What is the specific meaning of the flange model JB/T81-94?

Flange shapes and connection dimensions: GB national standards, JB Ministry of Machinery flanges, HG Ministry of Chemicals flanges; American standards ASME/ANSI RF flanges, JIS (Japanese standards). Pressure ranges: 1.0–2.5 MPa, 4.0–16 MPa, 1.0–4.0 MPa; pressure classes: Class150–Class1500; JIS classifications: 10k–20k. Flanges commonly used for control valves: JB Ministry of Machinery flanges, American standards ASME/ANSI RJ flanges, Japanese standards, German standards; pressure classes: Class150–Class2500; standards: JIS, JIP, DIN. Brief description of flanges: Pipe flanges, along with their gaskets and fasteners, are collectively referred to as flange connections. Flange joints are a type of component that is extremely common and widely used in engineering design. It is an essential component in piping design, as well as in fittings and valves; it is also a necessary part of equipment and its components (such as manholes, sight glasses, level gauges, etc.). In addition, other specialties such as industrial furnaces, thermal engineering, water supply and drainage, heating and ventilation, and automatic control also frequently use flange joints. Materials: forged steel, WCB carbon steel, stainless steel, 316L, 316, 304L, 304, 321, chromomolybdenum steel, chromomolybdenum vanadium steel, molybdenum disilicide, rubber-lined, fluorine-lined materials. Types: slip-on flanges, wafer flanges, butt weld flanges, ring joint flanges, socket weld flanges, and blind flanges, etc. The applicable standards include the GB series (**standards), JB series (Ministry of Machinery), HG series (Ministry of Chemical Industry), ASME B16.5 (American standard), BS4504 (British standard), DIN (German standard), and JIS (Japanese standard). International pipe flange standard systems: Internationally, there are mainly two systems for pipe flanges – the European system represented by German DIN (including the former Soviet Union) and the American system represented by ANSI pipe flanges. In addition, there are Japanese JIS pipe flanges, but they are generally used only for utility systems in petrochemical plants, and have little influence internationally. The following is an introduction to pipe flanges from various countries: 1. European system pipe flanges, represented by Germany and the former Soviet Union; 2. Pipe flange standards for the American system, represented by ANSI B16.5 and ANSI B16.47; 3. Pipe flange standards in the UK and France, with each country having its own two sets of standards. In summary, the internationally accepted pipe flange standards can be categorized into two distinct and non-interchangeable systems: one being the European pipe flange system represented by Germany ； The other is the American pipe flange system, represented by the United States. IOS7005-1 is a standard issued by the International Organization for Standardization in 1992; it is essentially a pipe flange standard that combines the pipe flange standards from the United States and Germany. The pipe flange connection dimensions of the two systems differ in terms of safety, making it impossible for them to be used together. It is most appropriate to differentiate between the pipe flanges of the two systems based on pressure ratings: for the European system, these are 0.25, 0.6, 1.0, 1.6, 2.5, 4.0, 6.3, 10.0, 16.0, 25.0, 32.0, 40.0 MPa, while for the American system they are 1.0, 2.0, 5.0, 11.0, 15.0, 26.0, 42.0 MPa. Current Status of Pipe Flange Standards in China and the Commonly Used Standards for Pipe Flanges in China’s Chemical and Petrochemical Industries
1. Imperial pipes (the internationally standard piping series): GB 9112–9125, SH 3406
2. Metric pipes (the commonly used domestic steel pipe outer diameter series): HGJ44–76, JB/T74–90

The connection dimensions of DIN standards differ from those of JB standards; details are shown in the table below:

| Standard | Thread (M)/Thread Hole (φ) Dimensions |
|----------|-----------------------------------|
| JB Series 2 | M22/φ25 (all), M30/φ34 (some), M36/φ41 (some), M42/φ48 (all), M48/φ54 (all) |
| New HG, ISO, JB Series 1, BS, ΓΟCT, DIN | M24/φ26, M33/φ36, M33/φ36, M39/φ42, M45/φ48, M45/φ48 |

Measures to be Taken When Using Two-Part Flanges
– Expand the thread holes of the first flange by 1 mm.
– Expand the thread holes of the first flange by 2 mm.
– Gaskets can be used.
– Gaskets can be used.
– The same as above.
– Gaskets can be used.

Note: “All” in the brackets in the table indicates that all specifications of fasteners are replaced by those of the second row. “\"Partial\" means that some of the fasteners of this specification have changed, but some of them remain unchanged and are consistent. When using HG new standard flanges in combination with JB old standard flanges, the following points should be noted: 1. The number of bolts for the three flanges is not consistent, and two of these specifications (PN0.25/DN500, PN0.6/DN500) have a direct impact on the compatibility ； For PN1.0/DN80HG, the number of standard bolts is 8, while for JB standard it is 4 ； 2. For some old-standard flanges (JB series 2), it is advisable to enlarge the screw holes by 1–2 mm; for others, washers can be used during installation ； 3. High-pressure pipe flanges with PN16.0MPa: the connection dimensions under the new HG and JB standards are completely different. Flange type and sealing surface type: Flange; Standard number; Sealing surface; Pressure class: PN, in MPa. Common flanges used with valves: Type code; Shape code. Plate type, flat welding: PL; HG20593, JB/T81-94, GB/T9119-2000. Raised face: RF; 0.25–2.5. Raised-face flat-welded flanges are commonly used and can be paired with various low- and medium-pressure valve types such as gate valves, globe valves, ball valves, etc. Full flat face: FF; 0.25–1.6. Necked type, flat welding: SO; HG20594, GB/T9116-2000. Raised face: RF; 0.6–4.0. Raised-face necked flat-welded flanges are a structure type that has been introduced in recent years and are widely used in petrochemical plants. Grooved face: MFM; 1.0–4.0. Tapered face: TG; 1.0–4.0. Full flat face: FF; 0.6–1.6. Necked type, butt welding: WN; HG20595, JB/T82-94, GB/T9115-2000. Raised face: RF; 1.0–25.0. Valves with a pressure class of PN4.0–PN10.0 MPa usually use raised-faced pipe flanges, such as Z41H-40, J41H-64, H44H-100, etc. For pressures above 160 MPa, ring-type connection faces are used, such as J41H-160. Butt-welded flanges can also be used with butterfly valves and check valves that employ clamp-type connections. Rough-faced MFM: 1.0–16.0; Grooved face TG: 1.0–16.0; Ring joint face RJ: 6.3–25.0; Fully flat face FF: 1.0–1.6; Integral flange IF: HG20596, JB/T79-94, GB/T9113-2000. Raised face RF: 0.6–25.0. For valves, integral flanges are generally used with a raised face for PN≤2.5, a rough-faced design for PN≥4.0, and a ring joint face for PN≥16.0; however, some manufacturers use a ring joint face for PN10.0 MPa and a rough-faced design for PN16.0 MPa. Valves for ammonia at PN2.5 MPa use a rough-faced design (FM) and require pipe flanges with a raised face. Rough-faced MFM: 1.0–16.0; Grooved face TG: 1.0–16.0; Ring joint face RJ: 0.6–25.0; Fully flat face FF: 1.0–1.6; Socket weld SW: HG20597, GB/T9114-2000. Raised face RF: 1.0–10.0. This is the structure commonly used in oil processing equipment introduced in recent years. Rough surface MFM: 1.0–10.0; Grooved surface TG: 1.0–10.0; Threads; Flanges: Th HG20598, GB/T9114-2000; Raised surface RF: 0.6–4.0. It is widely used in construction projects, is easy to install as it requires no welding, and is suitable for DN10–DN150 sizes. Full-face FF 0.6～1.6 butt welding, loose sleeve PJ/SE HG20599, JB/T84-94, GB/T9120-2000; raised face RF 0.6～4.0 – suitable for pipeline systems exposed to corrosive media. Flat welding, ring loose sleeve: PJ/RJ HG20600, JB/T83-94, GB/T9121-2000; Raised face: RF 0.6～1.6; Male and female faces: MFM 1.0～1.6; Grooved face: TG 1.0～1.6; Flange cover: BL HG20601, JB/T84-94, GB/T9123-2000; Raised face: RF 0.25～25.0; Used for pipe ends or as end caps. Rough surface MFM: 1.0–16.0; Grooved surface TG: 1.0–16.0; Ring joint surface RJ: 6.3–25.0; Fully flat surface FF: 0.25–1.6; Liner flange BL(S) HG20602; Raised surface RF: 0.6–4.0. Developed to save expensive heavy metal materials such as stainless steel. Raised surface M: 1.0–4.0; Grooved surface T: 1.0–4.0. American standard with butt welding at the neck: SO HG20616; American standard with raised surface RF: 2.0–26.0, suitable for American standard valves with PN2.5–5.0 pressure ratings. American standard with weld neck: WN HG20617; American standard with raised surface RF: 2.0–42.0. Raised surfaces are generally used for pressures up to PN11.0 MPa, while ring joint surfaces are used for pressures of PN15.0 MPa or higher. Ring connection surface RJ 2.0～11.0

2#, I’m truly extremely grateful!

Building 2# is great; it provides a systematic explanation of the specifications and models of flanges! Thank you. Among the information provided, the following point seems particularly important and serves as a key highlight: “The standard standards commonly used for pipe flanges in China’s chemical and petrochemical industries are as follows: 1. Imperial pipes (the internationally standard piping series): GB 9112–9125, SH 3406; 2. Metric pipes (the commonly used series for the outer diameter of steel pipes in China): HGJ44–76, JB/T74–90.” The difference between imperial pipes and metric pipes directly determines a series of differences in flanges. The choice of standard directly leads to different selections for pipes, flanges, and subsequent fasteners. This is also an important reason for the current chaos in material selection for design!