I have a question regarding foreign standards

Explanations for the Revision of the \"Regulations on Safety Inspection of Pressure Vessels\" (Version 99) and Interpretations of the Provisions 2. Explanations regarding the \"Selection of Standards for Pipe Flanges, Gaskets, and Fasteners\" Pipe flanges are standard components used to connect pressure equipment with pipelines. The fields involved are quite extensive, mainly including pressure vessels, boilers, pipelines, as well as mechanical equipment such as pumps, valves, compressors, refrigerators, and instruments. Therefore, the selection of pipe flange standards must take into account coordination among various related industries and should be aligned with international standards. The standards for pipe flanges cover a wide range of aspects; in addition to the pipe flanges themselves, they also relate to steel pipes (outer diameter, wall thickness). Thickness), nominal pressure class, gasket material and size, fasteners (hex bolts, double-headed bolts, nuts), threads (pipe threads, fastener threads), etc., are all closely related. Internationally (including domestically), there are mainly two systems of pipe flange standards: the European system (represented by DIN standards) and the American system (represented by American ASME B16.5 and B16.47 standards). Within the same system, the flange standards of different countries are generally compatible with one another (with regard to connection dimensions and sealing surface dimensions); flanges from two different systems cannot be used together. Table 1 shows a list of pipe flange standards for various countries. As can be seen from Table 1, there are numerous foreign pipe flange standards, most of which belong to the European system. However, in recent years, with the opening up to the outside world, American-style system flanges have also been increasingly widely used in industries such as petroleum and chemicals. During the revision of these regulations, it was proposed that pressure vessels should preferably use the pipe flange and gasket fastener standards HG20592—20614—1997 (European system) and HG20615—20635—1997 (American system). This recommendation is based on the following considerations: (1) The HG(1997) pipe flange standards cover both the European and American systems. In addition to the internationally standard series (commonly known as imperial pipes), the European system can also be applied to the domestically used series (commonly known as metric pipes), taking into account China’s specific conditions; thus, these standards cover both international and domestic standards for pipe flanges. (2) The standards are clearly divided into two systems, offering clear concepts, ease of use, and preventing confusion. (3) Wide range of applications: Nominal pressure rating: 0.25～42.0 MPa ； Flange types: 10 (plate butt weld, necked butt weld, necked fusion weld, integral, socket weld, threaded, fusion ring/plate loose fit, fusion ring/necked loose fit, flange cover, lined flange cover) ； Size: Dn10～2000mm ； Sealing surfaces: convex surface, fully flat surface, uneven surface, tenon-and-socket surface, ring connection surface. (4) A complete range of material types is available, using pressure-temperature grades in line with international standards. (5) Form a complete standard system for flanges, gaskets, and fasteners, ensuring strong compatibility. Some principles for the combined use of the three are established, providing guidance for their selection. In addition to their functions of being detachable and enabling connection, pipe flange joints must ensure sealing (control of leakage rates), which is their primary performance requirement. The factors that affect the sealing performance of flange joints include the following aspects, and a comprehensive consideration of these factors should be taken into account when making a selection. Flange pressure rating (depending on the system’s design conditions, the equivalent pressure resulting from pipe thrust and bending moments may be higher than the container’s design pressure, allowing for an increased pressure rating. ) Flange type (Flange stiffness: welded with neck > butt-welded with neck > plate-type butt-welded) Table 1 List of pipe flange standards by country European system American system Standard pressure grades Standard pressure grades DIN 2.5, 6, 10, 16, 25, 40, 64, 100, 160, 250, 400 Bar ASME B16.5(88) B16.47A(MSS SP44) B16.47B(AP1605) 150, 300, (400), 600, 900, 1500, 2500, (75) Lb ISO7005—1(92) 2.5, 6, 10, 16, 25, 40 Bar ISO7005—1(92) 20, 50, 110, 150, 260, 420 Bar BS4504 3.1—89 2.5, 6, 10, 16, 25, 40 Bar BS1560 3.1—89 150, 300, 600, 900, 1500, 2500 Lb NFE29203—89 2.5, 6, 10, 16, 25, 40 Bar NFE29203—89 20, 50, 100, 150, 250, 420 Bar JP17S—15—93 150, 300, 600, 900, 1500, 2500 Lb HG20592—97A 0.25, 0.6, 1.0, 1.6, 2.5, 4.0, 6.3, 10.0, 16.0, 25.0 MPa HG20615—92(Note 3) 2.0, 5.0, 11.0, 15.0, 26.0, 42.0 MPa GB9112–9123—88 0.25, 0.6, 1.0, 1.6, 2.5, 4.0 MPa GB9112–9123—88 2.0, 5.0, 10.0, 15.0, 26.0, 42.0 MPa GB2501–2508—89 Marine GBl0745–10745–10749—89 Marine 0.25, 0.6, 1.0, 2.5, 4.0, 6.4 MPa SH3406—96 2.0, 5.0, 10.0, 15.0, 26.0, 42.0 MPa Metric pipes HG20592—97B (replaces HGJ44—76—1989) 0.25, 0.6, 1.0, 1.6, 2.5, 4.0, 6.3, 10.0, 16.0, 25.0 MPa HG5001–5028—58 2.5, 6, 10, 16, 25, 40, 64 Bar JB74–90—941Ⅱ(Note 1, 2) 0.25, 0.6, 1.0, 1.6, 2.5, 4.0, 6.3, 10.0, (16.0, 20.0) MPa TOCTl2815–12822—80(Note 1) 0.25, 0.6, 1.0, 1.6, 2.5, 4.0, 6.3 ； 10.0, 16.0, (20.0) MPa Note 1: PN16.0 and PN20.0 MPa flanges specified in JB74–90 (1994), as well as PN20.0 MPa flanges specified in TOCT12815–12822 (1980), cannot be used in combination with PN16.0 and PN25.0 MPa flanges per DIN and HG standards. Note 2: In JB74–90(1994), there are three flanges (PN0.25MPa/DN500, PN0.6MPa/DN500, PN1.0MPa/DN80) that cannot be used in combination with flanges from other standards. Note 3: HG20615—1997 does not specify a pressure class of 75,400 Lb (a non-standard class); its large-diameter flanges belong to Series B of ASME B16.47.