OUTERWRAP FOR PIPELINE WRAPPING
AS PER IS:10221-1982 & AWWA C-203-91
Outerwrap is a nonwoven, thick, glass fibre mat that has been uniformly impregnated & treated with plasticized coal tar pitch or bitumen & dusted with talc powder or sand to prevent the layers from sticking together in the roll form. The finished outerwrap has a smooth uniform surfaced free of visible defects, is flexible & of uniform porosity to facilitate the release of hot gases and achieve better finishing
The finished outerwrap shall have the following physical characteristics as per IS : 10221 – 1982.
||N/150 mm of width, Min
||Tear strength (Transverse)
||Inner diameter of core
||63 to 75
Glass Fibre Tissue Base Membrane shall have the following physical characteristics as per IS : 10221 – 1982.
||The inner wrap shall have a porosity, when related to pressure difference across the sample of not less than 0.55 mm & not more than 1.9 mm of water guage, at an air velocity of 1 m/s.
||Unaffected under load in hot bitumen at 288° C for 1 minute
||There shall be no cracking when bent over a 3 mm radius, after immersing in water for 10-15 minutes through a 90° arc.
PHYSICAL CHARACTERISTICS OF OUTERWRAP AS PER AWWA-C-203-1991 ARE AS FOLLOWS::
Nominal thickness : shall not be less than 0.76 mm.
Mass : shall not be less than 5.4 kg./9.3 m' nor more than 6.8 kg./9.3 m' . The weight of the base membrane of glass fibre tissue shall not be less than 0.77 kg./9.3 m' .
Breaking strength : The average strength in the longitudinal direction shall not be less than 6130 N/m of width. The average breaking strength in the transverse direction shall not be less than 4730 N/m of width.
Pliability : There shall be no cracking of outerwrap as per AWWA-C-203-91.
Weight loss on heating : The loss of heating shall not be more than 2 % as per AWWA-C-203-91.
Sticking to Surface : During unroll shall not Stick to itself to such an extent as to cause tearing (at temp. between 0° C to 38° C).
OUTERWRAP APPLICATION :
Outerwrap shall be mechanically applied in a continuous end-feed machine or in a lathe-type machine. The outerwrap shall be applied to, but not buried in, the outer surface immediately following the final coat of enamel. If specified by the purchaser, the outerwrap should then be immediately followed by kraft-paper final wrap so that it can develop adhesion with the outerwrap.
PREVENTION OF OUTWRAP GASSING :
If low-porosity outerwrap that has been stored is applied under high-humidity conditions, "gassing" (the formation of craters or voids in the enamel beneath the outerwrap) shall be prevented by applying a film of outerwrap saturant or hot enamel to the underside of the outerwrape before it is drawn in to the enamel on the pipe.
OVERLAPPING OF OUTERWRAP :
The outerwrap as specified above shall be of suitable width of smooth, spiral application and shall be of uniform width. The side lap of the outerwrap shall be at least ½ in. (13 mm.). The outerwrap shall be applied neatly and smoothly with bleed-out between laps and shall be free of wrinkles and buckles.