Environmental Engineering Reference
In-Depth Information
Stream outlet
Secondary side
Fretting/wear
Primary side
SCC
Wall thinning
U-bend
B
A
SCC
A-B
IGA
Anti-vibration
bars
Inside
tubesheet
IGA
Tube
support
plate
SCC
SCC
Pitting
Top of
tubesheet
Sludge pile
Tubesheet
Denting
by S.S. Hwang of KAERI
Primary coolant outlet
Primary coolant inlet
7. 2
Various types of corrosion found inside and outside the steam
generator tubes.
metal surface when there is stable protection fi lm on the metal surface.
Depending on the size, shape and hardness of the particles and the cor-
rosion environment, mechanical damage can be accelerated. If there was
no protective fi lm on the surface, only erosion of the metal would occur,
but once the protective fi lm is removed, both corrosion and erosion will be
accelerated. Such corrosion occurs in OTSGs.
Figure 7.2 shows the diverse types of corrosion found inside and outside
steam generator tubes.
Experiences in different countries
Pull tube examinations of 92 tubes from some Korean nuclear power plants
have been carried out since 1989 (Hwang
et al
., 2007). The tubes had dif-
ferent types of failures such as pitting, ODSCC, primary water stress cor-
rosion cracking (PWSCC) and intergranular attack (IGA). A new type of
'PWSCC'crack was found during the ISI carried out after the chemical clean-
ing in 1990, and 22 tubes in SG A and 26 tubes in SG B had to be sleeved.
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