A STRUCTURAL INTEGRITY EVALUATION OF THE TANK FARM WASTE TRANSFER SYSTEM Page: 79 of 86
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WSRC-TR-2005-00532 March, 2006
Page iii of ix
c) Visual inspection of portions of stainless steel core pipe that had been removed
from service after 15 years indicated no significant wall thickness loss.
d) MIC degradation is primarily a localized phenomenon. No general wall thinning
of the material occurs, but rather pin-hole penetrations near welds in the pipe.
Thus this mechanism would not impact the nominal wall thickness of the transfer
line piping utilized for the structural calculations.
Protective coatings and/or thermal insulation prevent significant general corrosion of the
exterior surface of the carbon steel jacket. Visual inspection of sections of jacket piping
that were removed from service after 15 years indicated no significant wall thickness
loss. Isolated failures of jacket piping have occurred due to:
a) Pitting of the carbon steel jacket occurs at defects (i.e., holidays) in a protective
coating.
b) Corrosion of the carbon steel jacket occurs in local areas beneath thermal
insulation that has been disturbed.
Small pin-hole penetrations may form on the exterior of the jacket at these isolated areas.
The life expectancy of carbon steel jackets was estimated based on an actual case of
pitting damage within a region of local thinning. Two failure mechanisms were
considered: 1) wall loss due to general corrosion and 2) through-wall penetration due to
pitting corrosion. Based on general corrosion rates, the wall thickness of the jackets will
be sufficient for any reasonable service life (e.g.,on the order of 170 years or more). Pits
on the other hand were estimated to penetrate through wall after 80 years of service.
Therefore, through-wall penetration due to pitting corrosion would be the life limiting
mechanism for the carbon steel jacket. The transfer lines have been in-service for
approximately 20 to 50 years. Thus, occasions when the transfer lines fail the jacket
pressure test are expected to begin to increase more significantly sometime between the
years 2035 to 2065.
Finding #4: The transfer of sludge during waste removal operations or sludge and glass
frit particles from the DWPF recycle stream through the stainless steel core pipe is not a
significant erosion concern for the following reasons:
a) Low number of sludge or DWPF transfers performed.
b) The sludge particles are relatively non-abrasive.
c) Relatively low fluid velocities (i.e., less than 7.5 ft/s)
d) The concentration of the more abrasive glass frit particles in the DWPF recycle
stream is relatively low.
e) Results from erosion tests in pilot facilities at SRS indicate that erosion is not
expected to be significant.
f) Piping systems in other facilities at SRS (e.g., DWPF), constructed of similar
materials to the waste transfer piping, that have handled waste streams with
sludge and glass frit have been inspected visually and with ultrasonic
measurements and show no evidence of erosion.
g) There have been no known failures of core piping due to erosion in the tank farm.
Wall thinning of the stainless steel core pipe due to erosion will likely be insignificant for
a reasonable intended service life (e.g., on the order of 160 years or more). The carbon
steel jackets are not exposed to a flowing stream, and therefore erosion is not a concern.
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Wiersma, B. A STRUCTURAL INTEGRITY EVALUATION OF THE TANK FARM WASTE TRANSFER SYSTEM, report, March 9, 2006; United States. (https://digital.library.unt.edu/ark:/67531/metadc836317/m1/79/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.