The problem of flange weakness (continued) - pipe flange and container flange

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Flange standards and selection There are two types of flange standards used in petroleum and chemical industries. One is the pressure vessel flange standard, and the other is the pipe flange standard. 　　(1) Pressure vessel flange standards 　　　　 http://www.cngspw.com/Doc/data.WebNoteBooks/20060517191523/yalirongqifalanfenlei.gif 　　1． Flat welding flange A comparison of the two types of flat welding flange is shown in the table below, see diagram. Name Pressure level PN (MPa) Diameter range DN (mm) Temperature range Remarks Type B flat welding flange Type A 0.25, 0.6, l.0, 1.6300 ~ 2000-20 ℃ ~ 300 ℃ Type B flange has a cylindrical nipple with a wall thickness of not less than 16mm, thus making the Type B flat welding flange more rigid than Type A flat welding flange ； The welding seam of type A has a V-shaped groove, and the welding seam of type B has a U-shaped groove, so type B also has higher strength and stiffness than type A. Type B has a larger diameter range of 0.25 to 1.6 pressure level and can also be used for 2.5 The smaller diameter range of the two pressure levels 300~3000-20℃~350℃ is given in Table 4-16. The corresponding relationship and range of the nominal pressure and nominal diameter applicable to Type A and Type B flat welding flanges and butt welding flanges are given in Table 4-16. Table 4-16 Pressure vessel flange classification and specification type flat welding flange butt welding flange type A type B long neck standard number JB4701JB4702JB4703 simplified diagram http://www.cngspw.com/Doc/data.WebNoteBooks/20060517191523/biao4-16_1.gifhttp://www.cngspw.com/Doc/data.WebNoteBooks/20060517191523/biao4-16_2.gifhttp://www.cngspw.com/Doc/data.WebNoteBooks/20060517191523/biao4-16_3.gif Nominal pressure PN (MPa) 0.250.601.001.600.250.601.001.602.504.000.601.01.602.504.006.40 Nominal diameter DN (mm) 300 according to PN1.00 ———— — (350) 400 (450) 500 (550) 600 (650) — 700 — 800 900 — —1000 — (1100) 1200 (1300) — 1400 (1500) 1600 (1700) —1800 (1900) 2000 (2200)—According to PN0.60 2400 2600 2800 3000 Note: The nominal diameters in parentheses in the table should be avoided as much as possible. 　2. Butt welding flange Long neck butt welding flange has a thicker neck (schematic diagram c), http://www.cngspw.com/Doc/data.WebNoteBooks/20060517191523/4-40,1,2.gif http://www.cngspw.com/Doc/data.WebNoteBooks/20060517191523/4-43.gif This further increases the rigidity of the flange. Therefore, it is specified to be used in a higher pressure range (PN 0.6MPa~6.4MPa) and diameter range (DN300mm~2000mm), and the applicable temperature range is -20℃~450℃. It can be seen from Table 4-16 that the specifications of type B flat welding flange below DN 2000mm are included in the scope of long neck butt welding flange. The connection dimensions and flange thickness of these two flanges are exactly the same. Therefore, type B flat welding flanges below DN2000mm can be replaced by rolled long-neck butt welding flanges to reduce the production cost of the flange. 　　Both flat welding and butt welding flanges are available with or without lining rings. When the equipment is made of stainless steel, carbon steel flange 7 and stainless steel backing ring can be used to save stainless steel. The schematic diagram shows a Type A flat welding flange with a backing ring. 　 　　When using flange standards to determine flange size, the nominal diameter and nominal pressure of the flange must be known. The nominal diameter of the pressure vessel flange and the nominal diameter of the pressure vessel take the same series of values. For example, a DN 1000mm pressure vessel should be equipped with a DN 1000mm pressure vessel flange. 　　The determination of the flange nominal pressure is related to the flange's maximum operating pressure, operating temperature and flange material. Because when formulating the flange size series and calculating the flange thickness, the mechanical properties of 16MnR at 200°C are used as the basis. Therefore, it is stipulated that for the flange size determined based on this standard, at 200°C, its maximum allowable operating pressure is considered to be the nominal pressure of the flange with this size. For example, the so-called flange with a nominal pressure of PNO.6MPa refers to a flange with such a specific size. The flange is made of 16MnR. At 200°C, its maximum allowable operating pressure is 0.6MPa. If this PN0.6MPa flange is used at a temperature higher than 200°C, its maximum operating pressure will be lower than its nominal pressure of 0.6MPa. On the contrary, if it is used under conditions below 200℃, its maximum working pressure will still be determined based on 200℃. If the flange material is changed to Q235-A, then the mechanical properties of Q235-A steel are worse than 16MnR. This flange with a nominal pressure PN0.6MPa, even if it is operated at 200°C, its maximum allowable operating pressure will be lower than its nominal pressure. On the contrary, if the material of the flange is changed from 16MnR to 15MnVR, then since the mechanical properties of 15MnVR are better than 16MnR, the maximum allowable operating pressure of this flange with a nominal pressure of PN0.6MPa will be higher than its nominal pressure when operating at 200°C. In short, as long as the nominal diameter and nominal pressure of the flange are determined, the size of the flange will also be determined. As for the maximum operating pressure allowed by this flange, it depends on the operating temperature of the flange and what material it is made of. The flange materials specified in the pressure vessel flange standard are low carbon steel (Q235-A, 20g, etc.) and ordinary low steel (16Mn, 16MnR and 15MnVR, etc.). Table 4-17 is the conversion relationship between Type A flat welding flange and Type B flat welding flange. At different temperatures, their nominal pressure and the maximum allowable working pressure. Using this table, the operating temperature and design pressure given in the design conditions can be converted into the nominal pressure required to find the flange standard. For example, choose a flange for a vessel with an operating temperature of 300°C and a design pressure of 0.6MPa. Look up table 4-17 to see: If the flange material is 15MnVR, the flange size can be found based on the nominal pressure of 0.6MPa. If the flange material is 20R, the flange size must be determined based on the nominal pressure of 1.0MPa. Table 4-17 Maximum allowable working pressure for type A and type B flat welding flanges Nominal pressure PN flange material Working temperature °C Remarks＞20～200 250300350 0.25 Plate Q235-A, B Q235-C 20R 16MnR 15MnVR 15CrMoR 0.160.150.140 . 130.180.170.150 . 140.190.170.150 . 140.250.240.210 .200.270.270.260.250.260.250.23.22 Forging 20 16Mn 20MnMo 0.190.170.150 .140.260.240.220.210.270.270.260.250.60 Plate Q235-A, B Q235-C 20R 16MnR 15MnVR 15CrMoR 0.400.360.330.300.440.400.370.330.450.400.360.340.600.570.510.490.650.640.630.600.630.600.560.53 Forging 20 16Mn 20MnMo0.450.400.360.340.610.590.530.500.650.640.630.601.00 sheet Q235-A, B Q235-C 20R 16MnR 15MnVR 15CrMoR 0.660.610.550.500.730.670.610.550.740.670.600.561.000.950.860.821.091.071.051.001.051.000.830.88Forging 20 16Mn 20MnMo0.740.670.600.561.020.980.880.831.091.071.051.001.60 plate Q235-A, B Q235-C 20R 16MnR 15MnVR 15CrMoR 1.060.970.890.801.171.080.980.891.101.080.960.901.601.531.371.311.741.721.681.601.671.601.491.41 Forging 20 16Mn 20MnMo1.191.080.960.901.641.561.411.331.741.721.681.602.50 plate Q235-C 20R 16MnR 15MnVR 15MnVR 15CrMoR 1.831.681.531.381.861.691.501.402.502.392.142.05DN＜14002.722.682.632.50DN≥14002.672.632.592.20 2.612.502.33 Forging 20 16Mn 20MnMo 20MnMo 1.861.691.501.402.562.442.202.082.922.862.822.73DN＜14002.672.632.59 DN≥14004.00 Plate 20R 16MnR 15MnVR 15MnVR 15CrMoR 2.972.702.392.24 4.003.823.423.274.364.294.204.00DN＜14004.274.204.144.00DN≥14004.184.003.733.52 Forging 20 16Mn 20MnMo 20MnMo 2.972.702.392.244.093.913.523.334.644.564.514.36DN＜14004.274.204.144.00DN≥1400 For example, select a flange for a vessel with an operating temperature of 300℃ and a design pressure of 0.6MPa. Look up table 4-17 to see: If the flange material is 15MnVR, the flange size can be found based on the nominal pressure of 0.6MPa. If the flange material is 20R, the flange size must be determined based on the nominal pressure of 1.0MPa. 　　(ii) Pipe flange standards Since the nominal diameter of the container cylinder and the nominal diameter of the pipe represent different specific sizes, container flanges and pipe flanges of the same nominal diameter also have different sizes, and the two cannot be substituted for each other. In addition to flat welding and butt welding flanges, pipe flanges also include cast steel flanges, cast iron flanges, loop flanges, threaded flanges, etc. The selection method and steps for pipe flange standards are the same as those for pressure vessel flanges. In addition to GB9119.7-88, pipe flange standards are also commonly used: Ministry of Chemical Industry standards HG20592～HG20602-97 ； Sinopec standard SH3406-96, etc. Among them, the standards of the Ministry of Chemical Industry are divided into European system, American system, etc., and the European system is commonly used in my country. 　　Here is an example question 4-6 to help readers understand the standards and selection of flanges. Example 4-6: Equip a distillation tower with a pair of flanges connecting the tower body and head. The inner diameter of the tower is 1000mm, the operating temperature is 280°C, and the design pressure is 0.2MPa. The material is Q235-A. parse: According to the operating temperature, design pressure and materials used, it can be seen from Table 4-17 that the size of the flange to be selected should be checked based on the nominal pressure of 0.6MPa. Since the operating pressure is not high and the diameter is not large, type A flat welding flange and flat sealing surface can be used as shown in Table 4-16, and asbestos rubber plate is used as the gasket material. The dimensions of each part of the flange can be found in Appendix Table 9, and the flange is also drawn in the figure below. The materials selected for the connecting bolts are Q235-A and M20, a total of 36 pieces.