In the process of industrial development, in order to transport liquids or gases, various pipes, including plastic pipes and steel pipes, must be used. Its advantages are mainly reflected in chemical properties, corrosion resistance, wear resistance, self-lubrication is not easy to scale, high cleanliness, but plastic pipe is not resistant to high temperature and high pressure. Steel pipe belongs to metal pipe, its performance advantage is mainly reflected in material connection and unloading performance, high temperature resistance, high pressure resistance, impact resistance. In the pipeline system, in addition to the straight pipe, there are also various pipe fittings to form a pipeline system: for example, the pipe must use the elbow when turning; the pipe should use the reducer when changing its diameter; the tee & Cross when bifurcation; the pipe joint should be connected with the flange; In order to open the conveying medium, various valves should be used; expansion joints should be used to reduce the impact of thermal expansion or frequent vibration on the pipeline system. In addition, in the pipeline, there are various connectors and plugs connected with various instruments and instruments. In the pipeline system in addition to the straight pipe other than the fittings referred to as pipe accessories.

With the development of economy, in order to standardize the use of materials and the development of industry, countries have formulated relevant standards that meet their own development needs. ASTM/ASME (API), EN, JIS, GB.

ASTM is the abbreviation of American Society for Testing and Materials. The technical association was established in 1898. At that time, it was mainly to study and solve the problem of test methods for steel and other materials. With the continuous expansion and development of its business scope, the Institute's work center is not only to study and develop material specifications and test method standards, but also to include various materials, products, systems, service items characteristics and performance standards, as well as test methods, procedures and other standards.

EN (European standard): the adoption of such a standard, in accordance with the common obligations of the participating States, will confer legal status on the relevant national standard of a member State or revoke EN relevant standard of a State against it. Countries' national standards must be consistent with EN standards. EN standards have almost covered various fields such as construction engineering, mining, metallurgy, chemical industry, electrician, safety technology, environmental protection, sanitation, fire protection, transportation, housekeeping and so on. Develop, publish and promote the application of Europe standards and other standardization results for the benefit of the public through joint collaboration to contribute to economic, technical, scientific, managerial and public affairs rationalization, quality assurance, safety and mutual understanding.

Japanese industrial standards (JIS:Japanese Industrial Standards) are the most important and authoritative standards in Japanese national standards. Developed by the Japan Industrial Standards Survey (JISC) Association. According to the provisions of the Japanese Industrial Standardization Law, the JIS standard objects not only have special standards or technical specifications for drugs, pesticides, chemical fertilizers, silk, food and other agricultural and forestry products, but also cover various industrial fields. Its contents include: product standard (product shape, size, quality, performance, etc.), method standard (test, analysis, detection and measurement method and operation standard, etc.), basic standard (term, symbol, unit, priority, etc.).

GB is the national standard of China, which refers to the standard approved and issued by the competent authority of standardization in China, which is of great significance to the economic and technological development of the whole country and is unified throughout the country. The national standard is a unified technical requirement in the whole country. The competent administrative department of standardization under the State Council shall draw up a plan, coordinate the division of labor of the project, organize the formulation (including revision), and unify the examination and approval, and publication. Where the law provides otherwise for the formulation of national standards, it shall be implemented in accordance with the provisions of the law. The national standard is generally 5 years, after the number of years, the national standard will be revised or reformulated. In addition, with the development of society, the state needs to set new standards to meet the needs of people to produce and live. Therefore, national standards are dynamic information.