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APPENDIX
Comparison
of Various Schedules and Wall Thickness Values for Carbon Steel
Pipes
The
following tables offer a good visualization of the differences which
exist for various common size pipe at different schedules. The dimensions
of the blue thickness bars are technically to scale, although they
may display and print out differently depending upon your specific
computer system.
The
tables are meant to serve as a general guide in illustrating the
different relevant thicknesses between different pipe schedules,
and their importance to reliable system operation - not as an absolute
dimensional template.
Table
P-3 of wall thickness dimensions clearly illustrates the significant
difference which exists between standard and extra strong pipe.
A much greater difference exists at the larger diameter piping,
although the additional pipe wall is usually most needed at the
smaller and typically threaded pipe sizes.
For
10 in. and under, schedule 40 is equal to standard pipe, and schedule
80 is equal to extra heavy - although for larger sizes, the thickness
of schedule 80 defined pipe will increase significantly.
Table
P3
|
Size
|
Standard/Schedule 40
|
Heavy/Schedule 80
|
12
|
0.375
|
|
0.500
|
|
10
|
0.365
|
|
0.500
|
|
8
|
0.322
|
|
0.500
|
|
6
|
0.280
|
|
0.432
|
|
5
|
0.258
|
|
0.375
|
|
4
|
0.237
|
|
0.337
|
|
3
|
0.216
|
|
0.300
|
|
2-1/2
|
0.203
|
|
0.276
|
|
2
|
0.154
|
|
0.218
|
|
1-1/2
|
0.145
|
|
0.200
|
|
1-1/4
|
0.140
|
|
0.191
|
|
1
|
0.133
|
|
0.179
|
|
3/4
|
0.113
|
|
0.154
|
|
1/2
|
0.109
|
|
0.147
|
|
Today's
common use of schedule 20 and schedule 10 pipe for various services
is based upon the operating pressure rating it carries, and not
its thickness value. The use of schedule 40 pipe, considered as
"thin wall" to the use of schedule 80 decades ago, is now reduced
another 50% in thickness by choosing to install schedule 10.
The
below table well illustrates the limited amount of wall thickness
offered by such extremely thin wall pipe. In most applications,
this allows little or no room for corrosion to occur before reaching
minimum acceptable thickness limits, and failure.
Table
P4
|
Size
|
Schedule 20
|
Schedule 10
|
12
|
0.250
|
|
n/a
|
|
10
|
0.250
|
|
0.188
|
|
8
|
0.250
|
|
0.188
|
|
6
|
n/a
|
|
0.134
|
|
5
|
n/a
|
|
0.134
|
|
4
|
n/a
|
|
0.120
|
|
3
|
n/a
|
|
0.120
|
|
2-1/2
|
n/a
|
|
0.120
|
|
2
|
n/a
|
|
0.109
|
|
1-1/2
|
n/a
|
|
0.109
|
|
1-1/4
|
n/a
|
|
0.109
|
|
1
|
n/a
|
|
0.109
|
|
3/4
|
n/a
|
|
0.083
|
|
1/2
|
n/a
|
|
n/a
|
|
Very often, an
examination of pipe, whether by ultrasound of metallurgical means,
will provide a range of remaining wall thickness values. Where threaded
pipe is involved, that measured wall thickness value, minus its
thread cut, will show the true remaining thickness at the pipe ends,
valves, elbows, tees, and other fixtures. In many examples, remaining
thickness at the threads of 0.025 in. and below is not unusual.
The below table well illustrates the threat existing where pipe
has been deteriorated to its lowest limits.
Table
P5
|
Thickness
|
Relative Thickness
|
0.500
|
|
0.400
|
|
0.375
|
|
0.300
|
|
0.250
|
|
0.200
|
|
0.150
|
|
0.100
|
|
0.075
|
|
0.050
|
|
0.030
|
|
0.025
|
|
0.015
|
|
0.010
|
|
To
put it in perspective, an 8 in. fire sprinkler piping system constructed
in 1940 would have typically used schedule 80 pipe having a wall
thickness of 0.500 in. That same system constructed in 1980 would
have used schedule 40 having a thickness of 0.322 in. Today, schedules
20 and 10 are commonly found, having original thickness values of
only 0.250 in. and 0.188 in respectively.
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