Case
Study

 

The purpose of this case study is to provide an overall guideline of the design calculations involving a new offshore pipeline

Design Parameters & Data

An oil pipeline from Platform-A to Platform-B is proposed to be installed with the following design parameters:

Parameter

Value Units
Pipeline Material API 5L X60 -
Design Pressure 140 bar
Maximum Operating Pressure 100 bar
Minimum Arriving Pressure 80 bar
Design Temperature 60 oC
Maximum Operating Temperature 40 oC
Minimum Arriving Temperature 20 oC
Product Density 500 kg/m3
Flow Rate 30 kg/s
Design Life 25 years
Corrosion Coating Thickness 5 mm
Minimum Water Depth 30 m
Maximum Water Depth 40 m

The following are the design data used in the different calculations involved in the study. In general, these are historic data which depends on the particular field:

Parameter

Value Units
Storm Surge 1 m
Highest Astronomical Tide 2 m
Lowest Astronomical Tide 1 m
Wave Height - 1 year condition 2 m
Wave Period - 1 year condition 5 s
Wave Height - 100 years condition 5 m
Wave Period - 100 years condition 10 s
Surface Current Velocity 1 m/s
Ambient Water Temperature 15 oC
Hydrotest Water Temperature 35 oC
Soil Submerged Density 6 kN/m3
Soil Cohesion Factor 0 kN/m2
Soil Friction Angle 30 o
Soil Cohesion Factor 0 kN/m2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
Design Calculations & Results

The following table summaries the results of all the relevant design calculations. By clicking on each title, the detailed calculations can be examined:

Parameter

Value Units
Total Length 3660 m
Submerged Flooded Weight 85.877 kg/m
Pipeline Diameter 6 in
Erosion Velocity Limit 5.456 m/s
Wall Thickness    
   as per IP-6 12.7 mm
   as per ASME B31.4 12.7 mm
   as per BS 8010 12.7 mm
   as per DNV 1996 12.7 mm
   as per DNV OS-F101 12.7 mm
Corrosion Allowance 3 mm
Pipe Sinkage    
   Hydrotest Conditions 21.48 mm
   Operational Conditions 19.16 mm
Concrete Coating Thickness & Stability Parameters 30 mm
Insulation Thickness 0 mm
Thermal Decay Constant & Temperature Profile 0.728 -
Total Pipeline Expansion    
   Hydrotest Conditions 0.264 m
   Operational Conditions 0.579 m
Dynamic Spans Check as per DNV GL-14    
   Installation Conditions 15.90 m
   Hydrotest Conditions 15.79 m
   Operational Conditions 10.10 m
Dynamic Spans Limit as per DNV GL-14    
   Installation Conditions 15.00 m
   Hydrotest Conditions 7.00 m
   Operational Conditions 7.00 m
Dynamic Spans Limit as per DNV RP-F105 2002    
   Installation Conditions 19.00 m
   Hydrotest Conditions 12.00 m
   Operational Conditions 8.00 m
Dynamic Spans Limit as per DNV RP-F105 2006    
   Installation Conditions 19.00 m
   Hydrotest Conditions 14.00 m
   Operational Conditions 9.00 m
Static Spans    
   Installation Conditions 37.00 m
   Hydrotest Conditions 29.00 m
   Operational Conditions 22.00 m
Bar Buckling Spans as per DNV GL-14    
   Hydrotest Conditions 10.10 m
   Operational Conditions 7.20 m
Bar Buckling  Spans as per DNV RP-F105 2002    
   Hydrotest Conditions 10.84 m
   Operational Conditions 7.83 m
Spans Local Buckling as per DNV 1996    
   Installation Conditions Satisfied -
   Hydrotest Conditions Satisfied -
   Operational Conditions Satisfied -
Spans Local Buckling as per DNV OS-F101    
   Installation Conditions Satisfied -
   Hydrotest Conditions Satisfied -
   Operational Conditions Satisfied -
Static Spans    
   Installation Conditions 37.00 m
   Hydrotest Conditions 29.00 m
   Operational Conditions 22.00 m
Total Number of Anodes 20 -
Critical Velocity    
   Installation Conditions 1.930 m/s
   Hydrotest Conditions 1.997 m/s
   Operational Conditions 1.921 m/s
Added Mass Coefficient 2.0 -
Drag Coefficient    
   Installation/Hydrotest Conditions 0.86 -
   Operational Conditions 1.01 -
Concrete Stiffness Factor    
   Installation/Hydrotest Conditions 0.212 -
   Operational Conditions 0.250 -
Laying Radius 800 m