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The HG/T20537 standard for pipes is quite outdated; from a technical standpoint, it has become obsolete. Its scope of application is limited, and there are few types of steel pipes that can be produced in accordance with this standard. The GB/T12771-2008 standard is to be adopted; GB/T8163, GB3087, and GB/T9711.1 cannot be used for GC1-type medium pipelines. Additional note: Pipes that have passed individual ultrasonic testing and met the required standards may be used in pipelines specified in A1.1(1) of these regulations, provided that the design pressure is ≤4.0 Mpa. GB/T6479-2013 GB6479 specifies the low-temperature impact test for high-quality carbon steel ； It is optional for use in GC1 grade seamless pipelines. Among the three standards, the quality grades of pipes, from lowest to highest, are: GB9948 < GB5310 < GB6479. In terms of the application of each of these three standards, the requirements of SH/T3059 are more reasonable. For example, for steam media with a pressure of over 10 Mpa, it is more appropriate to use GB5310 rather than GB6479. GB/T 9948-2013 contains requirements for intergranular corrosion testing and supplementary technical requirements for steel pipes used in H2S-containing environments. GB/T5310-2017 GB5310 is a standard specifically formulated for steel pipes used in boilers; therefore, it is commonly used in steam and its condensate pipelines. SH/T3059 specifies for GC1-class medium pipelines with a design pressure of 10 Mpa or higher that, when seamless steel pipes are used at a design pressure of ≥10 Mpa, their manufacturing and inspection shall comply with the requirements of GB5310, GB9948, or GB6479; the inspection of stainless steel pipes shall meet the standards specified in GB/T14976 or higher. For other cases, grades based on foreign pipe material standards are used. TSG D0001 stipulates that when international or foreign standards are adopted directly, they must first be converted into corporate standards or project specifications. For GC1-grade pipelines, it is also necessary to file a record with the General Administration of Quality Supervision, Inspection and Quarantine. If necessary, the **General Administration of Quality Supervision, Inspection and Quarantine entrusts relevant technical organizations or institutions to conduct the evaluation. Among the foreign standards currently used in China, American standards are the most frequently adopted. The technology related to the application of pipes conforming to American standards is also quite mature. When using such pipes, it is necessary to comply with the relevant requirements stipulated in ASME B31.3. Regarding seamless pipe fittings, since they can be manufactured from steel pipes that comply with different standards, once the fitting standard is selected, it is necessary to specify the standard number of the raw material pipe, so as to ensure that the fittings meet the same performance requirements as the pipes. For forged pipe fittings, some designs also specify the grade of the forgings. As for valves, only GB/T20801.3 provides relatively detailed requirements for valves used in GC1-grade pipes. Most of the valve standards listed in GB/T20801.3 have been updated; therefore, when designing, it is advisable to select those standards specified in the tables of SH/T3059 that better meet the requirements of this standard. Bellows-sealed valves: For media that are extremely hazardous or highly hazardous, these types of valves can be considered from the perspective of personal safety. In ISO15848, the leakage at the valve stem is calculated based on the diameter of the stem, and the leakage is classified into levels (A50, B100, C1000 in PPMV units). The sealing mechanism for the valve cap or cover: ① Flange connection, with a minimum of 4 bolts, and gaskets that comply with the requirements specified in 5.1.9 of GB/T20801.3 ； GB50316 and ASME B31.3 also require that valves with valve covers fixed to the valve body using fewer than 4 bolts or U-bolts can be used only in applications involving Class D fluids. The type and material of gaskets are also included in the valve specification sheet. API 600 lists the available seal surface types for the connection between the valve body and the valve cover. Once the seal surface type has been determined, the appropriate type of gasket can be selected based on the actual conditions of the medium, in accordance with this provision as well as the requirements specified in HG/T20592–20635. ②Self-tightening structure ； This structure can effectively prevent leakage of the medium at the valve cover. This structural form is mentioned in API 6D and NB/T47044, but no detailed specifications are provided in either standard. ③Fully penetrative welded structure ； This structure is the most effective way to prevent leakage at the valve cover, and it is not limited by the valve size, operating pressure, or temperature. ④Cylindrical threaded connection; strength check passed, and metal seal welding is employed ； The valve cover with this structure is rarely selected in engineering design. ⑤A valve cover sealing structure with threaded connections shall not be used ； This type of structure is not only used for GC1-class medium pipelines; valves for other types of process medium pipelines are also rarely chosen for this purpose, and small valves that experience little vibration during operation and do not require frequent disassembly are generally used instead. ⑥Valves using non-metallic sealing materials for flammable fluids shall meet the requirements of fire testing, and their pressure-temperature ratings shall be determined based on the pressure-temperature ratings that the non-metallic materials can withstand. According to GB/T20801.3, expansion flanges and threaded flanges shall not be used for GC1 class pipelines ； In cases of severe cyclic loading or for GC1-class pipelines, where the nominal diameter of the socket weld joint is greater than DN50, socket weld connections shall not be used. SH/T3059 stipulates that plate flat-weld flanges shall not be used for pipelines carrying toxic and flammable media. GB50316 specifies for Class A1 fluids: (1) Flat welding (plate-type) flanges shall not be used ； (2) In addition to using weld lip gaskets, when selecting the nominal pressure of the flange, a margin of ≥25% should be reserved, and it shall not be lower than 2.0 Mpa in nominal pressure ； (3) When using soft gaskets, flanges with male-female surfaces or tenon-socket surfaces should be selected. All of the above require strict adherence to the specifications. Standards such as HG/T20592–20635 provide detailed information on the operating temperatures for various types of gaskets, as well as their compatibility with different types of flanges. When designing, it is possible to select the appropriate material and type of gasket by referring to these standards, along with the requirements outlined in GB/T20801.3 and SH/T3059. Usage restrictions: Gaskets made of flammable materials such as rubber must not be used in pipelines transporting highly oxidizing media. Fasteners specified in HG/T20592–20635; among the European standard series, these include hex head bolts, equal-length double head studs, and fully threaded studs ； The American standard series includes only hex head bolts and fully threaded studs; different selection standards result in different types of fasteners. HG/T20634 specifies that the use of hex head bolts and Type I hex nuts must comply with the following requirements: nominal pressure class ≤ Class150 ； Non-toxic, non-flammable media and applications without intense cycling ； Equipped with non-metallic flat gaskets. Except in this case, special-grade fully threaded studs and special nuts should be used. For fasteners of GC1 pipeline grade, only specialized fully-threaded studs and specialized nuts may be used. The types of fasteners specified in SH/T3404 are the same as those in HG/T20634, and the requirements for the use of fasteners in this standard are identical to those in HG/T20634. Branch connections as specified in GB/T20801.3: For GC1-class pipelines, the branch connection fittings shall be integrally reinforced branch connection fittings or tees ； For Fluids Class A1 as defined in GB50316, and Fluid Class A2, Grade II, standard tees should be given priority for branch connections, followed by branch saddles or embedded branches. Standard branch fittings should be used where standard connection fittings are available. If branch pipe fittings cannot be used, the provisions regarding reinforcement calculations in GB/T20801.3 and SH/T3059 shall be followed: reinforcement plates should not be used to reinforce pressure pipelines of grade GC1. The reinforcement ring cannot fit perfectly against the shell metal, resulting in poor heat transfer. When used at medium temperatures or above, there is a significant difference in thermal expansion between the two, which causes substantial thermal stress in the reinforced area ； In addition, the reinforcement ring is connected to the housing by lap welding, making it difficult to form a single unit with the housing, resulting in poor fatigue resistance ； Compared to other reinforcement methods, reinforced welded structures also have higher welding stresses. Given these defects in reinforcement by girders, an overall reinforcement approach can be adopted for branch design. Standard materials for steel pipes; ranges where the manufacturing processes for steel pipes and fittings are not permitted; GB/3091-2008 Carbon structural steel (1) Resistance-welded pipes (Note 6) ； (1) In accordance with the provisions of Articles 26 and 27 ； (Note 5)(2) Capacitive welding pipes and butted welded fittings (2) Severe cyclic service conditions ； (3) The operating pressure of resistance-welded pipes is greater than 1.6 MPa; GB/T9711.1-1997 Carbon steel (1) Resistance-welded pipes (Note 6) ； (1) GC1 grade pipeline ； (2) Design pressure greater than 4.0 Mpa ； (3) Severe cycling conditions: GB/T8163-2008 carbon steel seamless pipes and butt-welded pipe fittings; GC1-grade pipelines (Note 7). GB/T3087-2008, GB/T9711.1-1997; carbon steel electroslag welded pipes and butt-welded pipe fittings per GB/T9711.1-1997. GB/T12771-2008 austenitic electroslag welded pipes (without addition of filler metal or without radiographic inspection of welds) and butt-welded pipe fittings; (1) GC1-grade pipelines ； HG/T20537.3-1992 Stainless steel (2): Conditions involving severe cycling. HG/T29537.4-1992 Electroslag-welded pipes (with filler metal added, but without radiographic inspection of the welds) and butt-welded pipe fittings, where radiographic inspection of the welds is not performed. When austenitic stainless steel is used at temperatures above 540°C (above 425°C for castings), the carbon content in the material must be maintained at no less than 0.04%, and the material should be used in its solution-treated state. When austenitic stainless steel is used for extended periods at temperatures between 540°C and 900°C, appropriate protective measures should be taken to prevent the material from becoming brittle. For austenitic stainless steels, the possibility of intergranular corrosion should also be considered under the following conditions: (1) low-carbon (C≤0.08%) unsaturated stainless steels, when used after hot working or welding ； (II) Ultra-low carbon (C≤0.03%) stainless steel, used for extended periods at temperatures above 425°C.