Page 119 - Pipeline Rules of Thumb Handbook

106 Pipeline Rules of Thumb Handbook

where t = wall thickness, in. Substituting in formula and solving for P:
P = allowable working pressure, psi
(
.
.
D = outside diameter, in. 1 75 St - 0 057 )
P =
S = allowable stress, psi D+ 004 0 7 t
.
-
.
Y = a coefficient
u = under-thickness tolerance, in. The S-values are:
c = allowance for threading, mechanical strength, and
corrosion, in. Spec. API 5L Grade A—25,500psi
Spec. API 5L Grade B—29,750psi
Spec. API 5LX Grade X-42—35,700psi
In calculation of the tables, the values of Y, u, and
c were:
Example. Find pipe specification for a 12-inch line oper-
3
ating at 1,078psi: In the 12 / 4 -inch column these conditions
.
Y = 04 will be met using Grade X-42 pipe with 0.281-inch wall thick-
u = 0 125 t ( u = 121 2% of t) ness, Grade B pipe with 0.330-inch wall thickness, or Grade
.
c = 0 050-inches A pipe with 0.375-inch wall thickness.
.
Find the stress in pipe wall due to internal pressure
1
,
∏
Multiply / 2 by diameter by pressure and divide by wall 1 2 ¥ 24 ¥ 800 1 4 = 38 400psi
thickness to get stress in psi.
Example. Find the wall stress due to internal pressure in What wall thickness should be specified for a 30-inch dis-
1
a 24-inch pipeline having a / 4 -inch wall thickness if the pres- charge line where pressure runs 1,000psi and wall stress is to
sure gauge reads 800psi: be limited to 30,000psi?