Hydraulic Expansion vs. Mechanical Rolling Methods
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HydroPro, Inc. Hydraulic Expansion vs. Mechanical Rolling Methods
1. Hydr Hydrau auli lic c expa expand ndin ing, g, or Hydr Hydroo-ex expa pand ndin ing, g, is an inno innova vati tion on in expa expand ndin ing g tube tubes s into into tubesheets. tubesheets. It is completely different from roller expanding, expanding, whether the tube expanders expanders are driven electrically, by air, or hydraulically. 2. In Hydro-expa Hydro-expandin nding, g, the degree of expandi expanding ng is directly directly related related to the preset expandin expanding g procedure. The pressure is exactly repeatable and does not vary from tube to tube, no matter what shape the tube is in. But, in mechanical rolling, whether you use torque setting or appa apparen rentt perce percent nt tube tube wall wall reduc reductio tion, n, the the degre degree e of expa expand nding ing canno cannott be direct directly ly correlated. Furthermore, Furthermore, torque controllers measure only the power drawn by the rolls which can vary with the condition of the rolls and mandrel, lubrication, operator fatigue and other factors. 3. Mechani Mechanical cal rolling rolling reduces reduces the tube wall by: a) stretching stretching the tube tube radially, radially, and b) imposing imposing high unit rolling forces that cause the tube to extrude axially. Hydro-expanding, however, only stretches the tube radially. The amount of wall reduction is barely measurable and, in fact, the tube end pulls in slightly as the tube is bulged out rather, than extruding. 4. Hydro-ex Hydro-expan panding ding produce produces s no surface surface effects effects on the tube and almost almost no work-har work-harden dening. ing. You never get bell shaped or hour glass shaped tube ends. Therefore, the tube-to-wall contact is always uniform. 5. When you roller roller expand expand tubes into into grooved holes, tube tube metal extrudes extrudes into the grooves. grooves. But, when when you you HydroHydro-exp expan and d tube tubes s into into groov grooved ed holes holes,, the tube tube bulge bulges s into into the groove groove,, providing additional tightness at the contact of the groove edges with the tube. 6. Mech Mechan anic ical al roll rollin ing g may may caus cause e tube tube-e -end nd fati fatigu gue, e, depe depend ndin ing g upon upon the the freq freque uenc ncy y and and amplitude of the stresses the rollers apply. The frequency is far more effective in producing fatigue than the amplitude. amplitude. That is why five or seven roll expanders are used when the tube material is subject to fatigue. From the fatigue standpoint, Hydro-expanding is like having an infinite number of rolls. 7. The high contact contact stresse stresses s imposed imposed by rolling make it more likely likely that stress stress corrosion corrosion will cause tube-end failure. The transition from the reduced wall is a possible trouble source in rolled tubes. 8. You can Hydro-ex Hydro-expan pand d the tubes to the exact exact rear face of the tubeshee tubesheet, t, thereby thereby reducing reducing the chance of crevice crevice corrosion corrosion at the rear. This is accomplishe accomplished d by the uniformi uniformity ty of pressure being applied to the entire tube length at the same time. With mechanical rolling
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HP102061798
Hydraulic Expansion vs. Mechanical Rolling Methods
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methods you are pushing the tube material out the rear of the tubesheet and because of this, you create a very noticeable rear crevice, resulting in premature tube failure. 9. The extreme extreme ease ease of operation operation of the HydroPro requires almost no training. 10. If tube rollers cease and stall, the rolling rolling motor may spin and injure the worker. HydroPro HydroPro is completely safe. 11. To roll tubes into tubesheets tubesheets thicker than 2", you have have to step roll. This is time consuming and requires a tremendous amount of skill. You can Hydro-expand Hydro-expand tubes into any thickness thickness of tubesheet with one pass of the mandrel per tube. 12. When you re-roll leakers after hydro testing, testing, you further reduce the tube tube wall. Also, you may move the ligaments enough to start other leaks and may even cause ligament damage aroun around d the othe otherr tube tubes. s. This This can can also also create create problem problems s in havin having g to chase chase the the leaks leaks completely around the tubesheet, creating even more problems, and so on. With Hydroexpanding, because you can accurately control the exact expansion pressure, you can eliminate the problem of having to re-expand leakers. If you do have a leaker, you know exactly which pressure will provide a seal without disturbing any of the adjacent holes. 13. Expansion Expansion time depends on the tube material and averages averages from 2 to 5 seconds per tube. Only one worker is needed to do the work. Tube ends are prepared in the same way as for roller expanding. Note that tubes would tear up rolls and cages or break mandrels will damage o-rings and backups. 14. Hydro-expanding Hydro-expanding is successful in out-of-round holes holes and in holes distorted by tube plugging. However, axial scratches in the hole or tube material will cause leaks in any expanded tube to tubesh tubesheet eet joints, joints, regardle regardless ss whether whether expandin expanding g by rolling, rolling, near near contact contact explosi explosions, ons, compressing a rubber expander, or by hydro-expanding. Therefore, it is recommended that scratched holes be burnished free of axial scratches or a groove be cut into the tubesheet. It might be further noted that because of the uniformity of hydraulic expansion, it does further reduce the probability of axial scratches when retubing. The extraction of hydro-expanded tubes will be extremely even and uniform, thereby producing cleaner tube holes ready for retubing.
This page was downloaded from http://www.hpro.com.
REF
HP102061798
Hydraulic Expansion vs. Mechanical Rolling Methods
3
Error! Objects cannot be created from editing field codes. HydroPro, Inc. 910 Bern Court, Suite #100 San Jose, CA 95112 408 453-5070 FAX: 408 453-5199
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HP102061798
