FR2582071A1 - High-pressure enclosure - Google Patents

Abstract

a. High-pressure enclosure intended to resist high internal pressures. b. Enclosure characterised in that it is composed of a plurality of intermediate enclosures nested in one another and separated by gaps filled with intermediate fluids subjected to intermediate pressures lying between the internal pressure and the external pressure, the intermediate pressures decreasing from the inside towards the outside of the enclosure. c. The invention finds its application in the field of high-pressure enclosures.

Description

High pressure speaker
The present invention relates to high pressure enclosures for resisting very high internal pressures.

 It is not uncommon, when developing industrial equipment, and more particularly in the field of advanced technology, to have to test the behavior of materials under very high pressures of sometimes dangerous liquids or gases. (H, He, SH2) before use.

 This requirement is encountered for example in the field of drilling, where it is necessary to test the probes under artificially recreated conditions under very high pressures and temperatures, sometimes much higher than 1000 bar, composite materials, other industries, etc ..

 The safety regulations on the one hand, the reliability definitions on the other hand, require that such loudspeakers satisfy very strict criteria.

 These criteria make obtaining very high pressures extremely difficult or impossible; it is in all cases necessary to design speakers with very thick walls made of very sophisticated materials and therefore extremely expensive.

 In order to understand the limits indicated above, reference should be made to the attached drawing No. 1, which is a cross-section of a cylindrical tubular enclosure of axis x-x ', of thickness e, of internal diameter a and of external diameter b and inside which there is a pressure p1 much higher than the external pressure pe.

If we consider an elementary fragment of this enclosure situated at a distance r from its axis xx '(such that ar <= b, of radial length dP, and seen from axis xx' at an angle d, the laws of physics leading to equality
da
# r. rd # + #tdr d # - (#t + d # r) (r + dr) d <p = 0, where ar and a t respectively represent the radial and trangential elastic stresses depending on the constituent material of the enclosure to which is subjected the elementary fragment (r, dr, d).

By integrating the above equality over the entire tubular enclosure, the following formulas are obtained:
a = api - bpe - (pi - pe) ab
r - b2 - 2 2 2 2
#r (b - ar (b - a)
#t = a2pi + (pi - pe) a2b2b - ar (b - a)
r (b - a)
We see that the tangential stress at is 2 maximum when r is minimum, therefore for a unitary element located on the inner periphery of the enclosure (r2 = a2)
We deduce that
pi (a2 + b2)
a t max = = b2 2
-at
So that there is no risk of rupture, it is of course necessary that the maximum tangential stress atmax remains significantly lower than the own breaking stress of the constituent material of the enclosure.

For this, the thickness e of a tubular enclosure of mean radius r in a material whose breaking stress is equal to ot must at least be equal to

 To be able to safely withstand an internal pressure pi, k being the inverse of a safety coefficient required by the authorities, which is for example currently in France of 3 for compressed gases or a coefficient resulting from a reliability calculation.

 The formula above clearly shows that when the pressure inside the chamber becomes close to kat, the required thickness e tends to infinity.

According to the prior art, the problem posed therefore has no solution for attaining a pressure pi kat or P.> K.at
If we take the example of an alloy steel for which t = 130 daN / mm2, the internal pressure of all can hardly exceed 3 000 to 3 400 bars to meet the required standards.

In this case, for a tubular enclosure with a mean radius equal to 300 mm, the minimum thickness must be equal to

 This is an extremely large thickness relative to the radius of the enclosure, which makes it extremely expensive, especially considering that it must be made of a very sophisticated material such as that for example a martensitic stainless steel, to be able to withstand the phenomena of corrosion.

The present invention proposes to overcome the disadvantages of the conventional speakers described above, by providing an enclosure capable of withstanding extremely high internal pressures that can go
Up to its breaking characteristics, while having a satisfactory corrosion resistance, and being of a thickness and a significantly lower cost price; such an enclosure must of course also comply with the safety rules required by the Authorities.

 For this purpose, the invention relates to an enclosure of the above type, characterized in that it consists of several intermediate enclosures nested in each other, and separated by intervals filled with fluids or intermediate solids creating pressure intermediates between the internal pressure and the external pressure, the intermediate-pressure decreasing from the inside to the outside of the enclosure, the outer tube and / or the others can be auto-sintered.

 It is better not to self-scratch the internal enclosure to avoid creating risks of cracks or microcracks by hardening and internal stress formation.

 Most often, the enclosure according to the invention is, in fact, constituted by two intermediate metal enclosures separated by a minimum interval occupied by an intermediate fluid.

 Surprisingly, it was found that it was thus possible to significantly reduce the thickness of the speakers, and even to use for the external enclosure less sophisticated materials than those customary so far.

 For example, and according to another characteristic of the invention, the inner chamber is made of a high-performance steel, in particular a martensitic stainless steel, while the outer enclosure autofritty or not is a more common material.

The benefits that can be achieved through the speaker described above will be made more clear by the following examples
Example 1
According to the diagram n 2 in the appendix, which is a cross section of a cylindrical tubular enclosure constituted by two intermediate enclosures
A and B fitting one into the other with a minimum clearance and respective internal and external radii a and b on the one hand and b and c on the other hand, if we consider that the internal pressure of the enclosure A is equal to pi and the intermediate pressure to pe, a calculation identical to that carried out above makes it possible to reach equalities
First speaker A
b2 2ft + kat
= ak # t - pi + 2 pe
Second speaker B
pe + kt
c = bk # t - pe
If, as before
a = 300 mm, pi = 3400 bar and pe = 1400 bar, we obtain, for the first enclosure A
pi + k # t 2 34 + 43,33 2 28 = a2 77,33
b = ak # t = pi a 2pe 43.33 - 34 + 28 = 37.33
k # t - pi + 2pe
b = 1.44 a = 1.44 x 300 = 431.78.mm the minimum thickness of the first enclosure is therefore equal to 131.78.

Similarly, for the second speaker B, we obtain
C = b2 ko '+ pe - (1.44a) 2 43.33 + 14 = (1.44 a) 2 x
C - eg 43,33 - 14 -
c = 1.44 x 1.40 x = 2.01 a = 603.97 mm.

the minimum thickness of all two speakers A and B is equal to 303.97 mm.

 Comparing this result with the minimum thickness of 564 mm previously calculated for a similar simple enclosure, it can be seen that the use of a double enclosure makes it possible to obtain a saving in material of 51.13%.

 By using autofruffed tubes, the gain will be even more substantial.

The calculation above extended to an enclosure having a large number of intermediate speakers nested in each other gives for the radius of index n + 1
rn + 1 = r1 (k # t + #n)!
(k # t - pn + 2n-1)!
P and Pn-1 being the intermediate pressures for the tubes
n and n and nl indices.

 In this general case, to obtain a minimum mass enclosure for a given internal pressure must have a constant thickness e for a given number n, which corresponds to intermediate pressures in exponential progression.

Example 2
This example is intended to demonstrate that in the hypotheses considered above, it is possible according to the invention to exceed an internal pressure of 43.33 daN / mm 2, that is to say the limit of Kat in the case of an alloy steel for which 130 daN / mm2.

Indeed, if we take, for example, pi = 6000 bars, in the case of a single speaker, we would have

 We immediately see that this problem has no solution using only one speaker, since the denominator under the square root is negative.

By cons, if we consider the same example for a speaker consisting of two intermediate speakers A and B nested one inside the other with a minimum play, we have the same calculations above
For the first speaker A b = a pi + k # t - a 60 + 43.33 to 103.33
k # t - pi + 2pe = a 43.33 - 60 + 49.42 = a 32.75
therefore b = 1.78 a = 534 mm
the minimum thickness of the first enclosure is equal to 234 mm.

For the second enclosure B c2 b kat + pe = (1.78a) 2 X 43.33 + 24.71 = (1.68a) 2 X 68.04 kat = pe 43.33 - 24.71 - 18.62 therefore c = 1.91 b = 1.91 x 1.78a = 1020.78 mm.

 the minimum thickness of the second enclosure is therefore equal to 487 mm.

 We see that, in the case of a double enclosure, the problem has a solution corresponding to a minimum thickness of 720.78 mm for all two speakers.

Example 3
This example corresponds to the above example, in the case of a speaker consisting of three intermediate speakers A, B, C embossed into each other with a minimum clearance, as shown in Figure 3 annexed attached and respectively separated by fluids under pressures pel = 3530 bar and pe2 = 1624 bar.

 The inner and outer rays of these speakers are respectively equal to a, b, c and d.

We always put ourselves in the previous case,
2 for which k: 3, at = 130 daN / mm, a = 300, pi = 6000 bar.

For the first speaker, the equalities mentioned above become
2 2 + kat 2 60 + 43.33 2 103.33 k # t - pi + 2pe to 43.33 - 60 + 70.6 to 53.93
b = 1.38 a = 414 the minimum thickness of the first enclosure is therefore 114 mm.

For the second speaker:
c2 = b2 pel + Kat + 2pe2 = b2 35.3 +43.33 + 43.33 = b2 78.63
t - 35.30 40.51
therefore c = 1.39 b = 1.39 x 1.38a = 576 mm the minimum thickness of the second enclosure is therefore 162 mm.

For the third speaker
d2 2 pe2 + kat 2 16,24 + 43,33 2 o2 X
= = c ka - pe2 - 43.33
t-pe2 43.33 16.24 27.09
therefore, d = 1.48 - c = 576 x 1.48 = & 2.48 mm the minimum thickness of the third enclosure is therefore 276 mm.

 Thus, in this case the total minimum thickness of all three enclosures is equal to 552.48 mm, therefore less than 720.78 mm found in the case of an enclosure consisting of two secondary enclosures embossed one in the other.

 The above examples therefore show that it is technologically possible to manufacture enclosures meeting safety standards and capable of withstanding pressures equal to or even greater than the breaking strength of the chosen material.

In addition, the enclosure according to the invention makes it possible to achieve a saving in mass of the material used, and at the same time a very clear saving in manufacture, since if the first enclosure must necessarily be made of a very expensive material, the other enclosures can be in, more common materials, and this at all pressures
Similarly, this chamber gives particularly satisfactory results from the point of view of corrosion, the first chamber may be made of a stainless material, for example, and the others made of a current material with a protective liquid under pressure.

 Similarly, it should be noted that if the first internal enclosure must be subject to safety regulations, the others do not necessarily have to respond to it, if they are filled with liquid without gas or saturating vapor.

 Such a chamber can also be defined for lower pressures to gain weight and reduce the cost.

SCHEME 1

SCHEME 2

SCHEME 3

Claims (4)

R E V E N D I C A T IO N S  10) High pressure chamber designed to withstand high internal pressures, characterized in that it consists of a plurality of intermediate enclosures nested within each other and separated by gaps filled by intermediate fluids subjected to intermediate pressures between the internal pressure and the external pressure, the intermediate pressures decreasing from the inside to the outside of the enclosure.  20) Enclosure according to claim 1, characterized in that it consists of two intermediate metal enclosures separated by a small gap occupied by an intermediate fluid.  30) Enclosure according to any one of claims 1 and 2, characterized in that the inner chamber is a high-performance steel, for example a martensitic stainless steel, while the outer enclosure is a more common material.  40) Enclosure according to any one of claims 1 to 3, characterized in that the or the outer enclosure (s) are autofrittées (s).