US2220579A - Method of making boiler tubes and the like - Google Patents

Description

Nov. 5, 1940. T. E. MURRAY 2,220,579

METHOD OF MAKING BOILER TUBES AD THE LIKE Filed Deo. 28, 1934 2 Sheets-Sheet l BY /y/ ATTORNEYS No-v. 5, 1940. T. E. MURRAY 2,220,579

METHOD OF MAKING BOILER TUBES AND THE LIKE Filed Deo. 28, 1934 2 Sheets-Sheet 2 ATTORNEYS Patented Nov. 5, 1940 METHOD F MAKING BOILER TUBES AND Thomas E. Murray, deceased, late of Brooklyn, N. Y., by John F. Murray, Joseph B. Murray, and Thomas E. Murray, Jr., executors, Brooklyn, N. Y., assigner to Metropolitan Engineering Company, Brooklyn, N. Y., a company of New York Application December 28, 1934, Serial No. 759,459

12 Claims.

In certain prior patents (for example, No. 1,844,407,'February 9, 1932) there are disclosed boiler furnace walls composed of finned tubes; that is to say, tubes with anges extending continuously over the exposed portions, the tubes being erected alongside of each other with the flanges lling the spaces between them and forming a wall whichv is practically closed to prevent the passage of gases or any substantial quantity of radiant heat from the combustion within.

Such boiler furnaces are iired most frequently with coal dust, or it may be oil or gas, producing an intense degree of heat. y

In actual practice such anges have been welded continuously along the length of such tubes by arc welding (that is, by depositing along the joint welding metal melted by the electric arc) and this method lhas introduced internal strains in' the tube and also in the flange. A measurement of such a tube about 20 feet long would show a contraction of a considerable fraction of an inch in length after the application of the anges, indicating a very high degree of strain. Such strains have caused the tubes in some cases to split in use and have rendered the free edges of the flanges moresusceptible to oxidation at the high temperature prevailing, so that they have burned oiifl rapidly and could not be made in the beginning of the desired width.

The disadvantages of the continuous flange are set out more fully in application Serial No. 550,903, led July 15, 1931, disclosing the substitution for the continuous fin of a number of separate projections spaced slightly apart and providing a substantially unbroken wall.

rIhe present application is directed to the process of producing such units, that is, boiler tubes and the like with ilanges which for-al1 practical purposes form a complete wall, without the strains involved in the application of a continuous n welded along its entire length to the tube.

The accompanying drawings illustrate designs of boiler tubing and methods of production.

Fig. 1 isa side elevation of a i'ln tube for the wall of a Murray type of boiler.

Fig. la is an enlargement of a portion thereof to illustrate the separation of the iin into a'number of small separate projections.

Figs. 2 and 3 are elevations of a tube in process of application of projections thereto;

Fig. 4 illustrates diagrammatically the weld-v ing operation.

Fig. 5 is a perspective of one of the projec- 55 tions before welding it to the tube. g

Figs. 6 and 7 are, respectively, la horizontal section and an elevation of the upper part of a water wall.

Fig. 8 is a view similar to Fig. 1 of another wall of a boiler tube.

Fig. 9 is a perspective of the upper end of a tube showing a different design of the projections.

Tubes for boilers, super-heaters, economizers and various other heat exchangeapparatus are sometimes straight from end to end and are often curved in various ways along their length. The present invention is applicable to all such shapes and has particular advantages in connection with tubes that are curved. In Fig. 1, for example, there is a tube II having the main portion of its length straight and having its two ends Ibent in the same direction at a right angle for connection to drums or headers. The tube I2 of Fig. 8 has a slight bend at its upper end for connection to a steam drum I3, and its lower end bent in the opposite direction for connection to a headerl I4; the intermediate portion may also be bent at about the middle. Both these tubes are provided with ns, designated as a whole by the numeral I5, extending over the portions of their length which are exposed to the heat.

In making up tubes of this character into boiler walls (Figs. 6 and 7) they are arranged side by side, spaced apart from each other and with their nns abutting or overlapping so as to practically close the space between the tubes against the passage of heat to the outside wall I6, or to any outside insulation that may be provided.

It has been found that where such ilns are welded in a continuous strip over the whole or any substantial length of the tube, there are strains set up in the tube and in the strip which weaken them and sometimes cause cracks in the iin or in the tube under the conditions of use as above explained. It is proposed, therefore, to weld each fin in a succession of steps along the length of the tube applying the n in separate sections of such short length as to avoid the prev vious difliculties. 'I'hey may be spaced so closely to each other as to constitute in effect a complete wall without losing the advantage of applying them separately. Therefore, the fins I5 are composed of separate projections or segments I'I spaced as closely together as possible without interfering substantially with each other when they are distorted by the heat of the furnace and by the differences in temperature between the welded ends and the free ends thereof. `It has been found in practice that projections of this sort can be made to extend farther outward from the tube than the old continuous ns and that they have a longer life and impose less strain upon the tubes than in the old arrangement. 'Ihey are also advantageous in the making of bent tubes of the shapes illustrated, for example, in Figs. 1 and 8. A continuous n would have to be bent with the tube, of course. It is much easier to bend a fin made up with a line of separate small segments and imposes less strain .on the parts.

In the case illustrated in Figs. 1 and la there is assumed a steel boiler tube of 4 inches outside diameter and about isa of an inch in thickness and projections which are 3 inches Wide (the radial direction), 1 inch long (the direction lengthwise of the tube) and 1/4 inch thick, spaced apart from 116 inch to f8 inch. Such tubes are fairly described as long, small-diameter thin- Walled tubes. The invention is applicable, however, to various other kinds and sizes of tubing and to projections of various other dimensions and spacing. See for example, Murray & Lawrence Patent 1,929,444, October 10, 1933, illustrating variations in structure, and Hoer Patent 1,968,079, July 31, 1934, illustrating an automatic machine for applying the projections.

The electric resistance methods of welding, which are probably the most convenient in this particular work, involve the passage of a current through the tube and the end of the projection. In such methods there is a softening of the tube at the joint. For this reason, as well as for the considerations stated above, it is desirable to limit the total length of the tube covered by one welding operation. vIt is preferable to keep with, y

in a three inch length of the tube, assumingthe ordinary boiler tube above described. Within this length there may be applied at one operation either a single projection or iin-segment of about three inches length, or several such segments totaling about three inches.

The projections, therefore, are applied either one at a time along the line (simultaneously at opposite sides of the tube where two such ins are desired), or in groups of such a small number as not to exceed the length of tubing which will retain its form under the conditions of heat and pressure.

For example, in Fig. 2, the projections l1 are applied in groups of three at a time which, assuming the particular dimensions above stated, would involve a length of tubing of slightly over three inches. The operation may be performed simultaneously at two or more points in the length of the tube as illustrated by a second group of three projections. The spacel I8 must be maintained at such length that the heat applied at the two working points shall not be transmitted in any substantial degree from one to the other. Fig. 3 shows a second group of three projections applied following each of the two starting points. These operations are continued until the entire desired length is covered as in Figs. 1 and 8.

Fig. 4 illustrates a suitable electric resistance welding method. The tube l l is held clamped in the two parts i9 of a positive electrode. The projection il (or .group of such projections) is clamped between the two parts 2li of the negative electrode. The parts are brought into contact, as illustrated, and the lcurrent passed between them. rihey may be slightly separated to form sparks, as in the ordinary asli method, and thus softened or may be softened by the use of a high volume of current passed for a very brief time as in the Murray method., When they are suciently heated the current is cut oi and the parts pressed together in the direction of the arrows and thus welded.

In these welding methods the inner end of the projection Il is usually formed with a tapered portion 2| which is taken up or extruded or squeezed out in the Welding operation, leaving the welded contact area equal to or greater than that of the welded end of the projection.

Fig. 9 illustrates a diierent style of projection In making bent tubes, the projections are applied throughout the whole or the desired portion of the length of the tube while the latter is straight. When the heat of welding is dissipated the tube is bent. 'I'he interrupted n offers no substantial resistance to bending in the plane transverse to the fin. In the few cases where the t'ube requires bending in the plane of the fin, the projections may be spaced or shaped so as not to contact with each other within the desired degree of curvature of the tube.

What is claimed is:

1. A process for making tubes for boiler walls with practically continuous ns secured thereto which consists in separately welding to the tube 1in-segments spaced slightly from each other to compensate for irregularities of expansion and contraction in portions of said segments adjacent to the tube as compared with portions remote from the tube, with the segments in line and in suoient proximity to each other lengthwise of the tube to provide a substantially unbroken wall when used in connection with other similar tubes.'

'2. A process for making tubes for boiler walls with practically continuous finssecured thereto which consists in separately welding to the tube iin-segments spaced slightly from each otherV to compensate for irregularities of expansion and 'contraction in portions of said segments adjacent to the tube as compared with portions remoteffrom the tube, with the segments in line and in sufficient proximity to each other lengthwise of the tube to provide a substantially unbroken wall when used in connection with other similar tubes, said process comprising the welding of the segments to the tubes by an electric resistance method involving the passage of a heating current through the tube and the segments and the pressing of them together, the segments being applied in a succession of steps, each step embracing such a short portion of the length of the tube as to avoid heating the wall thereof suciently to permit substantial distortion under the pressure applied.

3. The process of claim 1, the segments being applied in a succession of steps along the length of the tube one at a time so as to avoid heating the tube over such a length as to permit substantial distortion under the pressure applied.

4. 'Ihe process of claim 1, the segments being applied in a succession of steps not greater than about three inches in length.

5. The process of claim i, applying said segments simultaneously at opposite sides of the tubes.

6. The process of claim 1, applying the segments simultaneously at points in the length of the tube so far apart as to avoid the transmission of any substantial quantity of heat from one to the other.

'7. I'he process of claim 1 appliedv to a steel boiler tube of the order of about four inches diameter and of an inch in thickness, and the segments being applied over a continuous length of not more than about three inches.

8. The process of claim 1 applied to the tube while it is straight, and thereafter bending the tube.

9. 'I'he process of claim 1 applied to the tube while it is straight, and thereafter bending the tube in a plane at right angles to that of the projections.

10. A process for making tubes with separate projections secured thereto, said process comprising the welding of the projections to the tubes by an electric resistance method involving the passage of a heating current through the tube and the projections and the pressing of them together without an internal mandrel but solely against the resistance of the tube wall, the projections being applied in a succession of steps along the length of the tribe, each embracing such a short portion of the length of the tube as to avoid heating the wall thereof sufliciently to permit substantial distortion under the pressure applied.

11.- A process of making tubular umts for boiler Walls and the like comprising a long, smalldiameter thin-walled steel tube with separate projections secured thereto, said process comprising the welding of the projections to the tubes by an electric resistance method involving the passage of a heating current through the tube and the projections and the pressing of them together, applying the projections in a succession of steps along the length of the tube not greater than about three inches in length.

12. A process of making tubular units for boiler walls and the like comprising a long, smalldiameter thin-walled steel tube with separate projections secured thereto, said process'comprising the welding of the projections to the tubes by an electric resistance method involving the passage of a heating current through the tube and the projections and the pressing of them together, applying such projections simultaneously at opposite sides of the tube.

JOHN F. MURRAY.

JOSEPH B. MURRAY.

THOMAS E. MURRAY, Jn. Eecutors of the Estate of Thomas E. Murray,

Deceased.

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