Chemical Engineering December 2012 - 48

Engineering Practice
CPI MACHINERY:
Commissioning,
Startup and Piping
Practical notes on installation, piping, support,
layout, nozzle-loads, stress analysis, precommissioning,
commissioning, startup and
operation of rotating machinery
Amin Almasi
WorleyParsons Services Pty. Ltd.
W
hen it comes to rotating machinery
(pumps, compressors,
gas turbines, steam turbines,
turbo-expanders, and others)
operating in the chemical process
industries (CPI), installation, piping,
support, pre-commissioning, commissioning
and startup play crucial roles.
Machinery maintenance and repair
can be quite costly, and perhaps because
of shortages of skilled manpower,
particularly at remote site locations,
CPI plants have given less attention to
technical details for machinery installation,
piping and commissioning.
When one considers that the initial
investment costs for a rotating machine
can be in range of $200-2,000/
kW ($0.2-2 million/MW), whereas
daily production loss can exceed $1-2
million for many modern (and large)
CPI plants, one can see that it is necessary
to protect these machines by
doing an adequate installation, piping,
commissioning and startup job.
Machinery piping design
Although there are rules and practices
adopted for the design of general CPI
plant-piping in order to facilitate the
design and to avoid common errors,
there are usually some special rules or
exceptions when it comes to piping associated
with CPI rotating machines;
failure to properly handle these exceptions
and special rules can cause difficulties
in the installation and create
problems during the operation of the
rotating equipment.
The piping between a rotating machine
and suction or discharge equipment
(such as suction or discharge
vessel or cooler) is critical, particularly
when the operating temperature
is very different than ambient temperature,
and when the piping sizes
are large. Sometimes both the rotating
machine and the peripheral equipment
are located on the same side of
the pipe-rack. In that case the connecting
pipe is supported on the pipe-rack
and during operation, and because of
the thermal difference, the piping generally
moves away from both pieces of
equipment. This layout and piping design
offers relatively smaller loads on
the equipment nozzles.
In some CPI units where space is constrained,
the rotating machine and the
equipment (suction or discharge equipment)
are situated on opposite sides of
the pipe-rack. In this case, the center
point of the line running on the piperack
acts like a pivot point. The connecting
line on both sides of this center
point will move toward the equipment.
This arrangement induces marginally
more loading on the equipment nozzle
46 CHEMICAL ENGINEERING WWW.CHE.COM DECEMBER 2012
FIGURE 1. Shown here are examples of centrifugal
compressor impeller assemblies (rotor
assemblies) ready for shop balancing
compared to having equipment on the
same side of the pipe-rack.
In many CPI plants, the discharge
of a rotating machine (compressor,
pump or others) is usually routed to
an air-cooler or a heat exchanger (intercooler
or after-cooler). Usually the
rotating machine is offset from the
air-cooler (or the heat exchanger). In
this case, the vertical thermal expansion
is absorbed by the deflection of
the horizontal legs and similarly, the
thermal expansion of the horizontal
legs is absorbed by the deflection of
the vertical legs. Another arrangement
is when the machine and the
air-cooler (or the heat exchanger) are
located in the same line and relatively
close to each other. In such case, it is
necessary to provide enough flexibility
to absorb the thermal movements.
Loop(s) should be provided. To support
a loop, it should be routed on a nearby
pipe-rack (if possible), or else a proper
structural support should be provided.
The offset location of the machine to
the air-cooler (or the heat exchanger)
provides better piping flexibility.
Steam turbines or turbo-expander
turbines (whether cryogenic or hotgas
type) are strain sensitive and
operate at very high temperature
difference with relatively low allowable
nozzle loads. Usually, numerous
layout details should be considered to
provide the maximum possible flexibility.
Even a good layout can create
a problem if proper supporting is not
considered. Good recommendations
for the turbine piping are as follows:
1. A flexible piping arrangement may
encircle the turbine.
2. Line stops may be located in such
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Chemical Engineering December 2012

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