Page 87 - Reliability and Maintainability of In service Pipelines

76 Reliability and Maintainability of In-Service Pipelines

t elapsed time
u is the velocity of the stream (m/s)
V b basic shear strength of length b at critical section
Φ the average flux of H 2 S to the wall
[ f strength reduction factor for flexure
strength reduction factor for shear
φ v
Δ reduction in wall thickness due to corrosion, (mm)
Δ max maximum permissible reduction in wall thickness (structural resistance or limit), (mm)
a multiplying constant
b exponential constant
B 0 empirical coefficient of elastic support
B d maximum width of trench (mm)
C L live load distribution coefficient
D f shape factor
D i inside diameter (mm)
D L deflection lag factor
D m mean diameter of pipe (mm)
D o outside and inside diameter (mm)
E modulus of elasticity of pipe (kPa)
0
E soil modulus (kPa)
tensile strength (MPa)
F y
H height of backfill (mm)
2
I moment of inertia per unit length (Kg:m =m)
K bedding factor
L effective length of pipe (mm)
M n flexural capacity (MPa)
2
P actual buckling pressure (N=m )
P a accepted probability of failure
P s wheel load (kPa)
P cr critical buckling pressure (kPa)
P W hydrostatic pressure (kPa)
R w water buoyancy factor
S f safety factor
t time of exposure (year)
t c time of failure (year)
r radius of pipe (mm)
T a allowable wall thrust (MPa)
T cr critical wall thrust (MPa)
W c Marston’s load per unit length of pipe (kPa)
W t initial wall thickness (mm)
Y vertical deflection of pipe (mm)
Y max maximum longitudinal deflection (mm)
distance from centroid of pipe to the furthest surface of pipe (mm)
y 0
Δ depth of corrosion (mm)
ΔX ring deflection (mm)
ϕ capacity factor
γ s unit weight of soil (kN=m )
3