Seamless Steel Pipe in Cold Storage Refrigeration Unit

In cold storage refrigeration systems, the most commonly used pipeline materials are 20# carbon steel seamless steel pipes, copper tubes, 10# carbon steel seamless steel pipes, and 16Mn low-alloy steel pipes. Except for low-temperature and low-stress working conditions, the lower limits of service temperatures for (GB8163) 10# carbon steel seamless steel pipes, 20# carbon steel seamless steel pipes, and 16Mn low-alloy steel pipes are approximately -29°C, -20°C, and -40°C respectively. Copper tubes cannot be used for ammonia refrigeration system refrigeration pipelines. For fluorine systems, when the pipe diameter of the device is below 20mm, copper tubes are generally used. When the pipe diameter is above 25mm, seamless steel pipes can be used.
Among them, 10# carbon steel seamless steel pipes are applied under working conditions where the warehouse temperature is lower than -29°C. Only some pipe diameters meet the low-temperature and low-stress working conditions. 20# carbon steel seamless steel pipes can be used for temperatures lower than -20°C and meet the low-temperature and low-stress working conditions. 16Mn low-alloy steel pipes are generally used as pipeline materials for carbon dioxide refrigeration systems and ultra-low temperature cold storage refrigeration systems.
According to national standards, any steel material with openings at both ends and a hollow cross-section, and a relatively large ratio of its length to the cross-sectional perimeter can be called a steel pipe.

The size representation of steel pipes: D - nominal outer diameter; S - nominal wall thickness.
Seamless steel pipes are classified by material into ordinary carbon steel pipes, high-quality carbon structural steel pipes, alloy structural pipes, alloy steel pipes, bearing steel pipes, and bimetallic composite pipes, coated pipes, etc. to save precious metals and meet special requirements. Seamless steel pipes can be further divided into hot-rolled pipes, cold-rolled pipes, cold-drawn pipes, and extruded pipes.

Cold drawing and cold rolling are secondary processing of steel pipes. Welded pipes are divided into straight seam welded pipes and spiral welded pipes. Stainless steel pipes are divided into two major categories, seamless pipes and welded pipes according to the production method. Stainless steel pipes generally use three hardness indicators, Brinell hardness, Rockwell hardness, and Vickers hardness, to measure their hardness.

When selecting, the material, specification, model, and connection method of the pipe should meet the requirements of the operating conditions (working pressure, working temperature, etc.). When ordering, it is necessary to indicate the standard number of the pipe, product name, steel grade, size specification, quantity (weight or length), delivery status, and other requirements.
Before pipeline installation, remove the oxide scale, debris, and rust inside the pipe and use it in time after cleaning it thoroughly. When not in use temporarily, cover the pipe openings at both ends with adhesive tape or pipe caps to prevent dust, debris, or moisture from entering. Pipeline cleaning can be done by mechanical cleaning with brushes or chemical cleaning with chemical solutions.
For pipe cutting, mechanical cutting or oxyacetylene flame processing cutting can be used. Pipes with a nominal diameter of 50 are generally cut with a cutting machine.

After processing, the pipe cut should be flat, without cracks, burrs, or deformations. The surface oxide scale should be removed completely. There should be no slag and oxide scale at the welded parts. When connecting pipes with tees, valves, etc., pay attention to the flow direction of the refrigerant. When connecting carbon steel, generally use argon arc welding for backing to ensure smooth and unobstructed inner walls and prevent welding slag from entering the pipeline. The groove form, angle, and size when connecting pipes and fittings should meet the design requirements.
After pipeline installation is completed, use dry compressed air or nitrogen to perform segmented purging and sewage discharge on the pipeline. The purging sequence should be carried out in turn according to the main pipe and branch pipes. Then perform pressure testing for leak detection, vacuum pumping experiment, painting, and insulation. The airtightness test of the pipeline can be carried out together with the airtightness test of the entire device.
The main faults that often occur in pipelines are flange leaks, weld leaks, and corrosion perforation of the pipes themselves. During daily use, operators must use the pipelines in accordance with operating procedures and conduct regular patrol inspections. Mainly check the following aspects:
a) Whether the in-use pipeline has over-temperature, over-pressure, over-load, and over-cooling;
b) Whether there is abnormal vibration in the pipeline and abnormal sound inside the pipeline;
c) Whether there is liquid hammer in the pipeline;
d) Whether the operation of pipeline safety protection devices is normal;
e) Whether the insulation layer is damaged;
f) Whether the supports and hangers are abnormal.
Whether it is a design unit, construction unit, or user unit, they all need to comply with the relevant national regulations on safety management of refrigeration pressure pipelines, establish and improve safety management systems, and operate and operate in a standardized manner as required.