Page 388 - Corrosion Engineering Principles and Practice

356 C h a p t e r 9 A t m o s p h e r i c C o r r o s i o n 357

exposed for three winter months at facilities on the Pacific coast [20].
What became evident in that study was that the pattern of the bluish-
.
green patina attributed to the corrosion product CuCl 2H O was not
2
2
uniformly distributed around the circumference of each copper rod.
A template with 16 points of the compass was placed onto the
outside of each copper rod that was on the most boldly exposed CLIMATs
of that study in order to visually quantify the intensity of the bluish-
green color. The relative degree of corrosion for each compass point was
assessed by assigning a number between 0 and 10 with 0 corresponding
to 0 bluish-green patina and 10 corresponding to 100 percent coverage of
the colored corrosion product. The average corrosion index for each of
the 16 points of the compass for the copper rods is shown in Fig. 9.30.
One attempt to correlate the directional corrosivity observed on
the copper rods with weather data was to plot the fraction of time

N
14.00
NNW NNE
12.00

NW 10.00 NE
8.00

WNW 6.00 ENE
4.00
2.00

W 0.00 E

WSW ESE

SW SE

SSW SSE
S
Patina index
Wind speed (knots)
Wind direction

FIGURE 9.30 Average corrosion index for the copper rods exposed on the
rooftop and the average wind speed recorded at the local weather station as
a function of the 16 points of the compass.