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11.1 Insulation
In the industrial processes it is necessary to maintain the temperature of
fluids, gases, and vapours during transit in pipelines. This means that heat
loss through pipe walls and equipment shells must be avoided or minimised
by certain mean. To avoid this heat loss pipes and equipments are insulated
with insulating materials like mineral wools such as rock, slag, glass, ceramic
and hair felt.
There are four main reasons for maintaining the temperature of a product in
pipeline transit:
• Many products are highly viscous or even solid at ambient temperature,
but can be reduced in viscosity or melted by heat to such an extent that
free flow is maintained and they can be easily pumped and controlled
• Other products require to be closely held at temperatures, which will
preserve their physical characteristics and avoid separation or a change of
chemical or physical state
• Pipeline heating is sometimes necessary to prevent freezing, particularly
in colder parts of the world where freezing of the product or perhaps
moisture particles in a gas stream can take place
• In other instances, pipe lines are heated to maintain a close control on
viscosity of the liquid prior to passing through a metering control unit
where a variation in density would upset the required accuracy
Typical products, which require heat application in pipe transit, are, resins,
polymers, waxes, tar, pitch, asphalt, sulphur, and many foodstuffs
Thermal insulating materials (including protection) should have:
• Resistance to attack by chemicals with which they may come into contact
• If this is not possible, then the insulation should be provided with a
resistant coating or jacket
• Resistance to moisture sufficient that they do not deteriorate under wet
conditions. This is important when operating in the open area.
• Cover to resist from vibration, mechanical shock, and abrasion, as most
insulants Insulations are mechanically weak, at least protection them
against damage
• Characteristics which allow them to be formed, as required, to effectively
insulate awkward pipe and fitting shapes
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11.1.1 Preparing an Insulation Specification
Because the plant as a hole is usually involved, it is seldom that
pipework alone forms a complete specifications. The specification has
also to cover all types of equipment, including heat exchangers, boiler
drums, dryer, distillation units, reaction vessels, pumps, and other
equipment. Similarly it is required to prepare Insulation Specification,
which is usually divided into two main sections, 1. Pipes and 2.
11.1.2 Data required to prepare Insulation Specification
• Pressure and temperature (If steam, saturated or superheated)
• Ambient air temperature
• Pipe outside diameters (Related to Standard Specifications where

• Pipe lengths
• Number of bends, valves, special fittings etc. and type of cover
• State any pipe fittings, valves, joints etc. which require periodical
removal of lagging
• Type of flange insulation required
• Type of insulation reinforcement
• Protective finishes required, related to possible leakage of oil or
corrosive chemicals, ingress of moisture, indoor or outdoor
operation, chloride stress corrosion
• If there is any fire risk
• Vibration or impact effects which will react on the piping
• Number of hours running/annum
• Number of years which plant will operate
• Cost of fuel and cost of heat distribution to point of insulation
• Guaranteed efficiency required, Expressed in terms of heat lost
• Insulation material to be employed
• Provisions for expansion to avoid crack deterioration of the
• Protection against moisture `leak through’ at pipe hangers
• Any special conditions of insulation application site, i.e. special
scaffolding, excessive heights, etc.
11.2 Heat Tracing
There are several ways of Heat Tracing to carry out pipe line heating, the
more common being as follows:
• Electric surface heating tapes or cables
• Jacketed pipe lines for use with steam and other heat transfer media
• External tracer lines-clip-on or welded on
• Use of heat transfer cements to improve rate of heat conduction
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The most effective and almost universal manner of producing all this information is
the pictorial dimensioned drawings, commonly termed `The Isometric Drawing’. This
type of drawing conveys a two-dimensional picture of a three-dimensional shape by
using the isometric draughting conventions of representing vertical directions by
vertical line on the drawing and representing horizontals to left and right of the
aspect point by lines included at 30° to the drawing sheet horizontal.
Ideally an isometric should show only one pipeline from start to finish and this should
be the aim in detail draughting. In practice, a minority of exceptional cases will be
found when a pipe is too complex to be clearly represented and must be broken
down into two or more simpler drawings; alternatively, some simple lines connected
together can best be shown on one combined drawing. In the latter case, however,
all the pipes must be to the same specification and, at a specification change point,
a new isometric should be started. The need to start and finish isometrics at
sensible points in the piping systems highlights the need, already noted, to locate
break points between separately numbered pipes in positions where new pipes

might be expected to start naturally.
Pipes and piping components are represented on the isometric by simple stylised
symbols, which are almost self explanatory and are commonly accepted. Some of
the commonly used symbols in Isometric Drawings are shown in FIG.6.
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Piping is a single bold line drawn along the pipe axis and typical symbols for other
items are shown. The shape of the pipe is shown correctly and all components are
correctly located relative to each other in the pipe, but no attempt is made to draw to
scale. Indeed, the reverse is true in that scale is completely sacrificed to clarity and
any complex portions (e.g., a control valve set) are drawn large enough to be easily
read and dimensioned, but long straight runs of pipe are foreshortened. Fittings are
drawn without regard to scale-for example, large and small valves may be drawn the
same size. A typical Isometric Drawing is shown in FIG.7.
• Check List for Isometrics
• General
o Study the layout checklist given in the previous section 8, for guidance
when the layout leaves some freedom in detailing
o Show all details with project north in the same direction
o Check certified equipment drawings for flange ratings
o Decide whether or not to include gasket thickness in dimensioning and
stick to the decision throughout the project. Usually gaskets less than
1/16 in. can be neglected; gaskets over 1/16 in. should be included
o Ensure pipe terminal co-ordinates and connecting nozzle identities are
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o Show P&ID and Piping Layout drawing numbers for reference on every
detail drawing
o Ensure all continuation points are highlighted and continuation drawing
numbers shown
o Try to show a reference dimension to a stanchion or floor beam to give
the erector a locating point, but do not show excessive pictorial detail
of adjacent plant or structures
o Indicate flow direction when pipes slope and when non-return valves
are fitted
o Show special fabrication requirements, e.g. x-ray or heat treatment if
o Draw boldly and simply. If using preprinted isometric grid paper, make
sure all drawn lines (including witness lines) are heavier and print
clearer than the grid lines
o Keep lettering and figures to about 3/16 in (5mm) minimum size and
easily readable
• Operation
o Look at each pipe individually to check that it can be vented or drained
either into another pipe or vessel or by fitting vent and drain points.
Never leave undrainable pockets in lines carrying hazardous or
corrosive liquids

o Make sure that valves and fittings are oriented correctly to flow e.g.
o Rotameters vertically upward
o Non-return valves work in correct direction of flow
o Globe valves have pressure underseat rather than on top
o Sight glass faces can be seen by operators
o Strainers are installed to makers instructions
o Ensure valve hand wheels and instrument faces point towards (but do
not foul) Operating areas and put note on detail drawing for erector’s
o To prevent solids depositing in glands, try to avoid mounting valves
with spindles horizontal or pointing downwards
o Try to avoid installing valves in vertical lines-the leg of liquid left in the
line above the valve when the valve is closed cannot easily be drained
o Put valves in off takes from pipe racks or racks of pipes outside the
pipe/supporting steelwork area for easy operation
o Leave room for temporary strainers in pipes to trap residues left in the
pipes during construction
o Check if any special cleanout procedure is required for compressor
feed pipes, instrument air or similar lines, and give details on drawings
o Avoid air pockets in pump suction lines. Reducers, if used, should be
eccentric type
o Try to leave 1 ½-3 diameters of straight pipe leading in to pump
suction to reduce eddies entering pump. On critical suction duties
(e.g., hot, volatile liquids or pumps with large suction lift), increase
straight length to maximum amount possible.
o If possible provide equal flow patterns to both pumps when installed
spare pumps are used
Page 39 of 48
o Fit priming connections to centrifugal pumps which draw liquid from
tanks blow pump levels-the pump cannot generate suction until the
impeller is running in liquid
o Consult instrument engineers for details of instrument mounting
generally, but some simple rules are:
o Put tapping for pressure point at side of pipe rather than top (this
forms an air pocket) or bottom (which allows solids to deposit on
o Thermometer pockets (usually ½ in. or ¾ in. nominal bore) should
be installed at a change in direction in the pipe either by fitting a tee
connection or a socket fitted into an elbow. Obstruction of flow is
minimized by this method of installation-for example a ½ inch
nominal bore pocket occupies only 29 per cent of the flow area of a
1 1/2inch pipe
o Thermometer pockets can cause serious obstruction to flow in lines
2 in nominal bore and below when installed across the pipe, e.g.
the ½ in. nominal bore pocket occupies 65 per cent of the flow area
of the 1 ½ in. nominal bore pipe. In these cases an enlarged
section should be provided

o Steam trap piping is important and maker literature should be
consulted for detailed guidance – valuable data are provided by
reputable manufacturers. In particular, observe the following:
o Always provide a strainer before a trap-no trap will work with dirt
under its seating
o Fit an isolating valve before the trap-otherwise, the plant has to be
shut down to maintain it
o On duties where good condensate removal is vital, fit a valved
bypass around the trap-the plant can then discharge condensate
while the trap is being maintained
o The discharge from every trap should either be visible (at a tundish
or sight glass) or capable of being tested by discharge to
atmosphere, otherwise it is impossible to check trap operation
o If traps discharge to a pressurized condensate main, an isolating
valve should be installed to protect maintenance workers and a
non-return valve fitted to prevent condensate blowing back from the
pressurized main when the trap is not discharging
o Trapping points in pipes should be taken off bottom of the pipes, to
prevent condensate being carried over the trapping point

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