Cleaning and liquid contact with solids – Apparatus – For work having hollows or passages
Reexamination Certificate
1997-09-15
2001-02-27
Stinson, Frankie L. (Department: 1746)
Cleaning and liquid contact with solids
Apparatus
For work having hollows or passages
C134S172000, C134S198000, C134S113000, C122S392000, C239S752000
Reexamination Certificate
active
06192904
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a flexible lance for machining or inspecting a tube bottom of a steam generator.
Endoscopic inspections of tube bottoms of steam generators demonstrate that in regions which have a poor flow of water of a secondary circuit through them, adhering impurities are left behind, having a height in some places that can be a few centimeters.
Such deposits are called kidney deposits due to the geometric shape of their distribution on the tube bottom. They are produced because loose deposits are left behind in an inner region of the heating tube bundle which has a poor flow therethrough, while in an outer region which has a better flow therethrough, they are entrained with the flow of a secondary side feed-water current. The deposits adhere to the tube bottom in an increasingly stronger manner as the operating duration rises. As a result of further depositing processes in the course of a number of operating cycles, deposit conglomerates grow in an expanse of a number of centimeters and have an increased metal and salt quantity concentration in comparison to loose impurities.
Analyses of those hard deposit conglomerates show a mixture composition that is essentially formed of magnetite. Besides other oxidation stages of iron, there are also increased salt quantity concentrations, in particular sulfates, silicates, and phosphates. Likewise increased chromium and nickel ratios are produced due to the depositing of metal shavings. The mechanical hardness in some places can exceed the hardness of the heating tube material so that when the growth is limited spatially, there is the danger of damage to the heating tubes, such as denting.
For that reason, examinations must be regularly carried out on the secondary side of tube bottoms of steam generators as to whether or not and in what quantity deposits have built up between the heating tubes. The deposits must then be removed in order to prevent damage to the heating tubes.
In the case of the adhering deposits, removal takes place primarily through the use of spray processes. However, intermediary spaces between the heating tubes can only be reached with difficulty due to the small tube spacing. The spacing is usually approximately 8 to 11 mm when the heating tubes are in a square configuration and can be between 3 and 4 mm in tighter triangular configurations. For that reason, chiefly spray processes are used, which have been disclosed, for example, in Published European Patent Application 0 084 867 A1, corresponding to U.S. Pat. Nos. 4,572,284 and 4,487,165. In that spray process, a high-pressure water jet is sprayed into the intermediary spaces between the heating tubes by a spray head disposed in a tube channel.
However, it has been found that deposits adhering in the inner region of the tube bundles can only be partially removed in that manner. In order to assure an efficient cleaning of the tube bottom, it is therefore necessary to guide a spray head directly into the intermediary spaces between the heating tubes and to aim a high pressure jet of fluid directly at the deposits inside the heating tube bundles.
A device which is suited therefor has been disclosed, for example, in Published European Patent Application 0 305 483, corresponding generally to Published International Patent Application WO 88/07156 and U.S. Pat. No. 5,065,703. The device disclosed therein includes a flexible spray lance which has a spray head on its free end, with a multiplicity of nozzles from which the spray fluid emerges. The flexible spray lance is formed of a flexible strip in which conduits are disposed that have circular cross sections. Metallic capillaries are inserted into the conduits through which the spray fluid is guided to the spray head. The strip and the conduits are produced in one piece out of a plastic through the use of extrusion.
The strip is supported in a rigid guide having a bent end with which it can be deflected by a predetermined angle. The rigid guide is supported in a transport device which is inserted into the tube channel of the steam generator and can travel along the tube channel. In order to drive the strip, a number of jointly driven gears are provided, having teeth which engage in corresponding perforations of the strip. The free end of the spray lance is oriented toward the tube gaps due to the bent end of the rigid guide.
However, the stability is limited with greater free arm length due to the use of a plastic with capillaries embedded in the longitudinal direction.
U.S. Pat. No. 5,036,871 has disclosed a device for cleaning the tube bottom in which a flexible strip is provided in lieu of a spray lance formed of a one-piece flexible strip. The flexible strip is composed of a multiplicity of individual members connected to one another, through which a high pressure hose is guided. In addition, a cable can be incorporated into this strip to increase its stability. Such a segmented strip is also used in the devices disclosed in U.S. Pat. No. 5,065,703 and U.S. Pat. No. 5,286,154 for inspecting and machining the tube bottom, in which an inspection lens system and mechanical machining tools, for example a drill or grasping mechanism, are used on a machining head. However, in order to be able to receive high pressure spray capillaries, the segments which are connected to one another are wide enough to ensure that very narrow tube gaps of the kind found in triangularly disposed heating tube bundles, can no longer be navigated.
U.S. Pat. No. 4,407,236 has disclosed a flexible spray lance which is formed of a spring steel strip, on which one or a number of capillaries for the spray fluid are fastened to one side. The capillaries are laid in a wavy manner and at the free end of the strip, they feed in a downwardly directed manner into a semicircular recess on the underside of the strip so that the spray fluid coming from them is directed downward onto the tube bottom. The strip is guided with its narrow sides into grooves in a top and bottom plate, which are introduced into the tube channel of the steam generator. The groove in the bottom plate causes a deflection of the strip onto a tube gap. The driving of the strip is carried out by a transverse force exerted on the strip from behind. That produces a high rigidity of the strip and in addition, is only possible in steam generators in which an inspection port is disposed at the same level as the tube channel.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a flexible lance for machining or inspecting a tube bottom of a steam generator, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which can also be inserted into narrow tube gaps.
With the foregoing and other objects in view there is provided, in accordance with the invention, a flexible lance for machining or inspecting a tube bottom of a steam generator, comprising a flexible metallic strip having a free end, a longitudinal direction and recesses disposed one after another in the longitudinal direction; a flexible supply line threaded through the recesses; and a machining or inspection head disposed on the free end and associated with the flexible supply line.
As a result of this measure, a very narrow construction of the flexible lance can be achieved so that even narrow tube gaps can be traveled.
In accordance with another feature of the invention, formations are respectively placed between the recesses in the longitudinal direction of the strip. The formations are for receiving the supply line and extend alternatingly on one side of the strip and then on the other. As a result, it is not necessary to bend the supply line when threading it.
In accordance with a further feature of the invention, the strip is formed of steel.
In accordance with an added feature of the invention, a spray head is provided as the machining device and the supply line is a metallic capillary, in particular a capillary formed of a nickel-titanium alloy.
In accordance with an additi
Henglein Rudolf
Secknus Otto
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
Stinson Frankie L.
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