Buying Guide

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WHAT MAKES A PLUMBING SYSTEM FAIL?
Failure in a copper plumbing system is rare, but may occur due to a variety
of reasons. The most common causes of failure are:
1. Excessive fluid velocity causes erosion-corrosion or impingement (to strike
or hit against) attack in the tube and/or fitting. For this reason, the copper
plumbing industry has establish design velocity limits for copper plumbing
systems to the following:
Hot Water > 140°F (60°C) 2 to 3 feet per second
(0.6 to 0.9 meters per second)
Hot Water 140°F (60°C) 4 to 5 feet per second
(1.2 to 1.5 meters per second)
Cold Water 5 to 8 feet per second
(1.5 to 2.4 meters per second)
2. Localized high velocities and/or turbulence. The presence of a dent, tube
ends which are not reamed or deburred before soldering, and sudden
changes in direction can all cause localized high velocity conditions.
3. Flux Corrosion is typified by pin hole leaks, generally in the bottom of
a horizontal line. Fluxes are mildly corrosive liquid or petroleum-based
pastes containing chlorides of zinc and ammonia. Unless the flux is
flushed from the system, it will lay in the bottom of the tube and remain
active. ASTM B 813, “Liquid and Paste Fluxes for Soldering Applications
of Copper and Copper-Alloy Tube,” limits the corrosivity of soldering
fluxes and ensures that these fluxes are flushable in cold water, which
facilitates easy removal of flux residue following installation.
4. Galvanic Corrosion may be defined as the destruction of a material by
electrochemical interaction between the environment and the material.
Generally, it is slow but persistent in character and requires the presence
of dissimilar metals. Galvanic corrosion requires the flow of an electric
current between certain areas of dissimilar metal surfaces. To complete
the electric circuit, there must be two electrodes, an anode and a cathode,
and they must be connected by an electrolyte media (water) through
which the current can pass. The amount of metal which dissolves at the
anode is proportional to the number of electrons flowing, which in turn
is dependent upon the potential and resistance of the two metals. The
use of dissimilar metals in a plumbing system may or may not create a
problem. For instance, copper and steel are perhaps the most common
dissimilar metals found together in a plumbing system. In closed systems,
such as a chilled or heating water piping, the use of dissimilar metals may
not create a serious problem; this is because there is virtually no oxygen
in the water and corrosion relations tend to be stifled. Where dissimilar
metals must be used, some codes require that they should be separated
by dielectric union or a similar type of fitting. The effectiveness depends
upon; distance between the metals on the electromotive-force series
(EMF) chart, ratio of cathode to anode area, degree of aeration, amount
of agitation, temperature, presence of dissolved salts, and other factors.
ABBREVIATED EMF SERIES
(Electromotive-Force Series; Common Piping Materials in Sea Water)
CATHODE (+) Passive
GOLD – Fixtures, Faucets, Plating
PLATINUM
SILVER – Brazing alloys, Silver-bearing solders
TITANIUM – Condenser tubes
MONEL (67% Ni - 33% Cu) – Specialty piping & equipment
CUPRO-NICKEL – Condensers, Marine, Nuclear
COPPER – Pressure, DWV, Gases, Air, Refrigeration, etc.
BRASS (85/15 - Red) – Cast fittings, Valves
BRASS (70/30 - Yellow) – Gas-cocks, Fittings, Connectors
LEAD – Solder, Pipe, Sheet, Coating, Lining
TIN – Solders, Coating, Lining
CAST IRON – Pressure, DWV
WROUGHT IRON – Pressure
MILD STEEL – Fire Protection
ALUMINUM – Refrigeration, Irrigation, some Solar
GALVANIZED STEEL – Pressure, DWV
ZINC – Coatings, Linings, some Fittings
MAGNESIUM – Water Heater Anodes, Cathodic protection for pipelines
ANODE (-) Active; Sacrificial Material
5. Dezincification is a type of corrosion in which brass dissolves as an alloy
and the copper constituent redeposits from solution onto the surface of
the brass as a metal, but in the porous form. The zinc constituent may
be carried away from the brass as a soluble salt, or may be deposited in
place as an insoluble compound. Dezincification is normally associated
with brass valves where the zinc content exceeds 15%. Generally, areas of
high stress, such as valve stems and gate valve bodies, are primary targets
of attack.
6. On rare occasion problems of corrosion by aggressive water, possibly
aggravated by poor design or workmanship, do exist. Aggressive, hard
well waters that cause pitting can be identified by chemical analysis and
treated to bring their composition within acceptable limits. Typically these
hard waters are found to have high total dissolved solids (t.d.s.) including
sulfates and chlorides, a pH in the range of 7.2 to 7.8, a high content of
carbon dioxide (CO2) gas (over 10 parts per million, ppm), and the presence
of dissolved oxygen (D.O.) gas. Soft acidic waters can cause the annoying
problem of green staining of fixtures or “green water”. Raising the pH of
such waters to a value of about 7.2 or more usually solves the problem, but
a qualified water treatment specialist should be consulted.
7. Aggressive soil conditions can be a cause for external corrosion of copper
piping systems. Non-uniform soil characteristics, such as different soil
aeration, resistivity, or moisture properties, between adjacent sections
of tube can create galvanic corrosion cells. Soils contaminated with high
concentrations of road salts or fertilizers containing ammonia, chlorides,
and nitrogen are known to combine with water to form acids. Any metal
pipe laid in ash or cinders is subject to attack by the acid generated when
sulfur compounds combine with water to form sulfuric acid.
U.S. customary units in this document are the standard; the metric units are provided for
reference only. The values stated in each system are not exact equivalents.