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WP-01 Rev. A
Settlement: Grooved Mechanical Piping Systems
By Larry Thau
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Deflection of pipelines within a structure is often a concern for
engineers designing and
specifying for pipe installation. If not adequately accommodated,
repeated stress on a piping
system can cause damage to equipment and threaten the structural
integrity of the building
itself. There are business implications of inadequate accommodation
for deflection that result in
unsatisfied owners, whose occupants may complain about
underperforming systems, noisy
pipes, damaged equipment or aesthetic impacts. These issues affect
the engineer and
contractor’s bottom-line, since they may need to perform numerous
call-backs in an attempt to
fix the problem.
With structures becoming taller, larger, and more complex in
design, addressing deflection and
settlement concerns creates an additional challenge for the
engineer. Because the business risk
is significant if a system design causes undue stresses on the
piping system, forcing rigidly
constructed piping/components to bend— it is essential for
engineers to understand the system requirements at the design stage
to alleviate or accommodate deflection and settlement.
Grooved mechanical piping systems can address forced pipeline
deflection or misalignment in a
piping system due to settlement and accommodate building sway due
to thermal transients and
wind loads in vertical risers. They also accommodate linear piping
movement from thermal
changes and building creep. Most often specified as a fast, easy,
safe and reliable alternative to
welding, grooved mechanical pipe joining has a long history of
effectively minimizing deflection
risks and accommodating for settlement in a variety of
structures.
Accommodating Deflect ion and L inear Movement w ith Grooved
Coupl ings
Grooved mechanical couplings are available with two distinct
performance features. One class
is designed as "rigid" and the other as "flexible". Rigid grooved
mechanical couplings are
designed to "fix" the joint in its installed position, permitting
neither linear, angular nor rotational
movement at the joints, although it is possible to achieve movement
by utilizing grooved
expansion joints. On the other hand, flexible grooved mechanical
couplings are designed to
allow controlled linear and angular movement at each joint, which
can accommodate pipeline
deflection, building creep and settlement.
Grooved mechanical couplings allow for movement in the pipe due to
the design of the
components. The dimensions of the coupling key are narrower than
the groove in the pipe,
allowing room for that coupling key to move in the pipe groove
while maintaining the pressurized seal of the gasket. Additionally,
the width of the coupling housing allows for pipe end
separation,
therefore leaving room for controlled linear and angular movement.
The mechanical coupling
remains a self-restrained joint and the unique pressure responsive
design provides sealing even
under deflection and pipe movement.
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Grooved mechanical couplings are a great alternative to welded
U-shaped expansion loops,
welded offsets, expansion joints and rubber bellows. These
couplings are easier and faster to
install and accommodate deflection and linear movement within the
design capability of the
coupling, all the while doing this within the product’s "free range
of motion". This means that
imparted deflections can be accommodated in smaller spaces, with
low stress on the
components.
Figure 1: Because the dimensions of the coupling key are narrower
than the groove in the pipe, and because the
width of the coupling allows for pipe end separation, there is room
for controlled movement while maintaining the
pressurized seal of the gasket.
Accommodating fo r Set tlement
Unanticipated pipeline deflection can damage a building’s equipment
or even compromise the
structural integrity of the building itself. The piping system
designs must work in concert with
the building design. Deflection imposed on a piping system may
occur due to uneven settlement, particularly when considering new
additions to existing structures. A newer
structure may settle at a greater rate and flexibility must be
designed into piping systems
crossing the structures.
Piping misalignment due to uneven building settlement is addressed
by using an even number
of flexible couplings and permitting the intermediate pipe to
"toggle" as the movement occurs.
To determine the number of couplings required, define the amount of
lateral misalignment on a
particular pipe run and the length of that pipe run. The objective
in designing for misalignment is
to achieve the required displacement using the minimum number of
couplings. Due to symmetry
around a transition point, the point of inflection is a pipe spool
and not a coupling. The numberof couplings and the length of the
pipe spools are two variables that can be altered to obtain
the
desired misalignment. Other factors, such as the maximum angle of
deflection at each coupling
and the maximum pipe end separation, are a function of the size and
style coupling being used.
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Figure 2: The drawing above shows how flexible couplings deflect
from the straight line to allow for building
settlement.
Accommodating for Deflection and Linear Movement Due To
Thermal Transients
Thermal transients may impose deflection on a piping system as the
pipe grows when heated
and contracts when cooled. All materials, including pipe,
machinery, structures and buildings, experience dimension changes
as a result of changes in temperatures. This will often occur
at
directional changes, or cause "bowing" at the mid points of long
straight pipe runs, resulting in
stress on the piping system and equipment.
Three common methods of accommodating thermal expansion and
contraction are:
• Provide an expansion joint
• Allow the system to “freefloat” and the pipe to move in a
desired direction through the
use of anchoring and/or guidance, if necessary taking into account
the capability of
branch connection or changes in direction which may result in
harmful bending
moments
• Utilize the linear movement and deflection capabilities of
flexible grooved couplings.
Flexible grooved couplings provide deflection capabilities to
accommodate pipe movement in
long straight runs or for use in expansion loops, and allow angular
flexibility and rotational
movement to take place at joints. To provide for these thermal
changes sufficient flexible joints
must be available to accommodate for the anticipated movement. In
order to determine the
appropriate number of couplings to use, compute the change in the
linear length of the piping
system by taking into account the length and size of the piping
system and maximum and
minimum operating temperatures.
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Figure 3: The grooved coupling allows for controlled angular
movement that may result from deflection.
The flexible mechanical joint can also be used in expansion loops
without inducing stresses in
the pipes, elbows or joints. The deflection capability of flexible
couplings allows for thermal
growth/contraction to be absorbed within the couplings at the
elbows as the thermal forces
induce deflection. A total of eight flexible grooved mechanical
couplings and four grooved end
90 degree elbows and three pipe spools are required to complete
each expansion loop. (Figure
A) As system temperatures lower and the pipe run contracts,
the loop expands and the
deflection capability of couplings accommodates this movement.
(Figure B) As system
temperatures increase the opposite effect occurs as the pipe run
expands and the loop
contracts with the couplings accommodating the deflection in the
opposite direction. (Figure C)
A significant benefit to using this configuration is that a
loop constructed in this manner will be1/2 to 1/3 the size of a
welded loop with the same capacity, and will accommodate the
movement without inducing stress into the pipe.
Figures A, B, C: The figures show how a grooved expansion loop can
contract and expand to accommodate the
growth and shrinking of a system from thermal transients.
Accommodating for Building Creep or Subsidence
Similar to thermal transients, deflection or linear movement
imposed on a piping system may
occur due to building creep. Building creep is the common term for
the amount of actual building
shrinkage that will occur over time. This is an important
consideration for high rise construction.
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Accommodating building creep can be addressed three different
ways using mechanical piping
systems: flexible system, rigid system or a combination of
both.
In a flexible grooved system utilizing only flexible grooved
mechanical pipe joints, risers are
installed with anchors at the top and bottom with the piping guided
every other pipe length to
prevent “snaking” of the line. A sufficient number of flexible
couplings must be utilized to
accommodate the anticipated movement. Pipe gapping of the pipe ends
within the coupling is
required in order to allow the riser to compress with the
building.
In a rigid system utilizing only rigid grooved mechanical pipe
joints, risers can be treated similar
to a welded system, and where movement is required expansion joints
or offsets are designed
into the riser to accommodate movement and prevent damage to
components.
By designing risers with a combination of both rigid and flexible
grooved joints, engineers can utilize rigid couplings to reduce
guiding requirements and the flexible grooved joints to
accommodate the movement required.
Accommodating Building Sway in Tall Bu ildings
Vertical riser piping in tall buildings is often subject to
deflection due to heavy wind loads which
cause the building to sway. Where the pipe is rigidly fixed to the
building structure, freedom of
motion must be designed into the piping to permit it to move in
unison with the building. Flexible
couplings have been successfully used on vertical risers to provide
the necessary freedom of
motion so that the pipe sways harmlessly with the building.
Examples of Accommodating Deflection, Bu ilding Creep and
Settlement
Grooved mechanical couplings are a great alternative to welded
expansion loops, welded
offsets, expansion joints and rubber bellows because they provide
rigid or flexible joints which
gives the system designer a variety of options for managing piping
movement and providing an
optimal system design.
On a recent high-rise project in Chicago, the engineer was able to
accommodate the piping
movement caused by building creep and thermal transients through
the deflection characteristic
of flexible couplings.
Taking into account the maximum Delta T (change in temperature)
that the piping would experience and the building creep, the
engineer calculated the amount of movement that would
occur within a given run of piping. Based on these calculations and
the building layout, he made
a decision to strategically locate anchors on the piping system
using rigid couplings on the
straight runs and applying flexible couplings at the systems
changes of direction. In one area,
the engineer anchored the run of pipe at the midway point between
the basement and the mid-
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level mechanical room. This anchor directed movement to the offsets
at both ends of the pipe
run, and minimized the movement that would have occurred if the
system was anchored at the
top or bottom of the run. Flexible couplings were applied at these
offsets to allow for deflection
which accommodated these movements, minimized the stresses in the
system all while performing under tight space constraints typically
found in high rise construction.
On a similar high-rise project in Dubai, the engineer was able to
accommodate the piping
movement caused by building creep and thermal transients through
the linear movement
characteristic of flexible couplings.
Also taking into account the maximum Delta T that the piping
would experience and the building
creep, the engineer calculated the amount of movement that would
occur within the main
vertical riser, and based on these calculations, he made a decision
to strategically place a
series of pre-gapped flexible couplings on the main vertical riser
at each floor to accommodate
total piping movement on a per-floor basis.
Several of the world’s tallest buildings have used the grooved
system to meet their deflection
needs. The Petronas Towers in Kuala Lumpur, Malaysia are the second
tallest buildings in the
world. To accommodate for structural movements and sway they
installed flexible couplings on
the riser pipes in order to provide angular deflection. In a
recently completed Chicago high-rise,
the engineer specified flexible couplings on the branch piping
coming off the main risers
because of their ability to provide a solution which allowed the
pipe to grow, shrink and sway.
Several Victaulic flexible couplings placed in a series were used
to accommodate the deflection
of the branch movement as the riser moves up and down.
The Bottom Line
Structural designs that include grooved mechanical pipe joints,
such as rigid and flexible
couplings, will alleviate the challenges faced in accommodating for
settlement and deflection. In
addition to the benefits in reduced footprint and added design
flexibility, grooved mechanical
joints assist in the creation of a trouble-free, durable and
easy-to-maintain structure for clients.
Contractors benefit from alleviated scheduling pressures and labor
challenges due to the ease
of installation with grooved mechanical joints. Grooved mechanical
joints also decrease or
completely eliminate the need for welding, which can significantly
impact the safety on a job and
through the life of a structure.
Engineers, owners and contractors can save time and increase a
structure’s lifespan by
planning for deflection and accommodating settlement in the design
phase. Grooved
mechanical pipe joints, whether rigid or flexible, offer a fast,
space-saving alternative to welded
joints.
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WP-02 Rev. A
Using Grooved Mechanical Joining Systems to Accommodate Thermal
Piping Movement
By Larry Thau June 2009
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The key to effectively accommodating thermal expansion and
contraction in a building is to allow the predictable, controlled
movement of the piping itself. This can be done in a variety of
ways, and the selection of a specific method is based upon the
engineer, the type of piping system and the project
parameters.
Thermal transients may impose stress on a piping system as the pipe
grows when heated and contracts when cooled. All materials,
including pipe, experience dimension changes as a result of changes
in temperatures and their coefficient of expansion. This often
occurs at directional changes or causes "bowing" at the mid points
of long straight pipe runs, resulting in stress on the piping
system and equipment.
When a system is subjected to temperature, it may experience
horizontal movement, vertical movement and angular deflection
simultaneously. Additional strains on the piping system vary based
on whether the piping is vertical or horizontal. For horizontal
piping, the major obstacle is typically the space constraints
around the length and turns of the pipe. For vertical piping,
considerations are different and should involve dynamic, static and
elevation head calculations
of the pressures and loads that are exerted on the bottom portion
of the pipe.
Carbon steel pipe will experience thermal expansion or contraction
at a rate of 0.75 inches for every 100° F change in temperature per
every 100 feet of pipe. Piping subject to temperature changes is
placed in a condition of stress, with potentially damaging reactive
forces on components or equipment. The forces generated during this
thermal dimension change are often significant and the movement
must be accommodated and controlled, to prevent transmission of
these stresses throughout the piping system.
Inadequate accommodation of this movement can result in business
risks caused by excess stress on the piping system, including
increased incidence of ruptures and leaks, increased stress on
boilers, chillers, valves and other equipment and components, and
increased
downtime and labor expenses. This can negatively impact the owners
of the building byresulting in increased maintenance costs and
potential business shutdowns.
When accommodating thermal expansion and contraction, the grooved
pipe joining system conforms to industry practices while providing
design flexibility, reducing stress on the piping system and
providing a more compact, inspectable and productive method of
installation over other pipe-joining methods such as welding or
flanging. Additionally, the grooved method has all sealing elements
combined within a metallic housing.
There are four common methods for accommodating thermal pipe
movement with a grooved system: 1) providing an expansion joint
utilizing grooved mechanical pipe components 2) allowing the system
to “free-float”
3) utilizing the linear movement/deflection capabilities of
flexible grooved couplings 4) providing an expansion loop utilizing
grooved mechanical components
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The selection of one of these methods is dependent on the system
type, the scope of the project and the engineer's preference. Since
it is impossible to predict all system designs, this article will
call attention to the design benefits and mechanical advantages of
the grooved piping method when used to accommodate thermal
expansion and contraction.
The grooved mechanical pipe joint Grooved mechanical couplings
allow for movement in the pipe due to the design of the components.
The dimensions of the coupling key are narrower than the groove in
the pipe allowing room for that coupling key to move in the pipe
groove. Additionally, the width of the coupling housing allows for
pipe end separation leaving room for controlled linear and angular
movement. The mechanical coupling remains a self-restrained joint,
and the unique pressure responsive design provides sealing even
under deflection and pipe movement.
Grooved mechanical couplings are a great alternative to welded
U-shaped expansion loops, welded offsets, expansion joints and
rubber bellows. These couplings are easier and faster to install,
accommodate movement within the design capability of the coupling,
all the while doing this within the products "free range of
motion.” This means that piping system movement caused by thermal
expansion and contraction can be accommodated in smaller spaces,
with low stress on the components.
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Accommodating thermal movement ut il izing expansion jo in
ts
Grooved mechanical couplings are available with two distinct
performance features. One class is designed as "rigid" and the
other as "flexible.” Rigid grooved mechanical couplings are
designed to "fix" the joint in its installed position, permitting
neither linear, angular nor rotational movement at the joints.
Flexible grooved mechanical couplings on the other hand are
designed to allow controlled linear and angular movement at each
joint that can accommodate pipeline deflection.
Expansion joints are devices that can be compressed or expanded
axially and are generally the most costly alternative for
accommodating thermal movement. A welded expansion joint is
typically an expensive specialty joint, flanged into the system and
requiring regular maintenance. More cost-effective expansion joints
utilize grooved mechanical couplings and specially grooved, short
pipe nipples with flexible couplings placed in long straight runs
of pipe and pre-set to allow the desired amount of contraction
and/or expansion. Axial movement can be adjusted by simply adding
or removing couplings. When a series of flexible couplings are
installed, the resulting grooved expansion joint will further
protect equipment by reducing vibrations and stresses in the
system.
Whether using specialty expansion joints or a grooved expansion
joint, the adjacent piping mustbe properly guided to ensure the
movement is directed into the device and no lateral movement is
experienced.
For proper operation of the expansion joint, the piping system
should be divided into separate expansion and contraction sections
with suitable supports, guides and anchors to direct axial pipe
movement.
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Anchors should be classified as main or intermediate for the
purpose of force analysis. Main anchors are installed at terminal
points, major branch connections, or changes of piping direction.
The forces acting on a main anchor are due to pressure thrust,
velocity flow and
friction of alignment guides and weight support devices.
Intermediate anchors are installed in long runs to divide them into
smaller expanding sections to facilitate using less complex
expansion joints. The force acting on the intermediate anchor is
due to friction at guides, weight of supports or hangers, and the
activation force required to compress or expand an expansion
joint.
Pipe alignment guides are essential to ensure axial movement of the
expansion joint. If the situation allows, the expansion joint
should be adjacent to an anchor within four pipe diameters. The
first and second alignment guides on the opposite side of the
expansion joint should be located a maximum distance of four and 14
pipe diameters, respectively. Additional intermediate guides may be
required throughout the system for pipe alignment. If the expansion
joint cannot
be located adjacent to an anchor, install guides on both sides of
the unit.
Grooved expansion joints may be used as flexible connectors;
however, they will not
simultaneously provide full expansion and full deflection.
Expansion joints installed horizontallyrequire independent support
to prevent deflection, which will reduce the available
expansion.
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Accommodating thermal movement ut il izing a Free-Floating
System Free-floating piping systems allow thermal expansion and
contraction without the use of expansion joints. As long as this
movement does not cause bending moment stresses at branch
connections, it is not harmful to joints and changes in direction
or to parts of structures and
other equipment. A free-floating system can be achieved by
installing additional grooved mechanicals joints or by installing
guides to control the direction of movement. Engineers must take
the effects of pressure thrusts into account when utilizing
flexible grooved couplings, as the pipe will be moved to the full
extent of the available pipe end gaps when allowed to float.
Ensure that branch connections and offsets are sufficiently long so
that the maximum angular deflection of the coupling is never
exceeded and that it can accommodate the anticipated total movement
of the pipes. Otherwise, it is advised to anchor the system and to
direct movements.
Flexible Grooved Couplings For Linear Movement and Deflection
Grooved mechanical couplings are an alternative to welded U-shaped
expansion loops, welded offsets, expansion joints and rubber
bellows. Associated with a free floating system, flexible couplings
are used in piping systems to accommodate piping thermal growth—
without any additional components or piping configuration required.
Certain characteristics distinguish
flexible groove type couplings from other types and methods of pipe
joining. When they areunderstood, the designer can utilize the many
advantages that these couplings provide.
By using flexible couplings at changes of direction and directing
the movement toward the directional change with properly placed
anchors and guides, movement is accommodated by the joining method
itself. This method also produces little or no additional stresses
in the system, unlike a welded expansion loop.
Flexible couplings also can be used strictly for their axial
movement capabilities. In this case, straight runs are anchored on
each end and the piping is guided at every other length. Each
flexible joint is pre-gapped (either fully gapped or fully
closed/butted) at installation to ensure that there are enough
couplings to accommodate the expected expansion and/or
contraction.
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The flexible grooved coupling allows for controlled angular
flexibility and rotational movement to take place at joints.
Flexible grooved type couplings allow angular flexibility and
rotational movement to take place at joints. In order to determine
the appropriate number of couplings to use, compute the change in
the linear length of the piping system by taking into account the
length and size of the piping system and maximum and minimum
operating temperatures.
Where full linear movement is required, a grooved expansion joint
can be used. Note, joints which are fully deflected can no longer
provide linear movement. Partially deflected joints will provide
some portion of linear movement. It is also important to consider
that standard cut- grooved pipe will provide double the expansion
and contraction or deflection capabilities of the same size
standard roll-grooved pipe.
When considering offsets utilizing grooved mechanical joints, the
offsets must be capable of deflecting sufficiently to prevent
harmful bending moments at the joints. If the pipes were to expand
due to thermal changes, then further growth of the pipes would also
take place at the ends.
Flexible couplings do not automatically provide for expansion or
contraction of piping. Always consider best setting for pipe end
gaps. In anchored systems, gaps must be set to handle combinations
of expansion and contraction. In free floating systems, offsets of
sufficient length must be used to accommodate movement without
over-deflecting joints.
Ensure anchorage and support is adequate. Use anchors to direct
movement away from or to protect critical changes in direction,
branch connections and structure. Spacing and types of supports
should be considered in accommodating anticipated pipe
movements.
Expansion Loops Utilizing Flexible Couplings and Fittings In
vertical straight runs of pipe, expansion loops utilizing a
U-shaped pipe configuration can also be designed into the piping
system to accommodate expansion and contraction. Expansion
loops can be designed as welded or grooved. Welded expansion loops
require eight welded joints and fittings to assemble. In a
welded expansion loop, the piping bends or flexes to accommodate
the straight run movement. Although this method works, the forces
to bend and flex the pipe are much greater than in a grooved loop,
and the forces generate a larger magnitude of stress which requires
larger anchors and guides to direct the movement and protect
components and structures.
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The flexible mechanical joint can be use in expansion loops without
inducing stresses in the pipes, elbows or joints. Also, it is
important to note that expansion loops utilizing rigid couplings
are not designed to accommodate angular deflection, however an
expansion loop utilizing rigid grooved copper couplings is designed
to conform to industry standards.
The deflection capability of flexible couplings allows for thermal
growth/contraction to be absorbed within the couplings at the
elbows as the thermal forces induce deflection. A total of eight
flexible grooved mechanical couplings, four grooved end 90-degree
elbows and three pipe spools are required to complete each
expansion loop. As system temperatures lower and the pipe run
contracts, the loop expands and the deflection capability of the
couplings accommodates this movement. As system temperatures
increase the opposite effect occurs as the pipe run expands and the
loop contracts with the couplings accommodating the deflection in
the opposite direction (See Figures A through C).
Using flexible couplings in an expansion loop configuration reduces
the amount of force needed to flex the loop, and the loop itself is
much smaller. A loop constructed in this manner will be 1/2 to 1/3
the size of a welded loop with the same capacity.
The space constraints of today’s buildings also make this a more
attractive option in HVAC piping, though welded expansion loops are
still required in some system applications.
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Making the Best Choice Grooved mechanical systems offer four
different methods to provide flexible, controlled movement of a
piping system. The selection of expansion joints, free-floating
systems, flexible
couplings or expansion loops will be based on the type of piping
system, the amount of anticipated movement and the mechanical
engineer’s preference.
In addition to effectively accommodating thermal expansion and
contraction, engineers should consider the additional benefits of
using the grooved method during construction, including a
simplified assembly process that is readily inspectable relative to
welded systems. Also, mechanical couplings reduce the need for
welding and reduce man hours and material handling on the site,
making for safer job sites and reduced risk of injury on-site.
During operation, the simple disassembly of a coupling reduces
chances of deferred maintenance and lengthy downtime for routine or
unscheduled maintenance.
Overall, choosing the grooved mechanical method is an efficient way
to accommodate excess stress on any piping system, eliminate
incidents of ruptures and leaks due to thermal expansion, decrease
maintenance needs of equipment, and simplifies the commissioning
process.
Larry Thau is Executive Vice President- Chief Technology Officer
for Victaulic Company, Inc. A practicing mechanical engineer for 35
years, he holds more than 35 patents and lectures on piping
technology around the world.
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Circuit balancing: A key to improving HVAC system operationand
control
David L. Hudson Victaulic Company, Inc.
Easton, PA
August 2009
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As many building superintendents would agree, the symptoms of
indoor climate problems within their buildings usually surface as
complaints from tenants. The living or working spaces are too cold
in winter, too hot in summer—or some combination of both extremes,
year-round.
In response to these temperature variations, building occupants
often compensate by using space heaters, opening windows and
adjusting thermostat settings. Additional adjustments to the HVAC
system may include larger pumps, resizing components, changing
night setback and morning startup times, and flow adjustments in
mains, branch lines and circuits independent of the impacts on the
entire HVAC system.
These types of “fixes” to alleviate cold and hot zones in a
building are typically ineffective and costly and usually do not
correct the situation.
For example, resetting a workplace HVAC system startup time from
7:30 a.m. to 5:30 a.m. means that the plant operates at capacity
two additional hours per day. This works out to a 25 percent
increase in energy consumption, which cancels out the energy
savings that night setbacks were designed to achieve.
As a result of such actions, building owners realize higher
energy and operating costs, additional wear on pumps and HVAC
components and reduced control valve authority throughout the
system.
System designers may be challenged to defend their design, pipe
sizing, operating parameters and adequacy of controls when the HVAC
system is simply unbalanced. Indoor temperature and climate
problems typically are not caused by control malfunctions or sizing
errors. Often they are traceable to incorrect flow rates in the
HVAC system due to improper terminal unit balancing. Engineers
typically design HVAC systems with excess capacity for the building
they support. Thus, the ability to provide the necessary heat or
cooling energy is present. Getting the energy to the terminal unit
and air handling unit (AHU) is the real issue.
Therefore, the key to HVAC system effectiveness and efficiency is
properly controlling flows throughout the entire system from
production and delivery units to terminal units for the comfort of
all building occupants.
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Balancing for comfort and control
HVAC systems are designed with balancing valves to maintain flow
conditions so that control valves may function properly. Proper
control valve function provides the correct flow to the heat
transfer coil resulting in the correct energy output (BTU) to the
building space.
Flow in an HVAC system is dynamic and always changing throughout a
typical 24-hour period. Due to heat gain from the sun and changes
in building occupancy rates, the demand for heating and cooling
output will vary not only throughout the day and night, but by
building sector. An effective and efficient HVAC system must
provide energy output when required and where required. Proper
Hydronic balancing is the key to making your HVAC system perform
properly and at the lowest cost.
Proper circuit balancing is essential to ensure that heating and
chilled water systems deliver correct flows to all terminal units
in the HVAC circuit, as specified by the system’s design flow. In
an unbalanced system, sectors of a building will have underflow or
overflow conditions that impact control valve authority and thus
the indoor climate in the building. For example, areas located
nearest to the energy production and delivery source could receive
excess flows, resulting in excessive heating or cooling. Likewise,
areas that are remote (farthest away) may experience inadequate
heating or cooling levels because of insufficient flow rates.
In terms of pure economics, each additional degree Fahrenheit
increase in
thermostat setting can add six percent to a building’s heating
costs, while every degree Fahrenheit reduction works out to an
additional eight percent increase in cooling costs.
A typical HVAC circuit incorporates balancing valves for each
terminal unit coil and AHU. To balance a coil using a manual
balancing valve, a technician needs to connect a differential
pressure gauge or handheld circuit balancing instrument to the
valve’s two metering/test ports. Based upon the valve size, hand
wheel position and the measured differential pressure, the system
flow rate through the balancing valve is readily determined with a
balancing instrument, balancing flow wheel or the valve’s
Cv characteristics. The valve hand wheel is then adjusted
to
obtain the required system flow rate.
Applying this technique to each balancing valve in the system
will achieve proper balance throughout the system so that all
circuits receive specified design flows for optimal performance.
When pumps, chillers and other components operate at the lowest
possible load, owners benefit from less wear and tear, longer
equipment service life, and savings in energy and maintenance
costs.
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Figure 1: Coil-CW/HW schematic drawing and Tour & Andersson
Coil Component
Manual balancing valves Engineers and contractors have a variety of
manual balancing valve configurations to choose from for HVAC
circuit balancing and control applications. Throttling
characteristics (the relationship between a valve’s adjustment
range and flow rate) also vary by valve type and are a key
determinant in each valve’s ability to be set to the desired flow
and must be verified using the balancing technique previously
described.
For example, a quarter-turn ball valve provides 90 degrees of
throttling adjustment range, as compared with the 1,440 degrees of
adjustment range
available with a four handwheel turn globe valve. As a result, many
engineers specify Y-pattern globe valves because of their ability
to be set precisely to control flows.
Depending on valve size, globe valves can offer full throttling
ranges using 2, 4, 8, 12 or 16 handwheel turns, and enable users to
obtain accurate readings of up to one-tenth of a handwheel turn.
Some valve manufacturers also provide vernier scales, digital
readouts, concealed memory and locking, tamper-proof settings and
other features designed to enhance flow rate accuracy and
controllability.
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Figure 2: “Comparison of throttling characteristics”
Comparison of throttling characteristics Generally speaking, a
higher number of handwheel rotations equates to more precise flow
control. This graph illustrates the throttling characteristics of
90 degrees (1/4 turn), 360 degrees (full turn) and 1,440 degrees
(four turn) balancing valves.
• A 90 degrees fully open-to-closed valve requires just
a 12 degree change in adjustment to equal a 30 percent change in
flow.
• A 360 degrees fully open-to-closed valve would
require a 96 degrees change in adjustment to equal the same 30
percent change in flow.
• A 1,440 degrees fully open-to-closed valve would
require 408 degrees of change in adjustment to equal the same 30
percent change in flow.
Real-time measurement and control
A variety of optional pressure drop ( ΔP) sensors and
balancing software programs are available to provide data links to
a building’s monitoring system. In addition, some handheld circuit
balancing instruments integrate ΔP sensors and
microprocessors into a portable, lightweight package that enables
contractors to perform circuit balancing without the need for flow
charts and pressure drop calculations.
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Balancing helps isolate system trouble spots The symptom is
typically improper heating or cooling. The cause is an improperly
adjusted balancing valve, clogged strainer/coil or other system
issue which changes the specified flow rate through a coil or AHU.
Diagnostic analysis can be made readily on the suspect coil or AHU
by checking the flow rate through the respective balancing valve.
Moreover, issues can be identified at a point when they can still
be corrected economically during building commissioning and before
tenant move-in.
For this reason, circuit balancing valves are integrated as part of
a building’s commissioning process. In addition to providing
engineers with a comprehensive record of specified and actual
flows, balancing helps simplify setup and monitoring of control
equipment. These advantages reduce capital costs along with
commissioning times.
Conclusion Far too many buildings are unnecessarily plagued by
temperature variations that can lead to tenant complaints and high
energy and operating expenses for owners. In most cases, these
faults can be resolved easily through proper balancing of the
heating or cooling system in conformance with original design
performance specifications.
In addition to providing occupant comfort and efficient energy and
operating costs, effective circuit balancing can aid in
troubleshooting the causes for improper heating or cooling. A
comprehensive circuit-balancing program should be integrated into
new building commissioning as a means of saving time and
energy and improving the long-term value of the building.
In the end, everybody wins. Tenants enjoy a comfortable living and
working environment, while building owners benefit from faster
startup times, savings in energy and operating costs, and enhanced
return on their capital investment.
David L. Hudson is a Senior Product Engineer for Victaulic Company,
Inc. He is a practicing mechanical engineer with more than 26 years
of experience. He can be reached at
[email protected].
Victaulic is the world’s leading producer of mechanical pipe
joining systems and the exclusive U.S. distributor of Tour
&
Andersson circuit balancing valves.
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Abst rac t
The dual agent fire extinguishing system generates a homogeneous
suspension of sub-10 micron water droplets and nitrogen gas that is
delivered at relatively high momentum with very low operating
pressures relative to existing fire suppression technologies. The
combined extinguishing characteristics of water and nitrogen
enhance the individual components: coupled with high delivery
momentum, the suspension has demonstrated fire extinguishment
capabilities and benefits that extend the boundaries of existing
single fluid systems. The science of generating the homogeneous
extinguishing agent is presented followed by a brief explanation of
the theory of fire extinguishment using the system. Fire test
results are then presented that demonstrate the Vortex capabilities
in total flooding and local applications.
1) Introduction
Fire protection systems are available today in a large variety of
configurations and with varying complexities. From traditional
water based sprinkler systems, the simplest and most widely used,
to the halocarbon agents and high pressure water mist systems. Each
system has unique advantages and disadvantages, depending on the
hazard application.
After an in-depth analysis of all existing fire suppression
systems, the researchers identified specific desired
characteristics of the new suppression system. The criteria called
for minimal wetting of protected surfaces, full fire suppression
capabilities, zero environmental impact, extended safe egress time
for occupants in case of discharge, simplified system design for
multiple zones and scalability that surpasses current water mist
technologies.
In order to achieve this, the design team decided that water
droplet size should be as small as possible thus reducing the
required water volume and simultaneously maximizing heat absorption
efficiency. It was recognized that a new water delivery and
atomization method would need to be developed in order to produce
very small water droplets while overcoming the drag effect inherent
with the projection of small water droplets. The resultant provides
enough agent momentum that the system can be effectively applied to
local application hazards for both combustible and flammable liquid
hazards.
The adiabatic flame temperature equation is used to demonstrate the
theoretical
advantage of a dual agent extinguishing system. The assumptions
made are discussedand analyzed against actual fire test data with
interesting results that may, with further testing and analysis,
explain some limitations associated with typical water mist systems
and lead to greater fire extinguishment efficiencies.
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2) Atomization
The atomization of water droplets is strongly tied to a parameter
called the Weber number,
σ
2 Δ
= [Eq. 1]
where ρ is the liquid density (kg/m3) U is the relative
gas-liquid velocity (m/s) L is the characteristic dimension of the
stream (m) σ is the surface tension coefficient (kg/s2)
At high Weber numbers the aerodynamic forces on the water
droplets dominate, causing the water stream to distort and
disintegrate in a process known as atomization. The atomization
process continues in a cascading manner until a critical value of
the Weber number is reached at which point the atomization process
is complete. As the Weber number decreases with smaller droplet
size the relative velocity also decreases.
The challenge is to create very small water droplets while
maintaining high momentum capable of over coming the aerodynamic
forces that would normally decelerate the droplets. This is
essential in the case of fire suppression where the system must be
able to deliver the water droplets to a fuel source while
potentially overcoming the fire plume velocities.
2.1) Agent Emitter
The agent emitter was developed using theory analogous to the
aerodynamic forces seen on a supersonic aircraft wing.
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Figure 1: Victaulic Vortex emitter cross-section
Figure 1 is a cross section of the Vortex emitter. Nitrogen at 25
psig enters the emitter while water at <5psig enters the water
jacket external to the nitrogen flow. The emitter is configured to
accelerate the nitrogen flow to a supersonic velocity thus exiting
the emitter as under expanded gas flow.
Shock Disks
Figure 2: Schlieren Photograph of Nitrogen Flow
Figure 2 is a picture, taken at the Penn State Gas Dynamics
Laboratory, which demonstrates the nitrogen density patterns in the
critical flow field.
As nitrogen exits the emitter at a supersonic velocity a
shock disk is formed. This is the result of the instantaneous
transition from sonic to sub sonic velocity and is seen as the dark
area between the emitter outlet and the emitter foil. As the
nitrogen contacts the emitter foil it is re-accelerated to
localized supersonic velocities which then creates additional shock
disks perpendicular to the flow field. Water exits the emitter
through the ring of concentric holes (see Figure 1) external to the
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This water is injected into the nitrogen flow field in the area of
the shock disks shown in
Figure 2. At this point the water is exposed to a region of very
high Weber number and thus rapid atomization. The resulting water
droplet distribution shown in Figure 3 is for the most part
comprised of < 10 μm size water droplets with a very tight
distribution.
Figure 3: Droplet distribution density, Underwriters
Laboratories
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The Victaulic Vortex system uses equal moles of water and nitrogen
in producing a homogeneous suspension of water and nitrogen. Figure
4 shows water being injected into the nitrogen flow and the
subsequent atomization. Of particular importance is the
understanding that after the water is atomized it is carried in the
nitrogen flow at equal partial pressures. At this point relative
velocity between the water and nitrogen is negligible, resulting in
a very small Weber number. Since the water is suspended in the
nitrogen, it maintains its momentum and is capable of being
projected for relatively large distances and in the process
becoming entrained in fire plumes.
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White Paper
Keeping Your Cool: Grooved Technology as a Means to More Efficient
Data Center Construction and Operation
By David Gibbons
July 15, 2009
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For many years, air cooled systems provided sufficient cooling
capacity for data centers;
however, increased computing density produces more heat and,
therefore, requires a more efficient cooling method. In larger data
centers, the most cost effective method of cooling is a chilled
water system. According to the Science of Aquatics, water is 4,000
times more efficient than air. This is why, in recent years,
companies like IBM have developed methods for bringing cooling
water directly into server racks.
In a chilled water system, chilled water is pumped out of the
mechanical room and into computer room air handlers by way of
under-floor water distribution lines. The air handler then removes
heat and humidity by drawing warm air through coils filled with
circulating chilled water. The water absorbs the heat from the air
and circulates back to the chiller where the heat is transferred to
a condenser water loop and eventually released through a cooling
tower.
Hard piping utilizing carbon steel pipe or copper tubing is common
in a chilled water system. Traditional pipe joining methods for
hard piping systems consist of welding, brazing or flanging which
generally work well in data centers; but, with increased loads,
frequent changes, and system expansions, these joining methods have
become problematic. Piping systems utilizing a welded, brazed or
flanged joining method are not easily accessible, feature limited
design flexibility, introduce fire hazards to the jobsite and
require lengthy system shutdowns to perform routine or unplanned
maintenance activities.
Grooved mechanical piping technology—a method of pipe joining that
requires no flame— provides a reliable piping system that
ensures efficiency in construction and operation of a data center
by reducing deployment time, providing an easily adaptable system
and reducing downtime during routine or unscheduled
maintenance.
Grooved pipe joining technology In 1925, Victaulic designed the
first grooved end pipe joining system for water and air service
piping. Recognized for its design flexibility and speed of
assembly, grooved end pipe joining technology transformed the
piping industry, leading to dramatic gains in building construction
productivity. That is why among HVAC specifying engineers, building
owners and installation contractors around the world, grooved
mechanical pipe joining is the preferred pipe joining solution for
both new construction and retrofit.
The mechanical joint, or coupling, is comprised of four elements:
the grooved pipe, the gasket, the coupling housings, and the nuts
and bolts. The pipe groove is made by cold forming or
machining a groove into the end of a pipe. The key section of the
coupling housing engages the groove. The bolts and nuts are
tightened with a socket wrench or impact wrench, which holds the
housings together. In the installed state the coupling housings
encase the gasket and engage the groove around the circumference of
the pipe to create a triple seal unified joint that is enhanced
when the system is pressurized.
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Installing a grooved mechanical piping system The installation of
the piping system using the grooved mechanical pipe joining method
leads to significant on-site man hours savings. On average, field
fabrication of a grooved system is up to 10 times faster than
welding and six times faster than installing a field-fabricated
flanged joint. The simplified assembly and installation leads to a
reduction in project calendar days by as much as one half,
optimizing labor risk management. The reduction in calendar days
realized by installing a mechanical piping system gives owners the
ability to meet, and even beat, compressed construction schedules
and avoid liquidated damages.
By reducing on-site man hours and eliminating the risk of fire and
release of noxious fumes, the installation of mechanical piping
systems increases jobsite safety and decreases overall risk when
compared with welding, brazing or soldering.
Most injuries on job sites occur via material handling, but the
most significant risks — in terms of potential impact on people and
businesses — are caused by fire and fume hazards. Mechanical pipe
joining eliminates fire, open arcs, sparks, flames and toxic-fume
hazards that are associated with welding, brazing, and soldering.
Welding is associated with a number of potential health risks, as
well as the risk of severe burns. By specifying a mechanical
pipe
joining system, an engineer reduces the owner's overall
risks, especially those related to project schedule, costs and
potential liability.
Depending on the type of project (e.g., new construction vs.
expansion/retrofit), hazards may become a risk not only to
construction workers, but also to the occupants of the structure
and surrounding facilities. When someone is welding, to comply with
mandatory safety regulations, all other work in the area must be
postponed, leading to costly downtime and possible employee
evacuation. Evacuations are beneficial to safeguard workers, but
business realities lead to yet another potential danger: the
pressure and rush to catch up from a shut down or loss in
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seal. When the multiple bolts are removed and the flanges are
pulled apart, the gasket will tear
and therefore needs to be replaced.
With a mechanical coupling, the compression loads on the gasket are
different than the flange. The gasket has a C-shaped cross section
seal that is pressure responsive and designed to handle cyclical
loading. Systems can be pressurized and depressurized repeatedly
for many years without fatiguing the elastomer material. Once
installed, these couplings do not require any routine or periodic
maintenance and can be left in place for the life of the
system.
Grooved piping systems provide a union at every joint for ease of
maintenance and future retrofits.
Operating efficiency is maintained during retrofit work, and
systems can remain live without
interrupting cooling because properly placed butterfly valves
installed using grooved couplings provide “dead-end” shutoff
service for isolation allowing for easy system expansions or re-
routing with little to no interference with existing operations.
Expansion projects can be completed in occupied buildings without
vacating the space because mechanical grooved piping does not
release noxious fumes or introduce a fire hazard eliminating the
need for hot-works permits or fire watch.
Protecting equipment using grooved mechanical piping systems In
addition to making maintenance fast and safe, a grooved mechanical
pipe joining system accommodates movement and deflections within
the piping system reducing the need for periodic product repair or
replacement and maintaining the operational integrity of the
piping
system. Traditional welded or flanged piping systems have rubber
bellows or a braided flexible hose to accommodate these movements;
however, these materials often wear out over time requiring costly
and time-consuming replacement.
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Flexible mechanical systems are engineered to allow the pipe to
move and vibrate within the coupling, therefore localizing
vibrations generated by HVAC equipment and reducing the amount of
noise transmitted down the pipe line. The elastomeric gasket,
contained inside the internal cavity of the ductile iron housing,
creates a discontinuity in the piping system which aids in
isolating vibrations therefore, protecting vital cooling equipment
within the piping system. Furthermore, the ductile iron housings
and gasket material have vibration dampening qualities
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of their own, also serving to absorb vibrations. Testing has shown
that systems utilizing three
consecutive flexible couplings near a source of vibration will
experience a similar level of noise dampening as those systems
using specialty products. Additionally, the ability of grooved
systems to accommodate system movement reduces loads at equipment
connections and keeps vital cooling equipment operating at peak
efficiency.
The flexible grooved-pipe couplings reduce the transmission of
stresses through a piping system, while the gasket and ductile iron
housing combine to dampen vibration.
Nowhere is it more important to plan ahead for disasters than in a
data center. According to The Uptime Institute, in 2001 a Tier III
data center allocated 1.6 hours per year for IT downtime and only
0.4 hours of downtime in a Tier IV. Because the cooling system is
vital to the operational integrity of the IT equipment, when the
cooling systems goes down it is only a matter of minutes before the
IT equipment begins to overheat.
Piping systems in earth quake prone areas will be exposed to forces
and deflections beyond normal static conditions. These seismic
forces can cause extensive damage when piping systems cannot
accommodate these movements. Mechanically joined grooved systems
can be designed so that the differential piping movement associated
with a seismic event will be accommodated. The inherent deflection
capability of the flexible grooved pipe coupling reduces
transmission of stresses through piping systems. The deflection
allowed by a flexible grooved-
pipe coupling reduces the transmission of stresses through a piping
system thereby minimizingpotential system damage. As mentioned
above, flexible and rigid couplings also provide discontinuity at
each joint which helps minimize pipeline stresses generated during
seismic movement.
Testing performed at the Real-Time Multi-directional Experimental
Laboratory at the Center for Advanced Technology for Large
Structural Systems at Lehigh University in Bethlehem, Pennsylvania;
U.S.A proved the suitability of Victaulic grooved mechanical
couplings to maintain operational integrity of piping systems
during seismic events.
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Conclusion Owners, engineers and contractors are challenged to
design, operate and maintain reliable and easily adaptable
facilities that accommodate a revolving door of innovative
technology. And while there are many construction and operational
concerns to take into consideration, a data center’s cooling
strategy is vital to all business operations. For cooling
strategies that include chilled water systems, grooved mechanical
piping technology provides a reliable piping system that maximizes
efficiency by reducing deployment time during new construction,
reducing downtime during maintenance and/or system expansions and
maintaining operational integrity of the piping system and
equipment on a day–to-day basis and in the unfortunate event of a
natural disaster.
For more information on the Victaulic Seismic Testing Program,
visit www.victaulic.com/seismic.
For more information on Victaulic solutions for data centers, visit
www.victaulic.com/datacenters.
Contact a Victaulic Sales Representative.
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WHITE PAPER
Piping system design impacts safety in every phase of a project
By John Rutt September 2008
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Under the ASME Code of Ethics of Engineers, it’s the first
of the fundamental canons: “Engineers shall hold paramount the
safety, health and welfare of the public in the performance of
their duties.”
Due to the nature of the work, this is a major challenge in
construction. According to the Bureau of Labor Statistics, the
construction industry has the second highest incidence rates for
cases with days away from work. (Refer to Table 1 below.) More
specifically, statistics compiled by the Construction Industry
Institute indicate the majority of construction injuries are
suffered by pipefitters, welders, plumbers, and the laborers who
assist them. (Refer to Table 2 below.)
Table 1
Of all the major industries, construction has the second highest
incidence rates of cases with days away from work.
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Table 2
Of all the leading crafts, those relating to piping systems have
the highest rate of occupational injuries and illnesses.
The inherent dangers of installing and maintaining piping systems
increase the importance of the mechanical engineer’s role in
designing for safety and accident prevention – both during the
construction of the project and throughout the lifecycle of the
facility. There are three fundamental areas where mechanical
engineers can positively affect safety: one, system
constructability, two, best practices for training construction and
inspection, and three, system
maintainability.
By specifying safer technology and methods in greater detail, an
engineer can minimize the impact of, or possibly even eliminate the
potential for, certain types of accidents and injuries. Although
most injuries on jobsites and in the workplace occur from material
handling, perhaps the most significant risks, in terms of potential
impact on people and business, are the fire and fume hazards
associated with welding, brazing and soldering on the
jobsite.
Safety in constructability: The mechanical pipe joining advantage
In the piping systems environment, mechanical pipe joining removes
a number of
U
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By specifying mechanical pipe joining, an engineer can
reduce these risks in the design phase, and thereby make a powerful
contribution to reducing an owner’s risks, costs and potential
liability. Furthermore, in keeping with the fundamental canon of
“holding paramount the safety, health and welfare of the public”,
that engineer can help create a safer environment for all
involved.
For example, in addition to the inherent risks of fire, potential
health risks associated with welding have been cited in studies and
include: • Irritation of the eyes, nose, chest, and respiratory
tract • Nausea, headaches, dizziness • Metal fume fever • Lung
cancer • Urinary tract cancer • Heart disease • Kidney damage •
Parkinson’s disease
Depending on the project environment (I,e., new construction vs.
expansion/retrofit), these hazards can become a risk to not only
the construction worker, but also to the occupants of the existing
structure and surrounding facilities. The initial use of
traditional joining technology can also limit the maintenance
options for, or efficiency of, future repairs, replacements and
retrofits.
Although there are established procedures and requirements
for fire prevention and fume ventilation during welding,
unfortunate incidents involving welding are
not uncommon in the news. Consider the potential risks to a
hospital or school retrofit project, where occupants may not be
easily evacuated or protected from these risks. Consequentially, to
protect people from these hazards, construction schedules often
must be rearranged and extended to allow off-shift work at the
times when the buildings are unoccupied. Eliminating hotwork where
possible reduces risk for the client, occupants and
contractors.
Grooved installation-ready coupling Mechanical pipe joining
requires no flame to join pipe, and involves no exposure to
hazardous fumes. The grooved mechanical pipe joint shown above
installs in
four simple steps. Lube it. Stab it. Join it. Drive it.
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Safety in practice: Increasing safety by specifying
procedures In addition to enhancing safety by specifying safer pipe
joining technology, an engineer can further contribute to a safe
environment by defining best practices in product selection,
training, installation and inspection. Performance-based
specifications typically provide a good general scope of acceptable
product and system performance requirements. In addition, engineers
can also name specific manufacturers that they consider to be
acceptable for the service and for high quality. Although it is
often perceived that “three manufacturers” for a product or system
must be specified to ensure an engineer’s non-biased objectivity,
the fact is that legal precedents have been set at the District
Court level which support the specifier’s right to issue a
proprietary specification that designates a sole supplier in
certain situations. The principles of the Massachusetts District
Court Case, Whitten vs Paddock (1974), established that 1)
proprietary specifications do not violate antitrust laws; 2) Few
brands of products are exactly alike and specifiers who want to
limit choices have every right to do so; 3) Other brands qualify as
“or equal” only when the specifier says so; 4) The specifier may
waive specifications in order to obtain a more desirable product
for the end user, but the specifier is the only one who can
determine if the product is more desirable; 5) The burden is on the
not-specified manufacturer or supplier to convince the specifier
that the product is equal for the purpose of the particular
project. This provides specifying engineers with even greater
control over the project, while also enabling them to ensure the
highest quality and system performance for their clients.
Another way for the engineer to influence the quality of
installations is by ensuring that those individuals installing the
systems are educated in the proper
installation requirements in accordance with the manufacturer’s
published instructions. Specifications can be written to include a
section requiring installing contractors to obtain training
directly from a manufacturer’s employees, in order to further
ensure proper installation of their piping products and
systems.
The final way an engineer can ensure that an acceptable system is
delivered to the client is by detailing mandatory inspection and
test procedures in the mechanical specifications. Selecting
products and systems that are easy to install and inspect further
increases the chances of having a successful start-up. For example,
some grooved coupling manufacturers provide for quality control
through easy visual confirmation of complete coupling installation.
Complete joint
installation is easily verified because the coupling is designed so
that the completed joint achieves metal-to-metal bolt pad contact.
Welding, on the other hand, requires x-rays for quality inspection.
System testing is an important practice that is typically detailed
in specifications to ensure system performance. Specifying that
manufacturers’ product (couplings, valves, specialties, etc.)
performance ratings allow for proper hydrostatic system testing
(typically 1.5 times the system operating pressure).helps to
further ensure system integrity.
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Grooved coupling allows for easy visual inspection, as proper
installation can be confirmed simply by checking that pad-to-pad
contact is made.
Safety after completion: Improv ing the safety of ongoing
maintenance Over the operating life of a facility, its piping
system will require three basic categories of maintenance. These
are: routine periodic inspection, physical changes or expansion,
and unscheduled repairs. Due to its intrinsic design qualities,
grooved mechanical pipe joining makes maintenance and system access
easier, faster and safer minimizing downtime and the negative
impact of any maintenance event
The advantage over welding and other methods in this area is
self-evident. When pipes are welded together, they have no union
point between them. In effect, they become a single, extended piece
of metal. On the other hand, a grooved coupling provides a union at
every joint, which allows for easy access to the system and
flexibility for future system expansion. To access the system all a
maintenance worker need only to unscrew one or two nuts and drop
the section out. There are no torches, no saws and no welding
machines needed. Even with flanged, lug or wafer type valves and
accessories, the compression of flanged connections create
significant maintenance challenges that dramatically increase the
time and manpower needed for replacements and repairs. Components
are difficult to remove, and often even more challenging to
reinstall. In contrast, grooved joints provide a true union and
eliminate many of the challenges associated with traditional
weld/flange systems. When the maintenance is complete, a mechanical
coupling makes it easy to quickly get the system up and running
again. The gasket is reinstalled, the coupling is placed back on
the pipe, fitting or component, and the two bolts are tightened. In
a welded system, repairs and maintenance demand that workers
actually cut out the damaged pipe section and weld it back
together: causing potential
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operational issues and safety hazards that are of particular
significance in existing facilities and occupied spaces.
Coupling disassembly provides easy access for maintenance or system
expansion.
As with any engineering challenge, all system characteristics
and design options must be thoroughly considered to find the
optimal solution. There are applications such as steam services,
for example, for which grooved piping systems are not suitable and
weld/flange systems are required. It is imperative that the
performance capabilities of the systems and products meet the
system performance requirements. For example, the proper gasket
material and design selection is one of the most important elements
to ensure the safe, long-term performance of a grooved mechanical
system. Advances in elastomer technology partnered with innovative
coupling and gasket designs provide performance in water
applications with temperatures up to 250 degrees F and pressures
from absolute vacuum up to 1000psi. However, all gaskets,
couplings
and components are not necessarily equal in performance and the
capabilities of each manufacturer and product must be evaluated
individually to confirm system and client requirements are
met.
The engineer has a vital role in improving safety at every stage of
a project’s lifecycle: from initial design, to installation, to
ongoing maintenance. By specifying mechanical pipe joining
solutions and their associated procedures, an engineer can have a
powerful and positive impact in creating a safer environment that
minimizes risk, increases efficiency, and brings greater value to
owners, contractors and occupants. For over 80 years, mechanical
pipe joining has been used in the world’s most demanding
applications because of its ability to provide
a wide range of design solutions to the engineer, however, nothing
is more paramount than the safety, health and welfare of the public
and grooved mechanical piping systems provide safety at every phase
of a project.
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By Larry Thau
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Noise carried through piping systems is becoming an increasing
challenge to owners,
engineers and contractors. The reasons for this include changing
design requirements
that place mechanical rooms on intermediate and top-floor building
levels, and greater
use of lightweight construction materials that tend to vibrate more
than traditional heavy
materials.
The business risk of not specifying systems at the design stage
that serve to attenuate
sound is that, frequently noise issues will continue to be a
problem throughout the
lifecycle of the structure. This can result in unsatisfied owners,
whose occupants may
complain that the objectionable noise is distracting to the point
that it effects
concentration and productivity. In this way, noise issues can also
have a bottom-line
impact on the Engineer or Contractor, who may need to perform
numerous call-backs to
attempt to fix the problem.
Therefore, it’s not surprising that a sizable industry has grown
around the idea of
minimizing piping-borne sound. This article will focus on the
proven sound attenuation
benefits of a technique commonly thought of as a
productivity-enhancing tool: the
grooved mechanical pipe joint. Most often specified when
contractors are seeking a
fast, easy, safe and reliable alternative to welding, grooved
mechanical pipe joining has
a long history of effectively minimizing noise and vibration in
applications around the
globe.
Mechanical equipment in piping systems creates vibration, which can
potentially lead to
significant noise issues. In most commercial and industrial
applications, occupants can
tolerate certain levels of background noise from the HVAC system.
The issue arises
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when the sounds become cyclic and droning, or on the other hand,
arrive in sudden
bursts when equipment switches on.
Of course, the surest way to avoid sound issues is to bring an
acoustics professional
into the project at the design stage. Yet budgets do not always
permit this, and there
are many construction-grade projects where the owner does not
consider sound to be a
critical issue, at least until after the fact. Those “conventional”
situations are the areas
being addressed here.
Traditional sound attenuation
When faced with the need to diminish noise and vibration from
equipment connected to
the circulation system, designers have traditionally specified
elastomeric flexible arch
connectors. These connectors create a discontinuity in the metal
piping (as opposed to
welding), so that less vibration is transferred down the line.
Additionally, they are
commonly constructed of nylon, Dacron® or polyester material to
help absorb vibration,
and are formed in a spheroidal shape to permit deflection in all
directions. This
advantage, however, is also the weakness of the elastomeric
arch.
Because the elastomeric flex connector’s shape allows pressure to
exert in all
directions, control units such as restraining rods, plates and/or
anchors are required.
These items are used to prevent excessive stretching of the
unsupported elastomer due
to system pressure thrusts. But when such thrusts occur repeatedly,
and the connector
is overextended through time, use and pressure, failure can result.
Additionally Flex
Connectors employ unrestrained rubber as a pressure boundary in
systems which
otherwise have continuous metallic encasement. This becomes a
particular concern in
high rise construction where large pressure differential are often
present.
The complexity of the reinforcing systems also means that
installation can be time-
consuming and post-commissioning adjustments can be required. As a
result, such
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connectors are usually placed only at the point where the pump or
other equipment
connects directly to the piping system.
Mechanical Joining: An alternate solution
In independent tests performed by NUTECH Testing Corporation/SE
Laboratories, Inc.,
a laboratory which specializes in environmental and field
mechanical testing, another
device was found to be at least as effective in sound attenuation
as flexible arch
connectors.
Interestingly enough, this “new” solution was invented over 90
years ago, and has a
major presence in the construction industry as a means for
simplifying pipe joining,
assuring reliable connections and shortening production schedules.
That method:
grooved mechanical pipe joining, also known as grooved pipe
joining.
Proven sound attenuation qualities
When the structure of a grooved pipe coupling is examined, it is
easy to see why it
effectively reduces sound transmission. The resilient elastomeric
gasket, contained
inside the internal cavity of the ductile iron housing, creates a
discontinuity similar to
that of a flex connector. The material from which the gasket is
made also serves to
absorb vibration.
Figure 1: The flexibility of grooved-pipe couplings reduces the
transmission of stresses through a piping
system, while the gasket and ductile iron housing combine to dampen
vibration.
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The key distinctions of a grooved pipe joint over a flex connector
are inherent in the
proprietary design of the coupling. Its unique construction enables
the gasket to seal
against the pipe, while the ductile iron housing provides both
space for the elastomeric
material to flex and containment to prevent overstretching.
Overall, the coupling works
to create a permanent leak-tight seal with no need for additional
reinforcement.
Additionally, ductile iron has vibration dampening qualities
of its own, so the external
housing also serves to absorb sound.
The sound attenuation characteristics of grooved mechanical
couplings are not a newly
discovered phenomenon. Testing conducted by L.S. Goodfriend and
Associates in 1970
– 1971 concluded that: “A substantial vibration reduction is
achieved in pipe systems
which employ the Victaulic Style 77 coupling.” (Actual measure
reduction in decibel
level ranged from 2.3 to 12.1 dB over a wide frequency range.)
{Note: Victaulic is the
world’s leading manufacturer of grooved mechanical joining
solutions.}
More recently, SSA Acoustics in Seattle, Washington conducted field
measurements at
the request of their client that showed “three Victaulic couplings
placed in series in a
pipe section have a comparable performance to twin-sphere neoprene
connectors, and
a superior performance to braided metal hoses. Victaulic couplings
dampened the
overall vibration amplitude by 80 – 90%.”
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