“Corrosion Issues and Materials for APC Systems” -- Hot Topic on January 16, 2014
There are new challenges for system designers who must protect ducts, scrubbers, fabric filters and heat exchangers from corrosion. These challenges were the focus on the Hot Topic Hour on the 16th.
Gary Hall, Consultant to and former Manager of Organic Technology for Sauereisen, Inc., discussed “Material Considerations for Maintaining FGD Infrastructure.” He advised attendees that permeance was the best indicator of corrosion resistance. Product comparisons show good permeance from flake glass vinyl esters with treated flakes and various FibreCrete products.
Product Comparisons of Permeance
|
|
Permeance |
Permeability |
|
Unfilled vinyl ester resin |
0.7700 |
0.0154 @ 20 mils DFT |
|
Flake Glass vinyl esters with treated flakes |
0.0028 |
0.0002 @ 70 mils DFT |
|
Standard flake glass vinyl esters |
0.0086 |
0.0006 @ 70 mils DFT |
|
Mica filled vinyl esters |
0.0628 |
0.0022 @ 35 mils DFT |
|
Urethane asphalt membrane |
0.0800 |
0.0048 @ 60 mils DFT |
|
1/8” woven roving reinforced Bis A epoxy |
0.0136 |
0.0017 @ 125 mils DFT |
|
FibreCrete novolak vinyl ester with topcoat |
0.0098 |
0.0005 @ 31/7 mils DFT |
|
FibreCrete novolak vinyl ester without topcoat |
0.0291 |
0.00081 @ 31 mils DFT |
|
FibreCrete novolak epoxy with topcoat |
0.0036 |
0.00018 @ 40/10 mils DFT |
|
FibreCrete novolak epoxy without topcoat |
0.0037 |
0.00015 @ 40 mils DFT |
DFT = Dry Film Thickness
Gary also warned that a combination of several corrosive acids such as bromidic and sulfuric are a more potent combination than if each attacked separately.
Lewis Shoemaker, Director of Application Engineering & Business Development at Special Metals Corporation, explained the corrosion history in FGD. Since the early 1980s, nickel-chromium-molybdenum corrosion resistant alloys have been widely used in FGD service, providing reliable service in the aggressive environment. In recent times, utilities tried to reduce costs by building FGD absorber vessels from duplex steels. In the USA, an estimated 85 vessels have been built and are suffering severe crevice attack, often within a few months of start-up. A corrosion testing program conducted by Special Metals Corp./Research & Technology has shown that an advanced grade of super-austenitic stainless steel, alloy 27-7MO, and nickel-chromium-molybdenum alloys C-276, 22 and 686 are resistant to FGD crevice attack. Thus, wallpaper cladding with thin alloy sheets is a viable repair scenario for the failing duplex steel vessels.
Bob McIlvaine led a discussion on new challenges such as corrosion of precipitators and baghouses when using bromine compounds, sulfuric acid corrosion of baghouses when firing high sulfur coals, and materials for heat exchangers. The application of fabric filters on high sulfur coal units has led to sulfuric acid corrosion problems. Lime injection and careful monitoring and control are solutions. Also, eliminating cold spots can prevent the gas from reaching the acid dewpoint. Midwesco has introduced a series of coatings which are applicable to fabric filters, spray dryer absorbers, and ductwork.
Bios, Photos and Abstracts are as follows: BIOS, PHOTOS, ABSTRACTS - JANUARY 16, 2014.htm
The individual presentations are as follows:
§ Corrosion Issues and Materials for APC Systems Webinar - Hot Topic Hour January 16, 2014 (Webinar Recording dated: 1/16/2014)
§ Material Considerations for Maintaining FGD Infrastructure by Gary Hall, Sauereisen - Hot Topic Hour January 16, 2014 (Presentation dated: 1/16/2014)
§ Nickel Alloys Solve Corrosion Problems in Wet Limestone FGD Systems by Lewis Shoemaker, Special Metals - Hot Topic Hour January 16, 2014 (Presentation dated: 1/16/2014)