Page 2642
Asian Journal of Engineering, Social and Health
Volume 3, No. 11 November 2024
Volume 3, No. 11 November 2024 - (2642-2662)
p-ISSN 2980-4868 | e-ISSN 2980-4841
https://ajesh.ph/index.php/gp
Enhancing Crude Oil Tank Inventory Stock Availability at PT Kilang
Pertamina for National Fuel Security
Yudi Ardhana1*, Mirwan Prasetiyo Soeweify2, Heri Sudrajat3,
Muhammad Fahrul Fauzi4, Dalih Fajar Nurjaya5
PT Kilang Pertamina Internasional Unit VI Balongan, Indonesia
Emails: yudi.ardhana@pertamina.com1, Mirwan Prasetiyo Soeweify2,
heri.sudrajat@pertamina.com3, muhammad.fauzi1@pertamina.com4,
dalih.nurjaya@pertamina.com5
ABSTRACT
In 2022, PT Kilang Pertamina International (KPI) Unit VI Balongan initiated the RDMP project to increase
crude oil capacity to 150 MBSD (Million Barrels per Stream Day) by adding equipment to the CDU.
However, refinery capacity growth faced challenges due to corrosion and leaks in the crude oil tank walls.
Repairing these issues through welding while the tanks were onstream posed safety risks, including
explosions. As an alternative, the COMPACT team implemented the FEA + Composite Patch solution, using
a cold work method to minimize risk and avoid downtime. Laboratory testing confirmed that the repair
increased material strength by up to 10%. Further structural analysis of tank 42-T-101B using standard
fitness-for-service (FFS) procedures revealed that the tank initially failed to meet safety criteria due to
metal loss. However, local defect analysis indicated that, if mitigated, the tank could meet the required
standards. Proposed mitigation measures, such as reducing the maximum allowable fill height (MAFH) or
adjusting the RSFa value, would ensure compliance. Composite patch repairs also showed significant
improvements in the tank's ability to withstand collapse, extending its lifespan by up to 62 years,
supporting the continued safe operation of the storage tank and contributing to national fuel security.
Keywords: Stock Availability Optimization, Compact Solution for Inventory Management, National
Energy Security of Supply.
INTRODUCTION
Indonesia's growing energy demands require a robust and reliable infrastructure to ensure
the continuous availability of fuel for domestic consumption and industrial activities (Rahman et
al., 2021). As the nation's energy needs expand, the role of efficient crude oil storage and
management becomes increasingly significant in supporting energy security and economic
stability (Le & Nguyen, 2019). Refineries and storage facilities serve as critical components in the
energy supply chain, enabling the safe and efficient handling of crude oil inventories (Lima et al.,
Improving Stock Availability of Crude Oil Tank Inventory Through the "Compact Solution" Method to
Maintain Security of Supply of National Fuel Fuel at PT Kilang Pertamina International Unit VI Balongan
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2016). However, maintaining the structural integrity and operational readiness of these facilities
presents both technical and logistical challenges that demand strategic planning and innovative
solutions (Wang, 2016).
PT Kilang Pertamina (PT KPI) plays a crucial role in ensuring the supply of fuel for Indonesia's
national energy needs. As part of its strategic efforts to maintain energy security, the company
continuously works to enhance its refining and storage capabilities (Anggraito et al., 2023). One
of the key challenges is ensuring the optimal availability of crude oil tank inventories to meet the
growing demand for fuel (Panda & Ramteke, 2019). In this regard, PT KPI's focus has been on
improving stock management systems and boosting tank storage capacity, particularly at critical
facilities such as the Balongan Refinery (Unit VI). These efforts are vital to maintain a steady
supply of fuel and avoid any disruptions that could affect the national economy (Milza & Rahadi,
2023).
The improvement of crude oil tank inventory stock availability is essential for safeguarding
Indonesia's energy security. Given the dynamic nature of crude oil supply chains, factors such as
fluctuations in production, geopolitical uncertainties, and unexpected disruptions can pose risks
to the national fuel supply (Dahri & Siallagan, n.d.). To address these challenges, PT KPI is
implementing innovative solutions to optimize stock management and enhance storage
efficiency. This approach not only ensures sufficient stock availability but also supports the
company's long-term goal of achieving energy self-sufficiency and securing a stable,
uninterrupted fuel supply for the country (Irzanova, 2023).
Hoarding Tank Tag No 42-T-101B, built and operated in 1993 by PT Pertamina International
Refinery RU VI Balongan with a maximum storage capacity of 67000 m3. In mid-2023 PT Kilang
Pertamina Internasional inspected the tank and reported 6 defects in the course-1 section, and
one defect in the course-5 section. To see the impact of the defects found, PT Kilang Pertamina
Internasional RU VI Balongan wants to conduct an engineering study on the operational feasibility
of the Hoarding Tank (Azhari & Salsabila, 2023).
Previous research conducted by (Ali et al., 2020) stated that the demand for inventory in
this study is modeled using Poisson distribution, considering constant lead times, and applies the
(Q, r) model with stock-out cost and backorder cost approaches. Both approaches lead to
improved service levels and reduced average inventory investment, with the stock-out cost
approach achieving an 8.88% increase in service level and a 56.9% reduction in inventory
investment, while the backorder cost approach shows a 7.77% improvement in service level and
a 57% decrease in inventory investment. These results positively impact plant uptime,
productivity, and reduced maintenance costs by efficiently managing maintenance stock, which
can be applied to various industries, including oil and gas.
This Fitness for Service (FFS) study work is intended to analyze the feasibility of Tank 42-T-
101B against the liquid level limitation of Tank 42-T-101B. The study of liquid level limitation is
important because it will have an impact on reducing the company's business performance. To
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Volume 3, No. 11 November 2024
determine the feasibility of the stockpile tank based on applicable standards, a more detailed
and comprehensive evaluation of the tank condition based on the actual condition of the tank is
required.
(a)
(b)
(c)
Figure 1. Location (a&b) of course-1 and (c) Visual condition of course-5 corrosion
on tank 42-T-101B [B.1][B.2]
Job Purpose:
1. Conduct FFS Level 1, 2, and 3 assessments on storage tank 42-T-101B.
2. Provide recommendations based on the results of FFS Level 1, 2, and 3 assessments on storage
tank 42-T-101B.
The urgency of this research stems from the critical role that crude oil storage tanks, such
as 42-T-101B, play in maintaining national fuel security. Any failure or operational inefficiency in
these storage tanks could disrupt fuel supply, which would have far-reaching economic and social
consequences. By conducting FFS assessments, potential risks can be identified early, ensuring
that necessary interventions are made promptly to avoid unscheduled downtime, thus
guaranteeing a stable and secure supply of fuel for the nation.
Based on the outlined objectives and benefits, this study aims to comprehensively evaluate
the current condition and structural integrity of storage tank 42-T-101B through Fitness-for-
Service (FFS) assessments at Levels 1, 2, and 3. By identifying potential risks and providing
evidence-based recommendations, the research seeks to enhance the tank’s operational
reliability and safety, ensuring its readiness for continued crude oil storage. Additionally, the
findings will support PT Kilang Pertamina in optimizing its storage infrastructure, contributing to
improved operational efficiency, cost savings, and national fuel security. This research
underscores the critical role of proactive maintenance and strategic management in safeguarding
Indonesia’s energy resilience.
Improving Stock Availability of Crude Oil Tank Inventory Through the "Compact Solution" Method to
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Volume 3, No. 11 November 2024
RESEARCH METHOD
This research is an applied research that aims to conduct a defect feasibility study on
storage tank 42-T-101B using API 653 and API 579 standards as the main guide in evaluating the
degradation of existing defects. The data analysis techniques used include visual inspection to
identify defects, Fitness-for-Service (FFS) assessment using Level 1, 2, and 3 methods from API
579, and quantitative risk analysis (QRA) to assess the potential impact of defects on tank
performance. Data collection techniques include on-site inspection, non-destructive testing
(NDT) such as ultrasonic, radiographic, and magnetic particle testing, and review of historical data
such as maintenance records and previous inspection reports. The main data sources are from
API 653 and API 579 standards, tank maintenance records, inspection results, as well as relevant
industry guidelines. This research aims to provide data-driven recommendations to ensure tank
structural integrity and support optimal crude oil stock availability at PT Pertamina Refinery to
maintain national energy security.
RESULT AND DISCUSSION
RESULT
FFS Level 1 & 2
FFS level 1, 2, and 3 calculations were performed to review the damaged stockpile tanks.
Figure 5 1 shows the steps involved in performing FFS level 1, 2, and 3 calculations.
Figure 2. Flowchart of FFS in the case of metal loss
The FFS analysis was conducted using the Part 4: Assessment of General Metal Loss (API
579-1/ASME FFS-1) standard. Thus, to maintain the conservativeness of the results, the
assessment was conducted using Part 4. In addition, API 579-1/ASME FFS-1 also recommends
performing calculations on Part 4 before going to Part 5 (API 579-1/ASME FFS-1, Paragraph 5.1.2).
Level 1 and Level 2 FFS Results
A summary of the FFS Level 1 and 2 results can be seen in table 1 as follows:
Yudi Ardhana, Mirwan Prasetiyo Soeweify, Heri Sudrajat, Muhammad Fahrul Fauzi, Dalih Fajar Nurjaya
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Volume 3, No. 11 November 2024
Table 1. Summary of FFS Level 1 and 2 results
Metal
loss
Level 1
Level 2
Location
MFHr
(m)
MFH
Assessment
Minimum
Measured
Thickness
Check
MFHr
(m)
MFH
Assessment
Minimum
Measured
Thickness
Check
#1
15.1
ACCEPTABLE
ACCEPTABLE
16.74
ACCEPTABLE
ACCEPTABLE
Shell#1
350°
#2
15.1
ACCEPTABLE
ACCEPTABLE
16.74
ACCEPTABLE
ACCEPTABLE
Shell#1 10°
#3
15.09
ACCEPTABLE
ACCEPTABLE
16.73
ACCEPTABLE
ACCEPTABLE
Shell#1 20°
#4
15.09
ACCEPTABLE
ACCEPTABLE
16.73
ACCEPTABLE
ACCEPTABLE
Shell#1 35°
#5
15.1
ACCEPTABLE
ACCEPTABLE
16.74
ACCEPTABLE
ACCEPTABLE
Shell#1
190°
#6
15.1
ACCEPTABLE
ACCEPTABLE
16.74
ACCEPTABLE
ACCEPTABLE
Shell#1
200°
#7
15.12
ACCEPTABLE
ACCEPTABLE
15.62
ACCEPTABLE
ACCEPTABLE
Shell#5
240°
FFS Level 3
Introduction
The FFS Level 3 assessment procedure refers to ANNEX 2D in API 579-1/ASME FFS-1
Fitness for Service. In ANNEX 2D of API 579-1/ASME FFS-1 Fitness for Service, all detailed stress
analysis procedures refer to ASME B&PV Code Section VIII, Division 2 (VIII-2), Part 5: Design by
Analysis. The assessment method in this ANNEX is based on the results of stress analysis using
numerical analysis.
Figure 3. FFS Level 3 assessment procedure
The procedures in this ANNEX are designed to evaluate defective components against
several failure modes, including:
a. Protection Against Plastic Collapse (2D.2)
b. Protection Against Local Failure (2D.3)
c. Protection Against Collapse from Buckling (2D.4)
d. Protection Against Fatigue Damage (Part 14)
For the FFS Level 3 assessment, the Protection Against Plastic Collapse method was chosen:
Elastic-Plastic Stress Analysis Method and Protection Against Local Failure: Elastic-Plastic
Analysis. Both methods were chosen because they can simulate the plastic condition of the
Improving Stock Availability of Crude Oil Tank Inventory Through the "Compact Solution" Method to
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material, making it closer to the actual material condition. It is different if only using the elastic
condition of the material, because it will be less close to the actual condition of the material.
Determination of acceptance criteria for each method uses the following logic:
1. Protection Agains Plastic Collapse: Elastic-Plastic Stress Analysis Method
If, 𝑃𝑑𝑒𝑠𝑖𝑔𝑛𝛽 < 𝑃𝑐𝑜𝑙𝑙𝑎𝑝𝑠𝑒 =>ACCEPTABLE
2. Protection Against Local Failure: Elastic-Plastic Analysis
If, 𝜀𝑝𝑒𝑞 + 𝜀𝑐𝑓 ≤ 𝜀𝐿=>ACCEPTABLE
Material Model
The material model is used as input to the finite element software with its mechanical
properties. Table 2 is the mechanical properties inputted in the modeling of tank 42-T-101B.
Table 2. Properties (mechanical properties) of materials
Materials
Density
(ton/mm )3
E (MPa)
v
YS (MPa)
UTS
(MPa)
Application
Reference
A-105
7.80E-09
190000
0.29
250
485
Pipe N1, N2, N6,
N7AB, N7CD, N8, N9
ASME BPVC 2021
Section II Part A-1
A-283 C
7.80E-09
200000
0.29
205
380
Tank bottom, Shell-5,
Shell-6
ASME BPVC 2021
Section II Part A-1
A-573 70
7.80E-09
200000
0.29
290
485
Shell-1, Shell-2, Shell-
3, Shell-4, Pad, M1,
N4, Reinforcement
Pad, Annular plate
ASTM A-573
SS41
7.80E-09
200000
0.29
245
400
Bracket
https://www.thewo
rldmaterial.com/jis-
g3101-ss400-steel-
equivalent-material/
Rockwool
1.92E-10
-
-
-
-
Insulation
Weekly progress 01
discussion
Model Geometry
1) Course Shell Model
Geometry modeling is done using CAD software as a prefix to create the three-dimensional
shape of Tank 42-T-101B. In general, the geometry of the tank model uses dimensions such as
Table 3.
Table 3. Summary of tank model geometry dimensions 42-T-101B
Description
Value
Unit
Shell ID
84600
mm
Area of inside shell
5.62E+09
mm2
Shell Height
15500
mm
Number of shell courses
6
-
Shell Thickness:
26.67
mm
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Description
Value
Unit
Shell#1
Shell#2
Shell#3
Shell#4
Shell#5
Shell#6
21.77
15.78
10.98
9.53
9.53
Shell Height:
Shell#1
Shell#2
Shell#3
Shell#4
Shell#5
Shell#6
2571
2571
2571
2570
2571
2571
mm
2) Finite Element Model
Once the geometry of the model is created, the finite element model is built by discretizing
the model geometry. Figure 4 is an overview of the model that has been imported into the
Abaqus software.
Figure 4. Overall tank model in Abaqus
Convergence Test
Convergence tests in finite element analysis (FEA) are an important process to ensure the
accuracy and reliability of simulation results (Szabó & Babuška, 2021). These convergence tests
examine how the solution of an FEA model changes with modifications to the element size or
mesh precision.
Boundary Conditions & Load Convergence Test
An overview of the boundary conditions can be seen in Figure 5 and Figure 6.
Figure 5. Boundary conditions of the bottom
tank
Figure 6. Boundary conditions at the
nozzle
Improving Stock Availability of Crude Oil Tank Inventory Through the "Compact Solution" Method to
Maintain Security of Supply of National Fuel Fuel at PT Kilang Pertamina International Unit VI Balongan
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Volume 3, No. 11 November 2024
The load in the convergence test uses hydrostatic pressure at a liquid height of 13990mm
as shown in Figure 7, and a gravity load to describe the dead load of the storage tank as shown
in Figure 8.
Figure 7. Load hydrostatic pressure (Liquid
Height 13990 mm)
Figure 8. Load gravity (9810 mm/s2)
Element Variations
Table 4. Variation of the number of elements
Mesh size (mm)
Element Number
500
73131
300
125583
200
244998
150
377109
Convergence Test was conducted using 4 variations of mesh accuracy, the number of
elements varied from 73131 to 377109 elements. An overview of the elements in the tank can
be seen in Figure 9.
Figure 9. Visual mesh convergence test
Convergence Test Results
The convergence test results show the maximum stress results occur in the area around
Nozzle 5. This point becomes the observation parameter for the stress value for each element
variation modeled.
Figure 10. Convergence test result
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In general, models with element sizes of 300 to 150 have differences of less than 5%. It can
also be illustrated graphically that the modeling has converged and can be used as a basis for
continuing the level 3 FFS analysis. In this work, the model to be used is the model with element
size 200. An overview and the difference in stress values in percentage can be seen in Figure 6
and Table 5.
Table 5. Difference in convergence test voltage results
Mesh size (mm)
Element Number
Max Stress (MPa)
Difference
500
73131
338
-
300
125583
354
4.7%
200
244998
359
1.4%
150
377109
361
0.6%
Figure 11. Distribution of convergence test stress values
Results of sensitivity analysis
Sensitivity analysis of thickness was conducted due to some differences in thickness data
from inspection results. The analysis condition is performed by giving a plastic collapse load in
each scenario. The results of the sensitivity analysis are shown in Table 15.
The results of the sensitivity analysis show that the smallest LF value is found in Scenario 1,
so the model with Scenario 1 configuration is used for further analysis (to maintain
conservatism).
Fitness for Service Assessment Level 3
Load Case
There are 5 loading combinations in the Global Criteria in accordance with API 579
standard. In addition, Load number 3 will be ignored because the equation after the snow load
is removed becomes the same as number 1 and because number 1 is more conservative. So the
loading for level 3 modeling only takes Load case criteria number 1, 2, 4, and 5.
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Volume 3, No. 11 November 2024
Figure 12. Design condition elastic plastic stress analysis [A.1]
The parameters used in the load combination calculation can be seen in Table 6. Specifically
for the β value, the value will be calculated based on the design margin and allowable Remaining
Strength Factor (RSFa). In this report, the RSFa value uses a conservative value of 0.9. This RSFa
value can be modified based on the equipment construction code.
Table 6. Load combination parameters RSFa 0.9
Parameters
Value
Description
β
2.25
Design Margin x RSFa
0.88β
1.98
-
0.71β
1.5975
-
0.36β
0.81
-
P (MPa)
0.1
Working pressure (atmospheric)
Ps (MPa)
0.123
Hydrostatic pressure
D (Kg)
896674
Deadload
T (°C)
65
Design Temperature
W (MPa)
0.00113364
Wind load
Liquid Level (mm)
13990
Design liquid level
E (N.mm)
6.1209E+10
Earthquake
RSFa
0.9
From FFS level 1 and 2
From the above parameters, the load values applied in the modeling can be seen in Table
18.
Table 7. Load case scenario
Criteria
Liquid
Level
P
Ps
D
W
T
E
Global
Criteria
Load Case 1
100%
0.1
0.123
896674
N/A
N/A
N/A
Load Case 2
100%
0.1
0.123
896674
N/A
65
N/A
Load Case 4
100%
0.1
0.123
896674
0.00113
N/A
N/A
Load Case 5
100%
0.1
0.123
896674
N/A
N/A
6.1209E+10
Local Criteria
100%
0.1
0.123
896674
N/A
N/A
N/A
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Global Criteria Result
In order for the tank to meet the FFS Level 3 acceptance criteria for the global failure mode,
the results of the Plastic Collapse Load analysis of the tank must meet the acceptance criteria for
all applicable Load Cases.
Based on the global criteria/Protection Against Plastic Collapse (PAPC), the tank with the
existing defect does not meet the FFS Level 3 acceptance criteria if it is filled with product with a
MAFH of 13990mm. Global Criteria results using RSFa 0.9.
Table 8. Results of global criteria RSFa 0.9
Criteria
Liquid
Level
P
Ps
D
W
T
E
Plastic
Collapse
Load
Factor
(PCLF)
β
Allowable
Load Factor
(ALF)
Status
Global
Criteria
Load
Case 1
100%
0.1
0.123
896674
N/A
N/A
N/A
2.109
2.25
1xβ=2.25
PCLF <
ALF
NOT PASS
Load
Case 2
100%
0.1
0.123
896674
N/A
65
N/A
2.109
2.25
0.88xβ=1.98
PCLF >
ALF
PASS
Load
Case 4
100%
0.1
0.123
896674
0.00113
N/A
N/A
2.102
2.25
0.88xβ=1.98
PCLF >
ALF
PASS
Load
Case 5
100%
0.1
0.123
896674
N/A
N/A
6.12E+10
1.893
2.25
0.88xβ=1.98
PCLF <
ALF
NOT PASS
Local Criteria Result
Based on the local criteria/Protection against local failure (PALF), the tank meets the FFS
Level 3 acceptance criteria if it is filled with product with a MAFH of 13990mm. Table 9 shows
the overall results of the local criteria.
Table 9. Local criteria results
Location
ɛpeq
ɛLu
αsl
m2
σ1
σ2
σ3
σe
ɛL
Assessment
Metal Loss#1
2.95E-03
0.24124
2.2
0.24124
3.81E+02
1.71E+02
0.00E+00
3.31E+02
0.16256
Accept
Metal Loss#2
5.60E-03
0.24124
2.2
0.24124
4.08E+02
1.93E+02
0.00E+00
3.53E+02
0.15951
Accept
Metal Loss#3
7.42E-03
0.24124
2.2
0.24124
4.22E+02
2.03E+02
0.00E+00
3.65E+02
0.15853
Accept
Metal Loss#4
1.15E-02
0.24124
2.2
0.24124
4.46E+02
2.19E+02
0.00E+00
3.87E+02
0.15763
Accept
Metal Loss#5
3.21E-03
0.24124
2.2
0.24124
3.84E+02
1.73E+02
0.00E+00
3.34E+02
0.16213
Accept
Metal Loss#6
5.40E-03
0.24124
2.2
0.24124
4.06E+02
1.92E+02
0.00E+00
3.52E+02
0.15963
Accept
Metal Loss#7
5.17E-05
0.27632
2.2
0.27632
2.04E+02
3.80E-01
-1.60E+00
2.05E+02
0.27797
Accept
Fitness for Service Assessment Level 3 Summary
To meet the FFS Level 3 acceptance criteria, the acceptance criteria for all failure modes,
both global (PAPC) and local (PALF) must be met. Based on the results of the FFS Level 3
assessment, the 42-T-101B storage tank with the existing defects does not meet the FFS Level 3
Improving Stock Availability of Crude Oil Tank Inventory Through the "Compact Solution" Method to
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Volume 3, No. 11 November 2024
acceptability criteria. Note that the acceptance criteria for global and local failure modes are
based on an RSFa=0.9 value, and a maximum fill height of 13990 mm.
Defect Mitigation
Non-Metallic Repair
Non-metallic repair is a method of repairing a damaged/defective surface using materials
that do not contain metal. Thus, non-metallic repair can be done when the equipment is in
operation, this is because non-metallic repair does not require heat. Referring to ASME PCC-2
2022, the materials that can be used as non-metallic repair are composites. The repair scheme
using composites based on ASME PCC-2 2022 is in Figure 13.
Figure 13. Non-metallic repair scheme [A.6]
From the repair scheme shown in Figure 28, the composite does not interact directly with
the defect, so the defective part needs to be leveled with the surrounding surface. Based on
ASME PCC-2 2022 the material for leveling the defect is called infill material. This infill material
serves to pass the load from the substrate/steel to the composite. The scheme of using infill
material on the defect is shown in Figure 14.
Figure 14. Schematic of defect filler material
Non-Matellic Repair Geometry Model
The configuration of the filler material for each metal loss is shown in Table 24, the
thickness of the composite to be used as a patch will be subjected to sensitivity analysis to
determine the optimal thickness.
Table 10. Thickness of filling material
Location
Remaining Thickness
(mm)
Target Thickness
(mm)
Thickness of filling
material (mm)
Metal Loss#1
25.52
26.52
1
Metal Loss#2
24.52
26.52
2
Metal Loss#3
22.52
26.52
4
Metal Loss#4
21.55
26.52
4.97
Metal Loss#5
25.52
26.52
1
Metal Loss#6
24.52
26.52
2
Metal Loss#7
7.05
9.41
2.36
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The composite modeling in Abaqus software is shown in Figure 15, the part given by the
composite is divided into 2, namely at the metal loss and around the metal loss. In the metal loss
section, the configuration sequence is substrate/steel, filler material, and composite. While
around the composite, the configuration is only substrate/steel and composite.
Figure 15. Composite model in Abaqus software
Non-Metallic Repair Analysis Results
Sensitivity analysis was performed to obtain the optimal composite configuration results.
The results of the sensitivity analysis are shown in Table 11 and converted to a graph in Figure
30, the simulation conditions are at design operating conditions.
Table 11: Results of sensitivity analysis of composite ply counts
Number of ply near ML
Total ply thickness
(mm)
Max. Stress1 (MPa)
Voltage reduction2
W.O Repair
0
302
0
5
10
299
0.828%
7
14
295
2.419%
9
18
292
3.247%
11
22
290
3.910%
1Result of max. stress in Metal Loss-3
2Voltage reduction compared to the condition without repair
Furthermore, sensitivity analysis is carried out by providing plastic collapse load conditions
for each variation in the number of ply, the results are contained in Table 26.
Table 12. Results of sensitivity analysis on plastic collapse loads
Number of ply near ML
LF
W.O Repair
2.109
5
2.326
7
2.327
9
2.328
11
2.329
In addition to the number of composite thicknesses, analysis was also carried out by varying
the patch overlap configuration against metal loss. The part that is used as a variation of the
patch configuration is in the metal loss section 3.
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Figure 17. Composite patch configuration variation code
The results of the analysis of the variation of the composite patch configuration are shown
in Table 13, the load conditions given in this analysis are the design operating conditions.
Table 13. Analysis results of composite patch configuration variations
NO.
Number of ply near
ML
Configuration
Max. Stress1 (MPa)
A
B1
B2
C1
C2
1
5
299.3
2
296.8
3
299.3
4
299.2
5
296.7
Composite Patch (COMPACT) Test Specimen Testing
Due to the absence of test standards relating to steel plates with defects patched with
composite patches, the dimensions of the test specimens are determined based on the
capabilities of the available tensile testing machine, along with the existing patching scheme. The
purpose of this test is to determine the effect of the addition of composite patches on the
maximum load that can be withstood by steel plates with defects. In general, the test specimen
is shown in Figure 18.
Figure 19. Overview of the test specimen, (a) Isometric, (b) Top view, and (c) Front view,
along with details of the patch area.
In general, the test specimens shown in Figure 19 above have the arrangement of test
specimens shown in Table 14.
Yudi Ardhana, Mirwan Prasetiyo Soeweify, Heri Sudrajat, Muhammad Fahrul Fauzi, Dalih Fajar Nurjaya
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Table 14. test specimen
No.
Part Name
Specimen/Component Provider
1
Steel Plate with defects
KPI
2
Filler Material
Composite Vendor
3
Adhesive
Composite Vendor
4
Composite laminate
Composite Vendor
5
Fixture Plates
PT LAPI ITB
6
Fixture Bolts
PT LAPI ITB
Visual Inspection and Sample Measurement
Visual inspection is carried out to determine the as it is condition of the specimen when
received and before testing. Furthermore, from all specimens received, the code is given
according to the type of specimen. Samples of metal plate specimens with local defects are coded
1 - 5. And for metal plate specimens with local defects combined with composite patches are
coded A - E. Documentation of visual inspection on all samples can be seen in Figure 29. And
documentation for each sample is presented in APPENDIX A.
Figure 20. Tensile Test Specimen
In addition to visual inspection, measurements were also taken of each sample to
determine the actual dimensions of each specimen. The following measurement results for each
specimen are presented in Figure 15 and Figure 16.
Figure 21. Actual Dimensions of Metal Plate Specimens with Localized Defects
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Figure 22. Actual Dimensions of Locally Deformed Metal Plate Specimens equipped with
Composite Patch
Test Equipment Specifications
The selection of test equipment is determined based on the actual dimensions of the entire
specimen, so that the capacity of the tool used is qualified during the test (de Bekker-Grob et al.,
2015). The existing tensile test equipment at the Faculty of Civil and Environmental Engineering
ITB has sufficient capacity to be able to test specimens. The following description of the tensile
test equipment specifications is shown in table 15.
Table 15. Specifications of Tensile Test Equipment
Tool Specifications
Model
:
E64.206
Rated Force Capacity
:
2000 kN
Column Configuration
:
6
Test Zones (single/dual)
:
Dual
Piston Stroke
:
250 mm/min
Piston Speed
:
0.5 - 70 mm/min
Crosshead Speed
:
390 mm/min
Test Width
:
640 mm
Maximum Tensile Space
:
920 mm
Maximum Compression Space
:
950 mm
Diameter of Round Specimen
:
15 - 70 mm
Thickness of Flat Specimen
:
10 - 70 mm
Compression Platen
:
240 x 240 mm (square)
Frame Dimension (height x width x depth)
:
3150 x 1310 x 1060 mm
Weight
:
8000 kg
Tensile Test Results
The results of tensile testing on metal plate specimens with localized defects have an
Ultimate Load of 267373 N. Details of the test results can be seen in Table16, and graphs for each
test specimen are presented in APPENDIX A.
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Table 16. Tensile Testing Results of Metal Plate Specimens with Localized Defects
Specimen
Area
Yield Point
Yield Strength
Ultimate Load
Ultimate Strength
[mm ]2
[Newton]
[N/mm ]2
[Newton]
[N/mm ]2
1
626.3
195397
311.99
295734
472.19
2
613.74
176091
286.91
268508
437.49
3
593.19
183217
308.87
271843
458.27
4
556.41
174689
313.96
271615
488.16
5
535.04
158042
295.38
229165
428.31
Average
584.936
177487.2
303.422
267373
456.884
The tensile test results on metal plate specimens with local defects equipped with
composite patches have Ultimate Load 1 at an average of 295803 N, while for Ultimate Load 2 at
an average of 286561 N. Details of the test results can be seen in table 17.
Table 17. Testing Results of Locally Deformed Metal Plate Specimens
which is equipped with Composite Patch
Specime
n
Area
Ultimate Load
1
Ultimate Load
2
Ultimate
Strength
Equivalent Ultimate
Strength*
[mm ]2
[Newton]
[Newton]
[N/mm ]2
[N/mm ]2
A
-
287940
290258
-
-
B
-
296838
279554
-
-
C
-
317134
316746
-
-
D
-
290072
271531
-
-
E
-
287031
274716
-
-
Average
584.93
6
295803
286561
505
*Equivalent Ultimate Strength is calculated based on the average area of metal plates with
defects
With the addition of composite fillings, there was an increase;
- Ultimate load of 9.6%,
- Equivalent Ultimate Strength by 10%.
Based on the calculation of FFS Level 1 and Level 2, the tank with metal loss defects does
not meet the acceptance criteria of FFS Level 1 and Level 2. So the assessment process needs to
be continued to FFS Level 3. FFS Level 3 assessment is carried out with two applicable failure
modes, namely global criteria/Protection Against Plastic Collapse (PAPC), and local
criteria/Protection Against Local Failure (PALF). In line with previous research conducted by (Yang
et al., 2022) stated that the economic impact of crude oil supply disruptions on social welfare
losses can be significant, as such disruptions lead to increased fuel prices, decreased industrial
productivity, and increased transportation costs, all of which negatively affect consumers and
businesses. Increasing the availability of crude oil tank inventory stocks, through increased
Improving Stock Availability of Crude Oil Tank Inventory Through the "Compact Solution" Method to
Maintain Security of Supply of National Fuel Fuel at PT Kilang Pertamina International Unit VI Balongan
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Volume 3, No. 11 November 2024
storage capacity and more efficient inventory management, helps mitigate these disruptions by
ensuring a stable and reliable fuel supply. Strategic petroleum reserves (SPRs) play a critical role
in maintaining national energy security during supply crises, enabling fuel price stabilization and
reduced welfare losses. By optimizing tank inventory management and expanding reserves,
countries can better manage supply shocks, protect social welfare, and reduce the negative
economic impact of crude oil shortages, ultimately improving fuel security and maintaining
economic stability (Yuan et al., 2020).
The study results based on the global criteria, Protection Against Plastic Collapse (PAPC),
indicate that the 42-T-101B storage tank with defects does not meet the FFS Level 3 acceptance
criteria under the design operating conditions (MAFH=13,990 mm) when using a Resistance
Strength Factor (RSFa) of 0.9. This means that, under these conditions, the tank's structural
integrity is at risk of failure due to plastic collapse, which occurs when the stresses exceed the
material's ability to maintain its shape without undergoing permanent deformation. As a result,
the tank is considered unsafe for continued operation without further mitigation to address the
defects and reduce the potential for collapse.
On the other hand, when the assessment is carried out based on the local criteria,
Protection Against Local Failure (PALF), the 42-T-101B storage tank with defects does meet the
FFS Level 3 acceptance criteria under the same design operating conditions (MAFH=13,990 mm)
and with an RSFa of 0.9. This suggests that, while the tank may be prone to failure under broader,
more global stress conditions (such as plastic collapse), the local failure potential is within
acceptable limits, meaning that the tank could still perform safely under certain localized
conditions. However, this finding also highlights that the tank's overall safety may be
compromised in other failure modes, and additional remedial measures may be necessary to
ensure full compliance with FFS Level 3 criteria.
Based on the results of points 2.a, and 2.b above, it can be concluded in general that the
42-T-101B storage tank with defects does not meet the FFS Level 3 acceptance criteria (with RSFa
0.9 and MAFH = 13990 mm). By not mitigating the existing defects in the 42-T-101B storage tank,
the results of additional analysis show that the 42-T-101B storage tank with defects can meet the
FFS Level 3 acceptance criteria, with the following options;
a. By continuing to use RSFa=0.9, the MAFH must be reduced to a maximum of 13200 mm.
b. Using the modified RSFa, which is 0.84. By using RSFa=0.84, the MAFH can be maintained in
accordance with the design condition of 13990 mm.
A defect mitigation analysis on the 42-T-101B storage tank in the form of non-
metallic/composite repair has been conducted, with the following results;
a. Under operating load conditions, where the stress level in the tank is still below the plastic
stress, the addition of composite patches to the defect area will reduce the stress level in the
defect area. However, this stress drop is relatively small.
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b. In loading conditions until plastic collapse, where the stress level in the tank has passed the
plastic stress, the effect of composite patches will be more significant in increasing the Plastic
Collapse Load of the tank.
c. The composite patch overlap in the circumferential direction is less significant in reducing
stress than the composite patch overlap in the axial (elevation) direction.
d. With the composite patch overlap (minimum 5 layers), the Plastic Collapse Load Factor
increased to 2.326, from the previous (without repair) 2.109.
e. By mitigating the overlap composite patch, the 42-T-101B storage tank can meet the FFS Level
3 acceptance criteria with a design MAFH of 13990 mm, and RSFa=0.9.
The results of the residual age study are as follows:
a) if no repair is carried out, and MFH is at the level of 13200 mm, and by using RSF 0.9, then
tank 42-T-101B has a remaining life of 10 years (thickness limit 26.47 mm).
b) if no repair is carried out and MFH is at the level of 13990 mm, and by using RSF 0.84, then
tank 42-T-101B has a remaining life of 16 years (thickness limit 26.44 mm).
c) if a non-metallic repair is performed and the MFH is at the 13990 mm level, and using an RSF
of 0.9, then tank 42-T-101B has a remaining life of 62 years (thickness limit of 26.21 mm). This
is assuming no degradation of the composite material used.
Thus, storage tank 42-T-101B with metal loss defects failed to meet the acceptance criteria
under FFS Levels 1 and 2, requiring further assessment under FFS Level 3. Evaluation under the
global criterion (Protection Against Plastic Collapse) indicates that the structural integrity of the
tank is at risk of failure due to plastic collapse unless mitigation measures are taken. However,
the tank meets the criteria under local failure conditions (Protection Against Local Failure). By
adjusting the Resistance Strength Factor (RSFa) or reducing the Maximum Allowable Fill Height
(MAFH), the tank can meet the FFS Level 3 criteria. In addition, composite patch repair can
improve the tank's ability to withstand pressure, thereby extending its service life to 62 years,
assuming no material degradation.
CONCLUSION
This research successfully addresses the critical issue of assessing and ensuring the
structural integrity of storage tank 42-T-101B through the application of Fitness-for-Service (FFS)
procedures outlined in API 653 and API 579. The study found that the tank initially failed to meet
FFS Level 1 and 2 criteria due to metal loss defects, and further FFS Level 3 analysis revealed that
while the tank met local failure criteria (PALF), it did not satisfy global failure criteria (PAPC) under
design operating conditions. Proposed mitigation measures, including reducing the maximum
allowable fill height (MAFH) to 13,200 mm or adjusting the RSFa value, along with composite
patch repair strategies, demonstrated the potential to restore the tank's structural integrity and
extend its remaining life to 62 years. These findings not only ensure the continued safe operation
of PT Kilang Pertamina’s storage tanks but also provide a valuable framework for managing
Improving Stock Availability of Crude Oil Tank Inventory Through the "Compact Solution" Method to
Maintain Security of Supply of National Fuel Fuel at PT Kilang Pertamina International Unit VI Balongan
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Asian Journal of Engineering, Social and Health
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similar infrastructure challenges in the future. The study’s contributions extend to offering
practical insights into defect mitigation, lifespan extension, and adherence to industry standards,
setting a benchmark for optimizing storage infrastructure in the oil and gas industry and
reinforcing Indonesia's energy security.
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Copyright holder:
Yudi Ardhana, Mirwan Prasetiyo Soeweify, Heri Sudrajat,
Muhammad Fahrul Fauzi, Dalih Fajar Nurjaya (2024)
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Asian Journal of Engineering, Social and Health (AJESH)
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