Methods Involving Loss of metal

Most direct measurements of corrosion utilize the weight loss of metal over a period of time on a small sample such as a coupon, wire, or strip. The dimensions of the coupon are important for several reasons. The ratio of surface area to coupon weight should be as high as possible to facilitate detection of small weight losses. This permits the shortest possible exposure period between weightings. Selection of the maximum surface-to-weight ratio, however, may still result in a relatively long test 

The coupon technique is by far the most common and most inexpensive method in current use. The preparation of coupons is discussed in some texts in general terms, and some standards have been set 

The analytical measurement of iron or other soluble metal content in the corrodent stream is another method directly related to metal loss. This technique can give poor results if the corrosion products are insoluble or adherent to the metal surface. If the method is used in a two-phase system, either both phases must be analyzed for metal ions, or particular care must be taken to put the dissolved metal into the aqueous phase. Quantitative measurements of dissolved metals are used frequently in acidic systems or in special cases where the corrosion products are known to be soluble. There are inexpensive colorimetric tests available for measuring iron, copper, and other metals in solution. 

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