium is gas, steam, liquefied gas, a liquid with a maximum working temperature higher than or equal to its standard boiling point, or a flammable, explosive, toxic, or corrosive liquid." Some pipelines in the refrigeration system fall within the scope of pressure pipelines, so strict attention should be paid to the selection of pipelines in the refrigeration system.
I. Pipeline Material Selection
There are copper pipes, seamless steel pipes, and stainless steel seamless pipes. (Copper pipes cannot be used in systems with ammonia refrigerant.)
(1) Copper Pipes
There are red copper pipes (industrial pure copper) and brass pipes (copper-zinc alloy). According to different manufacturing methods, they are divided into drawn pipes, rolled pipes, and extruded pipes. Generally, drawn pipes are used for medium and low-pressure pipelines. Red copper pipes are more commonly used in refrigeration units using Freon refrigerant, with the grade TP2. The outer diameter specifications (mm) are 10, 12, 16, 22, 28, 35, 42, and 54. The fixed length is generally 4 meters per piece. To facilitate bending, the copper pipe with a diameter of φ6*1 is in a semi-hard state H55 (Y2), and the others with different diameters are generally in a soft state o60 (M). (Copper pipes used in refrigerators will have special markings by the manufacturer.) The chemical composition, dimensional deviation, straightness, roundness, mechanical properties, and technological properties of the copper pipe materials shall comply with the requirements of GB/T17791 - 2017 "Seamless Copper and Copper Alloy Tubes for Air Conditioning and Refrigeration Equipment".
(2) Seamless Steel Pipes
There are 10# (for working conditions below - 29°C) and 20# (for working conditions below - 20°C, the most commonly used in cold storage refrigeration systems) carbon steel seamless steel pipes, which need to comply with the provisions of GB8163.

This steel pipe has a hollow section, no weld seam, can bear flammable, explosive, and toxic fluid media, and is suitable for conveying fluid media. The usual length of the steel pipe is 3000mm∽12500mm, and users can choose an appropriate fixed length (or multiple fixed lengths) according to specific conditions. The most commonly used length is 6 meters per piece. It is generally used for the suction header (branch pipe), exhaust header (branch pipe), and liquid supply pipe of the unit.
16Mn low-alloy steel pipes are generally applied to the pipeline materials of carbon dioxide refrigeration systems and ultra-low-temperature cold storage refrigeration systems. Some refrigeration units use stainless steel pipes as exhaust pipelines, which need to comply with the provisions of GB14976.
II. Determination of Pipe Diameter and Cleaning before Installation
The pipe diameter can be calculated based on the refrigerant flow rate in the pipe and the total pressure loss of the pipeline. The calculation is based on ensuring the minimum refrigerant pressure drop and the minimum refrigerant flow rate for effective oil return.
To prevent debris from entering the refrigeration system, causing damage to the refrigeration unit or blocking the pipelines, valves, filters, etc., the pipelines should be inspected and cleaned before processing and when configured into the refrigeration system. For pipelines that are not in use temporarily, the two ends must be blocked to prevent debris from entering.
The welding of copper pipes adopts nitrogen-shielded welding to prevent the generation of oxide scales. Since seamless steel pipes are prone to rust, the pipes should be cleaned before fabrication, and the oxide scales, dirt, and rust on the inner and outer walls should be removed until the metal luster appears on the pipe wall surface.

A rag, steel wire brush, or cleaning solution can be used for cleaning, but after cleaning, it should be dried to keep the inner wall of the pipe dry and avoid water from entering the system.
III. Installation Requirements