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.
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.
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.
| 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 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.
| 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 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.
| 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" | ||||||||||||||||||
© 2003 W. E. Johns
