Page 115 - Pipeline Rules of Thumb Handbook

102 Pipeline Rules of Thumb Handbook

Complete tables giving capacities of different types of tubular L t = L o (1 + .0000069t)
goods are given in chapters dealing with these types.
where L o = Length at atmospheric temperature
L t = Length after change of temperature t
Steel constants* (applicable to tubular goods)
p
Modulus: Section Modulus ( D - D 1 )
4
4
One cubic inch = 0.2833lb 64
One cubic foot = 489.542lb Polar Modulus ( 4 1 )
p
4
Specific gravity = 7.851 32 D - D
Approximate coefficient of expansion for commercial casing, where D = Outside diameter
drill pipe, and tubing is D 1 = Inside diameter
p = 3.1416
-6
Coefficient = 6.9 ¥ 10 per °F, over range from 0 to 400°F
Relation between twisting effort, torsional strain and stress of
Formula for expansion of pipe due to change of temperature
cylindrical shaft or tube
is as follows:
q T Cq
= =
* Engineering data Spang-Chalfant Division of the National Supply Co. r J L
How to calculate the contraction or expansion of a pipeline

Steel pipe contracts or expands approximately 0.8 inch per = 0 8 10 1
.
¥
¥
100°F temperature change for each 100 feet of pipe. For con- = 8 inches
struction in the U.S., slack is not normally needed in welded
lines for contraction or expansion unless abnormal variations Large temperature changes may arise on exposed line or in
are encountered. However, slack is often provided near road lines downstream from compressor stations.
crossings where the pipe may have to be lowered at some When slack is desired in a line, the amount of sag or rise
future time. needed may be estimated quickly. To provide for 0.8 inch of
movement longitudinally along the pipe, a sag of 21 inches
would be needed in a 100-foot loop. For a 150-foot loop, 31
.
Contraction = 08 ¥ inches are necessary. Such slack put into the line at time of
(
length of pipe feet) temp change ∞ ( F) construction might allow for lowering the pipe under road-
.
¥
100 100 beds without putting excessive stress upon the pipe.
Location of overbends, sags, and side bends should be con-
sidered when laying slack loops. When loops are placed, parts
Example. Calculate the amount a 1,000-foot section of
of the line should be backfilled to serve as a tie-down. Loops
pipeline would contract if laid at a temperature of 100°F and
should be lowered during the coolest part of the day when
cooled to a low of 0°F during winter operation. (Assuming
the line is the shortest. After lowering in, sags should rest on
the line were free of soil or other resisting loads.)
the bottom of the ditch; overbends should “ride high.” Side
bends should rest on the bottom of the ditch and against the
1 000 100 outside wall. The line should be lowered so that all sections
,
.
Contraction = 08 ¥ ¥
100 100 of the pipe are in compression.
Estimate weight of pipe in metric tons per kilometer

To estimate the weight of pipe in metric tons per kilo- Actual answer from pipe tables is 79 metric tons per
meter, multiply the nominal diameter by the number of six- kilometer.
teenths of an inch in wall thickness. This rule of thumb is based on a density of 490 pounds per
cubic foot for steel. For larger diameter thin wall pipe, this
Example. Find the weight of pipe in metric tons per kilo- approximation gives an answer usually about one percent low.
1
meter for 20-inch diameter pipe, wall thickness / 4 -inch. The accompanying table gives a comparison between actual
weights in metric tons per kilometer, as compared to that
)
4 ¥ 20 = 80 tons (metric per kilometer calculated by this rule of thumb.