Pipe joints or couplings – Repair
Reexamination Certificate
1999-10-21
2001-09-25
Jordan, Charles T. (Department: 3641)
Pipe joints or couplings
Repair
C376S260000, C376S282000, C376S286000, C376S463000
Reexamination Certificate
active
06293593
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to devices for repairing pipes. In particular, the present invention relates to an apparatus for repairing and providing a temporary seal around piping in an internal core spray-system of a nuclear reactor.
2. Description of the Related Art
The boiling water nuclear reactor industry has experienced extensive cracking in certain internal reactor parts. Among these parts is the core spray piping, which is presently being repaired or reviewed on most nuclear reactor plants.
The core spray piping functions to bring core spray flow through the core shroud from a source external to the reactor pressure vessel. The piping enters the vessel through a safe end above the shroud and immediately goes into a tee that divides the flow into two pipes. Each pipe curves around the interior of the vessel until it reaches a vertical section, and is supported with at least one support along the path. The vertical section extends down to the shroud where the piping enters through another safe end and terminates in a tee located in the sparger at the top of the shroud. There are typically two spray piping systems per reactor vessel which serve four half-circle spray spargers in the shroud. In most existing systems, the piping includes steel pipes and welded couplings which are susceptible to intergranular stress corrosion cracking due to the oxidizing environment of the reactor, welding process and the stagnant water typically present in the pipes.
The vertical section of piping typically includes a welded pipe coupling assembly immediately outside of the core shroud. This section of piping has been particularly prone to cracking, which can result in leakage or even structural damage to the internal core spray piping.
U.S. Pat. No. 5,735,551 issued to Whitman et al. discloses an L-shaped pipe repair apparatus for repairing the welded pipe assembly immediately outside of the core shroud. This apparatus includes first and second housings that are bolted together over the pipe to be repaired. A first seal is mounted within the housing assembly to seal against an outer circumferential surface of the pipe, and a second seal is mounted at an end of the housing assembly to seal against a wall of the core shroud. The housing assembly is retained in place against the outer wall of the core shroud by a threaded rod extending through the wall of the shroud or by a spring fixture that reacts against the wall of the reactor vessel.
The pipe repair apparatus of Whitman et al. suffers from the following disadvantages. First, the apparatus must be sized and machined precisely to fit the pipe to be repaired. The apparatus is not designed to accommodate differences in the outside diameters of the pipes. Second, the apparatus does not prevent cracks in the existing pipe from continuing to propagate and allowing the pipe to pull apart. Third, the L-shaped design of the apparatus is expensive to manufacture, difficult to install, and limits the versatility of the apparatus. The L-shaped design has limited usefulness in many cases since the cracks and leaks in the piping tend to occur in the welded couplings at varying distances above the elbow. The L-shaped design also prevents the apparatus from being used on straight sections of piping that are not adjacent to an elbow.
U.S. Pat. No. 5,737,380 issued to Deaver et al. discloses a replacement core spray line assembly for a nuclear reactor. This core spray line assembly provides a permanent repair of leaking or cracked core spray lines by replacing the lines with new pipes and connectors. This assembly does not provide a temporary repair assembly that can be quickly applied over existing piping as cracked conditions are found at a nuclear reactor plant.
Thus, there is a need for an improved apparatus that can be applied over existing piping to provide a temporary repair for cracked and/or leaking pipes and couplings in a boiling water nuclear reactor plant.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an apparatus for repairing cracked and/or leaking piping that solves the problems with the prior art arrangements described above.
It is a further object of the present invention to provide a pipe repair apparatus that is well adapted for remote installation, fast to install, reliable in use, and readily adapted to mate with the as-found conditions of a particular pipe configuration.
It is a still further object of the present invention to provide a pipe repair apparatus for core spray piping in a nuclear reactor that maintains the geometry of the original piping after installation, minimizes a leak rate upon a pipe break, has a long service life, accommodates any misalignment of the piping above and below the coupling, holds an end load equivalent to the original piping requirements, prevents axial movement of the piping in the event a pipe is broken and tends to pull apart, accommodates a possible axial movement of the piping should a pipe pull apart after breaking, and does not require preinstallation pipe preparation or measuring.
According to the present invention, a collar clamp assembly is provided for use as a temporary seal around a leaking pipe coupling of a core spray piping of a nuclear reactor. The collar clamp assembly comprises first and second housings having respective first and second ends and a pair of longitudinal edges between the ends. The housings have tongue and groove mating configurations along the longitudinal edges that provide a seal between the edges while allowing the housings to accommodate different outside diameters of pipe to be repaired. A plurality of fasteners secure the first and second housings together to form a closed conduit between the ends. The conduit is shaped to receive a length of the core spray piping including the leaking pipe coupling. First and second seals are located at first and second longitudinally spaced positions, respectively, on each of the first and second housings and extend around the closed conduit. The seals are generally coaxial and are oriented to seal the housings against an outer circumferential surface of the core spray piping on either side of the leaking pipe coupling.
The collar clamp assembly further comprises a grip structure configured to engage and grip an outer circumferential surface of the core spray piping and prevent the pipe coupling from pulling apart in a longitudinal direction. According to a first embodiment, the grip structure comprises a gripping ring installed in a groove adjacent to the respective first and second seals. In this embodiment, the first and second seals comprise raised metal rings formed on inner circumferential surfaces of the first and second housings.
According to a second embodiment, the grip structure is provided by the first and second seals themselves. In this embodiment, the seals comprise split washer locking rings having a sharp inner edge angled toward the leaking pipe coupling to engage the piping and prevent the pipe coupling from pulling apart in a longitudinal direction.
The collar clamp assembly according to the first embodiment has an extended length with inner and outer pairs of bulkheads formed in each of the housings. The outer pair of bulkheads are located adjacent to the respective ends of the housings, and the inner pair of bulkheads are located between and spaced from the outer pair of bulkheads. The first and second seals are located on the inner pair of bulkheads. The outer pair of bulkheads are sized to provide a generous gap between an inner circumferential surface thereof and an outer surface of the core spray piping to accommodate a misalignment of the piping. A side opening is defined by the housings and is configured to accommodate and allow an elbow of the core spray piping to protrude through a side wall near one end of the clamp assembly.
The collar clamp assembly according to the second embodiment has a shorter length and only one pair of bulkheads formed in each of the housings. The seals are located on the
Jordan Charles T.
Richardson John
Westinghouse Electric Company LLC
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