Mils penetration per year

Corrosion Rate by CBD Somewhat similarly to the Tafel extrapolation method, the corrosion rate is found by intersecting the extrapolation of the linear poi tion of the second cathodic curve with the equihbrium stable corrosion potential. The intersection corrosion current is converted to a corrosion rate (mils penetration per year [mpy], 0.001 in/y) by use of a conversion factor (based upon Faraday s law, the electrochemical equivalent of the metal, its valence and gram atomic weight). For 13 alloys, this conversion factor ranges from 0.42 for nickel to 0.67 for Hastelloy B or C. For a qmck determination, 0.5 is used for most Fe, Cr, Ni, Mo, and Co alloy studies. Generally, the accuracy of the corrosion rate calculation is dependent upon the degree of linearity of the second cathodic curve when it is less than... 

Ckjrrosion Rate Ranges Expressed in Mils Penetration per Year (1 Mil = 0.001 in)... 

Corrosion Rate Ranges Expressed in Mils Penetration per Year (1 Mil = 0.001 in) Source data compiled by J.S. Park from R. E. Bolz and G. E. Tuve, CRC Handbook of Tables for Applied Engineering Science, 2nd edition, CRC Press, Inc., Boca Raton, Elorida, (1973). ... 

Corrosion Rate—the rate at which corrosion occurs. It is usually reported in units of inches of penetration per year (ipy), mils of penetration per year (mpy), milligrams of weight loss per square decimeter per day (mdd) microns per year Orm/yr), or millimeters per year (mmpy). Note that 1/am = 0.0395 mils. 

Because corrosion is so uniform, corrosion rates for materials are often expressed in terms of metal thickness loss per unit time. The rate of uniform attack is reported in various units. One common expression is mils per year (mpy) sometimes millimeters per year is used. In the United States, it is generally reported in inches penetration per year (ipy) and milligrams per square decimeter per day (mdd). To convert from ipy to mpy, multiply the ipy value by 1000 (i.e., 0.1 in. X1000 = 100 mpy). Conversion of ipy to mdd or vice versa requires knowledge of the metal density. Conversion factors are given in Table 1.1. 

TYPICAL PENETRATION RATES IN CORROSIVE MEDIA, Mils (mm) Per Year... 

CORROSION RESISTANCE OF HAYNES ALLOY NO. 25 All results are expressed in mils (mm) penetration per year. Acid strengths are given in percent by weight. In some instances, no measurable penetration could be observed. These instances are noted by the word, "Nil." All data are steady-state as calculated from a minimum of five 24 hr test periods. 

Since it is often difficult to visualise the extent of attack in terms of depth from such mass-loss units as mdd, it is common practice to convert these mdd figures into others to indicate depth of penetration, i.e. inches per year (ipy), mils or mm y" . Such calculations suffer from the same defects as the mdd figures in that they take into account neither changes in corrosion rates with time nor non-uniform distribution of corrosion. However, since such conversions are often made it is desirable for the initial reporter of the test results to make the calculations accurately and to report corrosion rates in both mdd and mm y or similar units. 

Often, however, steel is subject to pitting attack by sea water. The deepest attack on steel is reported to be about 10 to 15 mils per year. The presence of mill scale on the steel—especially when it covers a large portion of the exposed area—significantly increases the rate of pitting, and penetrations of about 20 mils per year can be expected. This is a result of the mill scale serving as large cathodes to the small, bare anodic areas. Pitting attack often tapers off with continued exposure. 

Corrosion rate is normally expressed as a weight loss, per unit area, per unit time [milligrams per square decimeter, per day (mdd)] or as depth of penetration of the metal, per unit time [mil = 1/1000 in., per year (mpy)]. 

Galvanized steel plates showed some visual differences between cities, as seen in Figure 8. Some differences were also observed within the same city (e.g. Figure 9). These plates were cleaned using an ammonia wash followed by a chromic acid and silver nitrate dip (ASTM G1). Mils per year penetration rates are shown in Table III. Decreasing corrosivity follows the order ... 

A rate of penetration, that is, the thickness of metal lost. This may be expressed in imperial units, mils per year (mpy), a mil being a thousandth of an inch, or in metric units, millimeters per year (mm/y). 

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Corrosive Concen- PENETRATION RATE Mils per year ... 

Corrosion Rates The rate of corrosion may be expressed as corrosion penetration rate, that is, the thickness loss of material per unit of time CPR may be determined using Equation 17.23. Mils per year and millimeters per year are the common units for this parameter. 

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