US2864404A

US2864404A - Heat exchanger construction

Info

Publication number: US2864404A
Application number: US380214A
Authority: US
Inventors: Bruegger Ernest; Philip S Otten
Original assignee: Griscom Russell Co
Current assignee: Griscom Russell Co
Priority date: 1953-09-15
Filing date: 1953-09-15
Publication date: 1958-12-16
Anticipated expiration: 1975-12-16

Description

Dec.'l6, 1958 E. BRUEGGER x-:T AL -2,864,404

HEAT EXCHANGER CONSTRUCTION 5 Sheets-Sheet 2 Filed Sept. 15,. 1953 uw B m Hem m B W Q m7 w. s \|1/ mrs T 3 Q B'M, A L nP M av 5 Sheets-Sheet 3 E. BRUEGGER ETAL HEAT EXCHANGER CONSTRUCTION Dec. 16, 1958 Filed Sept. 15, 1953 EMSVKZTORM BY Phigmszgen gzew ATTRNEYS Dec. 16, 1958 E. BRUEGGER HAL 2,864,404

HEAT ExcHANGER CONSTRUCTION Filed sept. 15, 195:5 5 sheets-sheetA E t lI( V EN TORS .ribes rule el' Phizif ge d MAL mm NN.

Amm

Dec. 16, 1958 E. BRUEGGER ET AL 2,864,404

HEAT EXCHANGER CONSTRUCTION 5 Sheets-Sheet 5 Filed Sept. 15, 1953 INVENTORS Ernesirwegg'er Pklzfp S. ezz d MT ATmRNEYS Unite States HEAT EXCHANGER CONSTRUCTION Application September 1S, 1953, Serial No. 380,214

1 Claim. (Cl. 13S-38) The invention relates to heat exchangers such as steam generators, super heaters, etc., and to methods of making the same, and has particular significance in connection with heat exchangers of the shell and tube type in which a tube bundle Yis enclosed within a generally cylindrical shell, and the ends of the tubes of the bundle are secured in one or more tube sheets connected to the shell of the heat exchanger, and each of the tubes is a double walled tube with a leakage detector space provided between the two tubes to prevent-if failure of either of the tubes occurs-intermixing of for example, heated and heating or cooled and cooling liquids passed through and around the tubes, and also to provide means for detecting a leak in any of the tubes.

It has been known in the past to provide heat exchangers, such as surface coolers handling a primary medium to be cooled and a secondary cooling medium, with means for circulating the different mediums through and about a double walled tube comprising inner and outer tubes. Such tubes have been arranged to have surface to surface contact with a plurality of relatively large longitudinal passages or grooves formed between the two tubes communicating with a leakage detector compartment so as to convey fluids leaking through one of the tubes on failure thereof to the detector compartment to provide a visual indication of any such leakage. The double walled tube prevents intermixing of the cooled and cooling or heated and heating mediums if one of the inner or outer tubes fails due say to corrosion or the like.

In fabricating such double walled tubes the grooves ordinarily have been formed longitudinally in the inside surface of the outer tube, the grooves being relatively large and `few in number; and the tubes normally have been relatively small in diameter. In order to provide such grooves in the interior surface of the outer tube, such outer tubes usually have been made as an extruded product which has required the use of a soft metal or a soft metal alloy in order to form such a tube as an extrusion.

Sometimes the longitudinal internal grooves in the outer tube have been formed by a broaching operation rather than by forming the grooved tubes as an extrusion. Sometimes instead of forming the grooves in the inside surface of the outer tubes, the grooves have been formed longitudinally in the exterior surface of the inner tubes but here again unless such tube is formed as an extrusion difficulty has been encountered in forming such grooves in a thin walled small diameter tube of considerable length without weakening the tube walls or in the alternative making the tube wall sulliciently thick to avoid collapse in forming the grooves or when the tube is subjected to high pressure operation.

As a practical matter, the manufacture of the grooved tube has been limited to the use of soft metal, and to forming the same as an extrusion product with the grooves in the interior of the outer tube. These practical requirements involve the further disadvantage, in addition to the limitation ofthe soft metals or alloys which must atent O be used, that the manufacture of such extruded tubes is very excessively expensive.

These diiculties, disadvantages and limitations created an extraordinary problem in the construction 0f double walled leakage detector tubes for use in heat exchangers where high pressures, or high temperatures, or the charac; ter of the medium being circulated through or around the tubes, has required the use of tubes formed of other than soft metal that is a corrosion resistant metal such as stainless steel or nickel for both the inner and outer tubes or stainless steel for one and nickel for the other of the inner and outer tubes. Thin Walled small diameter tubes of considerable length cannot be formed as a practical matter as an extruded product from stainless steel or nickel. Prior to the discoveries of the present invention the cost of forming grooves by other means in either the inner or outer tube walls, or the cost of increased metal for thick walled tubes and the additional weight thereof, or combinations of these diiculties have prohibited the manufacture of double walled leakage detector tubes of stainless steel or nickel or combinations of the same.

Equipment using materials requiring the use of stainless steel or nickel tubes may have a low boiling point metal, or a low vapor pressure metal in molten state, or a molten salt, passed through the inner tube as a heating medium; and water to be converted into steam, or steam to be superheated, may be passed through the heat exchanger shell in heat exchange relation through the double tube walls with the heating medium for being heated.

As compared With soft metals or alloys both stainless steel and nickel have poor heat conductivity. Therefore it is most important when using stainless steel or nickel to have as large an area of metal to metal contact as possible between the inner and outer tubes for obtaining maximum heat exchange through the tube walls. Thus the size of the grooves which normally can be formed in an extruded product, must be materially reduced when using stainless steel or nickel in order to provide nearly complete metal to metal contact between the' exterior surface of the inner tube and the interior surface of the outer tube. Heretofore there has been no known way of forming grooves a few thousandths of an inch in depth or width, satisfactorily in a surface of a small diameter, thin walled stainless steel or nickel tube and such tube could not be formed as an extrusion.

In other prior art constructions, double walled or bimetal tubes have been made of steel and copper or brass for use in refrigerating equipment handling ammonia vapors. Difficulties were experienced in tube failure apparently due to gas formation at the interface of the two metals forming the double Walled or bimetal tube. This difficulty was obviated by providing shallow grooves in the surfaces of one of the tubes to convey any gas that may be formed away from the tube interfaces to prevent impairment of heat transfer and tube failure. The grooves in such tubes normally have been formed by a breaching or similar operation which again is not adapted for the manufacture of double walled tubes of stainless steel or nickel for some of the same reasons and because of some of the ditliculties encountered as hereinabove discussed.

It is an object of the present invention to provide a simple and inexpensive structure for overcoming 'the above mentioned difliculties.

Another object of the invention is to provide a double walled heat exchanger tube provided with leakage detection means in `which the inner and outer tubes are formed of stainless steel or nickel or lcombinations thereof for handling corrosive fluids at high temperatures or pressures.

Another object of the invention is to provide a double walled leakage detector heat exchanger tube which has maximum metal-to-metal contact between the concentric tubes.

Another object of the invention is to provide a double walled leakage detector heat exchanger tube utilizing thinner walled tubes than in `structures made in accordance with the prior art.

Anotherobject of the invention is to provide concentric double conduit tube arrangements with leakage de tector passages between the conduits and characterized yby greater ease of manufacture and a greater variety of metals which can be used for the inner and outer conduits.

Another object `of the invention is to provide a double walled leakage detector heat exchanger tube in which it is not necessary to use relatively soft metal for one or both of the concentric tubes.

Another object of the invention is to provide double walled tubes yof this type which are lighter in weight and characterized by asaving in cost proportional to the expense of materials used.

Another object of the invention is to provide do'ublc walled leakage detector heat exchanger tubes for use at higher temperatures and with more corrosive `fluids than prior art double walled tubes.

A further object of the present invention is to provide an improved method of providing leakage detector grooves in double walled tube structures comprising -inner and outer tubes having thinner walls and formed of -a greater variety of metals than possible with prior procedures.

These and other objects and advantages apparent to those skilled in the art from the following description and claim, may be obtained, the stated results achieved, and the described difficulties overcome by the methods, steps, procedures, products, articles of manufacture, constructions, combinations, sub-combinations, parts and elements which comprise the present invention, the nature of which are set forth in the following general statements, pre ferred embodiments of which-illustrative of the best modes in` which applicants have contemplated applying the principles-are set forth in the following description and shown in the drawings, and which are particularly and distinctly pointed out and set forth in the appended claim forming part hereof.

The nature of one aspect of the discoveries and improvements of the present invention may be stated in general terms as preferably including in a method of making a double walled leakage detector tube and shell heat exchanger construction particularly adapted for handling high temperature extremely corrosive iluids, the

steps of providingseparate inner `and outer conduits or tubes of corrosion-resistant metal such as stainless steel or nickel,'forming such tubes as small diameter, relatively thinwalled, tubes such as say with a tube wall of the order of one-sixteenth inch thick, forming a large number of longitudinal grooves having a width or depth of the order of -a few thousandths of-an inch in the outer surface of the inner tube by rotating the tube on its axis and forcing an axially ribbed, rotatable, relatively axially short, grooving roll radially against the outer surface of the tube while advancing the roll longitudinally of the rotating tube with the tube and roll axes parallel, to iron grooved portions complementary to the -roll ribs in the outer surface of the tube in a `helical path about the tube outer surface; co-ordinating and controlling the rate of roll advance and the length and spacing of the roll ribs such that when the tube makes one revolution the groove portions formed in the helical path are `aligned with the groove portions formed in such path during the previous revolution of the tube, so that when the roll has advanced from adjacent one end to adjacent the other end of the tube a series of continuous longitudinal grooves are formed in the outer surface of the tube; then telescoping the grooved tube with its longitudinally grooved portion within the outer tube and expanding the inner tube slightly within the outer tube to seat the grooved surface in intimate metal to metal contact between the grooves within the outer tube; then securing the ends of the inner and outer tubes within spaced tube sheets with the grooves communicating with a compartment between Such tube sheets. v

The nature of another aspect of the discoveries and improvements of the present invention may be stated in general terms as including in heat exchanger construction of either the bowed tube or bayonet tube type, double walled tubes composed of inner and outer tubes, the ends of the inner tubes being secured in a tube sheet communicating with one compartment, the ends of the outer tube being fixed in a second tube sheet spaced from the first tube sheet communicating with another compartment, there being a series of longitudinal grooves formed in the outer surface of that portion of the inner tube within the outer tube, said grooves communicating with said second compartment 'between said spaced tube sheets, the outer tubes having a relatively small diameter of the order of three-fourths inch outside diameter, the inner and outer tubes having a wall thickness of the order of one-sixteenth inch thick, the tubes being formed of metal or alloys such as stainless steel or nickel, and the grooves having Irelatively small depth and width of the order of a few thousandths of an inch, whereby intimate surface to surface contact between the grooves is obtained when a grooved inner tube is telescoped and expanded within an outer tube while providing passages through the grooves between the tubes for the detection of failure or leakage of either of the tubes.

By way of example, preferred embodiments of our improved heat exchanger construction and of improved parts thereof and of methods of making the same, are illustrated in the accompanying drawings, in which;

Fig. 1 is a horizontal sectional View of a heat exchanger of the bowed tube type having concentric conduits or double walled tubes and a leakage detector system constructed in accordance with the invention;

Fig. 2 is a vertical sectional view of the heat exchanger shown in Fig. l;

Fig. 3 is an end view looking at the left end of thc heat exchanger shown in Figs. l and 2;

Fig. 4 is a cross sectional view taken along the line 4 4 of Fig. 2;

eFig. 5 is a fragmentary enlarged vertical section adjacent the bottom of the left end leakage detector space as seen in Fig. 2;

Fig. 6 is an enlarged somewhat diagrammatic cross sectional view taken on the line 6 6 of Fig. 5;

Fig. 7 is a View in perspective showing the inner tube of Fig. 6 during one step of its manufacture in accordance with a preferred method of the invention;

Fig. 7a is a view similar to Fig. 7 showing a variation -in the method of groove forming;

Fig. 8 is a vertical sectional view showing another form of heat exchanger constructed in accordance with the invention; and

Fig. 9 is a cross sectional view taken on the line 9 9 of Fig. 8.

Similar numerals refer to similar parts throughout the several views of the drawings.

Referring to Figs. 1 and 2, we have shown a high temperature, high pressure heat exchanger adapted for use with very highly corrosive fluids and comprising two similar spaced apart headers indicated generally at 10 and 10', respectively.

Headers 10 and 10' are identical except opposite hand. For simplicity only the left hand header 10 is fully shown, and it comprises a head barrel portion 11 and a head cover 12 with the head cover secured as by bolts 13 to a ange portion 14 of the head barrel. The head barrel is secured as by an annular Weld 15 with an annular tube sheet 16 which will hereinafter be referred to as the outer tube sheet. An inner tube sheet 17 is located in spaced relation with respect to outer tube sheet 16 by a ring barrel 18 which, as hereafter more` fully explained, forms with the tube sheets, a leakage detector space l19.

The side of the inner tube sheet 17 opposite the chamber 19 is secured as by a-n annular weld 20 with a somewhat conically shaped section 21, the opposite end of which is secured by weld 22 with the exchanger shell 23 extending between the -two headers and two sets of tube sheets. The header and tube sheet arrangement is the same, except opposite hand, at the right end. Thus the header end assemblies and 10 are at the ends of the conical shell end sections 21-21; and include the

tube sheets

16, 17, 16', 17 and the detector space barrels 18, 18.

End chambers

24, 24 formed within vthe vrespective headers communicate with each other through a plurality of similar tubes 25 which are the inner tubes of the improved double tube construction. These inner tubes 25 are closely surrounded with eicient metal to metal heat transfer contact by outer tubes 26. The inner and

outer tubes

25 and 26 are bowed to one side as seen in Fig. 1, to permit differential expansion of the tubes with respect to shell 23, in operation, as is usual in the construction of bowed tube heat exchangers.

The tubes 25-26 are supported, while allowing for free sliding in the horizontal direction, by a plurality of support rings 27 provided within the shell 23. Each support ring 27 includes a plurality of horizontal support surfaces formed by transverse support slats 28 (see Figs. 2 and 4) so that the tubes are free to bow to a greater or lesser extent by sliding horizontally on the slats 28.

As is conventional in this general type of heat exchanger, the tlow of heating medium in the tubes is indicated by arrows 29 in one direction and the ow of heated medium in the shell around the tubes is indicated by arrows 30 from the ends of the shell toward the central portion thereof. With the directions of ow of heating and heated fluids as shown in the drawings the fluid within the tubes 25 flows from inlet member 32 to inlet header chamber 24, then through tubes 25 to outlet header chamber 24 then out through outlet member 32. The inlet and outlet members 32 and 32 are connected in a usual manner with a source of and a point of discharge for the heating medium. The fluid to be heated passing around the tubes 25-26 and within the shell 23 as indicated by the directional arrows 30 enters the shell through a pair of inlet conduits 33 and leaves the shell through a pair of outlet conduits 34, the

conduits

33 and 34 having connections, not shown, with a source of and a discharge for heated medium.

The leakage interceptor spaces 19 and 19 are each provided with a series of ports 35 formed of pipe sections 36 and caps 37 welded to each other and to the ring barrels i8 or 18. One of the upper ports 35a may be provided with a vent 38 and one of the lower ports 35b may be provided with a drain 39. The other upper, lower and side ports 35 (Fig. 3) may serve as inspection ports, being equipped with sight glasses if desired.

In Figs. l and 2, the head covers 12-12 are shown secured to the respective head flanges over sealing means including diaphragms 41 welded inside of flanges 14 beyond grooves 42. This head closure construction forms no part of the present invention, being described and claimed in co-pending Frank Boni, Jr., application Serial No. 337,324, tiled February 17, 1953.

Sections

21 and 21 have been referred to as somewhat conical because, referring to Fig. l, to accommodate the bowed tubes, shell 23 is oit center in a horizontal plane with respect to the leakage detector spaces 19 and 19 which in turn are off center with respect to the

headers

10 and 10. And in Fig. 2 the shell 23 is olf center in a vertical plane with respect to the leakage detector spaces and headers. This arrangement is also shown in Fig. 3 which is an enlarged end view taken from the left end of the heat exchanger as viewed in Figs. 1 and 2.

It is .to be understood that for purposes of simplicity only some of the tubes havebeen shown in the drawings. However, a usual complete `tube bundle, as is well known in the art, extends between the tube sheets 16 `and,.17 and 17 and 16. In Fig. 1, portions of only three double tubes 25-26 are shown and portions of only two double tubes are shown in Fig. 2. Only a portion of the complete number of tubes in the tube bundle is shown in Fig. 4. .It will be apparent from Fig. 4 that the support rings 27 carrying the cross slats 28 may be supported within the shell 23 by a plurality of circumferentially spaced shims 45 intervening between shell 23 and ring 27 and each welded to each of these members. As shown in Figs. ,2 and-4 shell 23 may be supported by a plurality of transverse base supports 46 carrying a pair of longitudinally extending bars 47 with fillet welds 48 connecting the longitudinal bars to the transverse bars andthe bars 47 t0 the shell 23.

In the Vbowed tube heat exchanger of Figs. 1 4, the ends of each tube of each double tube are mounted in tube sheets and ixedly secured therein. The headers are in communication with the inner passages in -the inner tubes and the leakage detector spaces 19 and 19 are in communication with leakage detector passages between `the inner and outer tubes as will be described.

Obviously the heat exchanger can be used for either heating or cooling but for purposes of explanation the heat exchanger of Fig. 1 may be a steam generator with a molten metal or salt used as the heating medium and flowing through tubes 25, and water to be converted 'into steam, the heated medium, passing through the shell 23. This can otherwise be described as the molten metal being the medium to be cooled and the water in the shell the Acooling medium.

Thus the cooling medium may be introduced through the inlets 33, and passes in the direction of arrows 30 within the shell 23 around the outer tubes 26 of the double tubes 25-26 and then discharges through outlets 34 as steam. With the arrangement described, the medium to be cooled, which may be a molten metal or salt enters through inlet 32 and passes in the direction of arrows 29 into chamber 24 of header 10 and through the inner tubes 25 of the double tube assemblies to the other end, then into chamber 24 of header 10', and out through the outlet 32' giving up its heat to the cooling water to convert the same to steam.

As previously stated, the double tube arrangement contemplates the possible passage of a high temperature, or high pressure, or highly corrosive molten metal or salt through the inner tubes 25 necessitating that they be made of a material which is strong and corrosion resistant at high temperature. Similarly the outer tubes should be formed of a similar material. Such material may be, for example, stainless steel or nickel. With small diameter, thin-walled tubes of such materials formed in long lengths, it has been diicult if not impossible to form grooves in either the inside of the outer tubes or the outside of the inner tubes to provide passages for the detection and collection of leakage in the event of tube failure.

We have solved these diiculties, and provided other new and useful results associated with greater metal to metal contact between the concentric tubes, greater ease of manufacture, greater variety of materials which can be used for each of the tubes of the double tube construction, and relatively greater ease of employing thinner walled tubes, by providing a relatively large number of relatively small dimensioned grooves in the outer surface of the inner tubes.

In accordance with the present invention, grooves are formed on the outside of the inner tube 25 by a rolling procedure similar to knurling. The rolling procedure is illustrated somewhat diagrammatically in Fig. 7 wherein a tube 25 is shown with grooves 51 being impressed in the outer surfacep52 ofthe tube, starting from a zone 52a forming tool 53 is forced or pressed radially against the l tube surface 52 during such rotation.

The roll 53 has axially extending ribs54 formed on its periphery complementary in cross-sectional shape to the shape of the grooves to be formed; and the roll rotates by pressure contact with the rotating tube. Assuming that the tube is rotated in a lathe-like machine, then after one revolution of the tube with the tool pressed thereagainst at the zone 52a, the tool is fed axially along the tube to roll groove portions 51a in the surface of the tube 25 in a helical path indicated by dot dash lines in Fig. 7, at 55, which line 55 shows the path traversed by the left hand end of roll 53 as it is fed and the tube 25 rotated. f

The tube may be supported during rolling in any well known manner, if necessary, depending on its diameter, length and wall thickness. Thus the tube may be supported on an arbor or mandrel; or back up rolls may support the tube opposite the location of roll pressure.

Alternately, the roll may be stationary and the tube fed axially from the head of an automatic screw machinelike machine for advancing the tube axially in a helical path past the roll.

The spacing of the ribs 54 on the roll 53, the axial length of the roll 53, and the rate of relative advance between the tube and roll are coordinated such that when the tube makes one revolution the groove portions 51a formed in the helical path 55 are aligned with previously formed groove portions. As a result, when the rolling has progressed to adjacent the other end of the tube, a series of longitudinally extending grooves 51 are formed in the outer surface 52 of the tube 25.

The shape of the grooves 51 is shown somewhat dia grammatically and in an exaggerated manner in the enlarged sectional view of Fig. 6. For example the inner tube 25 may have a 5A: inch outside diameter, the outer tube 26 a 3%: inch outside diameter and the wall thickness of each

tube

25 and 26 may be 1A@ inch. The grooves 51 may only be a few thousandths of an inch in depth or width and may have any desired spacing to provide a relatively large number of grooves. The crosssectional contour of the grooves 51 is not critical as it may be rounded, as shown, or fiat sided.

It is possible to form the grooves 51 in the surface of a stainless steel or nickel tube without distorting the tube or weakening the tube wall by large sized grooves, because the grooves are small in size and only localized pressure by the roll against the tube occurs at the point of Contact therebetween. On the other hand, it is not possible to form such grooves in the surface of such tubes, when made of stainless steel or nickel or the like, by extruding, broaching or machining, at reasonable cost or without substantially heavier walls,

Thus it is possible to use either nickel or stainless steel for both inner and outer tubes or to have either made of either stainless steel or nickel, thereby affording a new design freedom in the design of heat exchangers of the type described. This method of forming grooves in the outer periphery of a round but very hard thin walled tube is particularly advantageous because it is fast while at the same time no great forces are required for the operation beca-use the tool may be made quite short and it is forced against the tube surface the full depth of only one very small groove at any one time.

After the grooves 51 have been formed in the outer surface of the tube 25, the tube elements are ready for assembly in the heat exchanger. The outer tubes 26 are first assembled within the shell 23 with the ends thereof seated in the

tube sheets

17 and 17. The manner in which tube ends are secured within openings in tube sheets is well known `in the art and may include slightly 8 expanding the tube ends within the tube sheet openings, or welding the tube ends to the tube sheet, or both.

After the outer tubes 26 have been thus assembled, the grooved inner tubes 25 are telescoped through the outer tubes with the grooved portions extending slightly beyond the outer ends of the outer tubes 26 as shown at 52b in Fig. 5; and the ends of the inner tubes 25 are then xedly secured in the

tube sheets

16 and 16 by expanding or expanding and welding the same within or to the tube sheets in the usual manner. Before both tube ends are secured to the

tube sheets

16 and 16 an expanding tool is moved through the inner tubes 25 to slightly expand the inner tubes 25 within the outer tubes 26 to seat the inner tube surfaces between the grooves in intimate metal to metal contact within the outer tubes so that for heat transfer purposes the thus formed double tubes act as single members to provide eicient heat transfer from the inner surfaces of the inner tubes to the outer surfaces of the outer tubes.

The assembly of the double tubes 25-26 with the tube sheets may be modified by rst telescoping the tubes 25 Within tubes 26 with one end of tube 26 beyond an end of tube 25. Such tube end of tube 26 is then expanded within its tube sheet opening and welded thereto if desired. Then tube 25 is moved axially of tube 26 to permit the other end of tube 26 to be expanded, and welded in its tube sheet opening. Then one end of tube 25 is expanded, and welded if desired in its tube sheet opening. Then an expanding tool is drawn through inner tube 25 to expand its wall outward into intimate metal to metal heat transfer contact Within outer tube 26. Finally the other end of inner tube 25 is expanded in, and welded if desired in its tube sheet opening.

As shown in Fig. 3, each head cover 12 may be provided with a lifting eye 49 `for use in handling the heat exchanger during manufacture, shipment, installation and repair, or for removal of the head cover if necessary to replace one or more tubes.

As best shown in Fig. 5, the grooves 51 provide passages throughout the entire length of the double tubes between the inner and

outer tubes

25 and 26 thereof communicating with the leakage detector chambers 19 and 19. In the event of a failure of any of the

tubes

25 or 26, leakage of fluid through the failing tube will pass along grooves 51 to the chambers 19 and 19' where such leakage may be visible through inspection openings in detector ports 35 or from drains 39 in lower ports 35h. When any such leakage is detected, the heat exchanger may be shut down, the tube failure located and the tube replaced in the usual manner.

Thus by providing for leakage detection indicating tube failure, and correcting the same when detected, intermixing of the heating and heated or cooling and cooled liquids or uids may be prevented.

Although in Figs. l and 2 the leakage detector compartments 19 and 19 are shown as separate compartments, in some installations the barrels` 18 and 18 may be omitted and the passages between the inner and outer tubes of the

double tubes

25 and 26 may communicate directly with the atmosphere where any tube leakage will be immediately detected.

Furthermore, if desired, a third liquid or uid may be introduced into the leakage detector spaces 19 and 19 and circulated through the passages formed by the grooves 51 between the inner and

outer tubes

25 and 26.

A modified groove forming roll arrangement is shown in Fig. 7a in which the grooves 51 may be formed longitudinally in the outer surface of tube 25 by a forming roll 53a having helical ribs 54a thereon and with the roll axis angled with respect to the axis on which tube 25 is rotated. The roll 53a is forced against tube 25 with pressure and moved axially of tube 25 during tube rotation to form grooves 51 in substantially the same manner as described in connection with Fig. 7, except that at any one moment there is less rib area contact with the tube n.Surface nermitting highiloealized forming pressure to he exerted by roll '53a :against the :..resistanee-of hard, tough metal Such as stainless steel or niekel.

AA bayonet .tube .heat v-exeluanger is shown inligs. 8 ,and 9 ,including `:the improved double tube construction made in accordance with the present invention. T he bayonet tube heat exchanger indicated at 100 has a `main header 110 similar to the header 10 and may the equipped With a I head COVeIBuddiaphragmlhead `closure, not shown, .Similar t the head Cover 'andclosure in the heat exchanger shown rin vFigp1.

The header 110 preferably comprises .a barrel portion l1,1 1 secured by ,an annular ,weld 11:5 .to tube :sheet '.116 spaced Afrom la second tube ,sheet 117 by ring barrel 118 Welded .t0 the tube sheetsglland 11.7 to form a leakage deteCOr Space 11,9. Tube .Sheetg1'17 is connected by an annular weld 120 with heatexchanged shell 123, ,the other lend of the shell being closed by :a .dome 210 secured `by a weld 220.

In the construction ,of a bayonet tube heat exchanger, the inlet and outlet 'for the tube passages normallyare `at one end of the unit which may be the stationary end thereof and the :tubesandshellsare constructed to provide lfor relative differential longitudinal expansion and vcontraction.

A sealing ring 121 preferably is welded within the periphery of barrel portion 111 intermediate its V.ends and a series of nuts 1,22 are welded to .the sealing ring 121, to which studs `124 are secured for mounting .a pass plate 127 within the barrel portion 111 by nuts 128. The barrel portion 111 is thus divided intov two compartments 129 and 130, and a tube fluid inlet 131 and a tube fluid outlet 132 may communicate respectively with the compartments 129 4and 130.

The improved double Ytube vconstruction including inner tubes 125 and ou-ter -tubes -1'26 is mounted within the shell 123 with one end of each Vofthe outer tubes '126xed in the tube sheet 117 and one end of each of'the inner tubes 125 xed in the tube sheet 1 16, ferrules 133 preferably being provided for seating the ends of the inner tubes in tube sheet '116. Bayonet tubes 134 are mounted at one end in pass plate 127 and project, as shown, inside of the inner tubes 125, the open ends thereof preferably being supported by spacers 135. The unsecured ends of the double tubes 125-126 may be closed by return plugs 136 and 137 welded thereto.

Thus tube fluid may be pressed through the tubes through the inlet 131, compartment 129, the bayonet tubes 134 to the open ends thereof, then back around the outer surface of the bayonet tubes 134 and within the interior of the inner tubes 125 to compartment 130 and out through outlet 132.

The inner tubes 125 of the improved double tube construction 125-126 are provided exteriorly with grooves in a manner previously described so that passages are provided by such grooves between the inner and

outer tubes

125 and 126 communicating with leakage detector compartment 119 in a manner previously described.

Compartment 119 may be equipped with an inspection port 138 and a lower port 139 having a drain connection 140 for discharging any liquid leakage, thus indicating tube failure. A series of baflles 141 are mounted within the shell 123 on tie rods 142 between spacers 143, the tie rods 142 being secured to tube sheet 117 at one end and to the last baille 141 at the other end. Adjacent the tube sheet 117, one of the baffles 141a has connected thereto a horizontal baille plate 144 which enclose the cut-off upper ends of baffles 141b as well shown in Fig. 9.

The

baffles

141, 141a and 141b are provided with openings 145 through which the

double tubes

125 and 126 project, clearance spaces being provided by said openings 145 around the double tubes so that fluid passing through the shell can travel through such clearance spaces, as indicated by the arrows 146, from space to space be- Atitl-.een batlles in .close heating contact with ,the :outside-of .ticularly adapted `for useasa superheater, with steam passing into the shell .at 147 and being dischargedtherefrom through koutlet 148 as superheated steam, .the superheating being performed by the heating fluid circulated through the bayonet tubes 13.4 and double tubes and 126.

The shell 123 may be provided with any desired number of supports including ,cross members 149 and longitudinal members 150 (Fig. 9) welded to each other and to the shellfor supporting :the vsame on .a supporting surface; and drain opening connections 151 .and `152 may be connected with `compartment and ,the interior of shell L123 for draining these ycompartments when necessary.

Accordingly, the present invention provides a new meth- .od of making double tubes an'd =a new double tube structure which maybe used in vario-us `types of heat exchangers as illustrated and described inthe embodiments of the in- Vention disclosed. The Adouble tube construction may readily be manufactured to provide many small grooves in the outer surface of the inner tubes. Thin walled small diameter long length tubes may be formed ofmetal .such kas stainless steel and nickel with ymany `resultant advantages such as maximum Vmetal to metal contact between the inner ,and ,outer .tu-bes for efllcient heat transfer, greater ease of manufacture, greater design freedom from the standpoint of-metals that may be used to form .the tubes, elimination of a requirement that soft metals be used, and provision for the detection' of -lluidleakage Adue to tube failure and prevention of intermixing of shell and tube fluids.

Moreover, the improved method enables grooves to be formed in very thin walled tubes with Va costsaving where expensive materials are used and with a substantial weight reduction due to the ability of using thin walled tubes.

The construction of the present invention also provides other important and new advantages and results in that leakage warning may be given without endangering personnel, an'd leakage location determined without difficulty.

Thus, referring to Fig. 1, the leakage detector spaces 19 and 19 and the passages provided by grooves 51 may be filled with a fluid under pressure such as helium, air, water or mercury and sealed under such pressure. Suitable instruments for indicating or recording the pressure may be connected with one of the compartments 19 and 19. During operation of `the equipment, if the pressure un'der which such fluid is maintained in the compartments 19 and 19 and grooves 51 is a pressure intermediate the pressure within tubes 25 and outside fof tubes 26, and the pressure within tube 25 is lower than the pressure outside of tubes 26; then a decrease in the pressure of the fluid in compartment 19 indicates leakage through tubes 25 or the joints thereof, and an increase in pressure of the fluid in compartment 19 indicates leakage through tubes 26 or the joints thereof. A

If the pressure of such fluid in compartment 19 is maintained higher than the pressure inside of tubes 25 and higher than the pressure outside :of tubes 26, then a decrease in pressure of the fluid in compartment 19 shows leakage through one of

tubes

25 or 26 or the joints thereof. Similarly, if the pressure of the fluid in compartment 19 is maintained lower than the pressure inside of tubes 25 and outside of tubes 26, then' an increase in the pressure of the fluid in compartment 19 indicates leakage through tubes 25 Ior 26 or the joints thereof.

Thus, if either of the fluids in or around the

tubes

25 or 26 is lethal, toxic, explosive, inflammable or dangerous, and leakage occurs through one of

tubes

25 or 26,

` the construction provides for leakage detection which may Moreover, if any leakage does occur, the location of the leakage tube can be readily determined. When leakage is detected, the unit may be shut ol'l and head diaphragm 41 removed. If the pressure change indication of fluid in compartment 19 indicates leakage in one or more of the tubes 25, the compartment 19 may be pressurized, the outside ends of the tubes 25 in tube sheet 15 may be covered in the usual manner with a solution' such as a soap solution which will form bubbles from pressure leakage through the defective tube, and the location of the leak determined. The failing tube 25 can then be repaired.

lf the iluid pressure change in compartment 19 indi cates leakage in one or more of tubes 26, `one or more of

ports

35 or 35a may be opened and provided with sight glasses, the shell 23 pressurized and the compartment 19 slowly filled with water. As the water level in' compartment 19 rises, by observing through horizontal ports, the horizontal location of the leaking tube 26 can -be observed through bubbling in the water. At the same time, observation can be made vertically through one of the ports to determine the lateral location of the leaking tube. When the location of the leaking tube is thus determined, the 'tube can be repaired or blocked off in' the usual manner.

In the foregoing description, certain terms have been used for brevity, clearness and understanding, but no unnecessary limitations are to be implied therefrom beyond the requirements of the prior art, because such words are used for descriptive purposes herein an'd are intended to be broadly construed.

Moreover, the embodiments of the improved construction and method illustrated and described are by way of example, and the scope of the present invention is not limited to the exact details illustrated or described.

Having now described the invention, the construction 12 and mode of manufacture of preferred embodiments thereof, and the advantageous, new and useful results obtained thereby; the new and useful arrangements, constructions, parts, elements, combinations, subcombinations, methods, steps, procedures, principles and discoveries, and reasonable mechanical equivalents thereof obvious to those fskilled in the art are set forth in the appended claim.

Y We claim:

A small diameter, corrosion-resistant, double-walled leakage detector heat exchanger tube having nearly complete metal to metal contact between the walls of the double-walled tube and being adapted for containing corrosive fluids at high temperatures including inner and outer cylindrical tubes of corrosion-resistant metal selected from the class consisting of stainless steel and nickel, each of the inner and outer tubes having a wall thickness of the order of l/e thick, the outer diameter of the outer tube being of the order of 1%" diameter, the inner tube being provided with a plurality of longitudinally extending grooves having a width and depth of the order of a few thousandths of an inch formed into the cylindrical outer surface thereof, and the outer cylinderical surface portions of the inner tube between the grooves being seated in intimate metal to metal heat transfer contact with the inn'er surface of the outer tube thereby providing metal to metal contact between the inner and outer tubes greatly in excess of the total projected area of the few thousandths inch wide grooves whereby ecient heat transfer may be effected through .the walls of the double-walled tube.

References Cited in the tile of this patent UNITED STATES PATENTS 1,589,595 Hitchcock June 22, 1926 1,842,945 Price et al. J an. 26, 1932 1,886,403 Jones Nov. 8, 1932 2,187,555 Flindt Jan. 16, 1940 2,658,728 Evans Nov. l0, 1953 FOREIGN PATENTS 273,605 Great Britain July 12, 1927