TPi October 2010

Hydraulic Expansion The newest expansion method, hydro- swaging, was developed by request from Westinghouse engineers who were seeking a more effective method than roller expansion for nuclear steam generators. Because expansion pressures are applied uniformly, tube after tube, hydraulic expansion yields consistent joints throughout the tubesheet. The system is easy to operate with minimal training and the method has been applied successfully to expand tubes into tubesheets as thin as ¾" up to as thick as 33". Water pressure is applied to the tube ID over the full length of the joint in an accurately prescribed pressure zone, in

HydroSwage diagram

Hydraulic expanding leaves no residue and does not change the appearance of the tube ends because de-ionized water is used to expand the tubes. Used consistently and successfully on both non-weld and welded joints, it is successful in out-of- round holes and in holes distorted by tube plugging. As the pressure applied to the joint is controlled accurately hydraulic expansion does not cause ovalling or cracked ligaments, and because of its uniformity, it further reduces the probability of axial scratches when re-tubing. Extraction of hydro-expanded tubes is extremely even and uniform, producing cleaner tube holes ready for re-tubing. If a leaker occurs, the exact pressure that will provide a seal without disturbing any of the adjacent holes is known. Because of the fine control hydraulic expansion offers, it is not necessary to insert ligament supports in surrounding tubes when re-expanding. Tubes may be hydro-expanded to the exact rear face of the tubesheet, thereby reducing the chance of crevice corrosion at the rear. This is accomplished by pressure being applied uniformly to the entire tube length at the same time. Advanced hydro-swaging systems have a multi-member seal design that allows the operator to perform many expansions without replacing any elements of the sealing package. In addition, touch-screen and PLC technology is being adapted to hydraulic systems to allow storage and download of expansion data. Hydraulic expansion is quieter than most machines used in heat exchanger factories and in locations that utilise the heat exchangers, and it can be done safely anywhere.

one step producing clean and consistent joints. With this process stress, crevice corrosion and metallurgical changes are minimised. Because expansion is accomplished using only distilled or purified water, no lubricant is forced into the tube surface and there is no surface flaking or spalling inside the tube. A smooth transition from expanded to unexpanded areas, along with no change in tube material properties, greatly reduces strain hardening, tube fatigue and stress induced corrosion cracking. When hydro-expanding tubes into grooved holes, the tube bulges into the groove, providing additional tightness at the contact of the groove edges with the tube. The recommended groove for hydraulic expansion should have a width of three times the tube wall thickness and a depth of 0.2 times (20%) the tube wall thickness. The recommended shape of the groove is rectangular, and the edges of the groove need to be clean and square with no interruptions. Hydro-expanding produces no surface effects on the tube and almost no work-hardening. Bell shaped or hourglass shaped tube ends never occur and the tube-to-wall contact is always uniform.

Smooth transition from expanded to unexpanded areas groove penetration is accurate

Haskel International Inc – USA mbloodworth@haskel.com www.haskel.com

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Tube Products International October 2010

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