US3514009A

US3514009A - Pressure vessel assembly including a welded lid

Info

Publication number: US3514009A
Authority: US
Inventors: Robert B Emery; Gail F Davis
Original assignee: Halliburton Co
Current assignee: Halliburton Co
Priority date: 1968-11-19
Filing date: 1968-11-19
Publication date: 1970-05-26
Anticipated expiration: 1987-05-26

Description

May 26, 1970 R. B. EMERY ETAL 4 PRESSURE VESSEL ASSEMBLY INCLUDING A WELDED LID Filed NOV. 19, 1968 INVENTORS ROBERT B. EMERY GAIL F. DAVIS Wm H ATTORNEYS United States Patent 3,514,009 PRESSURE VESSEL ASSEMBLY INCLUDING A WELDED LID Robert B. Emery and Gail F. Davis, Duncan, Okla., assignors to Halliburton Company, Duncan, Ok]a., a corporation of Delaware Filed Nov. 19, 1968, Ser. No. 777,129 Int. Cl. B65d 43/16, 51/10 U.S. Cl. 220--32 16 Claims ABSTRACT OF THE DISCLOSURE A pressure vessel assembly including a vessel body, a pivotally mounted lid, and cam lid fasteners. The lid is an integral ductile steel member formed of a relatively thin, lightweight, dished head portion having a substantially circular edge that is welded in line contact with an internal substantially cylindrical surface of a thicker flange portion adjacent the upper part thereof. The flange is provided with a plurality of generally U-shaped fastening lugs circumferentially spaced about its outer periphery. Each fastening lugs is adapted to receive a longitudinal shaft member mounted on the periphery of the vessel body. Eccentric cams pivotally associated with each shaft are operable against spring biased plates to hold the lid in latched position.

BACKGROUND OF THE INVENTION This invention relates to pressure vessel assemblies. In particular, this invention relates to a pressure vessel assembly including a ductile steel welded cover, comprising a dished head and an annular flange. This cover is adapted to be pivotally mounted on a vessel body and latched in closed position by the cam fastener assemblies.

In the use of pressure vessels such as those adapted to store and pneumatically discharge bulk dry, granular cement or sand, it has been common for many years to provide a vessel cover or lid having a dome shaped head and an outer annular flange adapted to sealingly engage the upper surface at the open end of the vessel body.

The necessity for maintaining a substantially leakproof closure between the lid and the vessel body requires that a positive pressure fastening assembly be employed to hold the lid in sealing engagement with the vessel body. However, since recurring access to the vessel may be useful for the purpose of inspection, or in order to service an aerating media that may be used to fluidize bulk products, it has become common to pivotally mount the lid on the vessel body and to provide a releasable fastening assembly.

The moving parts of the fastening assembly may be normally conveniently attached to the vessel body. Therefore, it is often desirable to provide fastening lugs on the lid which lugs may receive parts of the fastening assembly and cooperate therewith to obtain the positive closure.

At least one prior pressure vessel of this type comprises a pivotable cast iron lid having a dished head and an annular flange provided with a plurality of circumferentially spaced, generally U-shaped fastening lugs on the outer periphery. When the lid is pivoted to a closed position, each lug receives a longitudinally extending shaft mounted on the vessel body periphery.

In the known prior device, a spring biased plate slidably mounted on the shaft is forced into engagement with the lid by means of an eccentric locking cam.

Although prior pressure vessel lids of the type described are often adequate, they are susceptible of improvement. For example, it is highly desirable to obtain a lid with a lightweight, thin dished head center section, and a rigid, substantially thicker outer section.

This construction partakes of the advantage of light Weight, which may provide convenience and safety for an operator who must open and close the vessels, while retaining strength at the points where pressure failure is most likely to occur. However, such lightweight units are not readily obtainable in cast iron construction due to problems that would be encountered in both casting an adequately strong, thin head section and in providing for cross-sectional changes between the head and the flange. As a result, cast iron covers of adequate strength are heavy and somewhat cumbersome.

The present invention is intended, in part, to surmount these difficulties by employing a pressure vessel lid wherein a thin dished head is welded to a thicker flange.

The formation of a pressure vessel lid by welding a dished head to a relatively thicker flange has been proposed, in the past, in connection with a pressure vessel cover that is bolted to the vessel rather than held in sealing engagement by releasable cam locking assemblies. Although such a lid may be adequate, insofar as it provides a desirable change of cross section between the head and the flange, it may not be entirely satisfactory from the standpoint of pressure distribution on the lid, or from the standpoint of ease of fabrication.

In this earlier welded lid, the weld between the flange and head is accomplished with the radially outermost circumferential portion of the head presenting a surface, usually frustoconical, to be joined to a similar frustoconical surface on the flange. With this arrangement, a variation from nominal dimensions of either surface, may result in a substantial increase in the number of possible planes that could be defined by contact between the flange and head.

All such contact planes in which the central axes of symmetry of the head and flange are not in absolute longitudinal alignment, result in a canted head that is subject to unequal pressure distribution. Such distribution may substantially contribute to unexpected failure of the pressure vessel, possibly having disastrous consequences.

It would, therefore, be highly desirable not only to construct a lid that provides a thin head and a thicker flange, but also to insure that the head and flange meet in line contact so as to minimize the possibility of incorrect contact planes. 7

Another disadvantage of the previously described pivotable cast iron structure which includes the U-shaped fastening lugs, resides in the fact that a great deal of lug breakage may be experienced. If the cover is dropped during transport, or subjected to impact loading during vessel closure, the cast iron lugs may be subject to brittle failure, thereby preventing completely successful operation of the fastening assembly, and establishing cracks that may propagate and render the lid unsuitable or dangerous for use in a pressure vessel.

It would, therefore, be desirable to provide a pressure vessel lid with a ductile flange to minimize the possibility of lug breakage.

SUMMARY OF THE INVENTION It is, therefore, a general object of the invention to pro-' vide the pressure vessel assembly, of the type that includes a dished head and an annular flange, intended to obviate or minimize disadvantages of the sort previously noted.

It is a particular object of the invention to provide a pressure vessel cover wherein a dished head is welded to an annular flange in such a manner as to minimize the pos sibility of unequal pressure distribution on the cover.

It is an other object of the invention to provide a pressure vessel cover with a dished head welded in line contact to an annular flange to facilitate assembly and to eliminate uneven alignment.

It is still another object of the invention to provide a ductile pressure vessel lid for use with a cam latching assembly that will minimize the possibility of breakage of the lid fastening lugs.

It is a further object of the invention to provide a method of making a welded pressure vessel lid that substantially minimizes the possibility of unequal pressure distribution on the lid.

It is a still further object to provide an improved pressure vessel assembly having eccentric cam locking assemblies that cooperate with a pivotable pressure vessel lid.

DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the invention intended to accomplish at least some of the foregoing objects comprises a pressure vessel lid adapted to be pivotally connected to a vessel body and to sealingly engage the surface at the open end thereof, while cooperating with a plurality of cam latching mechanisms.

The pressure lid includes a spherically dished cap or head portion having a substantially circular edge at the radially outermost portion thereof.

An annular flange is provided with an internal cylindrical surface having a diameter substantially equal to that of the circular edge on the dished cap, and the dome cap is integrally welded to the flange portion with its circular edge in line contact with the internal surface in order to minimize the possibility of canting of the cap that may result in an unequal pressure distribution on the lid.

Circumferentially spaced about the radially outermost portion of the flange, are a plurality of generally U-shaped fastening lugs adapted to cooperate with a cam locking assembly.

The cam assembly includes a stem or rod pivotally mounted, on a protrusion fastened to the body of the pressure vessel, for motion toward and away from the upper end thereof. When the lid is in closed position, the rod is receivable between the legs of the fastening lugs. An eccentric cam rotatably mounted on the upper end of the rod operates against a spring biased plate, to force the plate into engagement with the lugs and the upper, integral and substantially contiguous surface of the flange member.

Another aspect of the invention relates to the positioning of the dished head within the annular flange adjacent the upper end of the internal surface of the annular flange, thereby reducing the possibility of accumulating moisture on the external portion of the welded joint.

THE DRAWINGS The pressure vessel assembly constructed in accordance with the preferred embodiment of the invention is illustrated in the accompanying drawings in which:

FIG. 1 is a top view of a pressure vessel lid and cam latching assembly of the present invention;

FIG. 2 is a side view of a pressure vessel lid shown in FIG. 1 with the pressure vessel shown in phantom;

FIG. 3 is a partially broken away cross-sectional view of portions of the pressure vessel lid and cam latching assembly shown in FIG. 1 taken along line 3-3 therein;

FIG. 4 is a schematic cross-sectional view on an enlarged scale of the joint between the cap and flange portions of the pressure vessel lid shown in FIG. 1 taken along line 4-4 therein, and viewed as though the lid were oriented in generally vertical alignment; and

FIG. 4a is a cross-sectional view similar to FIG. 4, with the full penetration welds shown.

4 DETAILED DESCRIPTION General summary Referring to FIG. 3 of the drawings, a cross sectional view of a pressure vessel assembly according to a preferred embodiment of the invention is there shown.

The assembly includes a lid 2, having a dished cap portion 4 integrally secured to an outer annular flange 6. The lid 2 is pivotally mounted, as indicated at pivot means 8, on a vessel body 10. In its closed position, the lid 2 is held in sealing engagement with the outer surface 12 at the open end of the vessel body 10 by means of a plurality of cam latching assemblies 14.

A weldment 16 secures the cap or head portion 4 to the flange 6 while the head is in line contact with the flange portion to minimize the possibility of unequal pressure distribution on the lid 2 in a manner hereinafter more fully described.

Positioned in circumferentially spaced relation about the radially outer portion of the flange 6, and integral therewith, are a plurality of generally U-shaped, out- Wardly facing fastening lugs 18 (FIG. 1). These lugs 10 are adapted to receive portions of the cam latching assemblies 14 and latchingly cooperate therewith.

Each of the cam assemblies 14 is pivotally mounted on a support block 20. This block 20 extends radially outward from the outer circumferential surface 22 of the vessel body 10 at a longitudinal position spaced from the outer surface 12 at the open end of the body. In this way, the cam assemblies 14 may be swung away from the upper, outer surface 12 of the body to permit the lid to close, and then may be pivoted back into cooperating engagement with the fastening lugs 18 to effect a positive pressure sealed closure.

DETAILED STRUCTURE Cover structure The previously mentioned dished cap portion 4 and the outer annular flange 6 of the pressure vessel lid 2 are preferably constructed of ductile steel.

As illustrated, the cap 4 is in the form of a dome that is spherically dished so as to be symmetrical about a central axis indicated at 24. At the outer radial periphery 26 of the dome, the cap portion is slanted radially inwardly, as indicated at 28, thereby to define a substantially circular edge 29, of a first diameter d at the radially outermost part of the cap.

The outer annular flange 6, fabricated of plate-steel stock, is provided with an internal surface 30 that is substantially cylindrical and has a diameter d substantially equal to the diameter d of the previously described circular edge of the cap 4.

The domed head 4 is integrally secured to the flange 6, with the circular edge 29 of the head being substantially in line contact with the internal surface 30 of the flange, by means of the previously described weldment 16. Referring now to FIG. 4, first and

second bead portions

32 and 34 of the weldment 16 are shown as located on either side of the circular edge 29. The line contact between the head and flange is shown schematically as it would appear in the absence of penetration of the weld. However, in the preferred embodiment illustrated in FIG. 4a, a full penetration weld is employed. Therefore, it will be appreciated that the substantially cross-sectionally rectangular outer periphery 33 of the head, including the edge 29, and the adjacent, substantially cross-sectionally rectangular edge portion 35 of the flange will 'be obliterated by the

weldment bead portions

32 and 34 after the Welding operation. However, alignment is enhanced by the initial line contact.

The location of the

bead portions

32 and 34 on either side of the edge 29 results in a resistance to possible canting of the axis 24 of the head 4 with respect to the flange 6. The outer bead portion 32 overlies the edge 29 and extends over the adjacent surfaces of the head and flange to firmly resist forces tending to separate the two.

In the preferred and illustrated embodiment, the slanted surface 28 on the periphery of the head is inclined radially inwardly toward the pressure facing concave side 36 of the head to define a second circular edge 37. The inner bead 34 overlies the portion of the side 36 adjacent the edge 37 and seats in a triangularly cross-sectional pocket 38 located between the slanted surface 28 and the cylindrical surface 30. Thus, the rectangularly cross-sectional portion 33 of the cap adjacent the slanted surface 28 is completely encased by the weldment 16.

The head 4 and flange 6 are both rectangular in cross section and thus amenable to manufacture from platesteel stock. The rectangular shape allows for ease of manufacture for precise alignment purposes as opposed to the difliculty of fabricating alignment surfaces with compound curvatures.

Preferably, the line contact between the head and the flange is located at the longitudinally outermost position of the flange (with respect to the pressure vessel) so that the outer bead 32 will not rest in a deep depression that might be vulnerable to a large accumulation of water. The possibility of corrosion of the lid is thereby minimized.

The cross-sectional thickness t of the flange is sub stantially greater than the cross-sectional thickness t of the domed cap 4. In a lid constructed from ductile SA 515 Grade 70 steel for use at a working pressure of 50 p.s.i., and having a dish radius of about 18 inches and diameters d and d of approximately 18 inches, a minimum head thickness t as small as .0428 inch is permissible. With such a thin head, a substantial change in cross section between head and flange is necessary, and is readily obtained with the welded lid of this present invention.

Cover Seal An inwardly facing surface 40 (inward with respect to pressure from the vessel) of the flange 6 defines a plane generally perpendicular to the axis of symmetry 24 of the head 4. The surface 40 is adapted to mate with the upper,outer surface 12 of the pressure vessel in sealing engagement therewith. Adjacent the radially outermost portion of the flange 6, an annular groove 42 is provided in the surface 40 for receiving a sealing ring 44.

When the lid is in closed position, the sealing ring 44 engages the upper surface 46 of a vessel flange 48. The flange 48 is provided adjacent the open end of the vessel 10. Fastening of the flange to the outer surface 22 of the vessel, in circumferential engagement therewith, is accomplished by any suitable means, such as the weldment indicated at 50.

Cover Pivot and Handle As previously described, movement of the lid 2 with respect to the pressure vessel 10, between its open and sealed positions, occurs about the pivotal mounting indicated at 8.

The pivotal mounting 8 comprises a depending, generally U-shaped flange 52 that-is integrally secured to a generally flat outer peripheral surface 54 of the flange 6, preferably by means of a weldment 56. The U-lugs 58 of the pivot flange receive a pivot bolt 60 adapted to pass through spaced apertures 62 in a pair of spaced support arms 64 extending radially outward from the outer surface 22 of the pressure vessel 10. The support arms 64 may be attached, by welding or the like, to both the vessel and the previously mentioned flange 48, as indicated at 66.

At a point generally diametrically opposite, to the pivot mounting 8, the lid 2 is provided with a suitable handle 67 which may be conveniently attached thereto, between adjacent fastening lugs 18.

Cover Latches As previously mentioned, each of the fastening lugs 18 is adapted to receive parts of the cam fastening assembly 14. Each fastening assembly 14 includes a stem or rod 68 that is pivotally secured to the cam fastening support block 20.

The support block 20 includes circumferentially spaced walls 69 that may be integrally attached, by welding or the like, to the outer surface 22 of the pressure vessel and the upper vessel flange 46.

The pivotal mounting between the cam fastener stem 68 and the block 20 is accomplished by mounting the rod 68 within radially extending slot 70 located in a rotatable bearing member 71. The rod-like bearing member 71 is rotatably mounted in circumferentially spaced but axially aligned apertures 72 in the block Walls 69. Member 71 is prevented from sliding out of the apertures 72 by means of suitable snap rings 73 mounted over the bearing member adjacent the block Walls 69.

The rod 68 is preferably tightly, i.e. immovably fit in the slot 70 and the bearing 71 is preferably snugly but rotatably fit in the apertures 72.

The bottom part of the stem 68 is threaded, as indicated at 74, for cooperation with a nut 76 to thereby provide for limited adjustable sliding movement of the rod with respect to the hearing. The spacing between walls of the block 20 permits unobstructed pivotal movement of the nut and the lower end of the rod upon rotation of the bearing 71.

Referring now to FIG. 3, the rod 68 is there shown pivoted to its latching position. The rod is received between opposite legs 77 (only one of which is shown) of the associated U-shaped fastening lug 18. Slidably mounted on the rod, is a fastening plate 78 that is spring biased to an upward position on the rod by means of a helical coil spring 80. This spring is operative between the plate 78 and an annular shoulder 82 formed on the rod 68. The positioning of the shoulder 82 on the rod is not critical; it being only necessary to locate the shoulder at a position on the rod which will be sufliciently beneath the uppermost surface 84 of the flange member 6 so that the plate will be normally biased to a position above that surface 84.

At the upper portion of the rod is a rotatable cam member 86 having circumferentially spaced, rotatable and generally circular cam surfaces 88 and 90. These cam surfaces are eccentrically secured to the rod for rotation about a generally cylindrical bearing 91 having a slot 93 that receives, in a tight fit, the upper end of the rod 68. Upon clockwise rotation of the cam member 86 toward the lid 2, viewing the cam as shown as in FIG. 3, the cam surfaces 88 and 90 are operative against the bias provided by the spring to move the slidable plate 78 downward along the rod 68, into engagement with the upper, generally flat surface 84 of theflange and the uppermost, generally flat portions of the associated legs 77 of locking lug 18.

The cam may be provided with a finger-like projection 92 having a nose portion 94 that is engageable with the upper surface 84 of the flange 6 or with the domed cap 4, depending upon the extent of the arm 92. In the illustrated embodiment, the nose 94 engages the surface 84.

It will be appreciated that with the slidable spring biased plate 78 so dimensioned as to engage the legs of a locking lug and the upper surface of the flange immediately adjacent thereto, a positive sealing engagement between the flange and the upper surface of the pressure vessel is thereby obtained. Since, as previously mentioned, the fastening lugs 18 are made from ductile steel, pressure exerted by the plate 78 on the legs of the lugs will not be likely to cause brittle fracture of the lugs. Also, the nut 76 provides a squeeze adjustment for the ring 44 and flange '6 by permitting downward movement of the rod in the bearing slot 70.

7 Method of making the pressure vessel lid The previously described pressure vessel lid 2 is readily constructed by spherically dishing a thin plate steel head section and providing it with a radially inward slanted citcumferential wall that defines a substantially circular edge of a given diameter at the radially outermost portion of the head. v p

An annular flange section having a thickness substantially greater than the thickness of the dished head: is then formed with a mating cylindrical diameter substantially equal to the diameter of the circular edge of the head.

The dished head may then be "centered within the annular flange maintaining the circular edge substantially in line contact with the internal surface. In the preferred method, the plane of contact is located at the uppermost portion of the flange.

The flange and head are then welded together forming beads above and below the line of contact along the circular edge of the head. In the preferred method, the welding between the flange and the head isaccomplis'hed by means of a submerged arc welding process.

SUMMARY OF ADVANTAGES It will be seen that in following the present invention, a pressure vessel assembly is provided in which a ductile lid may be positively locked into sealing engagement by a cam assembly, without danger of damaging locking lugs on the head.

Of particular significance is the provision of a strong, rigid lid that may be cheaply fabricated and is lightweight, due to the thin cross section of the disihed head.

It will be appreciated that the rectangular cross sections of the head and flange employed in the present invention permit simple manufacture of the vessel lid. The alignment edges may be automatically produced without complex casting or machinery.

Also of importance in this connection is the line contact between the dished head and the flange. With such contact, the possibility of canting of the head with respect to the flange is substantially minimized. Thus, the maintenance of an equal pressure distribution on the head is enhanced.

Furthermore, the use of a double weld that completely encases the portion of the cap adjacent the flange provides added stability.

Although the invention has been described with reference to one preferred embodiment and method, it will be appreciated by those skilled in the art that additions, modifications, substitutions, deletions and other changes not specifically described, may be made which fall within the spirit of the invention as defined in the following claims.

What is claimed is:

1. A lid for use on a pressure vessel, the lid comprisa domedcap portion substantiallysymmetrical about a first central axis and having a: first thickness,- the outer radial periphery of said domed cap portion being slanted radially inwardly toward said central axis to define a substantially circular edge of .a first diameter at the radiallyoutermost part thereof, and

an annular flange portion substantially symmetrical about a second central axisand having a second thickness substantially greater than. the first thickness of said domed cap portion, said flange portion having an internal cylindrical surface with :a mating seconddiameter substantially equal to the first diameter of said circular edge on said domed cap portion,

said domed cap portion being integrally 'welded to said flange portion with said circular edge being substantially in line contact with said internal surface of said flange portion at the position of the second diameter thereof, thereby to insure that said first and second central axes are in substantial longitudinal alignment.

2. .A lid for use on a pressure vessel as defined in claim l-wherein:

said annular flange portion is constructed from ductile steel and is provided at its radially outermost periphery with a plurality of circumferentially spaced, generally U-shaped, radially outwardly facing, fastening lugs. g 3. A lid for use. in a pressure vessel as defined -in claim 2 wherein:

saidannular. flange portion has a lower substantially planar surface substantially perpendicular to 'its central axis for sealingly engaging the pressure vessel, and said lower surface is provided with a generally circular groove for receiving a sealing ring. i 4. A lid for use on a pressure vessel as defined in claim 2 including:

Y a hinge flange integrally fastened to said annular'flange at the outer periphery thereof, and depending downwardly therefrom, said hinge flange being provided with aperture means for receiving a pivot bolt.

5. A lid for use on a pressure vessel as .defined in claim 4 including:

a handle integrally secured to said annular flange portion at a position substantially diametrically opposed to said hinge flange.

6. A lid for use on a pressure vessel as defined in claim 1, wherein:

said internal surface of said annular flange portion is substantially right circularly cylindrical, and

said circular edge being welded in line contact with said internal surface substantially adjacent the uppermost portion thereof.

7. A pressure vessel assembly comprising in combination:

a vessel body having a closed end, and having an open end with a substantially planar, outwardly facing surface,

a ductile steel lid pivotally mounted on said vessel body for movement into overlying sealing relationship with the open end of said vessel body, said lid including:

a dished head substantially symmetrical about a central axis and having a first thickness, the outer radial periphery of said dished head defining a substantially circular edge of a first diameter,

and

an annular flange substantially symmetrical about said central axis and having a second thickness substantially greater than said first thickness of said dished head, and including,

an internal substantially cylindrical surface 'with a second diameter substantially equal to said first diameter of said circular edge on said dished head,

an upper substantially planar surface,

a lower substantially planar surface facing said outwardly facing surface of said vessel body for sealing engagement therewith,

a plurality of circumferentially spaced generally U-shaped, radially outwardly facing, fastening lugs, said fastening lugs being integral and substantially contiguous with said upper surface of said annular flange,

said dished head being integrally welded to said annular flange with said circular edge in line contact with said internal surfaceof said flange substantially adjacent the upper I most portion thereof,

a plurality of latch assemblies secured to the outer periphery of said vessel body and circumferentially spaced for cooperation with said fastening lugs, each of said latch assemblies includa shaft member extendable longitudinally of said vessel body and dimensioned so to'be receivable by one ofsaid U-shaped fastening lugs, said shaft member being dimensioned to extend substantially beyond said outwardly facing surface of said vessel body,

a plate member slidably mounted on said shaft member,

means for biasing said plate member toward a position on said shaft member beyond said outwardly facing surface of said vessel body by an amount greater than said second thickness of said annular flange,

eccentric cam means pivotally mounted on said shaft member adjacent the longitudinally upper portion of said shaft member, for moving said plate member, against said means for biasing, into overlying fastening engagement with the upper surface of said annular flange adjacent the fastening lug which receives said shaft member.

8. A pressure vessel assembly as defined in claim 7,

wherein:

said eccentric cam means includes a portion extcndable into overlying fastening engagement with the upper surface of said annular flange at a point radially inward of said plate member. 1

9. A pressure vessel assembly as defined in claim 7,

wherein:

said shaft member is longitudinally adjustable, and

said means for biasing includes an annular shoulder on said shaft member and a helical spring slidably mounted on said shaft member between said shoulder and said plate member.

10. A pressure vessel assembly as.defined in claim 7 including an annular groove in said lower surface of said annular flange,

a seal member mounted in said groove, said seal member being sealingly engageable with the axially outwardly facing surface of said vessel body.

11. A pressure vessel assembly as defined in claim 7 wherein:

said ductile steel lid includes a depending hinge flange integrally welded to said annular flange at the outer periphery thereof, and

aperture means in said hinge flange for receiving a pivot bolt mounted on said vessel body.

12. A method of making a lid for use on a pressure vessel,

forming a thin dished head section with a radially inward slanted circumferential wall defining a substantially circular edge of a first diameter at the radially outermost part thereof,

forming an annular flange section having a thickness substantially greater than the thickness of the dished head with an internal surface having a second diameter substantially equal to the first diameter of the circular edge of the dish head,

centering the dished head within the annular flange section with the circular edge in line contact with the internal surface of the flange portion, and

Welding the dished head to the annular flange at the point of line contact therebetween.

13. A method of making a lid for use in a pressure vessel according to claim 12 wherein:

the internal surface of the annular flange is formed substantially right circularly cylindrical.

14. A method of making a lid for use in a pressure vessel according to claim 13, wherein:

the dished head is centered within the annular flange inline contact at the upper portion of the internal surface of the flange.

15. A lid for use on a pressure vessel, the lid comprisa domed cap portion substantially rectangular in cross section and having a first thickness, the outer radial periphery of said domed cap portion being slanted radially inwardly to define an edge at the radially outermost portion thereof, and

an annular flange portion substantially rectangular in cross section and having a second thickness substantially greater than said first thickness of said domed cap portion, said flange portion having an internal cylindrical surface,

said domed cap portion being integrally welded to said flange portion with said edge being substantially in line contact with said internal cylindrical surface, the portion of said domed cap portion adjacent said internal cylindrical surface being completely encased by weldment both above and below said edgev 16. A lid for use on a pressure vessel, the lid comprising,

a domed cap portion having a radially outer periphery substantially rectangular in cross-section and slanted to define an edge at the radially outermost portion thereof,

an annular flange portion substantially rectangular in cross-section and having an internal cylindrical surface,

said domed cap portion being integrally welded to said flange portion with said edge being substantially in line contact with said internal cylindrical surface prior to Welding, and said periphery, including said edge, being weldment obliterated subsequent to welding and being completely encased by weldment.

References Cited UNITED STATES PATENTS 12/1966 Svenson 220 8/1969 Vogeli 22055 GEORGE T. HALL, Primary Examiner