Report on corrosion under insulation and
internal corrosion of TEG unit
Techno-Wings Co., Ltd.
March 07. 2018
Survey report from wall thickness measurement inspection, visual
inspection and fluid component analysis result of TEG
Ⅰ The types of corrosion thinning are described below
1. Corrosion under insulation of equipment nozzle
2. Corrosion reduction due to condensed water inside the equipment
manhole
3. Corrosion reduction of erosion on the back side of piping elbow for
two-phase flow
4.Corrosion reduction due to flash phenomenon
5. As an acceleration factor of corrosion thinning, it is moisture, Cl-.
Also, as moisture content increases, the iron content increases from the
analysis result.
Refer to DOC.07of the survey reference materials
3. Corrosion reduction of erosion on the back side of piping elbow
for two-phase flow
As shown in the corrosion loop of Doc.01, it occurred on the back
side of the piping elbow of rich glycol water removal equipment.
As a mechanism of two-phase flow,
・ ・ ・
・
・ ・ ・ ・
・ ・ ・ ・ ・
・ ・
Mist, water mass collision on the
back side of the elbow (1) It occurred mainly on the back side of the pipe
elbow.
(2)The temperature at which thinning occurs ranges
from 120 ° C to 250 ° C.
(4)Operating temperature does not occur because of
the low sensitivity of thinning in less than 100 ℃
piping.
(3)When the amount of moisture in the steam is high,
the mist collides with the wall of the pipe and causes
wall thickness reduction.
Schematic diagram of two-phase flow
Qualitative evaluation of the likelihood of damage caused by risk-based maintenance
Ⅰ Countermeasure for maintenance
As a risk-based assessment, which
showed a reduction measures in
maintenance.
Refer to the Maintenance Countermeasure (Ⅳ Countermeasure scheme)
The situation before the
maintenance countermeasure
Refer to Doc.10
insulation
N5
Impingement Attack
Corrosion under insulation:CUI
CUI CUICUI
CUI
CUI
CUICUI
50
50 50
5050
505050 50 50 80
50
50
80N9
N12B
N2 N11B
N12A
N1 N3 N6 N7 N8A N8B N8C N11A
2950
ID 9
50
50
IN
S.
9.5
TH
K
9820 V-160
M1
600
Schematic diagram "a"
“a”
Impingement attack has occurred at the exit of the internal nozzle with respect to N1.
CUI status of N1
Glass wool deteriorates, and they are seen to be wet.
CUI status of N7
The other inter-nozzle is presumed to be sound. Doc.02
Criteria for acceptable risk
Unacceptable risk
Negligible risk
ALARP region
As Low as Reasonably Practicable
It is necessary to
implement risk
reduction measures
and reduce risk as
much as possible
Examples of UK (Netherlands) figures
10-4 / year
10-6 / year
Doc.10