Volume-II of IV - GAIL

4.2.1 The wrap around sleeve shall be of a size such that a minimum overlap of 50mm
before applying is ensured (after shrinking) on both sides of the yard applied
corrosion coating of pipes.
In the cases where carrier pipe is installed by direct boring/ jacking, the overlap on
the mill coating for the leading edges of the joints shall be minimum 200mm. When
this extra overlap is achieved by providing an additional patch of heat shrink tape/
wraparound, it shall be applied in such a manner that the square edge of the patch
on the joint coating is in the direction opposite to the direction of boring/ jacking.
4.2.2 Before centering the wraparound sleeve, the bare steel surface shall be preheated
with torch moved back and forth over the surface or by induction heating. The
minimum preheat temperature shall be as recommended by manufacturer and shall
be checked by means of contact type temperature recording thermometer.
Temperature indicating crayons shall not be used Pre-heat temperature shall be
checked on every joint. Care shall be taken to ensure that the entire circumference
of the pipe is heated evenly. Temperature measuring instruments shall be
calibrated immediately before the start of the works and thereafter at intervals
recommended by the manufacturer of the instrument.
4.2.3 Upon pre-heating the pipe surface shall be applied with two pack epoxy primer of
wet film thickness 100 microns or as per manufacturer’s recommendation
whichever is higher, to cover the exposed bare metal of the welded field joint and
10mm min. onto the adjacent pipe coating if recommended by the manufacturer.
The wet film thickness of the primer shall be checked or every joint with a wet film
thickness gauge prior to installation of sleeve. Thickness gauge shall be calibrated
once per shift.
4.2.4 Immediately after application of epoxy primer, the wraparound sleeve shall be
entirely wrapped around the pipe within the stipulated time recommended by the
manufacturer. Sleeve shall be positioned such that the closure patch is located to
one side of the pipe in 10 or 2 O’clock position, with the edge of the undergoing
layer facing upward and an overlap of min. 50mm. Gently heat by appropriate
torch the backing and the adhesive of the closure and press it firmly into place.
4.2.5 A heat shrinking procedure shall be applied to shrink the sleeve in such a manner
to start shrinkage of the sleeve beginning from the center of the sleeve and heat
circumferentially around the pipe. Continue heating from the center towards one
end of the sleeve until recovery is completed. In a similar manner, heat and
shrink the remaining side. Shrinking has been completed when the adhesive
begins to ooze at the sleeve edges all around the circumference.
The complete shrinking of the entire sleeve shall be obtained without undue
heating of existing pipe coating and providing due bonding between pipe, sleeve
and pipe coating. The installed sleeve shall not be disturbed until the adhesive has
solidified.
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