Pipeline on bottom stability is an interaction of pipe, water and soil. The important factor that taken into account is the water flow whereby determining the magnitude and time variation of hydrodynamic drag and lift forces.
The second factor is soil. There have 3 friction will happened which are static, sliding and cohesive friction. So, it’s very important to understand the soil condition at the pipeline route area so that accuracy of analysis achieved.
These are some input provided for on bottom stability analysis :
1. Pipeline Data
Outside diameter
Wall thickness
Density of Pipe
Corrosion Coating Thickness
Corrosion Coating Density
Concrete Coating Thickness
Concrete Coating Density
Field Joint Material Density
Concrete Coating Cutback
Corrosion Coating Cutback
Pipe Joint Length
The second factor is soil. There have 3 friction will happened which are static, sliding and cohesive friction. So, it’s very important to understand the soil condition at the pipeline route area so that accuracy of analysis achieved.
These are some input provided for on bottom stability analysis :
1. Pipeline Data
Outside diameter
Wall thickness
Density of Pipe
Corrosion Coating Thickness
Corrosion Coating Density
Concrete Coating Thickness
Concrete Coating Density
Field Joint Material Density
Concrete Coating Cutback
Corrosion Coating Cutback
Pipe Joint Length
2. Wave and Current Data
Significant Wave Height (Hs)
Spectral Peak Period (Tp)
Wave Angle
Wave Spectrum Type
Water Depth
Current Velocity
Current References Height from Bottom
Peakedness Parameter
3. Physical Parameter
Density of Content
Density of Seawater
Marine Growth Thickness
Soil Type
Mean Grain Size – DNV RP E305
Roughness – DNV RP E305
Undrained Shear Strength (Su) – DNV RP E305
Lift Coefficient – –DNV RP E305
Drag Coefficient – DNV RP E305
Inertial Coefficient – DNV RP E305
Follow Part 9 for continuing of On Bottom Stability using AGA method
6 comments:
Can you elaborate on OBS through AGA? What is the difference between the two?
Thanks
Hye Rizwan,
thanks for your good question...
I'II give you some basic understanding of AGA and DnV RPE305. AGA/On Bottom Fatigue Analysis is actually less conservative compared to DnV. The input of analysis is similar but there is details on current velocity whereby it's applying Airy waves theory and Morison forces.
As per my experience before in Pegasus, client force us to run the AGA due to concern on reducing the concrete coating on pipe. But, luckily my analysis closed at Level 2 and not continuing to Level 3. If not, I need to run Level 3 where dynamic analysis is applied.
But, in standard practice DnV RP E305 has been choosed to avoid from problem happend in offshore during installation.
For my next part of On Bottom Stability lesson, I'll discuss further about AGA analysis.
Hi Asri,
What software do you use for Pipeline On-Bottom Stability Analysis?
Thanks
Loqman,
There's no specific software to do On Bottom Stability analysis.
Normally generate the calculation using Mathcad and excel spreadsheet.
Before that, please understand the calculation in DnV RP E305 first
TQ
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