| Pipes can be manufactured from steel, aluminum,
cupper,plastic and concrete.
Steel Pipe
Steel pipe is manufactured by several processes. Seamless
pipe,
made by piercing or extruding, has no longitudinal seam.
Other
manufacturing methods roll a strip or sheet of steel (skelp)
into a
cylinder and weld a longitudinal seam. A continuous-weld
(CW)
furnace butt-welding process forces and joins the edges
together at
high temperature. An electric current welds the seam in
electric
resistance welded (ERW) pipe. ASTM Standards A106 and A53
specify steel pipe. Both standards specify A and B grades.
The A
grade has a lower tensile strength and is not widely used.
The ASME pressure piping codes require that a longitudinal
joint efficiency factor E (Table 1) be applied to each type
of seam
when calculating the allowable stress. ASME Standard B36.10M
specifies the dimensional standard for steel pipe. Through
12 in.
diameter, nominal pipe sizes (NPS) are used, which do not
match
the internal or external diameters. For pipe 14 in. and
larger, the size
corresponds to the outside diameter.
Steel pipe is manufactured with wall thicknesses identified
by schedule or weight class. Although schedule numbers and
weight class designations are related, they are not constant
for all pipe sizes. Standard weight (STD) and Schedule 40
pipe have the same wall
Copper Tube
Because of their inherent resistance to corrosion and ease
of
installation, copper and copper alloys are often used in
heating, air
conditioning, refrigeration, and water supply installations.
There
are two principal classes of copper tube. ASTM Standard
B88
includes Types K, L, M, and DWV for water and drain service.
ASTM Standard B280 specifies air-conditioning and refrigeration
(ACR) tube for refrigeration service.
Types K, L, M, and DWV designate descending wall thicknesses
for copper tube. All types have the same outside diameter
for corresponding sizes. Table 3 lists properties of ASTM
B88 copper tube.
In the plumbing industry, tube of nominal size approximates
the
inside diameter. The heating and refrigeration trades specify
copper
tube by the outside diameter (OD). ACR tubing has a different
set of
wall thicknesses. Types K, L, and M tube may be hard drawn
or
annealed (soft) temper.
Copper tubing is joined with soldered or brazed, wrought
or cast
copper capillary socket-end fittings. Table 4 lists pressure-temperature
ratings of soldered and brazed joints. Small copper tube
is also
joined by flare or compression fittings.
Hard-drawn tubing has a higher allowable stress than annealed
tubing, but if hard tubing is joined by soldering or brazing,
the
annealed allowable stress should be used.
Brass pipe and copper pipe are also made in steel pipe
thicknesses for threading. High cost has eliminated these
materials from
the market, except for special applications.
The heating and air-conditioning industry generally uses
Types L and M tubing, which have higher internal working
pressure ratings than the solder joints used at fittings.
Type K may be used with brazed joints for higher pressure-temperature
requirements .
Ductile Iron and Cast Iron
Cast-iron soil pipe comes in XH or service weight. It is
not used
under pressure because the pipe is not suitable and the
joints are not
restrained. Cast-iron pipe and fittings typically have bell
and spigot
ends for lead and oakum joints or elastomer push-on joints.
Cast
iron pipe and fittings are also furnished with no-hub ends
for joining
with no-hub clamps. Local plumbing codes specify permitted
materials and joints.
Ductile iron has now replaced cast iron for pressure pipe.
Ductile
iron is stronger, less brittle, and similar to cast iron
in corrosion resistance. It is commonly used for buried
pressure water mains or in
other locations where internal or external corrosion is
a problem.
Joints are made with flanged fittings, mechanical joint
(MJ) fittings,
or elastomer gaskets for bell and spigot ends. Bell and
spigot and MJ
joints are not self-restrained. Restrained MJ systems are
available.
Ductile-iron pipe is made in seven thickness classes for
different service conditions. AWWA Standard C150/A2l.50,
Thickness Design
of Ductile-Iron Pipe, covers the proper selection of pipe
classes. |
