H2Tech - Q3 2022 - 34
MAINTENANCE AND RELIABILITY
will last more than 3 yr before the initial
cracks reach their critical flaw size,
whereas vessels D01, D10 and D12 have
relatively shorter lives (i.e., 1 yr, < 1 yr
and 2.3 yr, respectively).
The graph in FIG. 9 shows an example
of how the current cracks grow by fatigue
prior to becoming critical.
Takeaways and recommendations.
The FFS assessment and remaining life assessment
were carried out for the PSA vesTABLE
8. Cyclic stresses used for remaining life calculations
Cyclic stress = Max op. - min op.
Top nozzle, N02
Bottom nozzle, N01
Top head weld, H01
Middle body weld, H02
Bottom head weld, H03
Upper vertical weld, V01
Lower vertical weld, V02
sels D01-D12, where defect indications
were discovered in the welds during the inspection.
The main objective of the assessments
was to determine whether the vessels
with the defects were fit for service and
how long the vessels can be operated. The
following conclusions and recommendations
were made from the assessment:
* The selected critical cracks
assessed for vessels D01-D12
fell within the FAD envelope;
therefore, the cracks are acceptable
for continuing operation.
* The cracks in vessels D01 and D10
were found be the most critical.
* The remaining life of each vessel
was determined based on the
assumption that the current crack
continues to grow by fatigue as
a result of cyclic loading until it
reaches critical flaw size.
* The remaining life of most of the
PSA vessels (i.e., D02, D03, D04,
D05, D06, D07, D08, D09 and
D11) ranges from 3 yr-5 yr.
* Vessels D01 and D12 have relatively
shorter lives: 1 yr and 2.3 yr,
respectively. Vessel D10 has the
shortest life: 302 d.
* It is recommended to prioritize
vessels D10 and D01 for repair,
particularly the top nozzle weld
(N02 weld) in vessel D10 and
the middle body weld (H02 weld)
in vessel D01.
FIG. 8. A refined FAD of the D01-H02-2 defect and the D10-N02-2 defect.
* If normal operating conditions
change (especially the frequency
of cyclic loading and maximum
pressure), or there is a departure
from the operating conditions
assumed in this assessment
that could be detrimental, it is
recommended to carry out repeated
assessments under these revised
operating conditions to ensure the
vessel remains fit for service.
SANG-MO LEE has more than 26 yr of experience as a
Fixed-Equipment Engineer at SK Energy. His main tasks
include root cause analysis (RCA), troubleshooting,
FFS evaluation, maintenance procedures and technical
support for the refining and petrochemical business.
He earned a BS degree in mechanical engineering
and is qualified as a professional engineer for welding
and metallurgy by the South Korean government.
FIG. 9. Fatigue crack growth of the initial crack size to the limiting flaw size for D12-N02-3.
34 Q3 2022 | H2-Tech.com
OHGEON KWON is a Principal Consultant and Structural
Integrity Team Lead at Quest Integrity. Dr. Kwon has
more than 25 yr of experience and expertise in hightemperature
creep, FFS and remaining life assessments
for various components in the petrochemical, refining
and power generation industries. He earned his PhD at
Imperial College, London.
H2Tech - Q3 2022
Table of Contents for the Digital Edition of H2Tech - Q3 2022
H2Tech - Q3 2022 - Cover1
H2Tech - Q3 2022 - Cover2
H2Tech - Q3 2022 - Contents
H2Tech - Q3 2022 - 4
H2Tech - Q3 2022 - 5
H2Tech - Q3 2022 - 6
H2Tech - Q3 2022 - 7
H2Tech - Q3 2022 - 8
H2Tech - Q3 2022 - 9
H2Tech - Q3 2022 - 10
H2Tech - Q3 2022 - 11
H2Tech - Q3 2022 - 12
H2Tech - Q3 2022 - 13
H2Tech - Q3 2022 - 14
H2Tech - Q3 2022 - 15
H2Tech - Q3 2022 - 16
H2Tech - Q3 2022 - 17
H2Tech - Q3 2022 - 18
H2Tech - Q3 2022 - 19
H2Tech - Q3 2022 - 20
H2Tech - Q3 2022 - 21
H2Tech - Q3 2022 - 22
H2Tech - Q3 2022 - 23
H2Tech - Q3 2022 - 24
H2Tech - Q3 2022 - 25
H2Tech - Q3 2022 - 26
H2Tech - Q3 2022 - 27
H2Tech - Q3 2022 - 28
H2Tech - Q3 2022 - 29
H2Tech - Q3 2022 - 30
H2Tech - Q3 2022 - 31
H2Tech - Q3 2022 - 32
H2Tech - Q3 2022 - 33
H2Tech - Q3 2022 - 34
H2Tech - Q3 2022 - 35
H2Tech - Q3 2022 - 36
H2Tech - Q3 2022 - 37
H2Tech - Q3 2022 - 38
H2Tech - Q3 2022 - 39
H2Tech - Q3 2022 - 40
H2Tech - Q3 2022 - 41
H2Tech - Q3 2022 - 42
H2Tech - Q3 2022 - Cover3
H2Tech - Q3 2022 - Cover4