Notes on Pipe

Oddly, there is nothing about a ½" pipe that is ½", be it copper, iron, or PVC. The outside diameter of copper is 5/8", and the inner diameter is either 0.527", 0.545", or 0.569", depending on the series. So-called ½" iron pipe is 0.840" outside diameter and 0.622" inside. PVC is the same outside as cast iron, but it is 0.608", 0.528", or 0.480" inside.

If no dimension is ½", why call it ½" pipe?

Well, it seems that back in the beginning of time - copper pipe was introduced in the 1930's - copper pipe was indeed standardized at the nominal diameter inside with a 1/16" wall, making it 1/8" bigger on the outside. As the metallurgy improved, allowing manufacturers to use thinner metal (and thus increase profits), they increased the inner diameter rather than decrease the outer diameter simply to allow the pipe fit existing fittings.

As the manufacturers began to make bigger and bigger pipe, they found that 1/16" wall thickness was insufficient. Thus, the inner diameter of larger pipes is smaller than the nominal size, while smaller pipes are larger.

Wrought iron pipe has a similar history, though I don't know the details. When PVC was developed, it inherited it's outside diameter from iron pipe.

Copper Pipe

Dimensions

Wall thickness of copper pipe varies with the pipe schedule - the four common standards are named K, L, M, and DWV (Drain/Waste/Vent - non-pressurized), from thickest to thinnest. The printing on the pipe is color coded for identification; K is green, L is blue, M is red, and DWV is yellow.

Nominal
Pipe Size
O.D. I.D. Wall Thickness
K L M DWV K L M DWV
1/4" 3/8" 0.305 0.315 - - 0.035 0.030 - -
3/8" 1/2" 0.402 0.430 0.450 - 0.049 0.035 0.025 -
1/2" 5/8" 0.527 0.545 0.569 - 0.049 0.040 0.028 -
5/8" 3/4" 0.652 0.666 - - 0.049 0.042 - -
3/4" 7/8" 0.745 0.785 0.811 - 0.065 0.045 0.032 -
1" 1-1/8" 0.995 1.025 1.055 - 0.065 0.050 0.035 -
1-1/4" 1-3/8" 1.245 1.265 1.291 1.295 0.065 0.055 0.042 0.040
1-1/2" 1-5/8" 1.481 1.505 1.527 1.541 0.072 0.060 0.049 0.042
2" 2-1/8" 1.959 1.985 2.009 2.041 0.083 0.070 0.058 0.042
2-1/2" 2-5/8" 2.435 2.465 2.495 - 0.095 0.080 0.065 -
3" 3-1/8" 2.907 2.945 2.981 3.030 0.109 0.090 0.072 0.045

The pressure that a copper pipe can handle is dependant on the temperature and the size of the pipe - for more information, see Table 6, Publication 28E, of the CCBDA. The joints are usually rated for less pressure than the pipe.

During manufacture, copper pipe is drawn through a die - this work-hardens the metal, making it quite rigid. Flexible copper pipe (K and L only) is annealed afterwards to return it to the softer state.

Drawn copper pipe makes nice axles. A 1/2" copper pipe will fit nicely in a 5/8" bearing. Just remember that copper pipe isn't as strong as a proper steel rod, especially in bending, and that overtightening the set screws on a pulley can crush the pipe. K series pipe, having the thickest wall, will be strongest, but the difference is minor compared to using a larger pipe.

Copper pipe fittings can be used as bushings - a 1/2" pipe coupling is 5/8" ID, though you'll have to file off the nubs that keep the pipe from sliding all the way through. (There are special "non-nub" couplings available.) You can use a T with a cap, drilled for a grease fitting, on the branch to make a nice greasable bushing, or leave the cap off and use it like an oil cup.

Copper Pipe References:

PVC Pipe

PVC stands for polyvinyl chloride, a fairly soft plastic that can be worked with normal wood tools. Do not confuse it with ABS pipe, which is much thinner and brittle.

PVC pipe is available in three schedules; 40, 80, and 120. I believe it also comes in a thinner DWV schedule, but I have no data on that.

Dimensions

Nominal
Pipe Size
O.D. I.D. Wall thickness Weight
lbs/ft
Max
PSI
40 80 120 40 80 120 40 80 120 40 80 120
1/8" 0.405 0.261 0.203 0.068 0.095 0.045 0.058 810 1230
1/4" 0.540 0.354 0.288 0.088 0.119 0.081 0.100 780 1130
3/8" 0.675 0.483 0.407 0.091 0.126 0.109 0.138 620 920
1/2" 0.840 0.608 0.528 0.480 0.109 0.147 0.170 0.161 0.202 0.223 600 850 1010
3/4" 1.050 0.810 0.724 0.690 0.113 0.154 0.170 0.214 0.273 0.295 480 690 770
1" 1.315 1.033 0.935 0.891 0.133 0.179 0.200 0.315 0.402 0.440 450 630 720
1-1/4" 1.660 1.364 1.256 1.204 0.140 0.191 0.215 0.426 0.554 0.614 370 520 600
1-1/2" 1.900 1.592 1.476 1.423 0.145 0.200 0.225 0.509 0.673 0.744 330 470 540
2" 2.375 2.049 1.913 1.845 0.154 0.218 0.250 0.682 0.932 1.052 280 400 470
2-1/2" 2.875 2.445 2.289 2.239 0.203 0.276 0.300 1.076 1.419 1.529 300 420 470
3" 3.500 3.042 2.864 2.758 0.216 0.300 0.350 1.409 1.903 2.184 260 370 440
3-1/2" 4.000 3.520 3.326 0.226 0.318 1.697 2.322 240 350
4" 4.500 3.998 3.786 3.572 0.237 0.337 0.437 2.006 2.782 3.516 220 320 430
5" 5.563 5.017 4.767 0.258 0.375 2.726 3.867 190 290
6" 6.625 6.031 5.709 5.434 0.280 0.432 0.562 3.535 5.313 6.759 180 280 370
8" 8.625 7.943 7.565 0.322 0.500 5.305 8.058 160 250
10" 10.750 9.976 9.492 0.365 0.593 7.532 11.956 140 230
12" 12.750 11.890 11.294 0.406 0.687 9.949 16.437 130 230
14" 14.000 13.072 12.410 0.437 0.750 11.810 19.790 130 220
16" 16.000 14.940 14.214 0.500 0.843 15.416 25.430 130 220
18" 18.000 16.809 16.014 0.562 0.937 20.112 31.830 130 220
20" 20.000 18.743 17.814 0.593 1.031 23.624 40.091 120 220
24" 24.000 22.544 21.418 0.687 1.218 32.873 56.882 120 210

Wrought Iron Pipe

Wrought iron pipe is used for water supply in older houses. It comes either "black" or galvanized. Joints are made by threading pipe into cast iron fittings - unlike screw threads, pipe threads are tapered.

Dimensions

Nominal
Pipe Size
O.D. I.D. Wall
thickness
Thread
TPI
1/4" 0.540" 0.364" 0.088" 18
3/8" 0.675" 0.493" 0.091" 18
1/2" 0.840" 0.622" 0.109" 14
3/4" 1.050" 0.824" 0.113" 14
1" 1.315" 1.049" 0.133" 11.5
1-1/4" 1.660" 1.380" 0.140" 11.5
1-1/2" 1.900" 1.610" 0.145" 11.5
2" 2.375" 2.067" 0.154" 11.5
2-1/2" 2.875" 2.468" 0.204" 8

3/8" iron pipe is 5/8" O.D., making it a substitute (along with 1/2" copper pipe) for 5/8" rod. 1/2" copper couplings make fair bushings for iron pipe.

Cast Iron Pipe

Cast iron pipe is typically used for sewer lines and municipal water. It comes in eight classes, A through H, rated by pressure in increments of 100 feet of head. "Feet of Head" is a measure of pressure, equal to the pressure generated by a given height of standing water (think of a water tower). One foot of head is equal to 0.434 psi.

Dimensions

Nominal
Pipe Size
Class A
100 Foot Head
(43 psi)
Class B
200 Foot Head
(86 psi)
Class C
300 Foot Head
(130 psi)
Class D
400 Foot Head
(173 psi)
Class E
500 Foot Head
(217 psi)
Class F
600 Foot Head
(260 psi)
Class G
700 Foot Head
(304 psi)
Class H
800 Foot Head
(347 psi)
  O.D. Wall
Thickness
I.D. O.D. Wall
Thickness
I.D. O.D. Wall
Thickness
I.D. O.D. Wall
Thickness
I.D. O.D. Wall
Thickness
I.D. O.D. Wall
Thickness
I.D. O.D. Wall
Thickness
I.D. O.D. Wall
Thickness
I.D.
3" 3.80" 0.39" 3.02" 3.96" 0.42" 3.12" 3.96" 0.45" 3.06" 3.96" 0.48" 3.00"
4" 4.80" 0.42" 3.96" 5.00" 0.45" 4.10" 5.00" 0.48" 4.04" 5.00" 0.52" 3.96"
6" 6.90" 0.44" 6.02" 7.10" 0.48" 6.14" 7.10" 0.51" 6.08" 7.10" 0.55" 6.00" 7.22" 0.58" 6.06" 7.22" 0.61" 6.00" 7.38" 0.65" 6.08" 7.38" 0.69" 6.00"
8" 9.05" 0.46" 8.13" 9.05" 0.51" 8.03" 9.30" 0.56" 8.18" 9.30" 0.60" 8.10" 9.42" 0.66" 8.10" 9.42" 0.71" 8.00" 9.60" 0.75" 8.10" 9.60" 0.80" 8.00"
10" 11.10" 0.50" 10.10" 11.10" 0.57" 9.96" 11.40" 0.62" 10.16" 11.40" 0.68" 10.04" 11.60" 0.74" 10.12" 11.60" 0.80" 10.00" 11.84" 0.86" 10.12" 11.84" 0.92" 10.00"
12" 13.20" 0.54" 12.12" 13.20" 0.62" 11.96" 13.50" 0.68" 12.14" 13.50" 0.75" 12.00" 13.78" 0.82" 12.14" 13.78" 0.89" 12.00" 14.08" 0.97" 12.14" 14.08" 1.04" 12.00"
14" 15.30" 0.57" 14.16" 15.30" 0.66" 13.98" 15.65" 0.74" 14.17" 15.65" 0.82" 14.01" 15.98" 0.90" 14.18" 15.98" 0.99" 14.00" 16.32" 1.07" 14.18" 16.32" 1.16" 14.00"
16" 17.40" 0.60" 16.20" 17.40" 0.70" 16.00" 17.80" 0.80" 16.20" 17.80" 0.89" 16.02" 18.16" 0.98" 16.20" 18.16" 1.08" 16.00" 18.54" 1.18" 16.18" 18.54" 1.27" 16.00"
18" 19.50" 0.64" 18.22" 19.50" 0.75" 18.00" 19.92" 0.87" 18.18" 19.92" 0.96" 18.00" 20.34" 1.07" 18.20" 20.34" 1.17" 18.00" 20.78" 1.28" 18.22" 20.78" 1.39" 18.00"
20" 21.60" 0.67" 20.26" 21.60" 0.80" 20.00" 22.06" 0.92" 20.22" 22.06" 1.03" 20.00" 22.54" 1.15" 20.24" 22.54" 1.27" 20.00" 23.02" 1.39" 20.24" 23.02" 1.51" 20.00"
24" 25.80" 0.76" 24.28" 25.80" 0.89" 24.02" 26.32" 1.04" 24.22" 26.32" 1.16" 24.00" 26.90" 1.31" 24.28" 26.90" 1.45" 24.00" 27.76" 1.75" 24.26" 27.76" 1.88" 24.00"
30" 31.74" 0.88" 29.98" 32.00" 1.03" 29.94" 32.40" 1.20" 30.00" 32.74" 1.37" 30.00" 33.10" 1.55" 30.00" 33.46" 1.73" 30.00"
36" 37.96" 0.99" 35.98" 38.30" 1.15" 36.00" 39.60" 1.80" 36.00" 40.04" 2.02" 36.00" 38.70" 1.36" 39.98" 39.16" 1.58" 36.00"
42" 44.20" 1.10" 42.00" 44.50" 1.28" 41.94" 45.10" 1.54" 42.02" 45.58" 1.78" 42.02"
48" 50.50" 1.26" 47.98" 50.80" 1.42" 47.96" 51.40" 1.71" 47.98" 51.98" 1.96" 48.06"
54" 56.66" 1.35" 53.96" 57.10" 1.55" 54.00" 57.80" 1.90" 54.00" 58.40" 2.23" 53.94"
60" 62.80" 1.39" 60.02" 63.40" 1.67" 60.06" 64.20" 2.00" 60.20" 64.82" 2.38" 60.06"
72" 75.34" 1.62" 72.10" 76.00" 1.95" 72.10" 76.88" 2.39" 72.10"
84" 87.54" 1.72" 84.10" 88.54" 2.22" 84.10"

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© 2003 W. E. Johns