OPS-3108 Rev E
A-4
300
3000
58
.
0
72
.
0
≤
<
−
=
t
D
F
for
F
Et
D
F
F
y
y
y
b
since
ksi
F
F
so
t
D
y
b
60
75
.
0
80
1500
64
.
7
913
.
0
970
.
6
=
=
<
=
=
The average compressive stress fa is equal to (2P-Fp)/A (in our case due to
the effect of the pulley)
The maximum bending stress, fb is equal to My/I = Pey/I
For structural steel
(
)
2
'
149000
r
Kl
F
e
=
and
85
.
0
=
m
C
(See Roark’s)
The radius of gyration (r) for the riser section is given by:
A
I
r
=
Where I = Moment of Inertia about the axis of bending =
(
)
4
4
64
ID
OD
−
π
And A = Cross section Area =
(
)
2
2
4
ID
OD
−
π
For the riser section the OD = 6.970 in (minimum) and the ID = 5.145 in
(maximum)
Therefore
I = 81.46 in
4
and A = 17.4 sqin so
r = 2.163 in
where Fy = Material Yield Strength, 80 ksi
K = Effective Length Factor =1.0 (most conservative)
l = Unbraced length of column, in
E = Young’s Modulus, 30 x 10
3
ksi
r = Radius of gyration (see above)
D = Outside Diameter, 6.970 in
t = Wall Thickness, 0.913 in
P = Line Pull applied to wire, kips
e = Eccentric distance after pulley, 20 in
y = Distance from centroid to stress level (outer surface), 3.485 in
Fp= Tensile load caused by well head pressure psi