A pipe support or pipe
hanger is a designed element that transfers the load from a pipe to the
supporting structures. Loads include the proper weight of the pipe, the
material carrying the pipe, all pipe fittings attached to the pipe, and the
casing of the pipe such as insulation. The four main functions of pipe support
are to support anchors, guides, shock absorbers and specified loads. Pipe
support may be insulation material used in applications at high or low
temperatures. The entire design Structure of the pipe support assembly depends on the loading and operating
conditions.
Loads on piping system
Primary
Load
These are generally stable or durable types
of loads such as internal fluid pressure, external pressure, pipes acting on
gravity forces and fluid weights, forces relaxed or thrown down, waves created
by the effects of water / steam hammers.
Sustained Loads:
•Internal/external pressure: A pipe used
for the transportation of fluid is under the pressure of internal pressure. A
jacket pipe core or shell and tube exchanger, etc., may have a net external
pressure on a tube-like pipe. Internal or external pressure increases the
tension in the axial as well as peripheral (hoop tension) directions. The
radial direction also produces pressure, but this is often overlooked. Internal
pressure uses an axial force equal to the pressure time of the internal
cross-section of the pipe. F = p [^ d ^ 2/4]. When used to calculate the
external diameter pressure as well as the approximate metal cross-section as
the pipe cross-section, the axial stress can often be calculated as follows: S
= PD / (4 T).
• Deadweight: This is the pipe's own weight,
Which contains fluid, the weight of fittings, and other inline components
(valves, insulation, etc.).These types of loads work throughout the entire
cycle of the pipe. In horizontal pipes, this causes the bending of the load,
and the bending moment is normal and the shear stress is related. Pipe bending
occurs mainly for two reasons: distributed load weight (e.g., liquid weight)
and concentrated weight load (e.g. Valve weight). The weight of the risers
(vertical section of pipe) can be supported by riser clamps.
Occasional Loads:
• Wind Load : The piping, which is
located outside and thus approaching the wind, will be designed to withstand
the maximum wind speed expected during the operating life of the plant. Wind
power is modeled as a uniform load acting on the projected length of the
perpendicular to the wind direction. Wind pressure will be used for various
upgrades to calculate wind power using the formulas given below. Fw = Pw x S x
A, where Fw = The total wind force, Pw = The equivalent wind pressure, S = Wind
shape factor, A = Pipe exposed area.
• Seismic Load: Earthquake load is one
of the basic concepts of earthquake engineering, which means using
earthquake-induced agitation to structure. This occurs on the surface of the
structure either with the ground or adjacent structure or with Tsunami's
gravitational waves.
• Water Hammer: Water hammer (or liquid
liquid hammer) is a pressure rise or surge when force is forced to stop the
fluid (usually liquid but sometimes even gas) or to suddenly change direction
(change speed).The hammer of water usually occurs when the valve suddenly
closes at the end of the pipeline system and a pressure wave is spread across
the pipe. It is also called hydraulic shock.
• Steam hammer : Steam hammers, caused
by the sudden stop valve closure, are occasionally considered to increase the
pressure generated by the transient flow of super-heated or saturated steam
into the steam line. Although the flow is transient, for the purpose of piping
stress analysis, only the unbalanced force of the pipe section is calculated
and applied to induce pipe vibration on the piping model as a static equivalent
force.
• Safety Valve Discharge : The reaction
force from the relief valve discharge is occasionally considered to be a load.
After opening the safety relief valve in an open discharge installation, the
reaction force due to steady-state flow can be calculated in accordance with
ASME B31.1 Appendix II and applied to the piping model as a constant equivalent
force.
Just as the primary loads have their origin in some
force, secondary loads are caused by the displacement of some kind. For
example, the pipe nozzle attached to the storage tank may be under load if the
tank nozzle to which it is connected is going down. Likewise, the pipe
connected to the vessel is pulled upward as the vessel nozzle moves upward as
the character increases. Also, the vibration in the connected rotating
equipment can cause the pipe to vibrate.
Displacement Loads:
• The load
due to the thermal expansion of the pipe
• Load due
to thermal movement of the equipment
Pipe expansion or contraction can occur at higher or
lower temperatures, respectively, compared to the bled temperature once
assembled. Secondary loads are often periodic, but not always. For example, the
load caused by a tank settlement is not cyclical. The load due to the movement
of the vessel nozzle during operation is cyclic because the displacement is
withdrawn during shut-down and the new start-up resumes afterward. The pipe connected
to the cycle of hot and cold fluid undergoes similar cyclic loads and
deformation.
Types of
pipe supports
• Rigid Support
• Spring Support
• Snubber/Shock Absorber
Rigid
Support
Rigid supports are used to restrict a pipe
in a particular direction (in that direction) without flexibility. The main
function of rigid support is anchor, rest, guide or both rest and guide.
1) Stanchion/Pipe Shoe:
Rigid support can be provided from below or above. In the case
of bottom support, a post or pipe clamp base is generally used. Only rest-type
supports can be easily held in steel construction. To constrain in different
directions at the same time, different plates or lift lugs can be used. Pipe
anchors are rigid supports that restrict movement in all three orthogonal
directions and all three rotational directions, that is, restrict all six
degrees of freedom. This is usually a welded post that is welded or bolted to
steel or concrete. For anchors that are bolted to concrete, a special type of
bolt is needed, called an anchor bolt, which is used to hold the support in
concrete. Normal and frictional forces can be important for this type of
support. Graphite pads or PTFE plates are used as needed to reduce friction
effects.
2) Rod Hanger:
This
is a static constraint. In other words, it is designed to withstand only
tensile loads (do not apply compressive loads, in which case buckling can
occur). Rigid vertical support provided only from above. Consists of clamps,
eye nuts, tie rods, and beam attachments. The choice of rod hanger depends on
the pipe size, load, temperature, insulation, length of assembly, etc.Large
friction force is not generated because the hinge and clamp are included.
3) Rigid Strut:
This is a
dynamic component designed to withstand both tensile and compression loads. The
strut can be provided in vertical as well as horizontal directions. The V-type
strut can be used to restrict 2 degrees of freedom. It consists of rigid rigid,
rigid strut, welding clevis. The choice depends on pipe size, load,
temperature, insulation, and assembly length. When it comes to hinges and
clutches, no braking force works.
Spring
Support
Spring
Assist (or Flexible Assist) uses a helical coil compression spring (to adjust
the associated pipe movement due to loading and thermal increase). They can be
broadly categorized into variable effort support and constant effort support.
An important component of either type of support is the helical coil
compression spring. Spring hangers and supports usually use helical coil
compression springs. Springs are manufactured by either a cold coiling process
(if the wire diameter is less than 12 mm) or a hot coiling process. Springs are
classified into "light" and "heavy". Light springs are
usually cold formed. Heavy springs are manufactured by a hot coiling process.
Springs are designed using the formulae :- Spring Rate ( K ) =
(d^4 x G)/8 x (Dm)^3 x Wc Where: d = Wire Dia in mm, Dm= Mean Diameter of
Spring Coil, Wc= Total no of working coils, K = Spring rate or Spring Constant
in Kg/mm, G = Modulus of Rigidity normally 80,000 N/mm2 8154.9 kg/ mm2.
1.Variable Spring Hanger or Variable Effort
Support:
Variable approach known as variable hanger or Variables are used
to support medium pipeline(up to 50 mm) vertical heat transfer. VES units
(supports variable effort) are used to support the weight of pipes or
appliances as well as fluid loads (gases are considered weightless) when used
in relation to supporting structures. Movements are allowed in quantities.
Spring support can also be used to support lines that are subject to relative
movement that is usually due to erosions or earthquakes. A VES unit is quite
easy to construct with a pipe actually suspended directly from a helical coil
compressed spring as the cutting sectional sketch shows below. The main
components are:
1. Top Plate
2. Pressure plate
or Piston Plate
3. Bottom plate or
base plate
4. Helical Spring
5. Turnbuckle
assembly
6. Locking Rods
7. Name Plate
8. Can section or
cover
Typically, the client / engineering consultant will provide the
following data when issuing a variable effort unit inquiry:
1. Hot Load
2. Thermal Movement
(with direction i.e. up or + & down or -)
3. Maximum Load
variation in Percentage (LV % max), if Max LV is not specified then it is
assumed to be 25% as per MM-SP58.
4. Type of Support
i.e. whether hanging type, foot mounted type etc.
5. Special features
such as travel limit stop required if any.
6. Preferred
surface protection / Paint / Finish.
The hot load is the working weight of the auxiliary equipment
when the pipe moves from a "hot" position, ie a cold condition to a
hot or working position. Generally, MSS-SP 58 represents 25% maximum load
conversion (commonly called LV).
Salient Features-
• Allows movement
in vertical direction
• Load on pipe
varies with movement
Used where
• Displacement
< 50mm
• Load
variability < 25%
• Rod angulation
should be less than 4°
Load Variation (LV) or Percentage variation =[(Hot Load ~Cold
Load) x 100]/Hot Load or Load Variation (LV) or Percentage variation =[(Travel
x Spring Rate) x 100]/Hot Load Generally spring supports are provided from top
but due to layout feasibility or any other reason Base Mounted type support is
fixed to floor or structure & the pipe is made to “sit” on top of the
flange of the spring support.
2.Constant Spring Hanger or Constant Effort
Support:
When
facing large vertical movements, typically 150 mm or 250 mm, you have to choose
constant effort support (CES). If the load regulation exceeds 25% or the
maximum LV% specified on the variable hanger, you have to choose CES. It is
common practice to use CES for pipes that are critical to the performance of
the system, or so-called critical pipes, where residual stresses are not
transmitted to the pipe. With constant effort support, the load remains
constant as the pipe moves from the cold position to the hot position.
Therefore, regardless of the movement, the load remains constant over the
entire range of the movement. hence, it is called a constant load hanger. Hot
and cold loads are two different values that are controlled by travel and
spring constant, as compared to a variable load hanger where the load changes
with movement. CES units do not have a spring rate.
The
most common operating principle of CSH is the bell crank mechanism. The bell
crank lever rotates around the fulcrum. One end of the bell crank lever is
connected to a pipe "P", and the other end is connected to a spring
by a tie rod. Thus when the pipe moves down from cold to hot condition, the
point P moves down, and as it moves down the Bellcrank lever will rotate in the
anti-clockwise The direction connected to the spring and the tie rod are
retracted, further compressing the spring. As the pipe moves up, the bell crank
lever rotates (clockwise) and the tie rods connected to the spring are pushed
out, causing the spring to expand or relax.
Another
popular principle is three spring or adjusting spring mechanism. In this case,
one main vertical spring occupies the main load of the pipe. The other two springs
are arranged horizontally to balance the additional load applied upward or
downward.
Slobber
or Shock Absorber
Dynamic Restraints: The restraint
system performs a completely different function than the function of the
support. The latter is intended to support the weight of the plumbing work and
allow it to move freely under normal operating conditions. Restraint systems
are intended to protect plumbers, plants and structures from abnormal
conditions. It must not interfere with the support function. Conditions that
require the use of restraints are: • Earthquake. • Fluid obstruction. • Certain
system functions. • Environmental impact. In areas located on or near
geological fault lines, it is common to protect plants from potential seismic
activity. Such plants have very high requirements for dynamic constraints.
Fluid turbulence can be caused by the effects of pumps and compressors, and can
also flow in liquid form into pipes intended for transporting gases and
vapors.Some system functions, such as rapid valve closure, pumping pulsations,
and operation of safety relief valves, can cause random and sudden load
patterns in the piping system. The environment can be disturbed by high wind
loads or, in the case of oil and gas rigs on the sea floor, by the effects of
ocean waves. The restraint system is designed to address all these effects. A
restraint is a device that prevents any plumbing or plumbing connected plant
from occurring and being damaged one or more of the above phenomenon. It is
designed to absorb sudden load increases and transfer it from the pipe to the
structure of the building, suppressing opposing vibrations between the pipe and
the structure. Therefore, dynamic constraints must be very stiff, have a high
load capacity, and minimize free movement between pipes and structures.
Depending on the operating principle,
snubbers can be categorized as follows:
Hydraulic Snubber: Like a car shock
arrester, a hydraulic snubber is built around a cylinder containing hydraulic
fluid with a piston that moves fluid from one end of the cylinder to the other.
Fluid displacement results from pipe movement that causes the piston to
displace in the cylinder, resulting in one end of the cylinder being high
pressure and the other end being relatively low pressure. The speed of the
piston determines the actual pressure difference. Fluid passes through a
spring-loaded valve, and a spring is used to keep the valve open. When the
differential pressure across the valve exceeds the effective pressure applied
by the spring, the valve closes.This stiffens the snubber and effectively prevents
further displacement. Hydraulic snubbers are typically used when the axis of
the axis is in the direction of expansion or contraction of the pipe.Therefore,
the snubber must expand and contract in the normal operation of plumbing work.
Snubbers have low resistance to movement at very low speeds.
- Mechanical
Snubber: Even
though the application is similar to the hydraulic snubber, the pipe
slowing is due to centrifugal breaking in the snubber. A split flywheel is
made to rotate the steel ball radially outward, for a faster speed. The
axial displacement of the snobber can be prevented by breaking the steel
plates together with the steel balls. Linear displacement of the main rod
acting on the ball-screw or similar device creates rotation of the
flywheel. It is also very expensive.
- • A shock absorber suddenly
absorbs the energy of impulses or destroys energy from the pipeline. For
crossings and dashpots, see Shock Absorbent
- • An insulated pipe support (also
known as pre-insulated pipe support) is a load-bearing member and reduces
power dissipation. Insulated pipe support can be designed for vertical,
axial and / or lateral loading combinations in low and high temperature applications.
Adequate insulation of the pipeline increases the efficiency of the piping
system. For insulated pipes without "cold" discharge in the
interior environment, see Insulated Pipe.
- Engineered
spring supports support specific loads, such as the weight of pipes,
commodities, flanges, valves, refractories, and insulation. Spring
supports You also allow the supported load to travel from its installed
state to its operating position through a predetermined thermal deflection
cycle.
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