Environmental Engineering Reference
In-Depth Information
Single dmage in HET
Random disruption of
water chemistry due
to Cl, Na, pH and
other elements
January
February
1996
May
1994
March-April-
May 1996
1987
1992
Service time
9.27 Development of the process of damage of heat exchanger
tubes with time.
After establishing the root cause and the cause of damage, it is clear
that to prevent injuries of this type it is necessary:
• to prevent the accumulation of corrosive elements in boiler water of
SG from the condensate feed circuit (primarily copper and other elements);
• to perform mechanical and chemical cleaning of the secondary circuit
of SG, precluding the accumulation of products falling from the condensate
feed circuit.
Next, computational and analytical studies were performed to determine
the critical size of the defects in the HETs, the residual life of the tube
bundle, as well as the validation of flaw inspection detectability, the
influence of inspection detectability and hydraulic tests on the life and
reliability of tube bundles, the size of a coolant leakage through through-
wall cracks and, finally, a comprehensive assessment of the operational
safety of tube bundles taking into account their damage, technical measures
adopted in SPM-96 and upcoming operating conditions.
The fundamentally important final results of these studies are presented
in Figs. 9.28-9.33.
Figure 9.28 shows the results of calculation of the critical size of
defects in pipes during NOC, deviations from NOC and HT conditions. The
points on the same graph show the experimental results of the evaluation
of the critical size of through-wall defects obtained by Czech experts on
full-size tubes 137 . It can be concluded that the calculated and experimental
results correspond to each other. The analysis shows that HETs may
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