Capillary tube is a special, precise and high-quality round metal tube made by fine rolling and fine drawing. It usually refers to the tube under OD6.0mm. It is divided into capillary seamless tube and capillary welded and cold drawn tube. Generally speaking, compared with welding cold-drawn tube, capillary seamless tube has higher and stricter requirements on manufacturing conditions, process, detection, inspection, performance, shape and dimensional accuracy control, and is more suitable for high-end, precision and harsh conditions of the application.

In the new era, with the progress of science and technology, and with the high-end equipment components and advanced precision instruments on the new environment and new conditions of a variety of new materials demand,so generally, various strict requirements and challenges are put forward for capillary tube, which are generally shown in the following aspects:

1. With sufficient strength, i.e. high yield limit and strength limit, to ensure safety and economy.

2. With good toughness to ensure that brittle failure does not occur when the external force is loaded.

3. With good processing performance, including cold and hot processing forming and welding performance.

4. With good micro structure and surface quality, do not allow cracks and flakes and other defects.

5. With stable physical properties under various harsh environmental conditions, namely acid, alkali, salt, corrosion,high temperature and pressure resistance.

6. Materials used for high temperature components should have good high temperature performance, including sufficient creep strength, durable strength and durable plasticity, good high temperature microstructure stability and high temperature oxidation resistance, etc.