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This article is an explanatory section on the grade specifications for pipeline materials in a certain project; it is applicable to chemical engineering projects and can be used as a reference. 1 General Provisions 1.1 Scope This standard specifies the selection of piping materials for process units. 1.2 Referenced Standards When using this standard, the latest versions of the following standards shall be applied: GB/T 3091 “Galvanized welded steel pipes for low-pressure fluid transportation”; GB 5310 “Seamless steel pipes for high-pressure boilers”; GB/T 8163 “Seamless steel pipes for fluid transportation”; GB/T 9114.2 “Threaded steel pipe flanges with raised necks for PN1.0MPa (10 bar) and PN1.6MPa (16 bar)”; GB/T 9114.3 “Threaded steel pipe flanges with raised necks for PN2.5MPa (25 bar)”; GB/T 12459 “Steel butt-welded seamless pipe fittings”; GB/T 13401 “Butt-welded pipe fittings made of steel plates”; GB/T 14383 “Socket-welded pipe fittings made of forged steel”; GB/T 14626 “Threaded pipe fittings made of forged steel”; GB/T 14976 “Stainless steel seamless pipes for fluid transportation”; HG 20592 “Types and parameters of steel pipe flanges (European system)”; HG 20593 “Plate-type flat-welded steel pipe flanges (European system)”; HG 20595 “Butt-welded steel pipe flanges with necks (European system)”; HG 20596 “Integral steel pipe flanges (European system)”; HG 20601 “Steel pipe flange covers (European system)”; HG 20606 “Non-metallic flat gaskets for steel pipe flanges (European system)”; HG 20608 “Flexible graphite composite gaskets for steel pipe flanges (European system)”; HG 20610 “Wound gaskets for steel pipe flanges (European system)”; HG 20612 “Metal ring gaskets for steel pipe flanges (European system)”; JB/T 82.1 “Raised-face butt-welded steel pipe flanges”; JB/T 82.2 “Rising and falling face butt-welded steel pipe flanges”; JB/T 82.4 “Ring-connected face butt-welded steel pipe flanges”; JB/T 86.1 “Raised-face steel pipe flange covers”; JB/T 86.2 “Rising and falling face steel pipe flange covers”; JB/T 87 “Asbestos rubber gaskets for pipeline flanges”; JB/T 89 “Metal ring gaskets for pipeline flanges”; JB/T 90 “Wound gaskets for pipeline flanges”; SH 3059 “General rules for selecting materials for pipelines in petrochemical enterprises”; SH/T 3403 “Metal ring gaskets for pipe flanges”; SH/T 3404 “Fasteners for pipe flanges”; SH/T 3407 “Wound gaskets for pipe flanges”; SH/T 3408 “Steel butt-welded seamless pipe fittings”; SH/T 3410 “Socket-welded pipe fittings made of forged steel”; SY/T 5037 “Spiral-welded submerged-arc welded steel pipes for low-pressure fluid transportation pipelines”; GB/T 3624 “Tubes made of titanium and titanium alloys”; HG/T 3651 “Butt-welded seamless steel pipes made of titanium”. 2 General Provisions and Classification 2.1 Pipe Material Grades 2.1.1 Pipe material grades are determined based on design temperature, design pressure, requirements of the transported medium, as well as the performance and economic viability of the materials. The material, type, and specifications of pipes and pipe components shall be selected in accordance with this standard, based on the pipe material grades indicated in the “Process Piping and Instrumentation Diagram” (PID). The design pressure listed in the pipeline material grade table refers to the maximum allowable design pressure at the design temperature; the actual design pressure must not exceed this value for that grade to be used. 2.1.2 The pipe material grade consists of three characters: x x x| | || | a number, indicating the flange pressure rating; | | the serial number of the pipe grade for the basic material; a letter, indicating the code for the basic material; and a number, indicating the flange pressure rating in MPa. 2.1.2.1 The flange pressure ratings used in the pipe material grades are as follows: 1.6, 2.5, 4.0, 6.3, 10.0, 16.0, and 25.0 ； Note: The pressure grades in () are not included in this standard for the time being. 2.1.2.2 Basic material codes The basic materials and their codes used in the pipeline material grades are listed in the table below. Basic Materials and Codes Basic Material Code Basic Material A Carbon steel B16Mn S06Cr19Ni10, 00Cr17Ni14Mo2 U06Cr19Ni10 Sanitary grade TTA2 X Galvanized carbon steel E①2 1/4Cr1Mo F①12Cr1MoV Y① Lined steel pipe Note: ① Materials and their codes that may be adopted in future revisions of pipeline material grades. 2.1.2.3 The pipeline grade number indicates the variations in the specifications of pipelines and their components due to differences in the applicable media and corrosion margins, among other factors. This serial number is arranged in numerical order using ***. 2.1.3 When connecting pipes of different material grades, unless there are isolation devices such as blind flanges, the valves at the connection points of the pipes of the lower grade shall be selected according to those of the higher grade, and the boundary between the material grades of the pipes shall be indicated. 2.1.4 For pipelines transporting different media, the minimum pipeline material grades are specified as follows: a) For pipelines transporting oil and oil/gas, the grade is 1.6 MPa; when the design temperature (Td) exceeds 200 °C, it shall be 2.5 MPa. b) The pipeline for transporting liquefied hydrocarbons is 2.5 MPa. c) The pipelines for transporting gaseous or liquid ammonia are at 2.5 MPa. d) The pipeline for transporting hydrogen is at 2.5 MPa. e) The pipelines for transporting toxic chemical agents are at 2.5 MPa. 2.2 Steel pipes 2.2.1 The types and material selection of steel pipes shall comply with the following provisions. 2.2.1.1 For pipelines carrying oils, gas-oil mixtures, steam, additives, and chemical agents, seamless steel pipes should be used when the DN is 500 mm or less ； Steel coil pipes can be used when DN is greater than 500 mm. 2.2.1.2 For water and air pipelines with a design temperature (Td) of 100 ℃ or less, a design pressure (Pd) of 1.0 MPa or less, and a DN of 350 mm or more, spiral submerged arc welded steel pipes can be used, with Q235-B as the suitable material ； For air purification and domestic water pipes with a DN of 50 mm or less, galvanized welded steel pipes should be used, with the material being Q235-B galvanized. 2.2.1.3 The standard for steel pipes made of stainless steel is GB/T 14976. 2.2.1.4 The materials used for medium-pressure steam and condensate pipelines are 20#, with the steel pipe standard being GB/T8163. 2.2.2 Small outer diameter series pipe sizes can be selected as per the user’s requirements; in such cases, the standard for socket-welded pipe fittings should be GB/T 14383 (Series B). 2.2.3 When the wall thickness is not specified in the pipeline material grade table, or although it is specified the designer deems it necessary to recalculate it, such calculation shall be carried out to determine the value ； If the corrosion margin data differ from those listed in the pipeline material grade table, the pipe wall thickness should be recalculated manually. 2.3 Fittings 2.3.1 Long-radius elbows should be used when the direction of the pipeline changes. When short-radius elbows must be used, their maximum operating pressure should not exceed 0.8 times that of long-radius elbows. Plug and socket elbows can be used when DN is 40 mm or less ； Seamless elbows can be used when DN is greater than or equal to 25 mm and less than or equal to 500 mm ； Elbow bends can be used when DN is 20 mm or less ； The design supervisor may, without being restricted by the pipeline material grade table, establish specific unified regulations for the design project in accordance with the above requirements. For galvanized pipes with a DN of 100 mm or less, galvanized threaded fittings shall be used. For solid catalyst pipelines, elbows with a radius of curvature (R) of 6DN or greater should be used. 2.3.2 For pipes with a nominal pressure (PN) of 4.0 MPa or higher, branch connectors shall be selected from the branch connector table in the pipe classification table ； Pipes with a PN of 2.5 MPa or less can be determined according to the Unified Provisions for Design Techniques, by selecting from the branch pipe table in the pipe grade chart or by welding them directly. 2.3.3 The wall thickness designation of welded pipe fittings shall be the same as that of the butt-welded steel pipes they are connected to. 2.4 Valves 2.4.1 Pipes for process media shall use steel valves ； For pipelines carrying media such as water in non-freezing environments and unfiltered air, cast iron valves can be used when the design temperature (Td) is less than 100 °C and the design pressure (Pd) is less than 1.0 Mpa; however, steel valves can also be employed if required by the user or to simplify the range of available options. 2.4.2 The valve model shall be consistent with the P&ID diagram ； When a valve type different from that shown in the P&ID diagram is selected, approval from the process engineering team must be obtained, and the valve symbols in the P&ID diagram must be modified by them. 2.4.3 When both socket-welded valves and internally threaded valves are included in the same grade in this pipeline material grade table, socket-welded valves should be given priority when their quality and performance can be confirmed to be reliable. 2.4.4 In addition to selecting valves in accordance with the conditions mentioned above, the designer may choose new types of valves with suitable performance characteristics that are not listed in the pipeline material grade table, provided that approval is obtained from the process engineering team, who will then modify the valve symbols in the P&ID diagram. 2.5 Flanges 2.5.1 The pipe material grade specification designates them as HG flanges; aside from PN16.0 DN10–300 and PN1.0 DN80, these flanges are compatible with JB flanges in all other cases. The design supervisor can also decide whether to use GB flanges or JB flanges based on the project requirements. To clarify the outer diameter series of flanged connections, the outer diameter and wall thickness of these flanged connections must be specified in the master material list. When using chemical industry pipe flanges (European system), HG 20592 shall be followed. 2.5.2 The seal face type of the flange that connects to the valve and equipment nozzle shall match that of the flange on the valve and equipment nozzle. 2.6 Gaskets and Fasteners 2.6.1 When the nominal pressure of the flanges on valves, pumps, and equipment nozzles is higher than that of the pipeline grade, the material for gaskets, bolts, and nuts can be selected according to the design requirements of the pipeline. 2.6.2 Coiled gaskets used for smooth-faced flanges shall be equipped with an external positioning ring, while coiled gaskets used for male and female-faced flanges shall be equipped with an internal positioning ring. The material of the outer positioning ring is carbon steel ； The material of the inner positioning ring is determined based on the design requirements; it can be carbon steel, 0Cr13, 0Cr18Ni10Ti, or other materials. 2.7 Others 2.7.1 In addition to the general provisions mentioned above, pipelines of all grades and their components shall comply with the requirements of this standard. If any adjustments need to be made to the above general provisions, they should be included in the \"Uniform Design Specifications\" by the person in charge of the project. 2.7.2 When this standard cannot meet the design requirements, additional documents may be prepared by the person in charge of the relevant project area, and the principles for preparing such documents shall comply with the provisions of this standard. The patent holder’s process package includes specified pipes, which are selected in accordance with the patent holder’s requirements regarding pipe material grades. 2.8 Index of Pipe Material Grades: Grade Code, Applicable Media, Corrosion Margin in mm, Nominal Pressure in MPa, Design Temperature in °C, Basic Material. 1A1: Circulating water, chilled circulating water – 1.5–1.6, ≤200°C; Carbon steel. 1S1: Compressed air, instrument air, nitrogen, vacuum exhaust, purified chilled water, general materials – 1.6–300°C; 06Cr19Ni10. 2A1: Steam, steam condensate, heat transfer oil – 1.5–2.5, ≤200°C; Carbon steel. 1S2: Corrosive materials – 1.6–300°C; 08Cr17Ni14Mo2. 1U1: Process media materials – 1.6, CPL (clamp connection), ≤300°C; 08Cr17Ni14Mo2