Page 63 - Pipeline Rules of Thumb Handbook

50 Pipeline Rules of Thumb Handbook

The design of the pipe span can be speeded up with W = 36. At the intersection with the L scale, obtain a pipe
Figure 1. span of 68 feet.
Check the amount of deflection to make sure that it does
Example. Find the allowable span length for a 6-in. con- not exceed your piping practices or applicable design code.
tinuous steel pipe strung between supports. The esti-
mated loading (sum of pipe, fluid, dead, and wind loads) is
Source
36lb/ft. The allowable fiber stress for steel can be taken at
20,000lb/in. 2
Kuong, J. F., Petroleum Refiner 39, No. 10, 196 (1960).
From any suitable handbook, c for a 6-in. pipe is 6.625/2 =
4
3.3175in., I is 28.14in. Now calculate I/c = 28.14/3.3175 =
3
2
8.5in. Connect S = 20,000lb/in. on the S scale with 8.5 on Reference
the I/c scale to the intersection with the reference line. With
the reference line as a pivot, connect the pivot point with 1. Sweeney, R. J., Chem. Eng., 63, No. 3 199 (1956).

How engineers make pipe fit the ditch

By R. J. Brown

The five-men crews of engineers that keep track of the pipe neers set the stakes from one to two joints length behind the
and calculate side bends, overbends, sags, and combination corresponding numbered pipe.
bends can make money—or lose money—for any contractor
crossing rough terrain. If they function smoothly, the bending
crew and pipe gang have easy going and the lowering-in can Notes on Figure 1
be a breeze. But when they make mistakes, the welded-up
pipe may not fit the ditch and this spells trouble for the Note that joint 25 was measured 39.9 feet, and the gap
contractor. between stakes 24–25 and 25–26 was set at 29.9 feet to allow
a 10-foot lap for tie-in. This leaves a pup long enough to be
carried ahead and worked into the line. If the pups are dis-
Bending crew tributed over sections of bends, there is a possibility of saving
a cut in a full joint. In event the stakes catch up with the pipe,
As a rule there are two rod men, two chairmen, and one one joint is carried ahead of the stringing.
instrument man in the measurement crew. Their duties are
to measure each joint of pipe, number it, and stake its posi-
tion in the line. In addition they calculate degrees of bends, Calculating bends
etc. Here is the way they perform these duties:
The method used to determine the size of overbend and
sags is illustrated in Figure 2. Note that at 0 + 00 the instru-
Measuring and numbering joints ment is set up on the ditch bottom at a height of 5.0 feet. The
rod is set on the ditch bottom ahead of the radius of over-
(See Figure 1.) First, the crew measures all joints of bend. (Care should be taken to set neither transit nor rod on
pipe and numbers them from 0 to 100. (When 100 is reached, the arc of the change in slope.) The transit is moved behind
the numbering starts over.) Then, they stake the position of the radius of overbend at 1 + 00 and the height of the instru-
each joint of pipe in the line. They use stakes which are num- ment is measured to be 4.90 feet.
bered according to the pipe, with the number of the joint The rod is set just ahead of the change in radius of over-
behind on front of the stake and the joint ahead on back of bend and is read at 4.90 feet, establishing a slope of -1°. The
the stake. magnitude of bend can now be determined.

Stakes set back Add unlike angles

Because the setup gang will move the pipe back half a If the slope is positive and the tangent of the slope ahead
joint’s length and the pipe gang back another half, the engi- is decreasing, an overbend is established. If the slope is