– The first step in internal field coating system,
is to re-clean the internal cut-back area after the
root pass and hot bead. Attached to the internal line-up
clamp is a highspeed brush machine that impinges the
weld to remove soot, dust and slag created by the welding
The brush machine is centered on the weld and activated
for a pre-determined cycle. Upon completion of the cleaning
cycle, the brush machine is pulled forward slowly while
the vacuum machine travels over the weld to remove all
The resulting weld area is now prepared for the completion
of the weld, X-ray and coating. Attached to the stern
side of the vacuum unit is the cable that travels down
the pipe, through other internal machines and connects
to a stop trolley or buckle detector.
Coating Application – The internal
coating machine is connected to a battery-powered tractor
that travels through the pipe without umbilical cables.
All operations of the machine are controlled by a programmable
microprocessor built with military precision.
The coating machine is centered at the weld area while
the weld is induction heated from the outside to approximately
463 degrees F (239 deg C ). Once the weld is to temperature,
the technician removes the external control isotope
which signal the internal coater to go into a coating
cycle. The epoxy powder will be fluidized and blown
through the rotating spray head.
The spray head will rotate a pre-determined, but adjustable
number of times to deposit the specified width and thickness
of coating. The parent coating will be overlapped to
ensure an effective and continuous coating. The internal
coating machine must be removed from the pipe for servicing
and refilling at regular intervals, depending on pipe
Weld Inspection – A unique video
system allows for each coated weld to be visually inspected
for acceptance. A two-way communication link is used
to connect the external monitor and tape deck with the
internal video camera, in real time. The untethered
video tractor can transmit several miles into a pipeline
and provide clear pictures.