Page 212 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

190 CORROSION CAUSES

such as aluminum frames bolted to steel frames. These and other omissions of corro-
sion control have led to costly maintenance and repairs. The following shortcomings
have been identified as a result of an audit: (i) use of AISI 1010 carbon steel without
galvanizing or any protective coating; (ii) the presence of many galvanic couples and
the use of 2800 rivets that may act as locations for corrosion; (iii) use of painting
procedures that are not state-of-the-art standards; (iv) use of paints that give very
little corrosion protection such as the chemical agent-resistant coatings (CARCs)
that deteriorate rapidly in the presence of a corrosive environment.

3.31.4 Case Study of HMMWV
In spite of the availability of knowledge and technology, the manufacture of the
Army’s HMMWV did not use available knowledge during manufacture. One of the
most glaring faults was in the design and construction of the steel frame using AISI
1010 steel without galvanizing or any other form of protection. Holes were drilled in
the sides of the frame with no holes at the bottom to allow drainage of water and other
corrodents. This allowed water to stagnate leading to corrosion from inside out. This
being the case, it is beyond comprehension as to how one can expect the HMMWV
vehicle to wade through water up to 1.5 m (60 in.) deep without undergoing corrosion
damage.
The main problem is the use of carbon steel 1010 for the fasteners, handles, brack-
ets, and the frame. The corrosion data obtained on 275 vehicles are presented in
Table 3.16.
Most of these problems could be eliminated or prevented by using galvanized steel
or high-quality coatings. Other problems can be overcome by using polymers and
other alternative materials.
Use of dissimilar metals such as aluminum and carbons steel can result in galvanic
corrosion. The entire HMMWV vehicle is secured with more than 2800 rivets, and
this design affords the vehicle high-strength-weight ratio: each rivet is a preferential
site for corrosion.
A particular weakness of the HMMWV compared to standard commercial vehicles
is the coating system used. Most of the commercial vehicles use a multistep coating
process to both protect the galvanized steel and to enhance the appearance of the
vehicle. Electrodeposition or E-coating is used in the coating of ordinary vehicles.
Electrodeposition assures complete coverage of the vehicle. In the case of HMMWV,
spraying technology was used, and the resulting coating did not turn out to be as good
as the E-technology coating.
The corrosion protection of the HMMWV was to be provided by the military
coating specification Mil-C-46164 and the CARC. The CARC paint system consists
of a surface cleaning, epoxy primer, epoxy interior topcoat, and a polyurethane
exterior topcoat. The purpose of this coating was to provide chemical resistance
(penetration of the coating) and to aid in the decontamination of the vehicle in
case of chemical attack. The coating was to provide corrosion protection as well as