IE43293B1 - Sealing system - Google Patents

Description

The invention relates to a method, of sealing two oppositely-disposed sealing surfaces which are capable of incidental movement relative to one another e.g. as a result of heating, on flanges and valves made of heat or corrosion-resistant steel, using a prestressed X ring with rounded lips. The invention also relates to a sealed assembly.

Prestressed X-rings with rounded lips are already used for sealing Lhe axial gap between the parts to be 1θ sealed, when tho parts expand through heating (US-PS 3 542 -380).

Ih the case where the flanges to be joined slide on one another as a result of high pressure or negative pressure or non-uniform thermal expansion, it is desirable that the joint remains sealing-tight in the radial direction also, even when there are temperature differences of 400 to 500°C between the parts to be joined, e.g. as is normal in nuclear power stations.

According to the present invention there is provided a sealed assembly comprising two oppositely-disposed seal- 3 ing surfaces which are subject to incidental movement relative to one another, on flanges made of heat or corrosion-resistant steel, and a prestressed sealing ring of X-shaped profile having rounded lips, said profile having, when the ring is in an unstressed condition, an axis of symmetry which is inclined with respect to the sealing plane, the sealing ring having at least the same hardness as the flanges, the flange surfaces having a normal turned finish with a roughness of approximately 0.2 to 2.2 μ,ηι, the widths of the surfaces in contact not exceeding 0.2 to 0.3 mm, the surface force being from 200 to 450 kg/cm sealing periphery and the sealing process occurring in two steps, the first step being a prestressing of the sealing ring so as to harden its lips and to produce a radial sliding of the lips so as to smooth and harden the flange surfaces, whereas the second step is for the purpose of actual sealing.

The present invention also provides a method of sealing two oppositely disposed surfaces which are subject to incidental movement relative to one another, of flanges made of heat or corrosion-resistant steel, the flange surfaces having a normal turned finish with a roughness of approximately 0.2 to 2.2 μΐη, the widths of the surfaces in contact not exceeding 0.3 mm, the surface force being from 200 to 450 kg/cm of the sealing periphery, which method comprises inserting between the flange surfaces a sealing ring of X-shaped profile having rounded lips, said profile having, when the ring is in an unstressed condition an axis of symmetry which is inclined with respect to the sealing plane, the sealing ring having at least the same hardness as the flanges, prestressing the sealing ring so that the lips are caused to slide radially, thereby hardening the lips smoothing the flanges and hardening the flange surfaces, and applying a sealing force to the ring to seal the space between the flange surfaces. 293 - 4 The correspondence between the roughness of the surfaces to be sealed and the sealing force employed will usually be as shown in Table 1: TABLE 1 Height of profile, mm 2 Roughness of flanges Ra (CLA) μπι 0.2 — 0.8 μΐη Surface force, kg/cm Sealing periphery 200 3.6 7.2 0.6 — 1.2 gm 0.8 — 2.2gm 300 450 The sealing method and sealed assembly of the present invention are based on the discovery that, in order to obtain adequate sealing in a radial direction, it is particularly necessary for the sealing surfaces to remain undamaged. Accordingly, the seal lips must slide on the flange surfaces without damaging them. The desired object cannot be achieved simply by rounding the lip ends.

There is an additional phenomenon based on twisting the X-profile of the sealing ring through a certain angle, as a result of which the profile is prestressed and, under the action of part of the sealing force, the lip ends harden and become resistant to plastic deformation but also remain of rounded cross-section and smooth, and at the same time the flanges are smoothed in the parts where the lips slide and the sliding surfaces are simultaneously strain hardened.

The method of sealing in accordance with the invention produces an excellent seal and has the further advantage that the seals do not become unserviceable or the flange surfaces require re-machining after a single use, but the relatively expensive sealing rings can be frequently reused without re-machining the sealing surfaces, provided only that the sealing surfaces have a normal turned finish without further surface treatment, with the degree of rough43293 - 5 ness shown in Table 1.

An example of the invention is shown in Figure 1 of the drawings, which is a cross-section through one embodiment of a sealed assembly constructed in accordance with the present invention. The sealing ring is stress-free in the left hand side of he drawing and prestressed in the right hand side.

A sealing ring 3 is disposed between two flanges 1 and 2 and has outer sealing lips 4 and inner sealing lips 4’· Ring 3 has an external diameter and an internal diameter . A symmetrical axis 5 extending through the centre point of the annular profile includes an angle a with the planes of the flanges. The sealing ring has a height H, a width T and a lip radius r.

In a practical example, H=3.6 mm, T = 1 mm, q = 0.5 mm, de= 90 mm, = 82 mm, and a = 10°.

Afterthe first stage of the sealing process, the angle 0=0, All four lips of the sealing ring now lie between flanges 1* and 2·. The surface force pressing the lips on to the plane of the flanges can be divided into a horizontal and a vertical component. The horizontal component causes the sealing lip to slide, thus smoothing the flange along the parts where the lips slide, whereas the vertical component produces strain hardening of the sliding surface.

In normal seals, the sealing force produces furrows, grooves or the like in the flange surfaces which inevitably produce leaks when the seal is moved or relieved from pressure, so that the sealing rings cannot be used again. According to the invention, however, there is no adverse effect on the smoothness of the flange surface, so that high sealing-tightness is ensured even if the flanges slide to different extents, since the smoothing of the surface ensures perfect contact between the sealing lip and - 6 the flange surface. An important factor is that, owing to the prestressing, the lip ends become strain hardened and therefore become more resistant to plastic deformation, i.e. remain rounded in cross-section and smooth. Any difference between the internal and external pressure is caused by the difference between the diameters of the internal and external sealing lips.

As a result of prestressing, the internal lips become harder than the external lips, so that the different, i.e. greater surface pressure resulting from the smaller diameter does not deform them plastically and they do not lose the ability to slide as a result of non-uniform thermal expansion. The effect is that the flange surface is smoothed and a perfect sealing-tight contact is simultaneously obtained without deforming the sealing lips. An important factor is that only a small contact surface is loaded with the correct specific pressure (or Hertzian pressure). Thus, only a relatively small sealing force is required and the surfaces in contact are not damaged. The term sealing force according to the invention denotes the force at which adequate sealing-tightness is ensured without plastic deformation of the surfaces to be sealed, whereas all prior-art normal sealing systems are subject to plastic deformation.

In this first step of the sealing process, the smoothing of the flange surface takes up only about l/lO of the sealing force, i.e. only 30 kg/cm of the sealing force of 300 kg/cm sealing periphery, at a height H = 3.6 mm.

Thus, the smooth surface forms an ideal flat plane on which the rest of the sealing force (2/0 kg/cm in the example given) can be exerted without penetrating since only the stated specific pressure is exerted on the sealing surface.

The invention is based on the following detailed considerations: In order to obtain good sealing-tightness with flange surfaces having a given degree of roughness, two bearing widths of 0.2 to 0.3 mm are required per flange, if the elastic limit is not to be exceeded at a surface force of 300 kg/cm sealing periphery. At a lip radius of 0.5 mm and a surface force of 300 kg/cm sealing periphery, an elastically deformed contact surface between 0.2 and 0.3 mm wide is obtained. In that case the force used for sealing is 420 kg/cm This is divided between two sealing surfaces having a sealing area of 2 mm /cm, resulting in a 2 compressive pressure of 105 kg/mm on the hardened lip surfaces in the direction of the lip axis. The vertical compressive pressure on the hardened flange plane is thus 75 kg/mm . Tests show that this force is just sufficient to smooth the surface roughness of the flanges.

The prestressing results in a plastic deformation of the sealing ring whereby the four lips become strain hardened. Due to their smaller diameter the inner lips undergo a greater degree of deformation so that their strain hardening is somewhat higher than that of the outer lips. Experiments have shown that, as a result of deformation, the inner lips become up to 60% harder and the outer lips up to 25% harder compared with the ring itself before deformation. In order to obtain the same stress in seals having different parameters but made of the same material, i.e. with the same E modulus and the same Poisson’s ratio μ, the prestress angle a must be changed. For this purpose, the angle a can be calculated from the following formula, which is derived from the very similar deformation in cup springs; only the quantity T has to be determined experimentally. m2E1T log(D1/d1) h’tana 3(m2-l) (Df dx)2 nvena ς . h’tana (h-h’tana)(h- ———— )T+TJ F is the force in kg required for compressing the sealing ring through the angle a. - 8 F=K Dm in kg. K is the constant surface force per sealing length in kg/mm, i.e. the prestress remains the same for each sealing ring having a given profile height: D = ' (mm) m 2 d0 is the external diameter in mm d^ is the internal diameter in mm m — -, μ = Poisson's ratio (0.3 in this case) μ E = 2.1 x 10^ kg/mm2 (E modulus) d + d· H D =e 1+ _/Τ' cos (45° + a) 1 2 2 d. J* d, H e 1 Λ d. = -- ~ -/ 2 cos (45 + a) 1 2 2 h = h/Tsin (45° + a) H is the height of the sealing profile h* is the distance between the central lines of the contact surfaces between the sealing lips and the flanges as is shown in Figure 2 which is a partial cross-section of the X ring of Figure 1 showing dimensions H and h *.

T is the thickness of the lips · since the lips are joined together in a body, the value of T was determined experiment ally.

Xn the case, for example, of a profile height H=3.6, T is not 1 mm as in the foregoing practical example, but 1.55 mm. This is an average value based on experiments and calculations on seals having the following diameters: e e e 100 where / indicates diameter.

In Table 2 the values for h», the surface force K and T are given for the different profile heights.

TABLE 2 Profile height in mm 2 3.6 7-2 Surface force Ptot kg/mm 20 30 45 K=-i-P kg/mm 10 T mm h* mm 0.79 1.4 1.55 2.5 4.5 A solution for a is found for each diameter by numerical iteration. d , d,. m, Ε, H and T are known. In a first calcule 1 o IS ation, a is given values between 0 and 45° in 1 steps and the formula is calculated each time.

After running through all these values, the values for a on either side of the solution are found. Starting from these values, <χ is exactly determined in intermediate steps of 0.05°.

The above values for the E modulus and Poisson's ratio μ are correct when Inconel 600 is used (Inconel is a Trade Mark). On account of its great resistance to heat and corrosion, this material is very frequently used in the relevant industries when subject to the appropriate heating and corrosion. Consequently, for diameters between 50 and 250 mm, the - 10 angle a is as shown in Table 3 hereinafter: TABLE 3 d e *1 a 50 42 2.95 60 52 4.25 70 62 5.60 80 72 7.10 90 82’ 10.20 100 92 10.20 150 142 17.85 200 192 24.35 250 242 29.35 The following Table is obtained for 10 and 50 nun and a profile height H of 2 diameters between mm: TABLE 4 e 1 10 6 IS 11 25 21 30 26 35 31 40 36 45 41 50 46 At diameters between 250 height H of 7.2, the angles a Angle a in degree 0.45 1.050 3.150 4.55 6.0 7.55 9.15 10.85 and 2000 mm and a profile are as follows: - 11 - d TABLE 5 d a e 1 250 234 11.95 300 284 15.35 400 384 21.55 500 484 26.65 600 584 30.65 700 684 33.7 800 784 35.95 900 884 37-65 1000 984 38.95 1500 1484 42.25 2000 1984 43-35 The above-calculated results can be used to obtain uniform prestress even for different sealing-ring diameters and thus obtain uniform sealing and the full advantages obtainable according to the invention.

The resulting sealing system ensures excellent sealingtightness even if the flanges slide radially and there are higher than average temperature differences between the surfaces to be sealed. The sealing lips are in perfect contact without penetrating into the flanges, and the flanges can be safely moved relative to one another without impairing the sealing-tightness, even if the thermal expansion is different for each flange. The inner lips bear most of the surface pressure, since they bear on the inner diameter of the seal. This is likewise advantageous, since the lip and flange material are more strain hardened here and thus prevent the lip penetrating into the flanges.

This sealing mechanism, which results in the X-lips sliding along the flange plane, provides good sealing with relatively low surface pressure and, more particularly, ensures that no damage occurs to the sealing lips or flange - 12 surfaces, so that the sealing rings and flanges can be reused without additional machining.

Of course, if other materials than Inconel 600 are used, there is a change in E and μ., In that case a suit5 able prestress angle a must be chosen, depending on the elastic limit of the material, whereupon the coefficient K can be calculated.

Claims (9)

1. A sealed assembly comprising two oppositely disposed sealing surfaces which are subject to incidental movement relative to one another, on flanges made of heat or corrosion-resistant steel, and a prestressed sealing ring of Xshaped profile having rounded lips, said profile having, when the ring is in an unstressed condition, an axis of symmetry which is inclined with respect to the sealing plane, the sealing ring having at least the same hardness as the flanges, the flange surfaces having a normal turned finish with a roughness of approximately 0.2 to 22 gm, the widths of the surfaces in contact not exceeding 0.2 to 0.3 mm, the surface force being from 200 to 450 kg/cm sealing periphery and the sealing process occurring in two steps, the first step being a prestressing of the sealing ring so as to harden its lips and to produce a radial sliding of the lips so as to smooth and harden the flange surfaces, whereas the second step is for the purpose of actual sealing.

2. A sealed assembly as claimed in claim 1, wherein about l/ίΟ of the sealing force is used for prestressing and hardening the lips of the sealing ring, whereas the remaining sealing force forms a smooth strain-hardened surface on the flanges on which the sealing-ring lips slide without indenting the surface.

3. A sealed assembly as claimed in claim 1 or claim 2, wherein when the radius of curvature of the ends of the sealing lips is constant, the angle through which the sealing ring rotates relative to the flange plane is dependent on the ring diameter alone, in order to maintain uniform prestressing.

4. A sealed assembly as claimed in claim 1 substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

5. A sealed assembly as claimed in claim 1 substantially 4 32 9 3 - 14 as hereinbefore described in the specific Example.

6. A method of sealing two oppositely disposed surfaces which are subject to incidental movement relative to one another, of flanges made of heat or corrosion-resistant 5 steel, the flange surfaces having a normal turned finish with a roughness of approximately 0.2 to 2.2 gm, the widths of the surfaces in contact not exceeding 0.3 mm, the surface force being from 200 to 450 kg/cm of the sealing periphery, which method comprises inserting between the flange surfaces 10 a sealing ring of X-shaped profile having rounded lips,said profile having, when the ring Ls in an unstressed conditions, an axis of symmetry which is inclined with respect to the sealing plane, the sealing ring having at least the same hardness as the flanges, prestressing the sealing ring so IS that the lips are caused to slide radially, thereby hardening the lips, smoothing the flanges and hardening the flange surfaces, and applying a sealing force to the ring to seal the space between the flange surfaces.

7. A method as claimed in claim 6 substantially as 20 hereinbefore described with reference to the accompanying drawings.

8. A method as claimed in claim 6 substantially as hereinbefore described in the specific Example.

9. Two oppositely disposed flanges when sealed by a method 25 as claimed in any one of claims 6 to 8.