In Part One, we explored the metrics that measure municipal water system health. In Part Two we saw how poor infrastructure decisions can impact health. Now we’ll look at a history of piping materials and see how different choices can provide solutions to failing infrastructure.
History of Pipe – The Ancients
The earliest known use of what we would today consider pipe, rather than an open trench, comes
from Mesopotamia where clay pipes dating back to approximately 4000BCE have been discovered. Archaeologists believe that these molded clay pipes, complete with “tees” and mitered joints were used for stormwater drainage.
The Minoans (3000-1000BCE) had elaborate networks of tera cotta pipes for both water and wastewater. These networks were assembled as bell and spigot system and were sealed with cement. Minoan wastewater systems were the first to utilize a network of subterranean sewer mains that would “flush” waste into large cesspits.
The ancient Egyptians were the first to utilize metallic piping systems. Egyptian water systems featured copper pipe and fittings which fed and drained both public and private bathhouses. Some claim these copper lines fed both hot and cold water.
Ancient Rome the longest, most elaborate water and wastewater systems of the ancient world,
featuring both open aqueducts and closed, underground sewers. The Romans were prolific manufacturers of lead pipe, producing an estimated peak of 80,000 tons per year. Interestingly, many Roman pipes were stamped or inscribed with information about the manufacturer, much as one would find on modern piping products.
History of Pipe – USA
The city of Boston was the first in this country to build water and wastewater systems. In the mid-
1600’s, the city began building a network of wood pipe, which most New England cities would mimic. Wood remained the material of choice until the early 1800’s and continued to be installed across the country until the end of the 19th century. Wood pipe is still in service in many American cities, particularly East of the Mississippi.
In 1819, in a desire to transmit more water at higher pressures than their wood pipe would allow, the city of Philadelphia began installing cast iron water mains. Cast iron pipe wasn’t new as it had been installed in Germany’s Dillenburg Castle in 1455. CI would remain the product of choice until WW2 when the war effort prevented its production for domestic water applications. Thousands of miles of cast iron pipe are still in service across the country.
By the time WWII had ended, ductile iron had been discovered. DI is essentially cast iron with magnesium added while the material is still molten. DI, as the name implies, is more ductile than CI making it more resilient to impact and somewhat flexible. Like cast, DI is assembled with a bell and spigot system which is vulnerable to leakage in the case of ground movement, which is inevitable EVERYWHERE over time due to seismic activity, freeze-thaw, soil compaction, erosion, or other processes. DI, like all other metallics, is also susceptible to corrosion and tuberculation (biofilm). Corrosion can occur due to acidic or basic soils, or electrolysis of the soils. In some locations (NJ and Long Island being prime examples) both processes aggressively attack DI pipes, limiting their lifespan to 50 years or less. Cathodic protection systems can reduce the impact of electrolysis. DI can be protected from acidic and basic soils by wrapping the pipe in polyethylene, and the interior of DI pipes are lined with cement mortar to prevent tuberculation. However, if the poly wrap is punctured (and if it isn’t during installation it will be during a repair or tap) it is useless or even detrimental should moisture permeate the barrier. The cement mortar lining is significantly more brittle than the pipe itself, so if the pipe survives being dropped or struck with an excavator, there is no guarantee that the liner will also survive.
The plastics, namely PVC (poly-vinyl chloride) and HDPE (high-density polyethylene) were developed around the same time as DI pipe. Like DI, PVC is a bell and spigot system (fusible PVC exists, but is not particularly popular due to the threat of rapid crack propagation, or RCP. If a single “stick” of PVC cracks, the crack will run the length of the stick. If fusible PVC cracks the crack will run the length of the pipe). While PVC is not susceptible to corrosion or tuberculation, it is a brittle material whose ductile-transition point is 200° F. DI, despite having ductile in the name, is also a brittle material at normal operating temperatures. This is why DI, CI, and PVC pipes are bursting in Texas due to cold temperatures: the pipe cannot expand as the water freezes. Beyond just the risk (inevitability) of bell and spigot joints separating with ground movement, they are also vulnerable to root invasion, which can reduce flow and eventually severely damage pipelines.
HDPE is the only pipe mentioned here that is considered leak-free due to it being a fusible product. Being a thermoplastic, polyethylene can be melted and reformed while maintaining its pre-melt characteristics. If the idea of a leak-free piping system seems too good to be true, consider that 99% of all new natural gas distribution lines in this country are medium density polyethylene. Leaking water is bad, leaking gas is deadly. The Water Research Foundation found that HDPE pipes survived the 2011 Tohoku earthquake, which registered 9.1 on the Richter Scale, with ZERO failures. This is both because the pipe is fused and because polyethylene is a truly ductile material at normal operating temperatures (down to -180° F). This also means that HDPE pipes in Texas did NOT burst last week as they are able to swell as the water inside them freezes. HDPE, being viscoelastic, does not suffer from cyclical fatigue, so pressure surges do not present any long-term issues. Studies repeatedly show that the only failure mechanisms for HDPE pipes are third party damage (excavator and boring equipment) or improper fusion procedure.
So why wrap your DI pipe in polyethylene when you can just install polyethylene pipe? I have no idea. Nor do water engineers in virtually any country other than the US and Canada, where nearly all new water and wastewater lines are HDPE. Why not here? Well as all three of the modern piping materials (HDPE, DI, and PVC) were developed around the same time, fusible HDPE was seen as a natural replacement for welded steel, so its manufacturers entered and eventually dominated the same industries as steel (gas, oil, mining, heavy industry). DI and PVC being bell and spigot systems seemed like a natural replacement for CI, so their manufacturers entered and soon dominated the water and wastewater markets. All three materials share the same NSF-61 rating, blessing them as safe for use transporting potable water. Presently, HDPE has a 10% market share of the municipal water market in this country. Its market share in Western European countries is closer to 95%.
HDPE also lends itself to trenchless installation, the topic of Part 4, and the best way to make modernizing our municipal water systems cost effective.