On-Bottom stability design

[vietsov]

dear expats,

i have following data, pls. help me present the sequence to determine output data. I have done it subject to Dnv RP-305, however, i don't understand how to calculate the Critical phase angle and Pipe submerged weight. it's urgent.

OPERATION CONDITION 100 yr wave 10 yr current
Segment 2 WD= 67.7 m No trench

INPUT DATA Unit
Pipe Data
Line Pipe Specification (API 5L) - X65
Steel Pipe Outer Diameter mm 711.2
Wall Thickness mm 20.60
Steel Pipe Density kg/m3 7850
Inner Lining Thickness mm 0.00
Inner Lining Density kg/m3 0
Ext. Corrosion Coating Thickness mm 3.20
Ext. Corrosion Coating Density kg/m3 940
Internal Corrosion Allowance mm 0.25
Pipe Content Density kg/m3 88.9
Sea Water Density kg/m3 1025
Concrete Coating Thickness mm 45.0
Concrete Coating Density kg/m3 3030

Environmental Data
Minimum Water Depth m 67.03
Significant Wave Height m 6.3
Spectral Peak Period s 10.9
Current Velocity m/s 0.51
Height of Measured Current m 1
Angle of Attack Wave o 90
Angle of Attack Current o 90
Peakness Parameter - 1
Reduction Factor - 1.00
Soil Data
Soil Type - Clay
Grain Size for Silt mm 0.0625
Undrained Shear Strength Clay kPa 4.50

OUTPUT DATA Unit
Environmental Data
Wave Velocity m/s
Ave. Current Velocity m/s
Acceleration m/s2
Critical Phase Angle o
Pipe Data
Pipe Submerged Wt. N/m
Total Outer Diameter mm
SG for Pipe (filled) -
SG for Pipe (empty) -
Safety Factor
Hydrodynamic Force
Lift Force N/m
Drag Force N/m
Inertia Force N/m
Other
Velocity Ratio -
KC Number -
Friction Coeff. -
Calibration Factor -
Breaking Wave -





CL reduction factor - 0.9
CD reduction factor - 0.7
CI reduction factor - 3.29


many thanks for your help,

[FATHI]

[link Point to another website Only the registered members can access]
i am not a specialist ,but how knows , this might help
In DnV RP 305 , section 3.2 , you have this = see above attached file

Hope that one collegue will add more light to this

Take care

[vietsov]

[link Point to another website Only the registered members can access]
i am not a specialist ,but how knows , this might help
In DnV RP 305 , section 3.2 , you have this = see above attached file

Hope that one collegue will add more light to this

Take care

dear Fathi,

after find out the required concrete coating thickness, i would like to check the stability in 2 conditions: hydro test and operational, however, i don't know how to chose the wave and current velocity. pls advise me in which case we use 1year period, 5yr period, 10yr period and 100yr period? thanks so much

[mohamed abdelaziz]

I am intrested in offshore pipeline design I made my calculations based on your data and the results are
Concrete Coating Thickness 45.0 mm will not fulfill pipeline inplace stability
Concrete Coating Thickness 170.0 mm will fulfill pipeline inplace stability
P.L. submerged weight without content 1013.29 kg/m
P.L. submerged weight with content 1110.13 kg/m
Calibration factor 1.2
REFERENCES :
DNV RULES FOR SUBMARINE PIPELINE SYSTEMS
DNV-RP E305 ON-BOTTOM STABILITY DESIGN OF SUBMARINE PIPELINES
DNV-OS - F101 - SUBMARINE PIPELINE SYSTEMS 2.21 0.8
DNV-RP-F109 ON-BOTTOM STABILITY DESIGN OF SUBMARINE PIPELINES

[karim.emara]

Ref : DNV-RP-F109 Section 2.2
"For a temporary phase with duration less than 12 months but in excess of three days* a 10-year return period
for the actual seasonal environmental condition applies. An approximation to this condition is to use the most
severe condition among the following two combinations:
1) The seasonal 10-year return condition for waves combined with the seasonal 1-year return condition for
seasonal current.
2) The seasonal 1-year return condition for waves combined with the seasonal 10-year return condition for
current."