Condenser tube-to-tubesheet joint improvement

Abstract

A tube-to-tubesheet joint for steam condensers having a plurality of holes drilled in condenser tubesheets, a plurality of 8 mil triangular cut serrations in the wall surface of each hole, locating the serrations in a set positioned centrally of the wall surface, inserting a tube end into each hole, and forming a mechanical interference fit between tube wall and hole wall surface. In modified embodiment for thick tubesheets, plural sets of serrations with sets spaced apart may be formed in tubesheet holes.

Claims

1. A method for forming tube-to-tubesheet joints in exhaust steam condensers having spaced tubesheets, each tubesheet having interior and exterior faces with the tubesheets interior faces confronting each other, and the condensers further adapted to receive tubes extending by their ends between the tubesheets, the method comprising the steps of: forming a plurality of holes opening through the interior and exterior faces of each of the confronting tubesheets, the holes being aligned for receiving the ends of tubes, the holes being defined by cylindrical wall surfaces in the tubesheets, forming a plurality of serrations in the wall surface of each tubesheet hole, forming each serration as a triangular cut approximately 8 mils deep into each tubesheet hole wall surface, sticking tubes into the condenser for inserting the opposite ends of each tube into the aligned serrated holes, inserting a tool into each tube end situated in a serrated hole, and forming a mechanical interference fit between serrations and tube ends wherein outer tube wall impressions extend into the serrations.

2. A method as defined in claim 1 including the further step of forming the serrations in a central section of the tubesheet hole wall surface.

3. A method as defined in claim 2 which includes the step of locating the central section of serrations spaced equally from tubesheet exterior faces.

4. A method as defined in claim 1 including the further step of forming serrations numbering in a range of six to ten in the wall surface.

5. A method as defined in claim 1 including the step for forming eight serrations in the wall surface.

6. A method as defined in claim 1 in which in the step of forming an interference fit, tube impressions extend into serrations.

7. A method as defined in claim 1 in which the plurality of serrations extend concentrically of the wall surface of each tube sheet hole.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) Preferred embodiments of the invention have been chosen for detailed description to enable those having ordinary skill in the art to which the invention appertains to readily understand how to construct and use the invention and is shown in the accompanying drawing in which:

(2) FIG. 1 is a section view of tube-to-tubesheet joint according to the invention.

(3) FIG. 2 is an enlarged detail view of hole drilled in tubesheet showing serrations formed in the hole wall surface.

(4) FIG. 3 is an enlarged detail view of FIG. 2 showing tube impressions expanded into serrations.

(5) FIG. 4 is a modified embodiment of the invention applied to thick tubesheets.

(6) Referring to FIGS. 1 and 2, a condenser tube-to-tubesheet joint 10 comprises a normally vertically disposed tubesheet 12 with a plurality of drilled holes 12a to receive ends of thin walled condenser tubes 13. Two tubesheets at opposite ends of a condenser have aligned, drilled holes for forming tube joints. FIG. 1 illustrates one such tube joint.

(7) Typical tubesheet thickness T ranges from 1.0 to 1.50 in increments of 0.125. Tubesheet materials are selected from one of carbon steel, Muntz metal, aluminum bronze, silicon bronze, titanium, copper nickel, and stainless steels 304, 316, 317, 2205, and 2507. Typical tube diameters are , , 1.0, 1.125, and 1.25.

(8) In accordance with the invention, a plurality of holes are drilled through a tubesheet and hole edges bevelled 12b for ease of receiving a tube end and minimizing damage during sticking and operation on the back face. Within each hole, a set of preferably 8 triangular serrations 14 are formed in the cylindrical wall 12c defining each hole. The set of serrations are placed centrally of the hole with outermost serrations 14b-c of the set spaced equally from tubesheet faces 12d-e. For a 1 thick tubesheet, the serration set occupies a 7/16 length L within tubesheet hole with outermost serrations spaced equally from tubesheet faces.

(9) For tubesheet thickness in a range of 1.0 to 1.50 inches, the spacing of outermost serrations in each serration set is determined by: (T 7/16)/2 where T is tubesheet thickness.

(10) The serrations are triangular cuts into the hole wall having a depth preferably of 0.008 (8 mils), and are spaced apart a distance S, preferably 1/16. FIG. 1 shows a tube hole prepared with serrations for receiving and forming joint with tube. After insertion of tube into operating position within the hole, a hand-held manually operated tool is inserted into the tube end to form a mechanical interference fit of tube and hole in establishing the desired tube-to-tubesheet joint.

(11) FIG. 3 is an enlarged detail view of FIG. 1 with tube 13 in tubesheet hole 12a, the hole having serrations 14. After the tool has expanded the tube to establish a mechanical interference fit, tube impressions 13a extend into serrations 14.

(12) The joint described with reference to FIG. 1 is a preferred embodiment of the invention. Other embodiments vary the number and spacing of serrations within a drilled hole while maintaining triangular 8 mils form of each serration. A set of between 6 and 10 serrations may be employed while maintaining preferred 7/16 length of tubesheet for each serration set, and serration spacing between adjacent serrations accordingly.

(13) FIG. 4 is a modified embodiment of the invention particularly suitable for thick tube sheets. Instead of having a continuous set of serrations as in FIG. 1, there are installed two sets of serrations separated by a gap or space G between them. The length of space G is defined by available hole length. The serrations are 8 mil deep and within a set are typically spaced 1/16.sup.th inch apart. Space length starts at a minimum of .sup.th inch for 1.125 and 1.25 thick tube sheets, and maybe as large as for 1.5 thick tubesheets.

(14) An inventive method may be stated as comprising the following steps. Form a plurality of holes preferably by drilling in spaced tubesheets for receiving ends of condenser tubes, bevelling hole edges at tube sheet faces, forming a plurality of serrations within each tubesheet hole, the serrations located in a central section of the hole spaced equally from tubesheet faces, forming each serration as a triangular cut 8 mils into hole face, running tubes into the condenser to insert tube ends into drilled and serrated holes, and forming a mechanical interference fit between serrations and tube outer wall wherein tube outer wall impressions extend into serrations. For thick tubesheets, the plurality of serrations may be divided into plural sets of equal numbers of serrations with a space or gap located between sets.

(15) Various changes may be made to the structure embodying the principles of the invention. The foregoing embodiments are set forth in an illustrative and not in a limiting sense. The scope of the invention is defined by the claims appended hereto.