US3315836A - Pressure vessel closure - Google Patents

Description

April 25, G. BOON PRESSURE VESS EL CLOSURE Filed Jan.. 4, 1965 INVENTOR. GEORGE B. BOON BY 24 p z ATTORNEY United States Patent 3,315,836 PRESSURE VESSEL CLOSURE George B. Boon, Webster Groves, Mo., assignor to Monsanto Company, St. Louis, M0., a corporation of Delaware Filed Jan. 4, 1965, Ser. No. 423,049

3 Claims. ((31. 220-46) This invention relates to pressure vessels and to systems of the quick-opening type for closing and sealing vessels adapted to contain a medium which is subjected to high pressure and/or high temperature. Such pressure vessels are useful as boilers, heat exchngers and autoclaves in which chemical reactions take place under high pressure and temperature conditions.

In the past the closure systems for such vessels have not always been capable of providing satisfactory operation when subjected to the pressure and temperatures which have been desired. With large vessels, there have also been problems in the opening and closing of the vessels, particularly with respect to the sticking or jamming of the threaded elements of the closure. The placement, securernent and removal of such closure systems have been complex and have required an undue amount of manipulation which has resulted in protracted delays in changing over from the open and closed positions.

Many operations also require the frequent removal of the closure head, for example to permit charging the vessel with raw material or to remove the products. In order to provide for quick opening and closing with full access of such vessels, particularly in the larger sizes, a continuously threaded closure system is not practical, so that the prior art has employed bayonet and multiple-lug closures. However it has been found that these prior art systems, all of which permit only a small amount of closure movement suffer from jamming because of the so-called gasket reaction. The mechanism of such action is observed when the securing ring of the bayonet or lug closure is moved from the closed to the open position when the vessel is being opened. It is at this time that the gasket, upon being freed from the imposed pressure, reacts or springs back to its normal position. Such springing back, has been found to lock the closure head against the securing ring so that the entire assembly becomes jammed. It is therefore necessary to apply considerable force such as by means of levers, air hammers and the like to free the elements of the closure with the obvious danger of Warping or bending the individual parts.

Particularly diflicult problems have also been encountered in horizontally disposed vessels such as autoclaves and heat exchangers since the previously known gaskets and closure head assemblies have been difficult to align during the assembly of the closure elements.

The principal object of the present invention is to provide a novel sealing closure for a high pressure vessel which includes a planar deformable floating head used in combination with a restraining'head to permit quick and easy opening and closing of the closure assembly without sticking or jamming.

Another object is to provide such a closure in which a planar internal floating head coacts with a bearing ring, and with an outer restraining head to permit unitary movement and positioning of such heads. Horizontally situated pressure vessels have in the past been diflicult to open and close, requiring the use of cranes or hinge systems to permit swinging the closure door into place. The present invention provides a combination system for the placement of the internal floating head together with the outer restraining head. However this unitary system is also useful with vertical vessels when it is desired to handle the head system as a single unit.

For a better understanding of the invention, reference is made to the following detailed description of a representative embodiment as shown in the accompanying drawings, not drawn to scale, wherein FIGURE 1 is a side elevation in cross-section of one embodiment of the invention, while FIGURE 2 is an enlarged view of a portion ofFIGURE 1.

In FIGURE 1 the reference numeral 10 designates a pressure vessel having an outlet 11 which contains a medium (not shown) at high pressure and/or at high temper ature. The vessel 10 may be either horizontally or vertically disposed. Vessel 10 terminates as an axially extending unthreaded round mouth 12 of circular or elliptical shape. The mouth 12 is radially enlarged at its outlet, 11 to provide an internal annular shoulder surface 13 which is normal to the axis of the vessel. Seated on this shoulder surface is an annular elastic gasket 14 made of a metal such as copper, aluminum, a mild steel, stainless steel, Monel metal, etc.

The upper end of the outlet 11 is closed off by an unthreaded floating disc or head 20 which is received in the'mouth 12 and has a loose fit therein. The head 20 which is substantially planar, has the approximate rounded shape of the opening, e.g., a circular head for a circular opening, or an elliptical head for an elliptical opening. The head 20 is made of a ductile, high yieldstrength metal such as a low alloy steel for example the T-l type. The peripheral portion of the floating head 20 constitutes an axially extending lip or head as an annular edge, 21 shown in FIGURE 1, and in greater detail in FIGURE 2. Contacting of the planar ring or head 20 to provide a pressure seat occurs against the annular shoulder 13, specifically against the gasket 14.

The present invention makes use of a substantially flat inner disc or head which is not sealed to an outer or restraining head. The inner head which may be consid ered to be floating at the pressure vessel closure is easily fabricated from sheet or plate stock for example a high yield strength steel such as type T-1 steel. In a preferred embodiment of the invention, as shown in FIG- URES 1 and 2 the thin inner disc has an annular ridge at its circumference seating against the shoulder of the vessel, or preferably against a gasket on the shoulder at the mouth of the vessel or autoclave. The annular ridge or lip is readily fabricated on the disc by conventional techniques such as by Welding a bead, for example, using a hard facing metal or alloy such as a Stellite around the the edge of the disc. The welded deposit is then ground to a rounded seating surface.

The essential elements of the present closure or vessel assembly, in addition to the inner disc and the outer restraining head also include a bearing ring 70 to equalize the sealing pressure on the disc. The bearing ring may be fabricated from a suitable forging steel such as ASME SA182F1 or a forging stainless steel ASME SA182 F364. The bearing ring is chamfered, 71, at the inner circumferential edge so that the imposition of an interior pressure causes the disc to bow out against the concavity of the head, and with the circumferential edge of the disc tangentially aligning itself with the overall concavity because of the chamfering of the bearing ring. The chamfer may be produced on a simple ring by a grinding or milling operation so as to obtain either a substantially straight or slightly curved across section of the chamfer edge when viewed as a radial cross section of the entire bearing ring. It is important that the machining of the chamfer yield a continuously aligned edge relative to the concavity of theouter fixed head so that the imposition of an inner pressure within the said pressure vessel causes a substantially continuous bowing outward of the said planar disc against the concavity of the said outer restraining head and the said chamfer surface.

The bearing ring is also provided with a plurality of bolt holes 72 so that the bearing ring can be actuated as a unit with the restraining head. This is accomplished by a set of bolts or studs 30, with nuts, 31, springs 32 and washers 33. The bolts pass through the restraining head, and are threaded into the holes of the bearing ring to permit the securing together of' these two elements.

In order to provide a unitary assembly of the inner disc or floating head 20 with the aforesaid restraining head 4%, as well as the bearing ring 70, a set of lugs 22 extends radially from the said disc. These lugs permit screwing the disc to the bearing ring by means of screws 23. In this way the entire closure assembly can be lifted by a crane, or swung on hinges for positioning at the autoclave opening, either as a horizontal or vertical pressure vessel.

The rigid portion of the head assembly includes restraining head 4% which cooperates with the floating head or disc 20. The combination of floating head 26 and restraining head 40 are shown in FIGURE 1 as concave relative to the outlet 11. The concave inner surface can have various forms of concavity such as elliptical, parabolic or spherical. The radius of curvature of the concave surface of the restraining head has been found to be preferably maintained in the range such that the radius of curvature varies from to 100 times the diameter of the mouth of the vessel e.g., R=(5 to 100)D in FIGURE 1. For example with a round mouth opening of 26 inches, the radius of curvature is 240 inches in a specific example. It is in this range of proportions that the optimum flexing of the internal floating head or disc occurs when pressure is applied, and also permits elastic recovery after the pressure has been released. Thus the planar disc returns to a substantially flat condition after the release of the autoclave pressure.

The combination head of the present invention solves a difficult problem of unequal temperature distribution with resultant deformations in the metal parts. For example, the use of a 26 inch diameter, and 25 ft. length horizontal body autoclave which is kept hot between runs, and then is charged With a cold feed stock has been found to result in substantial temperature differences in the mouth or hub of the vessel. These temperature differences and the resultant deformation of the metal previously caused pressure leakage. However, the separate movement possible with the present floating head permits accommodation to such thermal deformations since the thinner floating head easily deforms to accommodate the deformations present in the mouth or hub of the vessel. This result cannot be obtained with integrally clad heads based upon a unitary layer of thin metal fastened to a heavier base metal, such as in conventional welded or rolled clad materials.

When the two heads 2% and 40 of FIGURE 1 are to be handled as a unit, a plurality of studs 30 hold such elements together for positioning during removal and securing operations with the stud 30 being held in place by nut 31, spring 32, and washer 33.

The head assembly is held in place relative to the body 1th by means of a circular or elliptical ring which may be split for ease of removal. In FIGURE 1, showing a circular head, a rotatable ring 50 engages lugs 41 on the restraining head 4%. When the vessel is being closed for pressure operations, rotatable ring 50 having interrupted lugs 52 cooperating with lugs 41 of the restraining head permit the approximate positioning of the head assembly consisting of the floating head 20 and restraining head 40 with ring 7%. Closure is then completed by tightening jack screws 42 which bear against the bearing ring, 70 so that a tight seal is made against gasket 14. Guides 60 provided with balls 61 aid in the movement of the bayonet closure assembly.

A sleeve bearing 53 of suitable anti-galling properties such as bronze or an impregnated porous bearing material is also desirable to aid in rotating ring 50 during the opening or closing operations.

The present invention provides a quick opening type closure which overcomes the difficulties encountered in prior art devices which were subject to sticking of the closure system as a result of the gasket reaction occurring after the release of pressure in the vessel. The present combination head system provides for greater movement of the head assembly, thus preventing the sticking difficulties described above.

The combination head assembly provides for a gap between the restraining head and the floating head before the jack screws are advanced to yield the gasket and provide a tight joint. When pressure is applied to the vessel, the elastic floating head then deforms by adopting a radius of curvature to conform to the spherical surface of the restraining head.

Upon the release of pressure in the vessel, the jack screws are retracted, which allows the spring loaded studs to lift the floating head from the gasket.

The combination head system also makes it possible to provide corrosion resistant materials at low cost for the interior of the vessel while providing a high strength rigid head against which the inner, corrosion resistant head flexes. In general the minimum thickness of the restraining head is at least 5 times that of the floating head, a preferred ratio being from 5 to times as thick. In this way it is also practical to provide an interior material of high elasticity in order to yield with pressure by accommodating itself to the precise shape of the rigid outer head. In this way a gasket may be dispensed with, by basing the yieldable sealing upon the elasticity of the inner head. However the invention also contemplates the use of a gasket made of an elastic material such as copper, soft steel, or stainless steel.

In horizontal vessels it is advantageous to mount the combination heads as a single unit. This is readily accomplished by providing a series of threaded bolt holes in the bearing ring. The floating disc is then screwed to the bearing ring. Screws or preferably studs are mounted through the larger holes of the head and threaded into the holes of the bearing ring. The studs may then be secured with nuts, or preferably with springs together with the nuts in order to control the tension. The combination assembly, thus screwed together is then readily handled as a unit by means of a crane or hinge to be swung directly in place upon the mouth of the vessel.

In assembly systems described above, the final closure of the head assembly is accomplished by tightening jack screws which are threaded through the outer rigid head, while the rigid head is secured against the vessel by the securing ring or a bayonet lock system. The jack screws then bear down upon the bearing ring. When the floating head or disc is used without a gasket, this head yields against the shoulder at the mouth of the vessel to achieve a leak proof joint. When a gasket is employed, the tightening of the floating head against the shoulder at the mouth of the vessel results in the yielding of the gasket, effecting a leak proof joint.

When pressure is generated or applied within the autoclave, the thin inner disc expands outward to a position concave relative to the autoclave interior. Thus the initially flat (or minutely convex because of its own weight) inner head or disc assumes a concave form upon application of pressure. Consequently, the disc assumes the concave surface of the outer head as well as the tangential chamfer of the bearing ring. The chamfer may be cut as a straight section when viewed as a cross section of the bearing ring, or may be ground as a substantially circular section continuing in alignment with the circular concavity of the restraining head. In this way the expansion stresses caused by the application of pressure and heat to the inner head or disc are freely transmitted to the outer head without substantial movement at the gasket. Such movement as does occur is consequently a simple rocking around the lip 21 of disc 20 Without incurring any sharp edges or dangerous expansion stresses.

In order to illustrate the improvement brought about by the present apparatus, relative to the use of a square edged ring, e.g. corresponding in position to the actually chamfered edge 71, the following conditions are representative of the imposition of a 10,000 lb. per square inch pressure in a vessel having an internal diameter of 26 inches when using a inch thick disc. In this example the concavity of the restraining head amounts to 0.36 inch. Under these conditions the stress at a sharp edge at the internal corner of the bearing ring amounts to 75,000 lbs. per square inch. In contradistinction the improved apparatus of FIGURE 2 with a 240 inch radius concavity of the restraining head, aligning with the chamfer e.g. with a straight line chamfer height of inch, has only a 30,000 p.s.i. bending stress under the same pressure conditions.

What is claimed is:

1. A pressure vessel comprising a pressure chamber having a rounded opening, a radially enlarged shoulder at the said opening, a planar seating surface on the said shoulder, a normally planar inner seating disc, an outer restraining head having the inner face thereof concave relative to the interior of the said pressure vessel, fastening means on the said outer restraining head, a bearing ring located between the said outer restraining head and the said planar disc, the said bearing ring having an inner circumferential chamfer on the face thereof which contacts the said disc whereby the imposition of an inner pressure within the said pressure vessel causes a bowing outward of the said planar disc against the concavity of the said outer restraining head and against the chamfer of the bearing ring.

2. A pressure vessel comprising a pressure chamber having a circular opening, a radially enlarged shoulder at the said opening, a planar seating surface on the said shoulder, a gasket on the said planar seating surface, a normally planar inner seating disc having a circumferential lip on the inner face thereof bearing against the said planar seating surface, an outer restraining head having the inner face thereof spherically concave relative to the interior of the said pressure vessel, fastening means on the said outer restraining head, a bearing ring located between the said outer restraining head and the said planar disc to equalize pressure on the said planar disc, the said bearing ring having an inner circumferential chamfer on the face thereof which contacts the said disc to the extent that the chamfer is aligned tangentially with the spherical concavity of the said restraining head whereby the imposition of an inner pressure within the said pressure vessel causes a bowing outward of the said planar disc against the concavity of the said outer restraining head and against the tangential chamfer of the bearing ring.

3. A pressure vessel closure having a rounded opening, comprising a radially enlarged shoulder at the said rounded opening, a planar seating surface on the said shoulder, a normally planar inner seating disc, an outer restraining head having the inner face thereof concave relative to the interior of the said closure, fastening means on the said outer restraining head, a bearing ring located between the said outer restraining head and the said planar disc to equalize pressure on the said planar disc, the said bearing ring having an inner circumferential chamfer on the face thereof which cont-acts the said disc, whereby the imposition of an inner pressure causes a bowing outward of the said planar disc against the concavity of the said outer restraining head and against the chamfer of the bearing ring.

No references cited.

THERON E. CONDON, Primary Examiner. G. T. HALL, Assistant Examiner.

Claims (1)

1. A PRESSURE VESSEL COMPRISING A PRESSURE CHAMBER HAVING A ROUNDED OPENING, A RADIALLY ENLARGED SHOULDER AT THE SAID OPENING, A PLANAR SEATING SURFACE ON THE SAID SHOULDER, A NORMALLY PLANAR INNER SEATING DISC, AN OUTER RESTRAINING HEAD HAVING THE INNER FACE THEREOF CONCAVE RELATIVE TO THE INTERIOR OF THE SAID PRESSURE VESSEL, FASTENING MEANS ON THE SAID OUTER RESTRAINING HEAD, A BEARING RING LOCATED BETWEEN THE SAID OUTER RESTRAINING HEAD AND THE SAID PLANAR DISC, THE SAID BEARING RING HAVING AN INNER CIRCUMFERENTIAL CHAMFER ON THE FACE THEREOF WHICH CONTACTS THE SAID DISC WHEREBY THE IMPOSITION OF AN INNER PRESSURE WITHIN THE SAID PRESSURE VESSEL CAUSES A BOWING OUTWARD OF THE SAID PLANAR DISC AGAINST THE CONCAVITY OF THE SAID OUTER RESTRAINING HEAD AND AGAINST THE CHAMFER OF THE BEARING RING.

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