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Comparative Analysis of Corrosion in two
Automotive Doors,
one equipped with an Electronic Corrosion
Protection Device,
and one Unprotected, serving as a
Control,
after 1,000 Hours of Salt Fog Exposure.
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Matco Project No. 906-50537
Sept 13th, 2006 |
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Gordon Kirkwood
Mehrooz Zamanzadeh, PhD
NACE Certified
Corrosion/Materials
Selection/Design/Cathodic
Protection
Specialist |
Sam Scheinman
Systems
Engineer
Technician
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Summary
Two automotive doors were exposed to 1000
hours salt fog at ~100ºF according to ASTM standard B117, in order to
determine the effectiveness of an electronic rust preventative module.
A long car door panel was sectioned exactly in half, and one half was
equipped with an Electronic Corrosion Protection Device (“Device”). The
other half door was left unprotected, as an experimental control
(“Control”).
The samples were evaluated by visual
inspection. Both the Electronically Protected and Control samples
exhibited significant corrosion after exposure. White rust deposits
(zinc oxides and hydroxide) were found on the surface of both the
electronically protected sample and the Control. Red (iron oxide)
deposits are clearly visible wherever the automotive paint coating is
breached or where galvanizing has been scraped, such as at bolts,
hinges, and handles. Severe localized corrosion has occurred on both
doors in areas where the metal has been cut, particularly at the edges
of the doors which were facing downward in the salt spray chamber and
where moisture dripped off. There does not appear to be any significant
difference of the amount of uniform corrosion occurring on the body of
the electronically protected and control doors panels. Cut metal edges
where carbon steel is exposed are severely corroded on both samples.
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Procedure
Two identically prepared car doors were used
for comparative analysis. To one door was attached an electronic rust
inhibiting module, installed according to the manufacturer’s
instructions. The other door was left unprotected. The doors were
placed inside a salt-spray chamber, and salt fog was introduced into the
chamber by an atomizer. The doors were oriented so as to place the
cut-open side downward to facilitate drainage. The doors were exposed
to 1000 hours of salt fog, then removed and documented
photographically. The electronic protective module was energized during
salt-fog exposure.
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Summary
of Changes
Both doors
showed moderate corrosion of the body panels, and extreme corrosion in
areas of diminished galvanizing such as at the insertion point of
fixtures, on hinges, or where the sheet metal was cut. The following
pictures detail the condition of the tested door panels after 1000 hours
of salt fog exposure. Figure 1 shows the exterior of both control and
electronically protected doors. Figure 2 shows a close-up of some rust
spots on the painted side of the electronically protected door which
were not similarly represented on the control door. However, these may
have been caused by holidays or pinholes in the electronically protected
door which may not have been present in the paint of the control door.
Figure 3 shows the interior of both doors. Figures 4, 5 and 6. show
comparative view of the cut edge of both doors, at the bottom or
road-side of the door (figure 4), at the middle of the door (figure
5), and at the top of the door, ie. the window-sill edge (figure 6).
The most extreme corrosion was expected to be found in these areas since
both samples were oriented in the exposure chamber so as to make this
the bottom side: salt water droplets would cling here for a time before
falling away, resulting in accelerated corrosion in this area. This
indicates that neither the control nor electronically protected door
could prevent corrosion in areas of collecting water. Figure 7 shows
the non-cut ends of the door panels, and figure 8. shows a detail of
the electronically protected door near the hinges. |
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Conclusion and Recommendations
Side by
side comparison of post-exposure photographs of corresponding areas on
the two car door samples leads to the assessment that both door panels
showed moderate corrosion on the flat expanse of panels, and severe
corrosion in areas where galvanizing was removed due to scratches,
fixtures, or cuts of the sheet metal. There is no significant
difference in the extent of corrosion on electronically protected and
control doors. Where localized differences are observed such as the
spots of red rust on the exterior of the electronically protected door
(figure 1), these differences are likely the result of differences
between the doors other than the presence of electronic protection,
such as more or less pinholes in the paint. Photographs of the
open-side of the doors (figures 4, 5, and 6) both show advanced
corrosion with significant accumulation of red rust iron corrosion
products. |
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Prepared by:
Gordon
Kirkwood
Systems Engineer
Sam
Scheinman
Technician
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Reviewed by:
Mehrooz Zamanzadeh, PhD
NACE Certified Corrosion/Materials
Selection/Design/Cathodic Protection
Specialist |
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*IMPORTANT NOTICE: It
is the policy of MATCO Associates that samples submitted as part of
contracted investigations are the responsibility of MATCO for only one
month after final reports on those samples have been issued. They may
then be discarded or otherwise disposed of. If you would like samples
returned or safeguarded for longer than one month, please make such
arrangements with this office in writing (include shipping provider and
account number). If the submitted samples are part of a claim or
potential lawsuit it is the client’s responsibility to make arrangements
to have the samples returned. Any testing not performed in MATCO’s
facility has been performed by established laboratories used by MATCO
Associates |
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Figure 1: Comparative Exteriors.
Control and Electronically Protected car door
samples. Both exhibit streaks of red indicating iron-oxides. These
indicate that there were holidays or pinholes in the paint on the
exterior of the door from which rust initiated. There appear to be
relatively more sites of red rust on the exterior of the electronically
protected door.
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Figure 2: Scattered Initiation Centers.
Detail of the scattered corrosion centers on the
exterior of the Electronically Protected car door. Rust streaks are
visible, with streaks trailing in the direction that was downward during
exposure. Some blistering of the paint is visible just above the 1",
1.5", and 2" marks on the ruler.
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Figure 3: Comparative Interiors.
Interiors of the two samples. White rust streaking
is visible inside the Control (initiated from the door lock mechanism)
and the hinge plates on the Device-equipped sample exhibit pronounced
red rust. |
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Figure 4: Comparative views of the non-cut ends
of the doors.
The latch-side of the Control sample and the
hinge-side of the Device-equipped sample.
Both are clean and free of rust on the body
panels. Red rust is clearly visible on the hinge plates on the
Electronically Protected sample. |
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Figure 5: Comparative views of cut edges of the
doors at the bottom edge.
(Top: Control. Bottom: Device-equipped). Doors
were positioned so that the cut which divided the original single door
into these two samples was aimed downward. Consequently, this is where
condensed salt-water collected before forming beads of moisture which
then dripped off the doors. It was thus expected that this area would
show the most pronounced corrosion and presence of corrosion deposits.
We hesitate to make comparisons based on this region however due to the
variability with which moisture can be expected to flow off two
not-completely-identically-shaped samples. |
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Figure 6: Comparative views of cut edges of the
doors at middle of the door.
(Top:
Control. Bottom: Device-equipped). |
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Figure 7:
Comparative views of cut edges of the doors at the top (windowsill) edge
of the door.
(Top:
Control. Bottom: Device-equipped). |
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Figure 8: Hinge
detail from the Electronically Protected sample.
Top image is the top
hinge. Bottom image is the lower hinge. Hinges showed far more
corrosion than the rest of the door, which is attributed to the
presence of less galvanizing and the fact that the hinges were found to
be somewhat abraded by service. Corresponding hinges are not present on
the control door since only one side of the door which was divided to
make these samples had hinges. |
