Piping Materials
Piping Materials
Piping Materials
Selection of Pipes
Several technical factors affect the final choice of pipe:
internal pressures,
coefficient of roughness,
hydraulic and
operating conditions,
maximum permissible diameter, internal and external corrosion problems, layingand
jointing, type of soil, special conditions, etc.
Selection of pipe materials must be based on the following considerations:
The initial carrying capacity of the pipe and its reduction with use,
defined, for example, by the Hazen – Williams coefficient. C. Values of Cvary for
different conduit materials and their relative deterioration inservice. They vary with
size and shape to some extent.
The strength of the pipe as measured by its ability to resist internalpressures and
external loads.
The life and durability of pipe
The case of difficulties in transportation, handling and laying andjointing under
different conditions of topography, geology and otherprevailing local conditions.
The safety, economy and availability or manufactured sizes of pipes andspecials
The availability of skilled personnel in construction and commissioningof pipelines.
The ease or difficulty of operations and maintenance.
The life and durability of the pipe depends on several factors includinginherent strength
of the pipe material, the manufacturing process along withquality control
handlingtransportation laying and jointing of the pipelinesurrounding soil conditions and
quality of water. Normally the design period ofpipelines is considered as 30 years.
Lined metallic pipelines are expected to last beyond the normal design lifeof 30 years.
However, the relative age of such pipes depends on the thickness and
quality of lining available for corrosion. The cost of the pipe material and its
durability or design life are the two major governing factors in the selection of the
pipe material. The pipeline may have very long life but may also be
relativelyexpensive in terms of capital and recurring costs and, therefore, it is essential
tocarryout a detailed economic analysis before selecting a pipe material.
The metallic pipes are being provided with internal lining either with cementmortar
or epoxy so as to reduce corrosion, increase smoothness and prolong the life.
Underground metallic pipelines may require protection against externalcorrosion
depending on the soil environment and corrosive ground water.
Protection against external corrosion is provided with cement mortar guiniting orhot
applied coal-tar asphaltic enamel reinforced with fiberglass fabric yarn.
The determination of the suitability in all respects of the pipeline for anywork is a
matter of decision by the Engineer concerned on the basis of therequirements for the
scheme. It is necessary that a quantitative and qualitativeassessment is made to arrive at
the most economical and reliable pipe materials.
Widely used because of its good casting qualities and continue to give satisfactory
service even after a century of use.
The pipes are Spigot and socket type. Several type of joints such as rubber gasket
joint known as Tyton joints, Mechanical joint and conventional joint known as
Lead joints are used.
Used for carrying potable water, sewer main etc.
2. Steel Pipe
Manufacture of steel pipes are mild steel plate grade Minimumtensile strength of
330 mpa, 410 mpa& 450 mpa confirming to IS 2062. (Steelplate of Minimum tensile
strength of 410 mpa is normally used)
Larger size of pipe are made by welding together the edges of suitably curved plates.
To be provided protection against corrosion. As against internal corrosion richcement
mortar or epoxy lining is be done internally by centrifugal process. The outer coating for
underground pipe line may bein cement - sand guiniting or not applied coal-tar
asphaltic enamel reinforced with fibre glass fabric yarn.
Small size of pipe having threaded ends could be joined with jointedmaterials like yarn.
A.C.pipesis made of a mixture ofAsbestos paste and cement compressed by steel roller
to form laminated materialof great strength and density.
5. Concrete Pipe
Reinforced cement concrete ( RCC ) pipes are classified as P1, P2 and P3 with test
pressure of 2.4 and 6 kg / cm respectively. For use as gravity main, the working pressure
should be 2/3 of the test pressure and for the pumping main,the working pressure should
not exceed half of the test pressure.
Jointed with RCC collars with jute yarn rope dipped in Cement mortar.
The PSC pipes are ideally suited for water supply mains where pressure inthe range of
6 kg / cm2 to 20 kg / cm2 are encountered.
PSC pipes consists of a concrete lined steel cylinder with steel joint ringswelded to its
ends wrapped with a helix of highly stressed wire and coated with dense cement mortar
or concrete.
PSC pipes are jointed with flexible rubber rings.
PSC pipe competes economically with steel for pipe diameter of 600mm and above.
The PSC pipes are classified as 4 KSC, 6 KSC, 8 KSC, 10 KSC, 12 KSC,16 KSC, 18
KSC, and 20 KSC pipe and that denotes the working pressureexcluding surge pressure
and the site test pressure will be 1.5 times of the above working pressure.
7. Bar Wrapped Steel Cylinder Pipes
Bar wrapped cylinder pipes (BWSC pipes) are being manufactured with the joints are
welded and covered with cement mortar coating. The joints are more reliable than
conventional rubber ring joints. The
O&M expenditure would be less. It is advantageous to use BWSC pipe in watersupply
and sewerage projects on grounds of good hydraulic properties, long lifebetter corrosion
resistant properties etc.
BWSC pipe has to be encouraged in water supply and sewerage projects inview of its
techno economic advantage and lesser O&M cost. The technicalcommittee instructed to
consider BWSC pipe as are of the alternative in watersupply and sewerage projects with
Techno economic consideration.
8. Plastic Pipes
Poly Vinyl Chloride ( PVC ) pipe conforming to IS 4898 – 1988. PVCpipes have
advantages of resistance to corrosion, light weight, toughness, rigidity, economical in
laying, jointing and maintenance, case offabrication.
Available in size of outer dia 20 to 315mm at working pressure of 2.5, 4,6, 10 kg / cm2.
Superior compared to conventional pipe especially AC.Jointing of PVC can be made
bysolvent cement, rubber ring joint, flanged joints, threaded joints.
For bedding pipe trench is filled with sand and compacted by tapping with wooden stick.
It is necessary to considered PVC pipesupto 315 mm OD as one of the alternative inwater
supply and sewerage projects with techno economic consideration.
9. Polyethylene Pipes
High density polyethylene pipe ( HDPE) has excellent free flowing properties.
Required for water distribution system ranging from 15-150mm dial and
occasionally upto 350mm
They can withstand movement of heavy trafficHDPE pipes can be jointing by welding.
Structural Requirements
Structurally closed conduits must resist a number of different forcesingly or
incombination.
Internal pressure equal to the full head of water to which the conduit can be
subjected ( ie. Hydrostatic Test pressure).
Unbalanced pressure at bends, constructions and closures
Water hammer
External load in the form of back fill, traffic and their own weight between
external supports (Piers or hangers).
Temperature induced expansion and contraction.Internal pressure including water
hammer creates transverse stress or hoop tension. Bend and closures as dead ends
of gates produce unbalanced pressuresand longitudinal stress. When conduits are
not permitted to change length,variations in temperaturelike wise create
longitudinal stress. External loads andfoundation reactions ( Manner of support )
including the weight of the full conduitand atmospheric pressure produce flexural
stress.
The yield test pressure to be imposed should be not less than the maximum
of the following:
1 ½ times the maximum sustained operating pressure.
1 ½ times the maximum pipeline static pressure.
Sum of the maximum sustained operating pressure and the maximum surge
pressure.
Sum of the maximum pipeline static pressure and the maximum surge pressure
subject to a maximum equal to the work test pressure for any pipefitting
incorporated.
The field test pressure should wherever possible be not less than 2/3 worktest
pressure appropriate to the class of pipe except in the case of spun ironpipes and
should be applied and maintained for atleast four hours.
Where the field test pressure is less than 2/3 the work test pressure, theperiod of
test should be increased to atleast 24 hours. The test pressure shall be gradually
revised at the rate of 1 kg / cm2/ minute.
In case of gravity pipe, maximum working pressure shall be 2/3 work test
pressure.