Can steel pipes lined with polytetrafluoroethylene be used for transporting liquefied hydrocarbons?
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Recently, I came across a project in which a factory processes sulfur-containing liquefied gas. The pipelines used for transporting this liquefied gas before desulfurization were suffering from corrosion issues. The factory replaced those pipelines with steel tubes lined with polytetrafluoroethylene on its own; after operating them for some time, good results were achieved. Now they want us to prepare a design drawing for them. The operating pressure for liquid hydrocarbons is 1.2~1.6 MPa (G), with a temperature of 40°C. The pipeline uses steel pipes lined with polytetrafluoroethylene, and the flanges are plate-type butt-welded flanges DN125-PN40, RF type. May I ask whether steel pipes lined with polytetrafluoroethylene can be used for pipelines transporting liquid hydrocarbons? Since the lining pipes are connected section by section using flanges, this increases the risk of leaks, giving an overall sense of insecurity. The regulations stipulate that plate-type butt weld flanges shall not be used for flammable and toxic media; based on this rule, we refused to provide them with additional drawings. Furthermore, after searching through all the standards, none of them state that lined steel pipes cannot be used for transporting flammable media such as liquid hydrocarbons. Can those who are familiar with it discuss this issue? If the flange is replaced with a butt-welded flange, can the lined steel pipe be used to transport flammable media such as liquid hydrocarbons? Are there any other requirements?
Steel pipes lined with polytetrafluoroethylene can be used to transport flammable media such as liquid hydrocarbons. Polytetrafluoroethylene boasts excellent corrosion resistance and a low friction coefficient, making it suitable for transporting various chemical media. However, to ensure safety, it is necessary to follow the relevant standards and requirements. First, you mentioned the selection of flanges. According to the specifications, plate flat welding flanges shall not be used for flammable and toxic media. Therefore, using butt-weld flanges on PTFE-lined steel pipes is a specification-compliant choice. Butt weld flanges can provide a stronger connection and reduce the risk of leaks. In addition to the choice of flanges, the following requirements also need to be considered: 1. Within the operating pressure and temperature range, steel pipes lined with polytetrafluoroethylene must be able to withstand the pressure and temperature of liquid hydrocarbons without experiencing leaks or damage. 2. The manufacturing and installation of polytetrafluoroethylene-lined steel pipes must comply with relevant standards and specifications to ensure quality and reliability. 3. Conduct regular inspections and maintenance to ensure the proper operation and safety of the PTFE-lined steel pipes. In summary, steel pipes lined with polytetrafluoroethylene can be used to transport flammable media such as liquid hydrocarbons, but it is necessary to comply with relevant standards and requirements, especially by selecting appropriate flange connection methods and strictly controlling operational parameters. For specific projects, it is recommended to consult professional engineers or relevant technical personnel for a detailed assessment and design. .
This post was last edited by bfdlwolf on 2023-7-5 09:24. According to the \"Technical Standards for Petrochemical Pipes with Non-metallic Linings\" (SH/T 3154-2019), under certain conditions, pipes with non-metallic linings such as those lined with polytetrafluoroethylene can be used for transporting flammable media. The relevant provisions of the \"Technical Standards for Non-metallic Lined Pipelines in Petrochemical Industries\" (SH/T 3154-2019) are as follows: This standard applies to the design, manufacturing, construction, and acceptance of non-metallic lined pipelines in petrochemical plants (units) where the nominal pressure is not greater than PN20 (Class150) and the design temperature does not exceed the allowable operating temperature range for the lining material. 4. 2. 14 Pipes transporting flammable media and those with non-metallic linings located in explosion-hazardous areas shall be equipped with anti-static measures. Metal wires should be used for bonding between the flanges of non-metallic lined pipes installed in explosive hazard areas. 5.3.3 The selection of flanges shall comply with the following provisions: b) For the flanges at the ends of steel pipes and pipe fittings, flat-weld flanges or loose-flange types should be used, and the seal surface type of the flanges shall be raised face (RF) ； For this project, in accordance with relevant regulations, the design pressure of the pipelines for transporting mixed liquefied hydrocarbons at normal temperature must take into account not only the pressure from operational pressure sources but also the saturated vapor pressure of the liquefied hydrocarbons when they are at rest. The design pressure of the pipeline should be determined to be greater than or equal to the actual saturated vapor pressure of the mixed liquefied hydrocarbon components at 50°C. If the design pressure exceeds PN20, it cannot be designed according to this standard.
Liquefied hydrocarbon pipelines generally require a design nominal pressure of not less than PN25; according to this standard, cannot steel pipes lined with polytetrafluoroethylene be used?
Yes. But for liquid hydrocarbon pipelines, \"it is generally required that the design nominal pressure be no less than PN25\" – I’m not sure which standard this is based on
From the Manual for the Installation Design of Process Piping in Petrochemical Plants, and internal regulations of Sinopec Design Institute
SH3059-2001 \"General Rules for the Selection of Materials in Petrochemical Pipeline Design\" 5.3.2 Unless otherwise specified, the minimum nominal pressure for flange connections on pipelines carrying toxic or flammable media shall comply with the following requirements: 1. The nominal pressure of SHA-class pipelines should not be lower than 5.0 MPa； 2. The nominal pressure of SHB and SHC grade pipes should not be lower than 2.0 MPa. SH3059-2012: This clause has been revoked. I did not consult the \"Manual for the Design of Process Piping Installation in Petrochemical Plants\" or the \"Internal Regulations of Sinopec Design Institute\", but I personally believe that the determination of pipeline design pressure should be based on relevant current standards and specifications