Selection of gasket

The selection principle of sealing gasket is: for the occasion with low requirements, it can be selected by experience, and it can be replaced when it is not suitable However, for those occasions with strict requirements, such as explosive, highly toxic and combustible gas, as well as highly corrosive liquid equipment, reaction tank and transmission pipeline system, etc., they should be selected according to the working pressure, working temperature, corrosiveness of sealing medium and the form of combined sealing surface Generally speaking, in normal temperature and low pressure, non-metallic soft gasket is selected; in medium pressure and high temperature, non-metallic and metal combined gasket or metal gasket is selected; in case of large fluctuation of temperature and pressure, elastic or self tightening gasket is selected; in low temperature, corrosive medium or vacuum conditions, special performance of gasket shall be considered In particular, the influence of flange conditions on gasket selection should be noted here (1) the influence of flange form: different flange forms require different gaskets Smooth surface flange is generally only used for low pressure, with soft thin gasket; under high pressure, if the strength of the flange is enough, smooth surface flange can also be used, but thick soft gasket, or spiral gasket with inner reinforcing ring or outer reinforcing ring should be used In this case, the metal gasket is also not applicable, because the required pressing force is too large, leading to large deformation of the bolt, making the flange not easy to seal If a metal gasket is to be used, the smooth surface shall be reduced to reduce the contact area with the gasket In this way, with the same bolt tension, the compression stress of the narrow smooth surface after reduction will increase (2) the influence of the surface roughness of the flange has a great influence on the sealing effect, especially when the non soft gasket is used, the surface roughness of the seal is one of the main causes of the leakage For example, when using metal gasket, if the roughness value is large, the gasket can not block the spiral groove formed by the knife pattern Under the pressure, the medium will leak out along the groove The requirement of soft gasket for flange surface finish is much lower This is because it is easy to deform, can block the processing knife grain, thus preventing leakage For soft gasket, too smooth flange is not good, because the resistance of interface leakage becomes smaller Therefore, different gasket requires different roughness of flange surface Table 29.3-15 lists the experience data of flange surface roughness required by various gaskets (3) hardness difference between flange and gasket the purpose of using gasket is to make the gasket produce elastic or plastic deformation to fill the flange surface with small unevenness and prevent leakage Therefore, the hardness of gasket material should be lower than that of flange material The greater the difference between them, the easier to achieve sealing When using metal gasket, in order to ensure the realization of sealing, the softer material should be selected as far as possible to make the hardness of metal gasket lower than that of flange by more than 40hb Table 29.3-16 shows the gasket selection standard of the Ministry of petroleum Table 29.3-17 shows the thickness and application scope of rubber asbestos board Table 29.3-15 surface roughness of flange sealing gasket type gasket name surface roughness remarks metal gasket ring gasket ＜ 0.8 self tightening gasket hope the surface is as smooth as possible Serrated gasket ＜ 1.6 semi metal gasket metal clad gasket ＜ 1.6 spiral wound gasket ＜ 12.5 spiral wound gasket ＜ 3.2 gas seal Asbestos rubber plate ＜ 12.5, asbestos cotton gasket ＜ 25, polytetrafluoroethylene gasket, polytetrafluoroethylene plate gasket ＜ 12.5 Polytetrafluoroethylene gasket < 12.5, rubber plate < 25, organic gasket oil seal < 25, leather gasket < 25 Paper gasket ＜ 25 table 29.3-16 gasket of Ministry of petroleum select standard medium flange nominal pressure / MPA medium temperature / ℃ flange sealing surface type select gasket name gasket material Oil gas, oil, liquefied gas, hydrogen, sulfurization catalyst (propane, acetone, benzene, phenol, furfural, isopropanol), less than 25% urea (mass fraction) ≤ 1.6 ≤ 200 smooth oil resistant rubber asbestos gasket oil resistant rubber asbestos plate ≤ 1.6 201-300 smooth spiral wound gasket 08 (15) steel strip, asbestos tape 2.5 ≤ 200 smooth oil resistant rubber asbestos gasket oil resistant rubber asbestos plate 4.0 ≤ 200 smooth (concave convex) 1) spiral wound gasket 2) corrugated iron wrapped asbestos gasket 0.8 (15) steel strip, asbestos tape, tinplate, asbestos board 2.54 201 ～ 450 2.54 451 ～ 600 spiral wound alloy gasket 0Cr13 (Cr13) or 2Cr13 alloy steel strip, asbestos tape 6.4-16.0 ≤ 450 trapezoid groove (elliptical groove) 1) oval section steel washer 2) octagonal section alloy steel washer 08 (10 steel) 451-600 steam 10.2 2.54 ≤ 250 251 ～ 600 smooth type (concave convex type) 1) spiral wound gasket 2) corrugated iron clad asbestos gasket 1Cr18Ni9 (1Cr18Ni9Ti) alloy steel 10.0450 trapezoidal groove type (elliptical groove type) 1) oval section steel gasket 2) Octagonal section steel washer 08 (15) steel strip, asbestos tape, tinplate, asbestos plate water 6.4-16.0 ≤ 100 08 (10) steel salt water ≤ 1.6 ≤ 60 smooth rubber gasket rubber plate ≤ 150 rubber asbestos gasket medium pressure rubber asbestos plate gas ammonia, liquid ammonia 2.5 ≤ 150 concave convex type compressed air, air, inert gas ≤ 1.6 ≤ 200 smooth type ≤ 98% sulfuric acid (mass fraction) ≤ 35% hydrochloric acid (mass fraction) ≤ 1.6 ≤ 90 smooth type liquid alkali ≤ 1.6 ≤ 60 smooth type 1) rubber asbestos gasket 2) rubber gasket Table 29.3-17 thickness of medium pressure rubber asbestos plate and rubber plate and applicable range, type and thickness mm applicable range, type and thickness mm applicable range, XB200 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6 ≤ 200 ℃, ≤ 1.5MPa xb450 1, 1.5, 2, 2.5, 3 ≤ 450 ℃, ≤ 6Mpa XB350 ≤ 350 ℃, ≤ 4MPa oil resistant 1, 1.2, 1.5, 2, 2.5, 3 for coal field, gasoline, etc Table 29.3-18 shows asbestos rubber gasket for raised face ductile iron pipe flange Table 29.3-19 shows the limit deviation of inner diameter and outer diameter of asbestos rubber gasket for convex ductile iron pipe flange Table 29.3-20 shows raised face steel pipe flange and asbestos rubber gasket Table 29.3-21 shows asbestos rubber gasket for steel pipe flange of concave convex type and mortise groove type Table 29.3-22 shows spiral wound gasket for steel flange Table 29.3-23 shows spiral wound gasket with outer ring Table 29.3-24 shows spiral wound gasket with inner and outer rings Table 29.3-18 asbestos rubber gasket for raised face ductile iron pipe flange (from GB / t12387-1990) (mm) nominal diameter DN gasket inner diameter d 1 nominal pressure pN / MPA gasket thickness t 1.01.62.0 2.5 4.0 5.0 gasket inner diameter d 0 25 34 according to PN4.0MPa according to PN4.0MPa 65.5 according to PN4.0MPa 71 71.0 1.5 ～ 3 32 43 75.0
82
80.5
40
49
84.5
92
94.5
50
61
102.5
107
109.0
65
77
121.5
127
129.0
80
89
134.5
142
148.5
100
115
162
162
172.5
168
180.0
125
1741
192
192
196.0
194
215.0
150
169
218
218
221.5
224
250.0
200
220
273
273
278.5
284
290
306.0
250
273
328
329
338.0
340