with an oxyacetylene torch. This causes the molten
Bolted Flange Joints
metal to fill the few thousandths of an inch
annular space between the pipe and the fitting.
Bolted flange joints (fig. 6-39) are suitable for
all pressures now in use. The flanges are attached
to the piping by welding, brazing, screw threads
The union fittings are provided in piping
(for some low-pressure piping), or rolling and
systems to allow the piping to be taken down for
bending into recesses. Those shown in figure 6-39
are the most common types of flange joints
repairs and alterations. Unions are available in
many different materials and designs to withstand
used. Flange joints are manufactured for all
a wide range of pressures and temperatures.
standard fitting shapes, such as the tee, cross,
Figure 6-42 shows some commonly used types of
elbow, and return bend. The Van Stone and the
unions/threaded pipe connectors. The union is
welded-neck flange joints are used extensively
most commonly used for joining piping up to 2
where piping is subjected to high pressures and
inches in size.
heavy expansion strains. The design of the Van
Stone flange makes it easier to line up the
fastening holes in the two parts of the flange.
Flared fittings are commonly used in tubing
lines. These fittings provide safe, strong,
dependable connections without the necessity of
threading, welding, or soldering the tubing. Flared
The majority of joints found in subassemblies
fittings are made of steel, aluminum alloy, or
of piping systems are welded joints, especially
in high-pressure piping. The welding is done
according to standard specifications which define
the material and techniques. Three general classes
of welded joints are fillet-weld, butt-weld, and
socket-weld (fig. 6-40).
Silver-brazed joints (fig. 6-41) are commonly
used for joining nonferrous piping when the
pressure and temperature in the lines make their
use practicable-temperatures must not exceed
425 °F; for cold lines, pressure must not exceed
3000 psi. The alloy is melted by heating the joint
Figure 6-40.--Various types of welded joints.
Figure 6-39.--Four types of bolted flange piping joints.