Painting and Corrosion Protection. Steel surfaces exposed to the
atmosphere, whether indoors or outdoors, require painting for protection against
corrosion. (Interior surfaces of sealed spaces/voids may be left unpainted.) All
paint systems fail eventually due to the "weathering" effects of the atmosphere.
Premature failures, however, are caused by the loss of adhesion or damage to the
paint film by rusting of the steel surface underneath. Crane paint systems are
comprised of several coatings of primers and topcoats. To obtain the full life of
any paint system, the steel surface must be properly prepared and the primers
should contain zinc (in the form of dust of organic or inorganic zinc compounds)
for rust inhibition by the galvanic process. There are several levels of surface
preparation (blast cleaning) and a wide variety of acceptable paint systems
available for use on cranes. The topcoats, normally epoxies or vinyls, serve to
reduce the demand on the zinc to retard the primer coating breakdown.
Major Navy activities have their own preferred paint systems, which
should be followed if their performance has been satisfactory. Other activities
should consult with NCC for the level of surface preparation and selection of the
paint system. The paragraphs that follow provide background information and
identify the important points that should be considered. The selections should be
made on the basis of comparison of coatings' properties with the crane operating
environment. The colors and color schemes are normally chosen by the crane owning
Bolts, nuts, and washers in exterior structural connections should be
cleaned, primed, and top coated after installation. The primer used should be
compatible with the surface preparation.
22.214.171.124 Surface Preparation. Steel Structures Painting Council has developed a
series of standards for preparation of structural steel surfaces for proper paint
adhesion in the expected service environment. The description of these standards,
both verbal and as photographic representations, and the process of achieving them
are detailed in ANSI A159.1. Those applicable to cranes include:
White Metal Blast Cleaning
Commercial Blast Cleaning
Brush-Off Blast Cleaning
Near-White Blast Cleaning
(Weld spatter is to be removed by hand or power tools prior to blast cleaning.)
Brush-Off Blast Cleaning is adequate for the preparation of faying
surfaces of structural connections which are only primed prior to bolting.
Commercial Blast Cleaning is relatively inexpensive and provides
satisfactory surface preparation for many service conditions. Small areas of
tightly adhering mill scale may remain.
Near-White Blast Cleaning removes practically all rust, mill scale,
and other detrimental matter from the surface. This level of surface preparation
is satisfactory for all but the most severe service conditions.