Corrosion of Exhaust and Filtration Equipment in a Radioactive Waste Incinerator Page: 4 of 17
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WSRC-MS-2002-00493 Page 3 of 16
September 30, 2003
with original wire drawing were visible on the surfaces. Elemental x-ray analysis confirmed the
wire was Type 304 stainless steel.
Pitting was the principal reason for failure of the prefilter. Pitting and possibly stress cracking of
the wire would be expected based on the wet gas and high chloride content. Scattered large
round bottom pits were seen. Wire break up resulted from pits growing across the wire or from
fracturing through the reduced cross section due to the pits.
It was plausible that corrosion was occurring on the filter chamber walls, on the internal support
structure for the filter, and everywhere else within the off-gas ductwork. The damage led to
investigation of adequacy of the quench and scrubber systems, cyclone separator, reheater and
general insulation.
HEPA Filter
The deposit on the HEPA filter was the same as on the prefilter, with about 5% iron oxide. A
thick build up on the flat entry surface decreased porosity and movement through the filter,
leading to eventual plugging. The accompanying increase in force at the entry face caused
maximum deflection at center and breakthrough of the paper membrane.
Ductwork
Ultrasonic thickness measurements of the 30 in. (76 cm) carbon steel duct indicated that metal
loss was uniform and not excessive. Thickness was 0.126 in. (3.2 mm) for the 10-gage (standard
steel gage) material, nominally 3.4 mm thick. Mild flaky rust could be easily delaminated or
separated at the inside wall, a result of exposure to the hot moist air environment.
The interior was studied with a video camera. Uniform surface rust, some loose scale, and
scattered traces of a greenish/yellow residue were observed, the latter along the invert and at
"high water marks" near the filter end. The water levels reached 7.5 cm above bottom. There
was no evidence of non-uniform or localized attack or deterioration. The particulate oxides
trapped at the filters had originated on these steel surfaces. Though only mild attack had
occurred, the steel corrosion rate for the environment could exceed 25 mm/y. As a result, a
protective coating (PLASITE* 4310(1) vinyl ester) was recommended to isolate the steel from the
acid conditions. Abrasive blasting to white metal was specified for the interior and the duct was
disassembled for this purpose (Figure 5). Several coats of the vinyl ester material were applied
to develop a specified 40-mil (1 mm) final protective coating.
HEPA Housing - Interior
Dye penetrant examination of the interiors of the HEPA filter housings revealed large cracks on
the prefilter access door seal area (Figure 6), and in heat affected zones of tack welds joining(1)PLASITE* is a registered trade name of Carboline Co.
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Jenkins, C. F. Corrosion of Exhaust and Filtration Equipment in a Radioactive Waste Incinerator, article, October 31, 2003; South Carolina. (https://digital.library.unt.edu/ark:/67531/metadc737680/m1/4/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.