Pressure vessel testing fixture

Details Pressure vessel testing fixture Pressure vessel testing fixture

1999-06-03

2001-07-03

Williams, Hezron (Department: 2856)

Measuring and testing

With fluid pressure

Clamp, plug, or sealing feature

C073S049100, C073S049500, C285S323000

Reexamination Certificate

active

06253599

ABSTRACT:

FILED OF THE INVENTION
The invention relates to the field of pressure testing pressure vessels. More particularly, the present invention relates to pressure testing cylindrical tubes.
BACKGROUND OF THE INVENTION
Composite pressure vessels are often fabricated as cylindrical tubes with hemispherical end caps. During the fabrication process, the filaments of graphite or glass are wound in a continuous pattern including both the cylindrical portion and the end caps. For materials and structures testing purposes, a cylindrical tube is an ideal specimen to represent the cylindrical portion of the vessel. For example, a composite cylindrical tube can be fabricated by either filament winding or tape wrapping techniques to have the same lay-ups angle as a cylindrical portion of a pressure vessel. The cylindrical tubes so fabricated will have the same mechanical properties as the cylindrical portion of the pressure vessel. The tube, however, can be fabricated at a small fraction of the cost of a pressure vessel with integral end caps.
A problem associated with realistic pressure testing of cylindrical specimens is that the tube ends must be sealed in such a manner that the tube does not leak, that there are no induced bending stresses at the interface between the tube and the end cap, and that the axial load of the internal pressure is carried by the cylindrical walls of the tube. In typical designs, a metal flange with an insert is utilized to bond the tube specimen using adhesive. The adhesive is under shear stress when the tube is internally pressurized. The shear strength of the adhesive depends upon the type of adhesive used, the bonding procedure, the material for the adherent, and the cure operation. However, regardless of how careful the bonding operation is conducted, the failure of a cylindrical composite tube under internal pressure often occurs at the end fitting of the tube interface. These and other disadvantages are solved or reduced using the invention.
SUMMARY OF THE INVENTION
An object of the invention is to provide a test fixture for pressure testing cylindrical tubes.
Another object of the invention is to provide end fitting fixtures for cylindrical composite tubes under high internal pressure.
Yet another object of the invention is to provide a test fixture for pressure testing cylindrical tubes to provide increased shear tension and to prevent leaks during pressure testing.
The present invention is directed to an improved end fitting test fixture for cylindrical composite tubes tested under high internal pressure. The ends of the tube are inserted into opposing end fixtures having a vertically extending flange abutting the inner walls of the tubes at both ends. A ferrule is disposed around and abuts the outer walls of the tube. A retaining ring is disposed around the ferrule, both of which have mating slanted abutting surfaces. The retaining ring is clamped down upon the end fixtures, the slanted abutting surfaces slide against each to apply a normal radial compression to the tube interface between the tube and flange at the inner walls of the tube, and between the tube and ferrule at the outer walls of the tube. This compression will generate a mechanical friction force, that is a shear force when the tube and the end fitting are being pulled apart longitudinally under high internal pressure testing. The radial compression increases the shear strength of the end fitting by an amount equal to the product of the compressive stress, the friction coefficient, and the contact area between the tube and the ferrule. The compression not only secures the tubes in the fixture but prevents leaks at the tube ends when inserted into the fixtures. These and other advantages will become more apparent from the following detailed description of the preferred embodiment.


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patent: 4197733 (1980-04-01), Holland et al.
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patent: 5217261 (1993-06-01), DeWitt et al.
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patent: 5511830 (1996-04-01), Olson et al.
patent: 5638869 (1997-06-01), Zaborszki et al.
patent: 2197410 (1988-05-01), None
patent: 02261995 (1990-10-01), None

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