Wall Thickness Design2 August 2006
Conclusion
American Petroleum Institute Recommended Practice 1111 (API RP 1111)
Det Norske Veritas 1981 (DNV 81)
Det Norske Veritas 2000 (DNV 2000)
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Introduction (cont’d)
Method of Comparison
The equations for the 4 aspects (e.g Internal Pressure Containment) are presented
The Wall Thickness for Internal Pressure Containment across the 4 design codes are determined
After all the 4 aspects are done a conclusion will be drawn as to which is the most and the least conservative of the 4 codes
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Specified Minimum Yield Strength
=
=
E = Longitudinal Joint Factor
T = Temperature Derating Factor
t = Nominal Wall Thickness
a)
b)
c)
The Power to Deliver™ #*
The specified minimum burst pressure (Pb) is determined by one of the following formulae:
(1)
(2)
Di = D – 2t = inside diameter of pipe
S = Specified minimum yield strength of pipe
t = Nominal wall thickness of pipe
U = Specified ultimate tensile strength of pipe
For low D/t pipe (D/t < 15), formula (2) is recommended
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Pa = Incidental Overpressure
Pd = Pipeline Design Pressure
Pt = Hydrostatic Test Pressure
Where
pli = Local Incidental Pressure
γm = Material Resistance Factor
Where
Pe = Elastic Collapse Pressure of Pipe
P0 = External Hydrostatic Pressure
v = Poisson’s Ratio (0.3 for steel)
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Where
a)
b)
c)
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Where,
Po = External Hydrostatic Pressure
Where Ppr = Propagation Pressure
a)
b)
Content density = 200 kg/m3 ; Wave Ht = 3.8 m
ASME B31.8
Conclusion
From the Comparison Table, it can be seen that, each aspect for each check, may result in different value for the Wall Thickness.
The highest value gotten for one particular check is taken (in bold).
From this it can be seen that the most conservative code is DNV 1981.
The least conservative is DNV 2000.
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