17
systems permitted specific line tonnages to exceed 535,700
t (600,000 ton).
Inspection of transfer pipe has developed in concert
with other industrial and municipal systems, with wall
thickness and/or photo records possible whether in shaft
or borehole systems. Acoustical pipe integrity testing, ultra-
sound, radiographic (computed tomography methods), and
radiometry are conventional techniques for evaluating wall
thickness which can be applied to accessible transfer lines.
Oilfield methods can be applied to borehole systems – cali-
pers, remote field eddy current, and magnetic/electromag-
netic imaging tools – for pipe condition evaluation. As an
example, calipers can be useful for pipes of distinct layers,
where the innermost layer is the wear media. Ultrasound is
not suitable for these configurations.
If available, inspection schedules can be initiated from
related historical records. If no history is available, it is pru-
dent to inspect relatively early in the expected life cycle. It
also can be advisable to have replacement pipe on hand or
on order when commissioning new systems.
Depending on configuration, observation of wear-
through may be possible, either directly or from mate-
rial cascading down annular space. That calls for prompt
replacement of damaged segments or the entire line, as
appropriate for the system. In-shaft systems typically have
selected segments replaced as needed. Collar-suspended
borehole systems can be designed to address the typical
high-wear segments at the top and bottom of a line. If the
upper segments are worn, the line can be lifted and those
segments replaced. If the bottom segments are worn, the
line can be lowered and the worn segments removed at the
underground station.
Underground Station
Underground station maintenance follows from that per-
formed for conventional material handling plants. Utilities,
travel ways, cranes/lifts, sump and fixtures may be common
to other facilities and their general maintenance will be in
order. Features specific to the transfer system will include
the diverter and may include cleanout components such
as hatch, coupling, and hydraulic power pack and/or air
compressor tools and fittings.
The diverter support – suspended or basal – and cou-
pling to the transfer line will require diligent attention. A
prudent consideration for a new installation is to gauge the
support – load cell, shock-pulse, strain, etc. – as an indica-
tor whether design closes with practice. Inspection of the
diverter itself will follow the cleanout cycle, the typical
distinction being whether a fixed base or a bottom hatch
are used. The entry and discharge orifices, along with
the diversion chamber itself, warrant internal inspection.
Contemporary cameras and devices permit that with rea-
sonable and safe distance and positioning.
Depending on diverter configuration and specific wear,
in-place external patches may be appropriate until a perma-
nent replacement device can be installed. That said, a com-
plete diverter assembly should be considered a critical spare
for the system. Mine shop or fabricator refit might then be
an option for a worn unit, with an opportunity for internal
patching, hard-facing, etc.
Hang-Up or Plug Clearing
Hang-ups or plugs which cannot be released by a diverter
cleanout (Washdown/Cleanout Provisions) entail mainte-
nance beyond scheduled washdowns and cleanouts. These
include set or cured plugs of cementitious material.
In shaft or borehole, the top of plug can be confirmed
from the surface station, using sounding line, piezometer,
borehole camera or other tools.
In a shaft, pipe segments can be pulled from the col-
umn and evacuated individually. Alternatively, with non-
cementitious material, it may be possible to release the plug
by vibration from the lowermost segments upward.
In a borehole, upon confirmation of the top of plug,
the surface and underground stations can be prepared for
the appropriate borehole work-over procedure. In a lower-
ing-removal-replacement procedure, new sticks are added
at the collar and the column is lowered with plugged seg-
ments removed at the underground station.
It may be desired to undertake conventional brushing,
reaming, or scraping of the plug, keeping the transfer line
intact. One approach would be to work over a solid plug
with tools centralized inside the pipe. Alternatively, the
plug could be piloted with a centralized bit and following
tools keyed on that pilot string. In each of these tool string
configurations, the cuttings would be circulated back to the
collar until breakthrough.
If the original line remains serviceable, it can return
to service in either a collar-suspended or grouted-in-place
configuration. With a collar-suspended configuration,
lowering-removal-replacement can be used to restore the
system.
If the initial line is of sufficient diameter, a full-length
insertion of a smaller diameter pipe may be possible to
restore service to a compromised system. That might be the
case if a line wears through and folds inward or a drill out
(including brushing, reaming, scraping) damages the origi-
nal line to the extent an insertion is required.
systems permitted specific line tonnages to exceed 535,700
t (600,000 ton).
Inspection of transfer pipe has developed in concert
with other industrial and municipal systems, with wall
thickness and/or photo records possible whether in shaft
or borehole systems. Acoustical pipe integrity testing, ultra-
sound, radiographic (computed tomography methods), and
radiometry are conventional techniques for evaluating wall
thickness which can be applied to accessible transfer lines.
Oilfield methods can be applied to borehole systems – cali-
pers, remote field eddy current, and magnetic/electromag-
netic imaging tools – for pipe condition evaluation. As an
example, calipers can be useful for pipes of distinct layers,
where the innermost layer is the wear media. Ultrasound is
not suitable for these configurations.
If available, inspection schedules can be initiated from
related historical records. If no history is available, it is pru-
dent to inspect relatively early in the expected life cycle. It
also can be advisable to have replacement pipe on hand or
on order when commissioning new systems.
Depending on configuration, observation of wear-
through may be possible, either directly or from mate-
rial cascading down annular space. That calls for prompt
replacement of damaged segments or the entire line, as
appropriate for the system. In-shaft systems typically have
selected segments replaced as needed. Collar-suspended
borehole systems can be designed to address the typical
high-wear segments at the top and bottom of a line. If the
upper segments are worn, the line can be lifted and those
segments replaced. If the bottom segments are worn, the
line can be lowered and the worn segments removed at the
underground station.
Underground Station
Underground station maintenance follows from that per-
formed for conventional material handling plants. Utilities,
travel ways, cranes/lifts, sump and fixtures may be common
to other facilities and their general maintenance will be in
order. Features specific to the transfer system will include
the diverter and may include cleanout components such
as hatch, coupling, and hydraulic power pack and/or air
compressor tools and fittings.
The diverter support – suspended or basal – and cou-
pling to the transfer line will require diligent attention. A
prudent consideration for a new installation is to gauge the
support – load cell, shock-pulse, strain, etc. – as an indica-
tor whether design closes with practice. Inspection of the
diverter itself will follow the cleanout cycle, the typical
distinction being whether a fixed base or a bottom hatch
are used. The entry and discharge orifices, along with
the diversion chamber itself, warrant internal inspection.
Contemporary cameras and devices permit that with rea-
sonable and safe distance and positioning.
Depending on diverter configuration and specific wear,
in-place external patches may be appropriate until a perma-
nent replacement device can be installed. That said, a com-
plete diverter assembly should be considered a critical spare
for the system. Mine shop or fabricator refit might then be
an option for a worn unit, with an opportunity for internal
patching, hard-facing, etc.
Hang-Up or Plug Clearing
Hang-ups or plugs which cannot be released by a diverter
cleanout (Washdown/Cleanout Provisions) entail mainte-
nance beyond scheduled washdowns and cleanouts. These
include set or cured plugs of cementitious material.
In shaft or borehole, the top of plug can be confirmed
from the surface station, using sounding line, piezometer,
borehole camera or other tools.
In a shaft, pipe segments can be pulled from the col-
umn and evacuated individually. Alternatively, with non-
cementitious material, it may be possible to release the plug
by vibration from the lowermost segments upward.
In a borehole, upon confirmation of the top of plug,
the surface and underground stations can be prepared for
the appropriate borehole work-over procedure. In a lower-
ing-removal-replacement procedure, new sticks are added
at the collar and the column is lowered with plugged seg-
ments removed at the underground station.
It may be desired to undertake conventional brushing,
reaming, or scraping of the plug, keeping the transfer line
intact. One approach would be to work over a solid plug
with tools centralized inside the pipe. Alternatively, the
plug could be piloted with a centralized bit and following
tools keyed on that pilot string. In each of these tool string
configurations, the cuttings would be circulated back to the
collar until breakthrough.
If the original line remains serviceable, it can return
to service in either a collar-suspended or grouted-in-place
configuration. With a collar-suspended configuration,
lowering-removal-replacement can be used to restore the
system.
If the initial line is of sufficient diameter, a full-length
insertion of a smaller diameter pipe may be possible to
restore service to a compromised system. That might be the
case if a line wears through and folds inward or a drill out
(including brushing, reaming, scraping) damages the origi-
nal line to the extent an insertion is required.