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Can Rust Preventer Really Leave NO Residue?

WEDNESDAY, SEPTEMBER 30, 2020


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The Great Struggle

Time is the blasting contractor’s great nemesis. Blast quickly, then get the coating on as soon as possible. Why the rush? Why, the rust of course!

That’s what bare steel does if you let time do its work. It goes by many names: flash rust, rust back. Some of them even sound pleasant: gingering, rust bloom. Bloom? How ironic. Everyone knows it’s an evil flower.

With the rise of wet abrasive blasting and waterjetting, the foe only seems stronger. He feeds on water. But a scrappy band of solutions have entered the fray and successfully fought back: rust preventers of varying compositions, some called inhibitors, some chemical rinse aids (CRAs), others surface passivators.

The makers of HoldTight 102, one of the aforementioned CRAs, have long been claiming that it leaves no residue; that you can apply coatings right over it or, rather, that there is no “over” it to speak of, since the surface is clean and non-reactive.

But skeptics would furrow their brows incredulously: Can a rust preventer or CRA really leave no residue? Hearing this objection so frequently, the research team at HoldTight never lost faith. But after many successful adhesion tests, conductivity tests and microscope analysis, they wondered, how could they clearly prove their claims?

The question was important, for if an inhibitor or passivator works by leaving a film or residue on a surface in order to prevent rust, then it must be removed prior to coating. Otherwise, the residue might react with the coating, potentially affecting adhesion or causing other problems for the coating’s lifetime. This removal step would add more time and costs for contractors and operators who are already squeezed from many directions.

So the research team decided to do something about it and devised a test.

Gas Chromatography

The testing method the team settled on was gas chromatography. This is a test method used to separate, analyze or identify the presence of chemicals in a sample. It is used widely in various sectors, including medicine and crime forensics.

When a TV detective instructs a subordinate to “get these samples back to the lab for identification,” one of the gadgets he vaguely has in mind is chromatography equipment. It can also be used to analyze coating samples.

Gas chromatography works as follows: A small sample of a compound is introduced into an inert carrier gas, and both are then passed through a heating element, typically a flame. The heated gas is then passed through a long tube or series of tubes, called a column. Different compounds travel at different velocities through the tube, and, like runners circling a race track multiple times, the faster compounds widen their lead over the slower ones. After adequate separation in this manner, the compounds exit the column into a detector, which identifies them separately.

The result is a graph, called a chromatogram. A chromatogram will have one or more lines running through it from left to right. The x (horizontal) axis is time—that is, the time it takes for different compounds to reach the detector. The y axis measures the abundance of a compound. A typical chromatogram will present a flat or gently sloped line, representing the inert carrier gas, with one or more pronounced peaks standing out at various intervals, each indicating the presence of a different substance.

Using Chromatography to Detect Residue

But how could the research team use such a method to detect the presence of residue on a bare steel surface after treatment with a CRA?

The method devised was as follows. The team, led by consultancy Woodson Engineering LLC, prepared two panels treated with HoldTight 102. After adequate drying time, the panels were submitted to an independent lab. Benchmark Labs in Houston, Texas, a reputable third party laboratory, was selected for the job.

The lab submerged the two panels it received in solvent (isopropyl alcohol) separately, and agitated them with sonication for one hour. These two solvent solutions, together with a sample of the CRA HoldTight 102, were then subjected to gas chromatography, producing three separate chromatograms, which were then compared against each other.

The reasoning was as follows: The chromatogram from the CRA would indicate one or more peaks along the x axis. If the chromatograms for the solutions extracted from the test panels presented similar peaks, this would indicate the presence of a residue. Even different peaks, if they indicated the presence of a substance other than isopropyl alcohol, might suggest a residue.

The team also decided that, while conducting this test procedure on HoldTight 102, they would also subject two similar available products to the same test.

Preparing the Panels

The material for the panels was new AISI 1018 mild carbon steel. Six steel panels were first washed with a solvent (xylene) and then abrasive blasted with virgin garnet to SSPC SP5/NACE No. 1 White Metal, with a 2- to 3-mil anchor profile.

“Take these boys to the lab.”

The applicator selected for the testing then obtained deonized (DI) water in order to power wash the panels using the different CRAs. The panels were then washed at a minimum of 1000 psi, using the different CRAs at the manufacturers’ recommended dilutions. HoldTight 102 and Chemical A were diluted at 50:1 ratios (water:additive), and Chemical B was diluted at a 100:1 ratio.

With each separate chemical, the applicator treated two test panels. These were left to dry adequately (72 hours), and then all six were submitted to the lab for the chromatography protocol described above.

The Results

The chromatogram lab results for HoldTight 102 indicated a strong peak for the CRA itself around six minutes into the test; whereas, the solutions extracted from the two test panels treated with HoldTight 102 presented no peaks on the chromatogram.

To the HoldTight research team, this test provided the strongest confirmation they had ever received that the 102 product leaves no residue when applied according to the manufacturer’s instruc­tions. If there had been a residue, it would have produced a peak at some point along the plates.

Figure 2 illustrates the chromatogram of HoldTight 102 alongside those of the solutions extracted from the two test panels.

Figure 2. Chromatogram of HoldTight 102 and test panel solutions

This provided, in their eyes, a definitive answer to the long-standing question, Can a rust preventer really leave no residue? The answer is a resounding YES indeed.

While the test results were encouraging with respect to HoldTight 102, they did not confirm the hypothesis that all such substances leave no residue. The chromatograms for Chemicals A and B, as well as the panels treated with them, were substantially different and indicative of the different chemistry of these other CRAs. They are shown in Figures 3 and 4.

Figure 3. Chromatogram of Chemical A and test panel solutions

Figure 4. Chromatogram of Chemical B and test panel solutions

The chromatograms from Chemical A and its test panels did not produce confidence that no residue was left on the surface. This substance merits further analysis and perhaps further testing. The chromatograms for Chemical B and its test panels indicated that there was a residue left on the surface.

Conclusion

The research team at HoldTight felt that the testing was conclusive enough with regards to HoldTight 102 to uphold the claim that their CRA leaves no residue. Their end users and strategic partners, who include contractors, specifiers, equipment manufacturers and coating manufacturers, can continue to use, specify and approve this rust preventer  product with confidence. Flash rust can, and must, be stopped.

Learn more at holdtight.com.

Claims or positions expressed by sponsoring authors do not necessarily reflect the views of TPC, PaintSquare or its editors.

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