Pipe materials
The
earliest known evidence of drain tile being used for plumbing was found in
Mesopotamia and is estimated to have been made around 3000 BC. The tiles were
made from clay mixed with short lengths of straw. Both brass and copper pipes
have been found in Egypt believed to have been made close to 2500 BC. The
Romans made extensive use of lead pipe by joining sheets of lead into piping to
carry their water supply and waste. During the Dark Ages following the fall of
the Roman Empire, plumbing development virtually ceased for centuries except
for isolated cases of plumbing installed in palaces and castles. In the 13th
century, blacksmiths formed sheets of iron and lap welded the seam to create
iron pipe. Though it is unclear as to when galvanized iron pipe was first used,
a French chemist named Melouin is credited with developing the process in 1742.
The earliest known use for cast iron pipe is for the water supply to a fountain
in Langensalza,Germany, built around 1560. In 1819 the first cast iron pipe
constructed in the US, was manufactured in Weymouth, New Jersey. Before that
time, cast iron pipe and fittings had to be imported from Europe. It was not
until the 1960's that the hubless cast iron pipe was brought to the U.S.
from Europe by way of
Canada. During the early 1900's, heavy-walled copper joined with threaded
fittings was in use, but limited to public buildings because of its' high cost.
However, during the 1930's light-gauge Copper tube and fittings were developed
which made copper economically feasible and increased it's popularity.
Polyvinyl Chloride(PVC) was produced experimentally in the 19th century but did
not become practical to manufacture until 1926, when Waldo Semon of BF Goodrich
Co. developed a method to plasticize PVC, making it easier to process. PVC pipe
began to be manufactured in the 1940's and was in wide use during the DWV
reconstruction of Germany and Japan following WWII. In the 1950's, plastics
manufacturers in Western Europe and Japan began producing acrylonitrile
butadiene styrene(ABS) pipe. The methods for producing cross-linked
polyethylene(PEX) was also developed in the 1950's. Plastic supply pipes have
become increasingly common, with a variety of materials and fittings employed,
however plastic water pipes do not keep water as clean as copper and brass
piping does. Copper pipe plumbing is bacteriostatic. This means that bacteria
can't grow in the copper pipes. Plumbing codes define which materials may be
used, and all materials must be proven by ASTM, UL, and/or NFPA testing.
Steel
Galvanized steel
potable water supply and distribution pipes are commonly found with nominal
diameters from 3/8" to 2". It is rarely used today for new
construction residential plumbing. Steel pipe has National Pipe Thread (NPT)
standard tapered male threads, which connect with female tapered threads on
elbows, tees, couplers, valves, and other fittings. Galvanized steel (often
known simply as "galv" or "iron" in the plumbing trade) is
relatively expensive, difficult to work with due to weight and requirement of a
pipe threader. It remains in common use for repair of existing "galv"
systems and to satisfy building code non-combustibility requirements typically
found in hotels, apartment buildings and other commercial applications. It is
also extremely durable. Black lacquered steel pipe is the most widely used pipe
material for fire sprinklers and natural gas.
Most
single family homes' systems typically won't require supply piping larger than
3/4". In addition to expense, another downside is it suffers from a
tendency to obstruction due to internal rusting and mineral deposits forming on
the inside of the pipe over time after the internal galvanizing zinc coating
has degraded. In potable water distribution service, galvanized steel pipe has
a service life of about 30 to 50 years, although it is not uncommon for it to
be less in geographic areas with corrosive water contaminants.
Lead leaching
Generally, copper tubes
are soldered directly into copper or brass fittings, although compression,
crimp, or flare fittings are also used. Formerly, concerns with copper supply
tubes included the lead used in the solder at joints (50% tin and 50% lead).
Some studies have shown significant "leaching" of the lead into the
potable water stream, particularly after long periods of low usage, followed by
peak demand periods. In hard water applications, shortly after installation,
the interior of the pipes will be coated with the deposited minerals that had
been dissolved in the water, and therefore the vast majority of exposed lead is
prevented from entering the potable water. Building codes now require lead-free
solder. Building Codes throughout the U.S. require the use of virtually
"lead-free" (<.2% lead) solder or filler metals in plumbing
fittings and appliances as well.
Corrosion
Copper water tubes are
susceptible to: cold water pitting caused by contamination of the pipe interior
typically with soldering flux; erosion corrosion caused by high speed or
turbulent flow; and stray current corrosion, caused by poor electrical wiring
technique, such as improper grounding and bonding.
Pin holes due to poor plumbing electrical
grounding and/or bonding
Pin-hole leaks can
occur anytime copper piping is improperly grounded and/or bonded; nonmetal
piping, such as Pex or PVC, does not suffer from this problem. The phenomenon
is known technically as stray current corrosion or electrolytic pitting.
Pin-holing due to poor grounding or poor bonding occurs typically in homes
where the original plumbing has been modified; homeowners may find a new
plastic water filtration device or plastic repair union has interrupted the
water pipe's electrical continuity to ground when they start seeing pinhole
water leaks after a recent install. Damage occurs rapidly, usually being seen
about six months after the ground interruption. Correctly installed plumbing
appliances will have a copper bonding jumper cable connecting the interrupted
pipe sections. Pinhole leaks from stray current corrosion can result in
thousands of dollars in plumbing bills, and sometimes necessitating the
replacement of the entire affected line. The cause is an electrical problem,
not a plumbing problem; once the plumbing damage is repaired, an electrician
should be consulted to evaluate the grounding and bonding of the entire
plumbing system.
The
difference between a ground and a bond is subtle. See Ground (electricity), find
the heading AC power wiring installations for a complete description.
Stray current corrosion
occurs because: 1) the piping system is connected accidentally or intentionally
to a DC voltage source; 2) the piping does not have metal-to-metal electrical
continuity; 3) if the voltage source is AC, one or more naturally occurring
minerals coating the pipe interior act as a rectifier, converting AC current to
DC . The DC voltage forces the water within the piping to act as an electrical
conductor (an electrolyte). Electric current leaves the copper pipe, moves
though the water across the nonconductive section (the plastic filter housing
in the example above), and reenters the pipe on the opposite side. Pitting
occurs at the electrically negative side (the cathode), which may be upstream
or downstream with respect to the water flow direction. Pitting occurs because
the electrical voltage ionizes the pipe's interior copper metal, which reacts
chemically with dissolved minerals in the water creating copper salts; these
copper salts are soluble in water and wash away. Pits eventually grow and
consolidate to form pin holes. Where there is one, there are almost certainly
more. A complete discussion of stray current corrosion can be found in chapter
11, section 11.4.3, of Handbook of Corrosion Engineering, by Pierre Roberge.
Detecting and
eliminating poor bonding is relatively straightforward. Detection is
accomplished by use of a simple voltmeter set to DC with the leads placed in
various places in the plumbing. Typically, a probe on a hot pipe and a probe on
a cold pipe will tell you if there is improper grounding. Anything beyond a few
millivolts is important, potentials of 200 mV are common. A missing bond will
show up best in the area of the gap, as potential disperses as the water runs.
Since the missing bond is usually seen near the water source, as filtration and
treatment equipment are added, pinhole leaks can occur anywhere downstream. It
is usually the cold water pipe, as this is the one that gets the treatment
devices.
Correcting the problem
is a simple matter of either purchasing a copper bonding jumper kit, composed
of copper cable at least #6 AWG in diameter and two bronze ground clamps for
affixing it the plumbing. See NFPA 70, the U.S. National Electrical Code
Handbook (NEC), section on bonding and ground for details on selecting the
correct bonding conductor wire size.
A similar bonding
jumper wire can also be seen crossing gas meters, but for a different reason.
Note,
if homeowners are experiencing shocks or sparks from plumbing fixtures or
pipes, it is more than a missing bond, it is likely a live electrical wire is
bridging to the plumbing and the plumbing system is not grounded. This is an
electrical shock hazard and potential fire danger; consult an electrician
immediately!
Plastics
Plastic pipe is in wide
use for domestic water supply and drainage, waste, and vent (DWV) pipe. For
example, polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC),
polypropylene (PP), polybutylene (PB), and polyethylene (PE) may be allowed by
code for certain uses. Some examples of plastics in water supply systems are:
· PVC/CPVC
- rigid plastic pipes similar to PVC drain pipes but with thicker walls to deal
with municipal water pressure, introduced around 1970. PVC should be used for
cold water only, or venting. CPVC can be used for hot and cold potable water
supply. Connections are made with primers and solvent cements as required by
code.
· PP
- The material is used primarily in housewares, food packaging, and clinical
equipment, but since the early 1970s has seen increasing use worldwide for both
domestic hot and cold water. PP pipes are heat fused, preventing the use of
glues, solvents, or mechanical fittings. PP pipe is often used in green
building projects.
· PBT
- flexible (usually gray or black) plastic pipe which is attached to barbed
fittings and secured in place with a copper crimp ring. The primary
manufacturer of PBT tubing and fittings was driven into bankruptcy by a
class-action lawsuit over failures of this system. However, PB and PBT tubing
has returned to the market and codes, typically first for 'exposed locations'
such as risers.
· PEX
- cross linked polyethylene system with mechanically joined fittings employing
barbs and crimped steel or copper fittings.
· Polytanks
- plastic polyethylene cisterns, underground water tanks, above ground water
tanks, are made of linear polyethylene suitable as a potable water storage tank,
provided in white, black or green, approved by NSF and made of FDA approved
materials.
· Aqua
- known as PEX-Al-PEX, for its PEX/aluminum sandwich - aluminum pipe sandwiched
between layers of PEX and connected with brass compression fittings. In 2005, a
large number of their fittings were recalled.
Fittings and valves
Potable water supply
systems require not only pipe, but also many fittings and valves which add
considerably to their functionality as well as cost. The Piping and plumbing
fittings and Valves articles discuss them further.
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