There are many ways to classify pipes. According to the material, they can be divided into metal pipes, non-metal pipes, and steel-lined non-metal composite pipes.

Non-metal pipes mainly include rubber pipes, plastic pipes, asbestos cement pipes, graphite pipes, fiberglass pipes, etc. The proportion of non-metal pipes used is relatively small compared to metal pipes, while metal pipes account for more than 85% of all process pipeline installation projects in most petrochemical plants.

The following focuses on welded steel pipes. Welded steel pipes, also known as seamed steel pipes, are generally made of steel plates or steel strips.

1. According to the surface treatment form of the pipe: divided into galvanized and non-galvanized. The galvanized surface is white, also known as white iron pipe or galvanized steel pipe; the surface is not galvanized, that is, ordinary welded steel pipe, also known as black iron pipe. Galvanized welded steel pipes are often used for pipelines that require relatively clean media, such as domestic water, purified air, instrument air, etc.; non-galvanized welded steel pipes can be used to transport steam, gas, compressed air condensed water, etc.

2. According to user requirements, welded steel pipes can be divided into two types when leaving the factory: one is with threads on the pipe end, and the other is without threads on the pipe end. The length of each welded steel pipe with threads on the pipe end is 4 to 9 meters, and the length of each welded steel pipe without threads is 4 to 12 meters.

3. Welded steel pipes are divided into thin-walled steel pipes, thickened steel pipes, and ordinary steel pipes according to the thickness of the pipe wall. Ordinary steel pipes are the most used in process pipelines, and their test pressure is 2.0MPa. The test pressure of thickened steel pipes is 3.0MPa.

4. There are many connection methods for welded steel pipes: threaded connection, flange connection, and welding. Flange connection is divided into threaded flange connection and welded flange connection, and welding methods are divided into gas welding and arc welding.

5. The specification range of commonly used welded steel pipes: nominal diameter 6 to 150mm.