A STRUCTURAL INTEGRITY EVALUATION OF THE TANK FARM WASTE TRANSFER SYSTEM Page: 38 of 86
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WSRC-TR-2005-00532 March, 2006
Page 31 of 69
surface pitting or voids were evident. The small thickness of the plate may have
precluded the development of any extensive sub-surface pits.
Another improper lay-up led to another concern about MIC in the transfer lines between
the H-Area waste tank farm and the DWPF [62]. In 1989 it was discovered that two of
the inter-area transfer lines between the auxiliary and low-point pump pits had
inadvertently been laid up with water for approximately two years. The neutral water
remained after hydrotesting and was contained in the annulus between the stainless steel
core pipe and the carbon steel jacket. Three inspections were performed to investigate
the possibility of MIC [70]. The first inspection consisted of a visual inspection
originating at the nozzle boxes of the auxiliary and low-point pump pits. Video probe
equipment was extended into the annular region for approximately 30 feet. All of the
welds were generally clean with no evidence of MIC. A hydrotest was performed on the
core pipe following this inspection. The lines passed the test which was performed at 375
psig. While this test cannot be used to conclude that MIC did not occur, it demonstrates
that the line is structurally intact and no through-wall penetration has occurred. Later
construction was required to remove a 307 foot section of the suspect transfer line near
the auxiliary pump pit. The removed portion was in two pieces allowing for complete
inspection of the segments. Video equipment was utilized to inspect 57 feet of annulus
space that contained four butt-welds. No evidence of MIC was found. Although it could
not be determined if MIC had occurred (only 20% of the line had been inspected), it was
concluded that no significant MIC had occurred.
During normal service, the high pH of the waste precludes growth of colonies that could
cause MIC. On occasion the stainless steel transfer line is exposed to neutral water,
primarily for flushing of the line after a transfer. In order to prevent conditions that
would be favorable to MIC, the lines are vented and drained after each flush. The
administrative corrosion control program also requires that known "low points" in the
transfer line system must be flushed with inhibited water (pH> 12) unless another waste
transfer is planned within the next five days [60].
The high pH of the waste in conjunction with the corrosion controls described above has
proven effective in preventing MIC. There have been no observed cases of MIC in the
stainless steel radioactive waste transfer core piping in the Tank Farms.
4.1.5 Erosion/Erosion Corrosion
Erosion may be defined as accelerated attack due to a rapidly flowing fluid that contains
solid particles capable of causing wear of the material [41]. Erosion-corrosion refers to
the removal of protective surface films by a flowing corrosive fluid, resulting in wear and
exposure of new, active metal to the corrosive fluid and ensuing chemical attack (See
Figure 19 [39]). Thus, erosion-corrosion incorporates a mechanical and an
electrochemical component. The flowing medium can be a single phase (e.g., liquid) or a
dual phase (e.g., solid and liquid). Attack in corrosive environments in the presence of
solid particles exhibits a highly directional pattern and is more likely to occur in elbows,
bends or T-joints in pipes such as the transfer lines.
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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/m1/38/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.