Â Â Â Â Â Â Â INTRODUCTION
1.1Â Â Â Â Â Â Â Â Â Â General
The AFANG field is located in block00 OML 419, approximately 45 km of the southeastern coast of Wakanda in approximately 40 meters water depth. The field, initially brought into production in 1997 is owned by the Joint Venture APC/PDP and is operated by APPDPLPC Nigeria Limited (APPDPLPCNL). The OML 419 block is shown in the following figure.
Figure 11: Project Scope
Figure 1â€‘2: AFANG Field Architecture
1.2Â Â Â Â Â Â Â Â Â Â Objective
The objective of this document is to confirm adequacy for use, the already selected pipeline concrete weight coating thickness for the 12inch APC2 to PDP1 Crude Export Line.
The line pipe has been coated with 2.7mm 3LPP coating, as well as 30mm concrete weight coating.
1.3Â Â Â Â Â Â Â Â Â Â Definitions and Abbreviations
Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â
Definition  
Company  APPDPLPC Nigeria Limited 
Contractor  Global Oceon Nig. LTD 
Supplier  The Party including its employees, agents, inspectors and other
authorized representatives Contracted by the Company/ Contractor to carry out the Procurement, Construction Installation and Commissioning activities on the Project 
Shall  Indicates mandatory requirement 
Should  Indicates preferred recommendation 
Table 11: Definitions
1.4Â Â AbbreviationsÂ Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Table 12: Abbreviations
Abbreviation  Definition 
API  American Petroleum Institute 
APS  Application Procedure Specification 
ASME  American Society of Mechanical Engineers 
CA  Corrosion Allowance 
CP  Cathodic Protection 
DNV  Det Norske Veritas 
DP  Dynamic Positioning 
3LPP  3Layer Polypropylene 
FJ  Field Joint 
FJC  FieldJoint Coating 
FOS  Factor of Safety 
HRC  Hardness Rockwell C Scale 
ID  Inner Diameter 
LAT  Lowest Astronomical Tide 
OD  Outside Diameter 
SG  Specific Gravity 
SMYS  Specified Minimum Yield Strength 
WT  Wall Thickness 
1.5.1Â Â Â Â Â Â Â Â Â Conflict of Information
Where conflict occurs between the requirements of this specification and referenced Codes and Standards, the CONTRACTOR shall notify the COMPANY in writing immediately for resolution. In the absence of such a statement, full compliance with the order of precedence below shall be assumed.
The order of precedence for the documents shall be as follows:
 Nigerian National Regulations Standards
 Project Specification
 International Codes and Standards
Where there are conflicts of interpretation, the principal will review to determine what should apply.
1.5.2 Project Documents
REF.  DOC No  DOCUMENT TITLE  REV. 
[R1]  LPNGHCD2023RPT018  Wall Thickness Calculation Report  1 
[R2]  LPNGHCD2023RPT017  Pipeline Design Basis  2 
Table 13: Reference and Document
1.5.3 Codes and Standards
REF.  DOCUMENT NUMBER  DOCUMENT TITLE  REV. 
[R3]  DNVGLRPF109  Onbottom stability design of submarine pipelines  – 
Table 14: Codes and Standards
2.0Â SUMMARY AND CONCLUSION
2.1Â Â Â Summary
The onbottom stability analysis has been assessed for the 12inch APC2 to PDP1 Crude Export Line and the conservative absolute static stability requirement was considered as per DNVGLRP F109. The Table 21 summarizes the results of the onbottom stability calculations.
Table 21: Absolute Stability Results for Significant Wave Height and Bottom Current Extremes
Flowline  Load Case  Condition  Concrete Weight Coating Thickness  Calculated Absolute Stability FOS  Allowable FOS  SG

Remark  
Horizontal  Vertical  
12inch APC2 to PDP1 Crude Export Line  Installation (empty)  1yr wave, 10yr Current 
30mm 
1.12  5.78 
1 
1.66  Satisfies the DNVGLRPF109 absolute static stability requirements.

10yr wave, 1yr Current  1.44  7.55  
Hydrotest  1yr wave, 10yr Current  1.43  7.19  1.96  
10yr wave, 1yr Current  1.84  9.36  
Operation (Corroded Case)  100yr wave ,10yr current  1.01  4.52  1.64  
10yr wave, 100yr current  1.06  4.72 
Note:
(1) The specific gravity is the ratio of empty weight in the air to buoyancy and must be greater than 1.15 to satisfy the onbottom stability requirements.
(2) The factor of safety (FOS) must exceed 1.0 to meet the DNVGLRPF109 absolute static stability requirements.
2.2Â Â Conclusion
It is confirmed that the already selected concrete weight coating thickness of 30mm is adequate and satisfies the DNVGLRPF109 absolute static onbottom stability requirement.
3.0Â Â DESIGN BASIS
3.1Â Â Pipeline Design Data
The table below detail parameters used in the calculation spreadsheet attached.
Table 3â€‘1: Pipeline Characteristics
Parameters  Units  Values 
Pipe Steel Outer Diameter (OD)  Inch (mm)  12.75 (329.3) 
Â Pipe Wall thickness  mm  12.7 
Â Â Design Pressure  Barg  144.0 
Design Temperature  (^{0}C)  80 
Pipe Grade  –  Â Â Â Â Â Â Â Â Â Â Â Â Â Â API 5L X65 
SMYS  MPa  Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â 448 
SMTS  Mpa  531 
Corrosion Allowance  mm  3 
Steel Poisson Ratio  –  0.3 
Single Joint Length  m  12.2 
AntiCorrosion Coating Thickness  mm  2.7 
Concrete Coating Thickness  mm  30 
Concrete Coating Poisson Ratio  –  0.2 
3.2Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Material Densities
The following material densities are used for the pipeline upheaval buckling analysis.
Table 3â€‘2: Material Properties
Material  Density (kg/m^{3})  Youngs Modulus (Mpa) 
Steel  7850  207000 
Anticorrosion Coating  1442  
Concrete Weight Coating  3044  
Seawater  1030 
Â
3.3Â Â Â Content Specific Gravity
The content specific gravity is 0.19.
3.4Â Â Â Soil Data
The following soil data taken from the Pipeline Design Basis [Ref.R2] are used in the analysis.
Table 33: Soil Data
Parameters  Units  Values 
Seabed Soil Type  –  Clay 
Bulk Unit Weight  kN/m^{3}  18 
Submerged Unit Weight  kN/m^{3}  – 
Â Undrained Shear Strength, Cu  kPa  4.90 
Â
3.5Â Â Â Environmental Data
3.5.1Â Â Water Depth
The following environmental data taken from the Pipeline Design Basis [Ref.R2] are used in the analysis.
Table 34: Water Depth
Â
Pipeline 
Water Depth (LAT)
(m) 

Minimum  Maximum  
12inch APC2 to PDP1 Crude Export Line  40.0  40.0 
Â
3.5.2Â Â Â Â Â Â Â Â Â Â Wave and Current Data
Wave and current data along the pipeline routes are extracted from the Pipeline Design Basis [Ref.R2] as shown below.
Table 35: Significant Wave Height and Associated Current
Table 36: Bottom Current Extremes
Table 37: Wave and Wave Associate with Steady Current Extremes
Â Â Â Â Â Â Â Â Â Â Â 3.6Â Â Â Marine Growth
The table below provides growth estimates
Table 38: Marine Growth ThicknessÂ
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4.0Â Â DESIGN METHODOLOGY
4.1Â Design Life
The onbottom stability analysis was based on the absolute static stability criteria set out inÂ Â Â Â Â Â Â Â Â Â DNVGLRPF109. Inhouse spreadsheet has been used for the onbottom stability analysis.The analysis was performed considering a minimum water depth of 40m which represents theÂ Â Â Â Â Â Â Â Â Â Â Â Â Â Â worstcase scenario. The effects of the wave induced velocity along the pipelines are insignificant atÂ Â Â this water depth. The stability requirements for the pipeline were determined for installation, hydrotest and operation conditions.
The submerged weight of the pipelines satisfies the Onbottom stability requirements ofÂ Â Â Â Â Â Â Â Â DNVGL RP F109. A pipeline can be considered to satisfy the absolute static stability requirement if:
 Lateral Stability check
 Vertical Stability check
Where;
Y_{sc }:Â Â Â Â Â Â Â Â Safety Factor
W_{s} :Â Â Â Â Â Â Â Submerged weight of the line (N/m)
ÂµÂ : Â Â Â Â Â Â Â Soil friction factor
F_{y }Â : Â Â Â Â Â Â Â Peak Horizontal force (N/m)Â eq. 3.40 in DNVGLRPF109
F_{Z} : Â Â Â Â Â Â Â Peak vertical force (N/m)Â eq. 3.41 in DNVGLRPF109
F_{r }Â : Â Â Â Â Â Â Â Passive Resistance Force (N/m)
4.2Â Â Â Assumption
The following assumptions have been made:
 Flat Seabed.
 Minimum water depth has been conservatively considered for the pipeline stability analysis.
 Environmental loading is assumed to act perpendicularly to the pipeline (i.e. Î¸c = 90Â°).
 Minimum content density has been considered for the operating conditions for the production line as the worstcase scenario.
 The most conservative coefficient of friction (Âµ=0.2) has been used in this analysis.
 Pipeline penetration and trenching was not considered.
 Marine growth was not considered for hydrotest and installation cases.
 Additional weight due to anodes or any other miscellaneous Pipeline appurtenances are considered as negligible.
4.3Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Load Cases
The following load cases had been assessed:
Table 41: Load Cases
Condition  Analysis Water Depth  Sig. Wave Height  Peak Period  Current  Content  Corrosion allowance  Marine Growth 
Installation  Minimum Water depth along the Route w.r.t LAT  1year  1year  10year  Empty  3 mm  0 mm 
10year  10year  1year  
Hydrotest  Minimum Water depth along the Route w.r.t LAT  1year  1year  10year  Water  Â Â Â Â 3 mm  0 mm 
10year  10year  1year  
Operation
(Corroded Case) 
Minimum Water depth along the Route w.r.t LAT  10year  10year  100year  Crude  Â Â Â Â 2.7 mm  59 mm 
100year  100year  10year 
5Â Â RESULT
The result of the concrete weight coating check for 12inch APC2 to PDP1 Crude Export Line is presented in the Table 51 below. See calculation spreadsheet in appendix 1.
Table 51: Results Summary
Flowline  Load Case  Condition  Concrete Weight Coating Thickness  Calculated Absolute Stability FOS  Allowable FOS  SG

Remark  
Horizontal  Vertical  
12inch APC2 to PDP1 Crude Export Line  Installation (empty)  1yr wave, 10yr Current 
30mm 
1.12  5.78 
1 
1.66  Satisfies the DNVGLRPF109 absolute static stability requirements.

10yr wave, 1yr Current  1.44  7.55  
Hydrotest  1yr wave, 10yr Current  1.43  7.19  1.96  
10yr wave, 1yr Current  1.84  9.36  
Operation (Corroded Case)  100yr wave ,10yr current  1.01  4.52  1.64 