Which standard should be used for PTFE-lined pipes?

Currently, the commonly used standards in the field of PTFE-lined pipes in China are HG/T 20538 and HG/T 4584. Among them: 1. HG/T 20538 \"Steel Chemical Piping with Plastic Lining\": – This standard is widely used; it is a mature standard that has been in use for a long time in the chemical industry and enjoys high recognition. It covers aspects such as the selection of materials for PTFE-lined pipes, processing techniques, dimensional tolerances, and inspection requirements. - It is usually widely used in general, large-scale production. 2. HG/T 4584 \"Fluorine-lined pipes and fittings\": It sets out more detailed and stringent process control and quality requirements compared to HG/T 20538; for example, there are clear and strict specifications regarding the control of lining thickness, material performance criteria, and inspection of surface defects. - HG/T 4584 is more suitable for engineering projects or high-end chemical plants that require higher levels of corrosion resistance, reliability, and stability. Overall, the HG/T 20538 standard is widely used in the industry, whereas HG/T 4584 imposes stricter manufacturing requirements, offering greater assurance regarding quality and corrosion resistance, making it more suitable for projects with high standards. .

HG/T20538 is quite commonly used; it is a standard applicable to all plastic-lined pipes. HG/T4584 is mainly used for pipes with steel linings and PTFE, etc., under isostatic pressing conditions. In terms of tolerance to temperature and pressure, the requirements specified by HG/T4584 are certainly higher.

The standard selection for PTFE-lined pipes (pipes with a polytetrafluoroethylene PTFE lining) must be determined based on the application area, properties of the medium, and local regulations. The following are the common classifications and descriptions of international and domestic standards: 1. Internationally recognized standard – ASTM standards (American Society for Testing and Materials). ASTM D3295: Applies to steel pipes, fittings, and flanges with PTFE linings, covering dimensions, pressure ratings, and corrosion resistance. ASTM F1545: Standard for sanitary piping systems with PTFE lining (such as in the food and pharmaceutical industries). ISO standard ISO 161: General standard for thermoplastic pipe systems, with some provisions applicable to plastic-lined pipes. ISO 9001: Quality management system requirements to ensure compliance with manufacturers’ processes. DIN standard (Germany) DIN 28060: PTFE-lined pipes and fittings designed for use in chemical equipment, with an emphasis on chemical resistance. 2. Chinese **standards (GB) and industry standards**: GB/T 38015-2019 “Technical requirements for corrosion-resistant alloys used as linings in steel-plastic composite pipes and fittings”, which specifies the technical requirements for steel pipes lined with plastic (including PTFE). HG/T 20538-2016 \"Technical Requirements for Chemical Industry Linered Steel Pipes and Fittings\" specifies the design, manufacturing, and inspection requirements for PTFE-lined pipes, and is widely used in the chemical industry. HG/T 21562-2014 \"Steel Pipes and Fittings with PTFE Lining\" specifies in detail the thickness of the PTFE lining, the adhesion strength, and the methods for pressure resistance testing. GB/T 23711.1-2019 \"Pressure vessels with fluoroplastic linings – Part 1: General requirements\" can be used as a reference for high-pressure fluoroplastic-lined pipes. 3. Special industry standards: FDA or EU 1935/2004. The food and pharmaceutical industries must comply with health standards to ensure that PTFE linings are non-toxic and do not cause migration. ASME B31.3 Code for Design of Piping Systems for Chemical Processes: If PTFE-lined pipes are to be used in high-pressure and high-temperature conditions, they must meet the relevant material and pressure requirements. 4. Key selection parameters: Temperature range: PTFE linings are generally suitable for temperatures ranging from -196°C to +260°C. Pressure rating: Commonly PN6~PN16; special design is required for high pressures. Media compatibility: It is necessary to check PTFE’s resistance to acids, bases, and organic solvents (e.g., hydrofluoric acid requires special treatment). Connection method: flange (HG/T 20592), threaded, or butt weld. 5. Manufacturer standards: Some companies (such as Thermo Fisher and Saint-Gobain) may have internal standards that need to be customized according to customer requirements (for example, a lining thickness of ≥2 mm). Recommendation: The chemical industry should preferentially use HG/T 20538 or ASTM D3295 ； The food/pharmaceutical sector must comply with FDA or ISO 15874 ； Export projects are carried out in accordance with the standards specified by the customer (such as DIN or ASME). During design, it is essential to confirm the standard details with the manufacturer and conduct pressure tests (such as a pressure retention test at 1.5 times the design pressure).