BEYOND
Fittings” and MSS SP-75 “
Specification for High-Test, Wrought, Butt-Weld-ing Fittings.” Common configurations
for these large fittings include tees,
elbows, reducers and caps.
Flanges are the piping components
that allow pipe joints and other devices
to be bolted together in pipelines.
Flanges come in sizes from NPS ½
through NPS 144 and larger. A flange
by itself is useless—it must be attached
to another component or piece of pipe.
Many industrial valves have flanged
ends, which must be able to accurately
mate up with flanges on other pieces of
equipment. Standards for industrial
flanges are primarily covered in two
ASME documents: B16.5 “Pipe
Flanges and Flanged Fittings, NPS ½
through NPS 24,” and B16.47, “Large
Diameter Steel Flanges, NPS 26
through NPS 60.” Flanges are made in
the same classes as valves: 150, 300,
600, 900, 1500 and 2500. These are
valve and flange type classes, NOT fitting classes (i.e., 3000 and 6000).
LARGE FLANGE
STANDARDIZATION
Because parallel standards have been
accepted over the years, the B16.47
document lists two independent sets of
dimensions for flanges in sizes NPS 26
through NPS 60. They are listed as
Series A and Series B flanges. Series A
flange dimensions are based on those
originally created in MSS SP- 44,
“Steel Pipeline Flanges.” The Series B
flange dimensions are based on those
originally created in API 605 “Large
Diameter Carbon Steel Flanges.” For
the valve user, the two styles may create
confusion, because they are not interchangeable and both are used on large-diameter valves. For the valve distributor, having two series of flanges often
means costly duplicate inventory of
large-diameter valves.
Just like valves and fittings, flanges
are available in several different vari-eties. The most common flanges today
are those that are buttweld on one end
and flanged on the other. These are
called welding neck flanges, nicknamed
“weldnecks.” These weldnecks are used
extensively in pipe fabrication to allow
other flanged components to be
attached to the pipeline. The weldnecks
rely on a high-integrity, “
full-penetra-tion weld” to attach them to the pipe.
Another type of weldable flange is the
slip-on. This flange is easier to weld to
the pipe, but it relies on a lower integrity fillet weld, instead of a full penetration weld to attach it to the pipe.
Other types include the threaded,
socketweld and blind flanges. The
threaded and socketweld flanges are for
attaching threaded or socketweld end
pipe to other flanged components, while
the blind flange is a dead-end piping
component bolted to another flange at
the end of a pipe run.
Unlike threaded or socketweld connections, flanges require gaskets for
them to seal. The most common type of
flange gasket is spiral-wound, which is
usually made of graphite and stainless
steel. Other gasket materials such as
sheet Teflon are used in low-temperature and low-pressure applications. A
type of flanged connection used for
higher pressures and temperatures is
the ring-type-joint (RTJ). RTJ flanges
excel in applications in which there are
harsher conditions, but a flange-type
connection is needed for easy disassembly. RTJ flanges use an oval metallic
gasket that is softer than the flange
material and that deforms slightly when
assembled.
Some applications call for special
connections—unique fittings that are
usually proprietary designs. The most
common of these are the grooved type,
which are used in water and wastewater
piping systems. Groove connections are
designed primarily for lower pressures
and temperatures.
Other unique high-pressure/high-temperature flange connections rely on
finely polished angled components similar to those on unions. These hub-type
flanges are often used in very severe
applications where piping disassembly
is still required.
Although flanges and fittings are
simple items, they are critical to the
proper design and operation of a piping
system, and they must be sized and
selected properly. Just as a pile of Tin-kertoy sticks by themselves are not very
handy without the round wooden hubs
that join them, pipes would be pretty
useless without the flanges and fittings
that connect them, turning them into
complete piping systems. VM
GREG JOHNSON is a contributing editor to Valve
Magazine and president of United Valve
( www.unitedvalve.com), Houston. Reach him at
greg1950@unitedvalve.com.
