New Developments in Coatings Technology - ACS Publications

Chapter 13

Polyamide-11 Powder Coatings: Exceptional Resistance to Cavitation Erosion 1

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T. Page McAndrew , Marc Audenaert , Jerry Petersheim , Dana Garcia , and Thomas Richards Downloaded by UNIV LAVAL on July 11, 2016 | http://pubs.acs.org Publication Date: August 30, 2007 | doi: 10.1021/bk-2007-0962.ch013

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Technical Polymers R&D, Arkema Inc., Research Center, 900 First Avenue, King of Prussia, PA 19406 Technical Polymers R&D, Arkema S.A., Centre d'Etude de Recherche & Développment, Route du Rilsan, Serquigny, 27470, France Technical Polymers Business Development International, 2000 Market Street, Philadelphia, PA 19103 Analytical and Systems Research, Arkema Inc., Research Center, 900 First Avenue, King of Prussia, PA 19406 3

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A first application of polyamides in the 1930's was replacements for metals. Seventy years later, a similar application is discovered for Polyamide-11 - cavitation resistant coatings that enable replacement of high-cost metals in demanding water applications. Polyamide-11 powder coatings are shown to have exceptional resistance to cavitation erosion - substantially better than other polymer coatings such as epoxies, and better even than stainless steels. Gravimetric, photographic, and spectrophotometric data are presented.

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© 2007 American Chemical Society Zarras et al.; New Developments in Coatings Technology ACS Symposium Series; American Chemical Society: Washington, DC, 2007.

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Introduction Polyamide-11 O f the hundreds of polyamides developed since the 1930's, only one excels as a coating - Polyamide-11. See Figure 1.

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Figure 1. Polyamide-11 [poly(l1-aminoundecanoic acid)]. Polyamide-11 is also callednylon-JΊ'.

To understand this, see Figure 2, which compares Polyamide-11 to Polyamide-6 and Polyamide-6/6 - commercially the two most important polyamides. (1) Polyamide-11 has features that make it very well-suited to coatings: melting point is low (185°C) - enabling convenient processing water absorption is low (approximately 2% by weight) - enabling good corrosion protection (absence of water inhibits the corrosion reaction) - see Equation 1 impact resistance is high (approximately 50 kJ/m ) 2

2Fe + 0

2

+ 2H 0 Ο 2

2 Fe

2+

+ 4 (OH)' E° =+1. 26 volts

0)

Polyamide-11 is unique in another aspect - it has a natural source. The monomer, 11-aminoundecanoic acid, derives from castor oil. (2)

Rilsan Fine Powders Arkema Inc. makes Rilsan® Fine Powders - thermoplastic powder coating products comprising Polyamide-11. Powders are applied by ordinary powder coating methods - electrostatic spray, fluidized bed dipping, and thermal spray. Worldwide, they have been used for over 40 years in water industry

Zarras et al.; New Developments in Coatings Technology ACS Symposium Series; American Chemical Society: Washington, DC, 2007.

Downloaded by UNIV LAVAL on July 11, 2016 | http://pubs.acs.org Publication Date: August 30, 2007 | doi: 10.1021/bk-2007-0962.ch013

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Figure 2. Comparison of polyamides.

applications, such as coatings for pumps, valves, couplings, and pipes. This utility is based upon excellent resistance to corrosion, abrasion, impact, and acidic/basic water-treatment chemicals. In the United States, Rilsan® Fine Powders are approved by several regulating agencies: •

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American Water Works Association - A N S I / A W W A C-224 - Nylon-11Based Polyamide Coating System for the Interior and Exterior of Steel Water Pipe, Connections, Fittings and Special Sections Underwriters Laboratories - Standard 1091 - Butterfly Valves for Fire Protection Service N S F (National Sanitation Foundation) International - NSF/ANSI Standard 61 - Drinking Water System Components - Health Effects

Recently a discovery was made that enhanced the utility of Rilsan® Fine Powder coatings in the water industry - exceptional resistance to cavitation erosion.


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Cavitation Erosion In high-velocity water, low-pressure regions form, where water vaporizes to form bubbles. When these bubbles move to high-pressure regions, they collapse. This is called cavitation. This collapse generates shock waves that erode surfaces nearby. This is called cavitation erosion. Cavitation erosion commonly causes premature failure of hydraulic equipment such as pumps, valves, pipes, turbines, and propellers. (3, 4) Recent work examined the cavitation erosion of metals employed in municipal water systems - stainless steel, cast iron, bronze, brass, and copper and concluded that stainless steel was the most resistant, by far. (5) Because of cost, use of high-performance materials like stainless steel usually is not practical. A protective coating that resists cavitation erosion would be of enormous value - improving equipment lifetimes and enabling use of lower-cost metals. As described presently, the cavitation erosion resistance of Rilsan® Fine Powder coatings far exceeds that of other polymer coatings, and exceeds even that of stainless steels. This enables coated carbon steel (much lower cost) to be used instead of stainless steel where cavitation erosion is an issue.

Experimental Sample Preparation Coatings were formed on carbon steel panels (approximately 3 mm thick) at Arkema Inc. facilities in King of Prussia (PA) and Serquigny (France). Panels were prepared by abrasive blast cleaning, followed by washing with either fresh liquid toluene or trichloroethylene vapor. Powder coating materials were used as received, and applied according to manufacturer's specifications. Regarding comparative metals: carbon steel panels (Type S-36) were from Q-Panel Lab Products (Cleveland, OH); steel alloy (CA-6-NM), stainless steel (316-L), ductile cast iron (65-45-12), brass (85-5-5-5, C D A 836) and phosphorus bronze (CDA 510) were from Metal Samples Company (Munford, AL). Samples were 0.5 inch squares — cut from interior areas of panels to avoid any edge effect. Most samples were mounted as is. However, because of thinness, samples of carbon steel and bronze were mounted on a support piece of steel with epoxy.


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Measurement of Cavitation Erosion Cavitation erosion was measured at K T A Tator, Inc. (Pittsburgh, PA), using a method based on A S T M G-32-98 (Standard Test Method for Cavitation Erosion Using Vibratory Apparatus). The ultrasonic probe was a Sonics and Materials, Inc. (Newton, CT) Model VC-501 - which produced 500 watts oscillating at 20 kHz. The diameter of the horn tip was 0.5 inch and the amplitude of the oscillation was 62 microns (peak-to-peak displacement). The distance between the probe tip and the sample surface was approximately 1 mm. The volume of immersion water (distilled/deionized) was approximately 1 liter. Samples were placed approximately 1.2 cm below the water surface. Water temperature was maintained between 22°C and 27°C. Water contained a proprietary (to K T A Tator, Inc.) corrosion inhibitor to prevent weight changes due to corrosion of exposed metal surfaces. Exposure to cavitation was performed continuously for a fixed time. Then the sample was removed, dried in a dessicator and weighed. After this, exposure continued. Loss (microns) was calculated according Equation 2: 4

10 χ (weight loss in grams) Loss = j — — τ(sample area in cm ) χ (specific gravity in grams I cm ) 2

(2)

2

Sample area was 1.6 cm (i.e., 0.5 inch ). Values of loss versus time are shown in Figures 3 and 4. Each value is an average of three (from three different panels). Optical imaging was performed with a Nikon® SMZ800 stereo microscope (magnification approximately 10X) using reflected light and an Optronics® digital camera. A T R infrared spectroscopy was performed with a Thermo Electron Corporation Nicolet® Nexus® FT-IR. Resolution was 4 cm" . 1

Results and Discussion Values of loss versus time are shown in Figures 3 and 4. Photographs before and after testing are shown in Figures 5, 6 and 7. From Figure 3 it is seen that Rilsan® Fine Powder coatings show far better performance than the thermoset epoxy products, Scotchkote® 206N (3M) and Resicoat® R5 (AkzoNobel, Inc.). Photographic data support this. From Figure 5 observe that Rilsan® Fine Powder products undergo only a small loss of gloss, whereas both thermoset epoxy products undergo substantial pitting - to the point of exposing metal. These results are not surprising. Crosslinked coatings, such as epoxies,



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Figure 3. Loss data for coatings.

Figure 4. Loss data for coatings and metals.



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Figure 5. Photographs of coatings.

Figure 6. Photographs of coatings and metals.



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Figure 7. Photographs of coatings and metals.

would not be expected to withstand very well the impact of cavitation-generated shock waves. The data shown in Figure 4 are quite interesting. Rilsan® Fine Powder coatings show substantially better performance than brass, bronze, ductile cast iron, carbon steel, and stainless steel 316-L. These data are supported by photographic data shown in Figures 6 and 7. Concerning weight loss data, Rilsan® Fine Powder coatings perform approximately the same as Steel Alloy (CA-6-NM). However, photographic data show clearly that Steel Alloy (CA-6-NM) undergoes a visual change, whereas Rilsan® Fine Powder coatings undergo almost none. Thus the cavitation erosion resistance of Rilsan® Fine Powder coatings would be regarded as better than that of Steel Alloy (CA6-NM). Some work was done to understand the process of material loss that occurs during cavitation erosion, infrared spectra are shown in Figures 8, 9, and 10, for the coatings, Rilsan® Fine Powder Black 7450 A C F B , Scotchkote® 206N, and Resicoat® R5, respectively. Rilsan® Fine Powder Black 7450 A C F B exhibits virtually no change after exposure to cavitation. The very small loss shown in Figure 4 appears to result only from a mechanical process. B y contrast for Scotchkote® 206N and Resicoat® R5, there are substantial changes in the infrared spectra. There are notable increases in the areas of 3,400 cm" and 2,900 cm" , corresponding to - O H and sp C - H , respectively. Exposure to cavitation 1

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Figure 8. A TR infrared spectra of Rislan® Fine Powder Black 7450 AC FB coating. Shown are before and after 8 hours exposure to cavitation.

Figure 9. ATR infrared spectra of Scotchkote 206N coating. Shown are before and after 4 hours exposure to cavitation.



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Figure 10. ATR infrared spectra of Resicoat® R5 coating. Shown are before and after 0.5 hour exposure to cavitation.

clearly caused a chemical change, possibly oxidation and chain scission, contributing to the very rapid loss of coating observed.

Conclusions Rilsan® Fine Powder coatings have exceptional resistance to cavitation erosion - substantially better than other coatings and metals used in water industry applications - most notably stainless steels. For applications where cavitation erosion is a concern, Rilsan® Fine Powders enable replacement of high-cost metals like stainless steels with lower-cost coated metals, like coated carbon steel. Seventy years after the discovery of polyamides, another metalreplacement application has been identified.

Acknowledgements Measurement of cavitation erosion at K T A Tator, Inc. was performed under the direction of William D . Corbett, Technical Services Administrator. Thanks are extended to Christophe Valentin (Powders R & D Department, Arkema S.A.,


200 Serquigny, FR) for preparation of some of the coatings. Philip L . Drooks of Metropolitan Water District of Southern California (La Verne, C A ) is acknowledged for highlighting the criticality of the cavitation erosion phenomenon, and advice on materials important to the water industry.

References 1.


2.

3. 4. 5.

Nylon Plastics Handbook; Kohan, M ., Ed.; Hanser/Gardner Publications, Inc.: Cincinnati, O H , 1995: pp 576-582. Apgar, G . B . and Koskoski, M . J . in High Performance Polymers. Their Origin and Development; R.B. Seymour and G.S. Kirshenbaum, Eds.; Elsevier Science Publishing Co., St. Louis, M O , 1986, pp 55-65. Lecoffre, Y . ; Cavitation; A . A . Balkema Publishers, Brookfield, V T , 1999, pp 244-291. Rahmeyer, W.J. Journal A W W A , May 1981, 270-274. Chan, W . M . , Cheng, F.T., and Chow, W.K. Journal A W W A . 2002, 94 (8), 76-84.


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