A STRUCTURAL INTEGRITY EVALUATION OF THE TANK FARM WASTE TRANSFER SYSTEM Page: 42 of 86
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WSRC-TR-2005-00532 March, 2006
Page 35 of 69
4.1.6 Thermal Fatigue
Thermal expansion or contraction caused by temperature changes may act against a
constraint and result in thermal stresses. Temperature gradients along and through the
material, internal or external structural constraint, and numerous short-term heating
and/or cooling cycles are necessary for thermal fatigue to occur. Low cycle, high stress
thermal fatigue was identified as the cause of leakage in the stainless steel core pipe of
one high level waste transfer line (see Figure 20 [9]). Transfer line # 501, which is near
the 1H evaporator, failed in a straight, anchored section of the core pipe. The
combination of anchoring the internal pipe to the jacket, restricting the space for
expansion, and having multiple lines within the same jacket intensified the stresses on the
transfer line. The line had been in service for approximately 4.5 years and had
experienced approximately 5500 thermal cycles [9]. The cycles resulted from transfer of
concentrated waste from the evaporator at 115-135 C alternated with desalination
backflushes with water at 20-50 C. The 502 transfer line, which is adjacent to the 501
line in the same carbon steel jacket, also showed indications of cracks at the anchor plate
between the jacket and the core pipe. This second line had been in service for only six
months and had experienced approximately 100 thermal cycles.
A comprehensive piping flexibility study was performed in 1980 to identify other lines
which may be susceptible to thermal fatigue [10]. The study encompassed 72 different
piping systems and included 152 transfer lines. These transfer lines involved Tanks 1-37
and 44-47. The analysis was performed with the computer program PIPELINETM with
ANSI/ASME pressure piping code stress intensification factors and allowable stress
criteria. The actual operating conditions that each line had experienced (i.e., waste and
flush temperatures, frequency of transfers, flushes and shutdowns, etc.), and was
projected to experience in the future, were utilized in calculations to project the total
usage cycles for each line. The dimensions of the lines, the distances between elbows,
and the constraints on the lines were also considered.
On the basis of the analysis, three transfer lines indicated high stress areas subject to
fatigue [82]. These are listed in Table 9. The lines most susceptible were those
associated with the evaporators and the Concentrate Transfer System (CTS). In each
case, the high stress locations were at core to jacket anchors. To reduce the likelihood of
failure the projected total usage cycles were reduced by increasing the flush water
temperature from 20 C to 120-135 C. In addition, a higher level of surveillance was
performed [82]. It should also be noted that the lines associated with the CTS are no
longer in service.
Piping flexibility analyses are routinely performed on new transfer lines [83]. Thus any
piping that has been designed and installed since 1980 has also been analyzed.
4.2 Carbon Steel Jacket Pipe
Corrosion is a chemical or electrochemical reaction between a material, usually a metal,
and its environment that produces a deterioration of the material and/or its properties. In
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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/m1/42/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.