CLIMAT coupons

Some variations of the basic coupon specimens can provide rapid material corrosivity evaluations. The helical coil adopted in the ISO 9226 methodology is a high surface area/weight ratio coupon that gives a higher sensitivity than panel coupons of the same material. The use of bimetallic specimens in which a helical A91100 aluminum wire is wrapped around a coarsely threaded bolt may provide additional sensitivity and forms the basis of the Classify Industrial and Marine Atmospheres (CLIMAT) coupon [11 18]. 

The mass loss of the aluminum wire of a CLIMAT coupon after 90 days of exposure is considered to be a relative measure of atmospheric corrosivity. However, the results vary greatly between the various combinations of materials suggested in the ASTM standard [11], The aluminum wire on copper bolts has been found by many to be the most sensitive of the three proposed arrangements in the ASTM standard. The use of triplicate coupons on a single holder additionally provides an indication of the reproducibility of the measurements and the use of vertical rods can reveal directional information on the corrosive agents as will be illustrated in the following examples. 

A CLIMAT coupon with three copper rods installed at the NASA Kennedy Space Center (KSC) beach corrosion test site (Fig. 9.27) is shown immediately after it had been installed [Fig. 9.28(a)], after 30 days [Fig. 9.28(F)], and after 60 days [Fig. 9.28(c)]. KSC having the highest corrosivity of any test site in the continental United States [19], the mass loss recorded even after a shorter exposure than usual can be very high. In the present example it was already 16 percent of the original aluminum wire after 60 days. The base support of these CLIMATs having been purposefully installed parallel to the sea coast the directional effect of the marine salts may be illustrated by comparing the front and back of the exposed CLIMATs [Fig. 9.29(a) and (F)]. 

Figure 9.28 A CLIMAT coupon with three copper rods immediately after it was installed at the Kennedy Space Center beach corrosion test site (a), after 30 days (b), and after 60 days (c).

Figure 9.29 Close-up pictures of a CLIMAT coupon exposed at KSC for two months (a) seaside and (b) backside.

Figure 9.32 Metal coupons in a plastic test rack exposed at the Kennedy Space Center beach corrosion test site besides a CLIMAT coupon. (Courtesy of Battelle)...

Figure 9.43 Coated panels exposed on an atmospheric test rack in a marine environment with CLIMAT coupons for corrosivity calibration.

Costa V (2003) Museum s air quality in a tropical climate evaluation by using metaUic coupons, 5th Indoor Air Quality Meeting, Norwich (United Kingdom) http //iaq.dk/iap/ iaq2003/2003.13.htm... 

The common method of testing the durability of a paint or coating and its effectiveness in inhibiting or reducing corrosion of the metal substrate is to expose coupons or samples to an accelerated weathering conditions that is, by exposure to harsh climate conditions that includes intense sunlight and rain or in a weatherometer which is an instmment that cycles these conditions rapidly and thus attempts to predict long-term exposure effects in very short time intervals. 

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