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Atmospheric Corrosion in the Laboratory and the Role of Mass Loss Coupons in Test Monitoring

A series of experiments was conducted to examine the repeatability of corrosion rates of various coupons, cleaning procedures prior to exposure inside a test chamber, and removal of corrosion byproducts after their exposure.

Product Number: 51317--9125-SG
ISBN: 9125 2017 CP
Author: Sean Fowler
Publication Date: 2017
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$20.00
$20.00

Recent developments in salt spray corrosion test methods have created automotive OEM standards with stringent requirements beyond the capabilities of yesterday’s test chamber technology. The essential elements for accurately replicating atmospheric corrosion as experienced in cars and trucks were incorporated into the first generation of automotive cyclic corrosion test methods in the early 1990’s. The impact of these methods was somewhat diminished due to significant challenges with repeatability and reproducibility. Dueling results between suppliers and customers created distrust of all laboratory corrosion testing a distrust which persists to this day. These problems mirrored those experienced by users of the original neutral salt spray standards generations earlier.Those earlier generations of salt spray test usersperformed numerous round robin studies using painted scribed panels and corrosion coupons to determine which test parameters required tighter tolerances. Today’s conformity testing programs for ASTM B117 typically use corrosion coupons as the basis of interlaboratory comparisons. Following this trend users of the cyclic corrosion test standards began using corrosion coupons as a test monitoring tool and as a referee in cases of dispute between laboratories. As they did for the neutral salt spray methods corrosion coupons highlighted the deficiencies of the early CCT cycles and the chambers designed to run them. Again test tolerances were tightened in an effort to achieve sufficient reproducibility that the new methods could be relied upon for quality control and supplier qualification.Underlying the use of corrosion coupons is the assumption that they are a reliable monitoring tool. But are they? This paper will examine some of the sources of variability in the manufacture cleaning and evaluation of mass loss coupons specified in various salt spray based laboratory corrosion tests. Concurrent with the corrosion coupon discussion will be a comparison of today’s modern automotive corrosion test methods with those developed a generation ago. The conclusion will provide straightforward guidance about when the application of corrosion coupons is advantageous and the significance of the results.

Keywords: atmospheric corrosion, mass loss, salt spray, laboratory corrosion, corrosion coupon, corrosion panel

Recent developments in salt spray corrosion test methods have created automotive OEM standards with stringent requirements beyond the capabilities of yesterday’s test chamber technology. The essential elements for accurately replicating atmospheric corrosion as experienced in cars and trucks were incorporated into the first generation of automotive cyclic corrosion test methods in the early 1990’s. The impact of these methods was somewhat diminished due to significant challenges with repeatability and reproducibility. Dueling results between suppliers and customers created distrust of all laboratory corrosion testing a distrust which persists to this day. These problems mirrored those experienced by users of the original neutral salt spray standards generations earlier.Those earlier generations of salt spray test usersperformed numerous round robin studies using painted scribed panels and corrosion coupons to determine which test parameters required tighter tolerances. Today’s conformity testing programs for ASTM B117 typically use corrosion coupons as the basis of interlaboratory comparisons. Following this trend users of the cyclic corrosion test standards began using corrosion coupons as a test monitoring tool and as a referee in cases of dispute between laboratories. As they did for the neutral salt spray methods corrosion coupons highlighted the deficiencies of the early CCT cycles and the chambers designed to run them. Again test tolerances were tightened in an effort to achieve sufficient reproducibility that the new methods could be relied upon for quality control and supplier qualification.Underlying the use of corrosion coupons is the assumption that they are a reliable monitoring tool. But are they? This paper will examine some of the sources of variability in the manufacture cleaning and evaluation of mass loss coupons specified in various salt spray based laboratory corrosion tests. Concurrent with the corrosion coupon discussion will be a comparison of today’s modern automotive corrosion test methods with those developed a generation ago. The conclusion will provide straightforward guidance about when the application of corrosion coupons is advantageous and the significance of the results.

Keywords: atmospheric corrosion, mass loss, salt spray, laboratory corrosion, corrosion coupon, corrosion panel

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