PART 3
EXECUTION
3.1
PREPARATION
3.1.1
Pit, Edge, and Weld Preparation
Visibly rough flame-cut steel and weld metal shall be ground with a disk
wheel grinder or other tool to produce a smooth contour prior to abrasive
blasting. Grinding of flame-cut edges and welds shall also be performed to
the extent necessary to etch heat-hardened metal. Pits with an aspect
ratio of greater than unity (as deep as they are wide) shall be ground with
an abrasive disk or other tool prior to blasting. Pits with sharp edges,
undercut pits, and pits with an irregular horizontal or vertical
orientation shall also be ground smooth prior to abrasive blasting.
Grinding shall smooth all of the rough and irregular surfaces to the extent
necessary to allow the entire surface of the pit to be blasted and coated.
Sharp edges shall be ground prior to abrasive blasting to a uniform minimum
diameter of 3 mm 1/8 inch.
3.1.2
Abrasive Blasting
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Note: Consideration should be given to
high-pressure water washing when the substrate to be
metallized has previously been exposed to a chloride
environment. Chloride environments are marine
exposures or bridges to which de-icing salts are
applied. High-pressure washing should be performed
before abrasive blasting.
A profile range is specified and is dependent on the
type and thickness of metallizing to be applied.
Specify a 0.05 to 0.07 mm (2.0 to 3.0 mil) profile
for systems 1-Z, 4-Z-A, and 7-A; 0.06 to 0.09 mm
(2.5 to 3.5 mils) for systems 2-Z, 5-Z-A, and 8-A;
and 0.07 to 0.10 mm (3.0 to 4.0 mils) for systems
3-Z and 6-Z-A.
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Ferrous surfaces to be metallized shall be solvent and blast cleaned to a
white metal grade in accordance with SSPC SP 5. The compressed air used
for abrasive blasting shall be clean and dry. Abrasive blast media shall
be dry and free of grease and oil. The surface profile as measured in
accordance with subparagraph Blast Profile, shall be between [0.05 and
0.07] [0.06 and 0.09] [0.07 and 0.10] mm [2.0 and 3.0] [2.5 and 3.5] [3.0
and 4.0] mils. Special care shall be taken to achieve the specified blast
profile on welds and flame-cut edges. In some cases it may be necessary to
either grind these surfaces with a disk wheel grinder or other tool prior
to blasting or to use a harder abrasive blast media. If recycled abrasives
are used, the particle size distribution of the working mix shall be
maintained such that a consistent blast profile is obtained. Weld spatter
not dislodged by blasting shall be removed with impact or grinding tools
and the surface shall be brought to the proper profile. Surfaces shall be
dry at the time of blasting. Acceptable surfaces shall be free of all
visible contaminants including grease, oil, soot, and dust prior to
receiving the first coat of metallizing.
SECTION 09971A
Page 21
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