Executive Summary
This document describes the comparative performance of an anti-
corrosion coating, VCI
Primer, as applied on clean, pristine (white) and corroded (rust covered) steel in both
laboratory and real time applications. Performance is compared when applied as a first coat or primer with and without addition of a vapor phase migratory corrosion
inhibitor (VCI Agent), and to a commercial zinc containing anti-corrosion primer. In all instances the VCI Primer, containing a VCI Agent, gave superior performance with respect to appearance, adhesion, surface
rusting and loss of surface coating. There are variables in performance between the several comparative test cause by variations in substrate, surface profile,
and primer dry film thickness. These variables along with exposure time and conditions have produced a
range of degrees of performance. There is a definite trend in all results that performance is superior to present commercial primers on rust covered steel with the VCI Agent added, and equal to zinc containing primers on white steel. Application of the VCI Primer on rust covered steel can change the approach to steel maintenance painting by reducing the need to remove all surface rust prior to painting, which is the most costly step and many times is what inhibits performance of maintenance painting.
Background
Surtreat Holding, LLC and Shore Corp cooperated on a U.S. Army Corps of Engineers (COE) sponsored contract to develop a steel anti- corrosion primer using a 50/50 two part polyamide epoxy, MIL-DTL 24441, by adding a vapor phase migratory corrosion inhibitor (VCI Agent).
Laboratory scale primer samples, containing the VCI Agent added to Part A at a concentration, such that the resulting dry film contains 2.5 Wt. of it, were prepared and delivered to Matco Services, a Pittsburgh based corrosion consulting company, and the corrosion resistance performance measured on pristine and rust covered steel panels after exposure in a salt fog chamber. Examination of panels after 500 hours in the salt fog chamber showed a significant difference between those coated with straight primer and primer plus VCI Agent on both white pristine steel (degree of creep 3.0 vs. 2.5mm) and degree of rusting (4 vs. 8) and rust covered steel (degree of creep 8 vs. 2 mm) and degree of rusting (3 vs. 8) where 10 is no signs of rust.
Surtreat and Shore combined their proprietary rights to the VCI Agent solutions and the addition to paint to from VCI Coatings, LLC, which commissioned further performance testing by KTA Tator, a paint consulting firm located in Pittsburgh. The MIL specification primer with and without VCI Agent added was supplied to KTA. This primer was made by SIMCO Coatings as a production run, where they added the VCI Agent as a 40 Wt. % solution to Part A. This is also the same paint that was supplied to the COE as part of the R&D contract for outdoor exposure testing and painting steel doors in Corpus Christi Texas. Paint with and without VCI Agent was applied on white and corroded steel panels and exposed in the salt fog chamber for 750 and 1000 hours. This extended time was required to obtain any difference between the panels. At 1000 hours the largest degree of change was in the corroded panels with respect to degree of creep. There was no observed difference with respect to degree of rusting. It is believed that the difference between the Matco and KTA test results are due to the differences in the degree of steel surface abrasion caused profile and dry film thickness.
Comparative performance has also been measured on a corroded steel nut and bolt assemblies and corroded steel bridge
support pedestals that show observable differences in the degree of rusting between surfaces coated with a primer with and without the VCI Agent added.
Matco Services VCI Primer Performance Measurements
Several chemical forms of amine carboxylate type vapor phase migratory corrosion inhibitors, dissolved in N-butyl alcohol to form 40 Wt. % solutions, were added to Part A of the MIL- DTL 24441 primer and delivered to Matco Services. Matco conducted two performance test sets using different types of steel panels. The first used smooth surface 1008 carbon steel panels in the pristine and corroded states. The corroded panels were formed by exposure for 24 hours in the salt fog chamber. The primer was applied to give a dry, film thickness of 4 mils. Only the corroded panels gave any useful results, since the coating delaminated from the smooth pristine panels during exposure in the salt fog chamber due to lack of surface profile needed for adhesive bonding. The rough corroded surface gave good adhesion. Table 1 presents performance results after exposure in salt fog chamber (ASTM B117) for 500 hours. Measurements of adhesion, ASTM D3359, (2B vs.4B), resistance to creep, ASTM D1654, (2 vs.9) and rusting, ASTM D610, (8 vs.10) all showed better performance with addition of the VCI Agent. Figure 1 presents pictures of the scribed and un-scribed sides of the panel with and without the VCI Agent and support the numerical ratings on Table 1. The X scribed area on the panels coated with primer plus VCI Agent does not show well since no rust was formed to give a color contrast in the photos.
A second set of panels used 1008 steel that had been surface abraded to 2 mils with one set exposed in the salt fog chamber to form a rust covered surface. The panels were coated with primer containing two types of VCI Agent (C-10 and C-12) to form an average of 3 mil dry film surface with adhesion measuring between 5 and 4B. Relative resistances to corrosion were measured after 500 hours in salt fog chamber and results are reported on Table 1. All panels coated with the primer plus VCI Agent showed a definite increase in resistance to corrosion as measured by degree of creep (3.5 vs. 6) and degree of rusting (2 vs. 8). The larger numerical rating equals a lower degree of corrosion impact. Figures 2 showed picture of typical panels on the scribed and un-scribed sides with and without the VCI Agent added, and serve to reinforce the numerical ratings on Table 1.
The Matco performance measurements show a definite increase in anti-corrosion performance due to addition of the VCI agents on both the white pristine and corroded rust covers steel surfaces.
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TABLE 1 |
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MATCO SERVICES PERFORMANCE EVALUATION OF VCI COATINGS ANTI-CORROSION PRIMER |
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MIL-DTL 24441 PRIMER PLUS VCI LABORATORY ADDITION OF 2.5 WT. % VCI AGENT |
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500 HOURS IN SALT FOG CHAMBER PER ASTM B 117 |
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SMOOTH 1008 CARBON STEEL PANELS CORRODED BY 24 HR. IN SALT FOG CHAMBER |
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COATING TYPE |
ADHESION RATING |
DFT |
DEGREE OF CREEP |
DEGREE OF COROSION |
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RATING |
% LOSS |
MM |
RATING |
mm |
X SIDE |
FLAT |
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BASIC PEIMER |
2B |
15 |
4.2 |
2 |
6.6 |
8 |
8 |
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PRIMER + VCI |
4B |
5 |
4.4 |
9 |
0.3 |
10 |
10 |
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AVERAGE OF 3 PANELS 4 MEASURMENTS ON EACH |
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1008 CARBON STEEL PANELS BLASTED WITH 80 GRIT BLACK REAUTY |
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COATING TYPE |
PANEL CONDITION |
ADHESION |
DFT |
DEGREE OF CREEP |
DEGREE OF CORROSION |
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RATING |
% LOSS |
MM |
RATING |
MM |
X SIDE |
FLAT |
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BASIC PRIMER |
PRISTINE |
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5B |
0 |
2.4 |
5.25 |
3 |
2 |
4 |
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PRIMER + C-10 VCI |
PRISTINE |
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4B |
5 |
2.4 |
6.5 |
2.5 |
7 |
8.7 |
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BASIC PRIMER |
PRE-CORRODED |
4B |
5 |
2.3 |
3.5 |
8 |
1 |
3 |
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PRIMER + C-10 VCI |
PRE-CORRODED |
5B |
0 |
1.8 |
6.5 |
2 |
5 |
7 |
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PRIMER + C-12 VCI |
PRE-CORRODED |
5B |
0 |
1.8 |
5.8 |
3 |
6 |
8.8 |
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ADHESION: ASTM D3359 |
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DFT: ASTM D3359 |
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DEGREE OF CREEP: ASTM D1654 |
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DEGREE OF RUST: ASTM D610 |
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