US3410447A

US3410447A - Pressure vessel closures

Info

Publication number: US3410447A
Application number: US594714A
Authority: US
Inventors: Mcfarland John
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1965-11-18
Filing date: 1966-11-16
Publication date: 1968-11-12
Anticipated expiration: 1985-11-12
Also published as: DE1525685A1; GB1159292A

Description

Nov. 12, 19 68 J. M FARLAND 3,410,447

PRESSURE VESSEL CLOSURES Filed Nov. 16, 1966 2 Sheets-She et 1 Inventor A llorney;

Nov. 12, 1968 J. MCFARLAND 3,410,447

PRESSURE VESSEL CLOSURES Inventor 627w 1%! haze/Va waziz azam A ltornem United States Patent Office 3,410,447 PRESSURE VESSEL CLOSURES John McFarland, Norton-on-Tees, England, assignor to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain Filed Nov. 16, 1966, Ser. No. 594,714 Claims priority, application Great Britain, Nov. 18, 1965, 49,083/ 65 9 Claims. (Cl. 220-25) ABSTRACT OF THE DISCLOSURE A pressure vessel including an inwardly dished cover and, in the vessel mouth, a sealing face of smaller diameter than the cover, the cover being distortable elastically to permit insertion into the vessel mouth, is disclosed. Alternatively the closure includes a cover held in position by a retaining ring securable to the vessel shell and preferably a seal formed between the cover and both the vessel mouth and the retaining ring.

This invention relates to pressure vessel closures which, by the use of principles of construction not previously applied to such closures, are much lighter than closures at present in use.

The design of closures for pressure vessels produces serious problems, one in particular being, how to provide for a closure of a wide enough bore to allow the installation and maintenance of catalyst beds and baskets, heat exchangers and other internal equipment. Covers such as flat plates, whose strength depends on resistance to bending stresses, have been commonly used but have the disadvantage of excessive weight.

We have now realised that a more satisfactory solution to this problem can be attained if the closure presents a convex face to the pressure in the vessel. Although our solution appears to waste some of the volume of the vessel we have realised that the expense of having the somewhat larger vessel is outweighed by the lighter construction of the cover which we are able to use.

According to one aspect of the invention there is provided a pressure vessel closure including a substantially spherically dished cover presenting its convex side to the inside of the vessel, and a sealing face in the vessel mouth of smaller diameter than the cover, the cover being distortable elastically to give it an elliptical circumference whose lesser diameter is small enough to permit insertion into the vessel mouth.

Substantially spherical is intended to mean in the shape of a section of a sphere or of an oblate or prolate spheroid suitably having an axial ratio not greater than 30% different from unity. The section of the sphere of spheroid is preferably at least 0.4 of its total volume, that is, the dished cover when undistorted subtends in a diametral plane an angle of at least 144. Preferably, the angle is between 170 and 180. It can if desired be more than 0.5 of the volume, but there is normally nothing to be gained by this, unless it is desirable to have spare metal to make possible later re-machining.

In order to elfect the elastic distortion of the cover there is preferably provided means for example a screw jack or hydraulic jack mounted diametrically in the concave side of the cover. The cover can be provided with projections for the purpose of applying such means, for example a portable jack.

According to the invention in its second aspect there is provided a pressure vessel closure including a substantially spherically dished cover presenting its convex side to the inside of the vessel, the cover being of a peripheral diameter about equal to the diameter of the mouth 3,410,447 Patented Nov. 12, 1968 of the vessel and being held in position by a retaining ring securable to the vessel shell.

For the substantially spherically dished cover to be used in the closure according to this aspect of the invention the section of the sphere or spheroid is preferably bet-ween 11% and 42% of its total volume. In other words the angle subtended on a diametral plane by the cover is preferably between 40 and The required thickness of the cover is less, for a given pressure load, the greater the subtended angle.

In this closure a seal is preferably formed between the cover and both the vessel mouth and retaining ring. By this means the pressure load is balanced by two forces, namely the resistance of the vessel mouth to radial expansion and the resistance to shear of the retaining ring securing means.

Closure covers for this aspect of the invention are preferably shaped so that the application of pressure in the vessel has the effect of tending to distort them nearer the shape of a section of a sphere.

Since closure covers according to either aspect of the invention are lighter than those of previously proposed closures it is convenient and economic to make them of corrosion resistant metals and alloys. This enables the full advantage of the invention to be obtained, since it is then unnecessary to provide extra thickness to allow for corrosion.

The closure can be a full-bore closure or smaller. Sealing rings of types well known to designers can be used if desired.

One preferred form of the invention in its first aspect is shown in FIGURES 1 and 2 of the accompanying drawings. FIGURE 1 shows in section the closed end of a pressure vessel with the cover in place and FIGURE 2 shows the detail of the sealing face. The shell 10 of the pressure vessel is flared at 12 and inwardly flanged at 14 to form a seating for the cover 16. When the vessel is at pressure the cover 16 is forced into contact with the seating, but at other times it is desirable to employ holding clamps of which one is shown at 18.

In order to apply or remove the cover a jack is set up diametrically across the cover and operated to widen or narrow the cover. Whether narrowing or widening is adopted, the result is a narrowing in one direction, so that the cover can be passed through the opening.

The cover is of true spherical form when under zero pressure: that is, when pressure is applied, edge bending moments are produced and must be allowed for in calculating the maximum principal stresses in the cover.

A preferred form of the invention in its second aspect is shown in FIGURE 3 of the accompanying drawings, which figure also shows in section the closed end of a pressure vessel with the cover in place. The shell 20 of the pressure vessel is thickened at 22 to carry the securing studs 24 for the retaining ring 26. The cover 28 forms a seal with the retaining ring at 30 and with the pressure vessel mouth at the slightly bevelled face 32. When the vessel is at pressure the load tends to lift the cover 28 and to flatten it against the retaining ring 26. The flattening is opposed by the resistance to radial enlargement of the vessel mouth and the retaining ring.

In assembling the closure the cover 28 is placed loosely in position. Before application of the retaining ring 26, the cover 28 projects slightly all round the mouth of the vessel. The retaining ring 26 is then applied and secured by tightening the studs 24, thus forcing the cover 28 into the sealing position as shown. Edge bending mornents exist when the cover is under zero internal pres sure, but the cover is so designed that at a designated pressure the shape becomes purely spherical and bending stresses are reduced to zero.

3 A The following table shows how great a saving in cover 6. A pressure vessel closure including a substantially weight results from using pressure vessel closures accordspherically dished cover presenting its convex side to the ing to the invention, the covers being made of 1% Cr/ inside of the vessel, the cover being of a peripheral diam- Mo pressure vessel steel. eter about equal to the diameter of the mouth of the ves- TABLE Flat Plate This invention This invention Pressure, Diameter, (Bridgman Type Joint) FIGS. 1, 2 FIG. 3

p.s.i.g. inches Thickness, Weight, Thick- Weight; Thick- Weight inches lbs. ness ness 1, 000 22 2. 25 1 229 0. 25 5s. 9 0. 25 27 5, 050 60 13. 6 11, 000 Not practical 3. 5 3, 500

I Commonly such covers are made much heavier than this, for example 1,200 lbs.

I claim: sel and being held in position by a retaining ring secur- 1. A pressure vessel closure including a substantially able to the vessel shell outside of said vessel. spherically dished cover presenting its convex side to the 7. A pressure vessel closure according to claim 6 in inside of the vessel, and a sealing face in the vessel mouth which the spherically dished cover is a section of a sphere of smaller diameter than the cover, the cover being disor spheroid and contains between 11% and 42% of the tortable elastically to give it an elliptical circumference volume of that sphere or spheroid. whose lesser diameter is small enough to permit inser- 8. A pressure vessel closure according to claim 6 in tion into the vessel mouth. which a seal is formed between the cover and both the 2. A pressure vessel closure according to claim 1 in vessel mouth and the retaining ring. which the dished cover when undistorted subtends in a 9. A pressure vessel closure according to claim 6 in diametral plane an angle of at least 144. which the cover is made of a corrosion resistant metal or 3. A pressure vessel closure according to claim 2 in alloy. which the angle is between 170 and 180. References Cited 4. A pressure vessel closure according to claim 1 in UNITED STATES PATENTS which in order to effect elastic distortion the cover is provided with jack means mounted diametrically on its 1922 6/1877 Kemper 22O 25 concave side to narrow said cover, or with projections FOREIGN PATENTS for the purpose of applying such means. 324,526 10/1929 Great Britain 5. A pressure vessel closure according to claim 1 in Xihgfh the cover is made of a corrosion-resistant metal or JAMES M ARBERT Primary Exammen