 Question #1: Differences in
types of iron
The water works representatives tell me that cast iron pipe is
no longer manufactured for water service, and I need to specify
ductile iron pipe. What is the difference?
Answer:
Cast iron is a commonly used term to describe many types of iron.
The word "cast" simply identifies the method used to
produce the finished product, and not to describe the material
itself. The casting method involves pouring the iron in a molten
or liquid form into a mold which defines the shape of the finished
product. Irons are also sometimes identified by color or physical
properties. The most common iron is gray iron (the color of the
iron once it has cooled). Cast iron soil pipe and fittings are
produced from this type of iron. Cast iron tubs, drains, many
iron body valves, fire hydrants, automotive engine blocks, brake
drums, manhole covers and wrecking balls are also made of this
type of iron. Ductile iron is a form of cast iron in which the
addition of magnesium to the gray iron mixture in its molten state
reforms the graphite flakes (which occur in gray iron) into nodular
shapes. While it is true that "gray" cast iron water
pipe is no longer manufactured, ductile iron is still a type of
cast iron. For more information on ductile iron water pipe follow
this link to DIPRA
(Ductile Iron Pipe Research Association). Also an informative
site is The
Urban Conservation Glossary, by Neil Grieve. For a pictorial
depiction of the making of cast iron soil pipe and fittings see
our foundry photos.
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Question #2: Coupling Standards
Occasionally a representative will suggest that I specify a particular
type of coupling in my specification by brand name. Is there a generic
standard that I can reference for the different types of couplings
that will identify the different types of couplings without naming
a specific manufacturer?
Answer:
There are three standards for couplings referenced in each of the
model plumbing codes; they are as follows:
- CISPI 310 - This standard covers stainless steel shielded couplings
with a rubber (ASTM C564) gasket sleeve. These couplings are the
most widely used, and have been produced since the early 1960's.
We estimate that 1 1/2 billion have now been installed. These
couplings are produced by numerous manufacturers and are sold
by all of the cast iron soil pipe and fittings manufacturers.
- ASTM C1277 - This standard covers stainless steel and cast iron
shielded couplings with a rubber (ASTM C564) gasket sleeve. This
standard, which was completed a couple of years ago, covers all
types of shielded couplings.
- ASTM C1173 - this standard covers transition couplings used
to join different types of piping materials in underground installations.
The couplings can be shielded or unshielded, and the gasket material
is not required to meet a specific standard. A standard is, however,
currently being developed for the gasket material through ASTM,
but it has not yet been completed. An ASTM subcommittee has also
begun work on a standard to cover shielded transition couplings
for use above and below ground, but this standard has not been
completed. Follow this link for information on other specifications
which affect our industry.
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Question #3: Longevity
We are working on a remodel of a 40 year old building and have been
asked to make a recommendation on the condition of the cast iron
soil pipe and fittings. What is the life expectancy of cast iron
soil pipe and fittings?
Answer:
The oldest installations of cast iron pipe are in underground lines,
both water and gas. Many are over 100 years old, and some date back
200 - 400 years and are still in use. Many older buildings with
cast iron installed inside are approaching the 100 year mark. We
would suggest a good physical examination of any exposed piping
and removal of a section to examine the interior for possible signs
of corrosion. If the wall thickness of the pipe still falls within
the specified dimensions, the pipe need not be replaced. It is important
to note that the wall thickness on the older piping may not and
need not be uniform. Centrifugal casting of pipe began roughly 35
years ago and results in a very uniform wall thickness. The pipe
produced before centrifugal casting was statically cast - a process
which produced pipe with some differences in wall thickness. This
variable wall thickness should not be a concern as long as the thinnest
wall thickness is equal to or greater than the specified minimum
thickness. Contact the CISPI representative
in your area to get advice on proper methods of measuring wall thickness
and the minimum wall thickness required by the specific standard.
For a thorough discussion of the corrosion resistance of cast iron
soil pipe follow this link.
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Question #4: Underground Installations
Can I use hubless cast iron soil pipe and fittings below ground,
and is there anything special I need to do to protect the couplings?
Answer:
Hubless cast iron soil pipe and fittings are allowed for
underground installations by all of the model codes. Since the 300
series of nickel chromium stainless steel is even more resistant
to corrosion than cast iron, the stainless steel hubless couplings
used to join hubless cast iron soil pipe require no more special
protection against corrosion than the pipe itself. Even though all
of the model codes allow hubless pipe and fittings below ground,
a few local jurisdictions have local amendments which require that
only hub and spigot be used underground. It is always best to check
local amendments. For a thorough discussion of the corrosion resistance
of cast iron soil pipe follow this link. For a more thorough discussion
of underground installation procedures see Chapter 4
of the Cast Iron Soil Pipe and Fittings Handbook.
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Question #5: Deflection
When one is using hub and spigot pipe with rubber compression gaskets
or hubless pipe with stainless steel and rubber couplings, is there
a maximum allowable joint deflection recommended?
Answer:
The Cast Iron Soil Pipe Institute and its members recommend a five
degree maximum deflection limit. This assures a good tight joint.
For more than five degrees of deflection, fittings should be used.
Question #6: Temperature ranges
What is the maximum temperature for cast iron soil pipe and fittings?
Answer:
The limiting factor in the operating temperature range for cast
iron soil pipe and fittings is the gasket material. ASTM C564 gasket
materials can be safely used up to 212°F. If a special situation
requires an operating temperature above this limit, special gaskets
can be used, but these are costly and not readily available. It
is always wise to check with the pipe and fittings manufacturers
before specifying a special gasket.
Question #7: Availability of Materials
I have reviewed the ASTM and CISPI standards and cannot find a special
fitting which I need. Does this mean that it is no longer available?
Answer:
The ASTM and CISPI standards include all of the most popular fittings;
however additional fittings not found in the standards may be available.
Don't give up until you have checked with the manufacturers. Email
The Institute if you need help, or contact
a specific foundry directly.
Question #8: Thrust Restraint
I sometimes see cartoons in advertisements for hubless couplings
and the couplings are shown leaking. Does this really happen, and
what would cause a coupling to leak?
Answer:
Properly installed hubless couplings do not leak or fail. Hubless
couplings used to join hubless pipe and fittings together utilize
a rubber gasket sleeve which is compressed by a stainless steel
shield and clamp assembly. On the few occasions in which leaks have
occurred, the leaks were caused by movement in the joint and resulting
partial separation. These movements are usually caused during tests
when installers attempt to test multiple floors without proper thrust
restraint. Thrust occurs when a column of water fills a vertical
stack. A ten foot column of water (recommended for testing purposes)
produces pressure of 4.3 PSI at the base of the column, but thrust
increases as the diameter of the column of water increases. A four
inch stack with ten feet of hydrostatic head produces 65 pounds
of thrust at the base of the stack: a ten inch stack with the same
ten feet of hydrostatic head produces 337 pounds of thrust even
though the pressure in both stacks is only 4.3 PSI. This thrust
pushes against the pipe and fittings at the base of the stack where
the vertical line turns horizontal. This force, if the piping is
not properly restrained, can cause the joint to move, which could
result in partial joint separation, and leaks (especially in large
diameter pipe and fittings). For information on blocking or thrust
restraint contact us for a copy of our installation instructions.
Question #9: Hanging and Support
Does cast iron pipe require special support or hanging?
Answer:
Cast iron pipe and fittings is simple to properly hang and support.
There are a few basic rules:
- A hanger should be located within eighteen inches of each
coupling or hub for lengths up to ten feet.
- For multiple joints within a four foot length, a hanger should
be located at alternate couplings or hubs.
- Support should be provided at each floor for vertical stacks.
- Information on hanging, seismic and sway bracing see General
Installation Instructions in Chapter 4 of the Cast Iron
Soil Pipe and Fittings Handbook.
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