Apparatus for removing sludge deposits

An apparatus for removing sludge from the tubes and tubesheet of a steam generator. A support structure is adapted to be mounted at an access port of a steam generator. A lance tube extends from the support structure into the steam generator. A spool attached to a high pressure hose is received in the lance tube. A pinch roller assembly mounted on the support structure is used to move the cylinder through the lance tube. High pressure water flows through slots drilled in the spool and out holes in the lance tube against the tubes and tubesheet. A rocker motor causes back and forth rotation or rocking of the lance tube to create a sweeping action. The lance tube may also be adjusted axially to insure that the water streams are directed to the tube lanes.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is generally related to equipment for cleaning steam 
generators and in particular to a high pressure fluid lance for cleaning 
sludge off the tubesheet and tubes by access to an open tube lane. 
2. General Background 
In nuclear power stations, steam generators such as recirculating steam 
generators (RSG's) are used for heat exchange purposes in the generation 
of steam for driving turbines. Primary fluid which is heated by the core 
of the nuclear reactor is lead through a collection or bundle of tubes in 
the RSG. A secondary fluid, generally water, which is fed into the space 
around the tubes receives heat from the tubes to provide a continuous 
steam generation cycle. Due to the constant high temperature and severe 
operating environment, a sludge mainly comprised of iron oxide such as 
magnetite builds up on the lower outer portion of the tubes and on the 
tube sheets that support the tube bundle. Since the sludge build up on the 
tube bundle and tube sheets reduces heat transfer efficiency and can cause 
corrosion, it is preferable that the tubes and tube sheets be cleaned 
periodically to remove the sludge. 
Conventional RSG sludge lancing consists of the use of segmented lances, 
usually screwed together, that are moved into and out of the tube bundle 
by an externally mounted indexer. Operation of these lances requires that 
the lance sections be removed or added as the lances are retracted or 
advanced. The addition or removal of lance sections requires that the 
sludge lancing operation be stopped and it requires the presence of 
personnel in a radioactive area. Depending on the job and the number of 
passes required with the lance, as much as one half of the time scheduled 
for the operation involves adding and removing lance sections. This 
results in increased radiation exposure of personnel and unproductive down 
time of the nuclear steam supply system. 
Patents related to sludge lancing-that applicants are aware of include the 
following. 
U.S. Pat. No. 4,079,701 discloses a system for removing sludge from a steam 
generator wherein headers are arranged at the elevation of the sludge to 
be removed and a fluid lance is moved along the line between the headers. 
U.S. Pat. No. 4,424,769 discloses an apparatus for the removal of sludge 
deposits on the tube sheet of a steam generator wherein a lance assembly 
is moved into and through the steam generator by a driving mechanism. 
Cleaning is carried out in successive sequences with different lances that 
direct cleaning fluid to the tube plate in different zones more and more 
remote from the lances. 
U.S. Pat. No. 4,515,747 discloses a wheeled transporter that is pulled by 
cables along the tubesheet between the tube bundle and the steam generator 
shell. Inspection equipment or a nozzle for cleaning the tubesheet may be 
attached to the transporter. 
U.S. Pat. No. 4,566,406 discloses a steam generator having a manifold with 
a plurality of nozzles for cleaning sludge from the tubesheet. The 
manifold is rigidly attached to the tubesheet and remains in place during 
normal operation of the steam generator. 
U.S. Pat. No. 4,700,662 discloses a sludge lance wand for cleaning once 
through steam generators. A curved high pressure fluid feed tube has a 
plurality of feed tube extensions attached at one end and nozzles attached 
at a second end for directing fluid toward the tubesheet as the wand is 
moved through the steam generator. 
U.S. Pat. No. 4,757,785 discloses a steam generator sludge removal 
apparatus wherein a track is assembled between the once through steam 
generator outer shell and circular shroud around the tube bundle. A 
motorized carriage driven on the track directs high pressure fluid toward 
the tube bundle through windows in the circular shroud. 
SUMMARY OF THE INVENTION 
The present invention addresses the equipment needs for cleaning steam 
generators in a straightforward manner. What is provided is an apparatus 
for removing sludge deposits from the tubes and tubesheet of a steam 
generator. A tubular support structure has a flange extending radially 
from one end for mounting at an access port on a steam generator. A tube 
received in the support structure extends beyond the flange into the steam 
generator. The tube has a plurality of holes spaced along the length of 
the tube that extends beyond the support structure. A spool closely 
received within the tube has an axial bore closed at one end and the 
central portion of the spool is drilled to provide slots therein. A high 
pressure hose is attached to one end of the spool so as to be in fluid 
communication with the axial bore in the spool. A drive mechanism mounted 
on the support structure at the end opposite the flange grips the high 
pressure hose to cause movement of the hose and spool through the tube. 
Water under pressure travels through the hose to the spool and exits the 
drilled slots into the tube. This water under pressure in the tube exits 
the holes spaced along its length and removes sludge on the tubes and 
tubesheet. A second drive mechanism mounted on the support structure may 
be used to cause back and forth rotation of the tube to cause the water 
jets to contact a larger area and create a sweeping action along the 
tubesheet toward the outer edges of the tube bundle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings, it is seen in FIG. 1 that the invention is 
generally indicated by the numeral 10. Sludge removal apparatus 10 is 
generally comprised of tubular support structure 12, lance tube 14, spool 
16, high pressure hose 18, means 20 for causing spool 16 and hose 18 to 
move axially in lance tube 14, means 21 for axially adjusting the position 
of lance tube 14 in support structure 12, and means 22 for causing back 
and forth rotational motion or rocking of lance tube 14 in support 
structure 12. 
As seen in FIG. 1, support structure 12 is elongated and has first and 
second ends 24, 26. Flange 28 extends radially from first end 24 and is 
provided with bores 30 therethrough that are spaced to allow support 
structure 12 to be bolted to an access port of a steam generator such as a 
manway or manhole. This allows the portion of lance tube 14 that extends 
beyond first end 24 to be positioned between tube rows in the steam 
generator. 
Lance tube 14 is movably received in support structure 12 to allow axial 
adjustment of the position of lance tube 14 relative to support structure 
12 and the tubes inside a steam generator and to allow for a back and 
forth rotating or rocking motion of lance tube 14 during sludge removal 
operations. The portion of lance tube 14 that is housed within support 
structure 12 has an elongated collar 34 attached thereto that cooperates 
with axial adjustment means 21 and rotation means 22 to cause such 
movement of lance tube 14. The portion of lance tube 14 that extends 
beyond first end 24 of support structure 12 is provided with a plurality 
of holes 32 that are spaced apart approximately one hundred eighty degrees 
around the circumference of lance tube 14. The spacing of holes 32 along 
the length of lance tube 14 corresponds to the pitch of spacing of the 
tubes in the steam generator to be cleaned. Roll pin 33 is provided 
through the end of lance tube 14 to prevent spool 16 from exiting lance 
tube 14. 
Spool 16 has its ends sized to provide a close tolerance fit within lance 
tube 14, approximately 0.0003 inch, while still allowing movement 
therethrough. The central portion of spool has a reduced diameter that is 
drilled to provide three slots 36 spaced one hundred twenty degrees apart. 
Spool 16 has an axial bore that is closed at one end. The open end 38 is 
adapted to receive connector 40 on high pressure hose 18. This places the 
axial bore and holes 36 in cylinder 16 in fluid communication:: with high 
pressure hose 18. 
Hose 18 is any suitable high pressure hose capable of delivering liquid 
under pressure to cylinder 16 and is connected at one end to a high 
pressure liquid source not shown. 
Means 20 for causing axial movement of spool 16 and hose 18 in lance tube 
14 is generally comprised of a dual gear motor driven pinch roller 
assembly 42, 44. As best seen in FIG. 2, assemblies 42, 44 are each formed 
from a frame 46, drive motor 48, pinch roller 50, position encoder 52, 
pinch roller drive belt 54, and position encoder drive belt 56. Assemblies 
42, 44 are spaced apart one hundred eighty degrees apart around support 
structure 12 so that pinch rollers 50 are in opposing positions. Both 
pinch roller assemblies 42,44 are hingedly mounted on support structure 12 
as indicated at numeral 58. This allows pinch roller assemblies 42,44 to 
be pivoted away from support structure 12 to allow insertion or removal of 
spool 16 and hose 18. Clamp 60 is used to hold first pinch roller assembly 
42 in its operational position adjacent second assembly 44 to provide 
pressure of pinch rollers 50 on hose 18 during cleaning operations. Any 
suitable clamping means may be used to insure that the proper pressure is 
maintained on hose 18. 
Means 21 for axially adjusting the position of lance tube 14 is provided in 
the form of alignment drive motor 62, pinion gear 64, and adjustment ring 
66. Rotation of pinion gear 64 causes corresponding rotation of adjustment 
ring 66. Adjustment ring 66 is threadably engaged with threaded area 68 on 
elongated collar 34. Rotation of adjustment ring 66 thus causes axial 
movement of collar 34 and lance tube 14. 
Means 22 for causing back and forth rotational or rocking motion of lance 
tube 14 is comprised of rocker motor 70, pinion gear 72, sector gear 74, 
and rocker position encoder 76. Rocker motor 70 is mounted on support 
structure 12 and drives pinion gear 72 which engages and drives sector 
gear 74. Sector gear 74 has its base attached to collar 34 for causing 
corresponding movement of lance tube 14. Rocker position encoder 76 is 
mounted on support structure 12 and driven by pinion gear 72 for 
indicating the relative radial position of holes 32 in lance tube 14. 
In operation, lance tube 14 is formed from one or more sections threaded 
together to provide a lance tube that spans either the radius or the full 
diameter of the steam generator. Lance tube 14 is inserted in the access 
hole and support structure 12 is bolted to the steam generator. Pinch 
roller assemblies 42,44 are separated and spool 16 is inserted into lance 
tube 14. Hose 18 is used to manually push spool 16 to approximately the 
first set of holes 32 in lance tube 14. Pinch roller assemblies 42,44 are 
closed and locked on hose 18. High pressure water flow into hose 18 is 
then started and axial adjustment means 21 is used to move lance tube 14 
so that holes 32 are aligned with the lanes between the tubes in the steam 
generator. Rocker position encoder 76 is used to verify the correct 
rocking action. Spool 16 is driven to the end of lance tube 14 by pinch 
roller assemblies 42, 44, the function of position encoders 52 is 
verified, and the counter is zeroed. Lancing can now begin without the 
need for personnel to return to the steam generator for all six passes of 
spool 16 up and down lance tube 14. The rocking action sweeps the impact 
point of the water along the tubesheet into the annulus and to the 
suctions at the outer edge of the bundle. At the end of each pass spool 16 
is aligned with annulus wash holes 78 in lance tube 14. This dumps the 
entire water flow into the annulus in both directions to provide a direct 
flow for cleansing the annulus. 
Because many varying and differing embodiments may be made within the scope 
of the inventive concept herein taught and because many modifications may 
be made in the embodiment herein detailed in accordance with the 
descriptive requirement of the law, it is to be understood that the 
details herein are to be interpreted as illustrative and not in a limiting 
sense.