consideration is made. Deviations and abnormal conditions
are the main focus and the study concentrates on how a
compressor package (or a station) will cope with abnormal
conditions, rather than how it will perform under normal
conditions. The study is comprised of a review of each sub-
system operation, examining each possible cause of a wide
range of abnormalities and their consequences.
HAZOP provides the opportunity for engineers and
personnel to think creatively and examine ways in which
hazards or operating problems might arise. To reduce the
chance of missing something, the study is carried out in a
systematic manner, using guide words to consider on each
line, item and each type of hazard in turn.
The results of a HAZOP depend heavily upon the
experience and attitudes of the team members and the
leadership style adopted. Members of the team should have
good experience, knowledge and skills, and should also have
the authority to approve actions decided upon.
HAZOP process
The HAZOP team focuses on specific portions of a system
called ‘nodes’. Generally, these are identified from P&IDs
of facility or package before the study begins. A process
parameter is identified, for instance pressure, and an intention
is created for the node under consideration. A series of guide
words is then combined with the parameter pressure to create
deviations. For example, high pressure, low pressure, etc. The
team then focuses on listing all the credible causes of the
deviation beginning with the cause that can result in the worst
possible consequence. Once the causes are recorded the team
lists consequences, safeguards and any recommendations
deemed appropriate. The process is repeated for the next
deviation and so on until completion of the node. The team
moves on to the next node and repeats the process.
A HAZOP study is a teamwork task that requires high
standards of teamwork and communication. A successful
study is based on the foundation of trust, respect and mutual
understanding for the unique contribution that each team
member brings to the study.
HAZOP study
The following checks are important for any machinery
packages:
)
)
Low and high pressures, low and high temperatures, low
and high speed and generally low/high values of any
parameters should be considered.
)
)
The “what if” analysis is an important tool to identify
hazards and operational problems.
)
)
Provisions for leak testing, inspection and maintenance
should be verified.
)
)
All vendor package battery limits should be properly
identified and suitable isolations should be provided.
)
)
Relief philosophy needs attention.
)
)
Commissioning and start-up requirements such as different
testing, cleaning, etc., should be respected.
It is recommended to start the HAZOP of each section by
a systematic perspective approach, which should be followed
by a line-by-line approach. For each system, it should be
verified how to isolate/de-isolate the system, allow gases
to be introduced safely into the system, use and manage
instruments, alarms, interlock systems, shutdown systems
and control valves. Routines for gas flows, information on
each package and mechanical equipment, interfaces, non-
return valves, lockable valves, etc., need also attains. For each
hazard or problem, the cause should be verified and the
consequences should be determined. The rank of risk should
be identified and then the safeguards, reservations and actions.
A brief machinery package layout review is usually included in
a HAZOP. Safety equipment, showers and fire-fighting facilities
are often reviewed. Access is an important issue for review for
any machinery or compressor package. Major isolation valves
require attention. Instrument stands and package control local
panel need proper access for operation.
Practical notes
The P&IDs are generally the most important documents
and the study should be conducted on an approved set. For
machinery and compressor packages, the vendor and plant
P&IDs should be ready. In addition, the package general
arrangement drawings (GADs) and completed data sheets for
the whole package scope, including lubrication oil system,
cooling system, etc., are required.
For an ordinary unit, the optimum number of persons for
a study team is five to eight. However, the case is different
for a complex machinery package where the manufacturer
representatives and rotating machinery specialists are
involved. For rotating machinery packages, the experience,
knowledge, representation and diversity required for an
effective study would require nine to 12 persons. In this
case, special precautions would be required to guide and
control discussions. Some experts might be required to act
as a reviewer rather than participate in actual discussions.
In a rotating equipment package HAZOP study, for example,
the rotating equipment expert is a reviewer, supervising
the discussions between the rotating equipment vendor
representative and the operation team leader, only involved in
discussions in rare cases of necessity. However, the presence of
the rotating equipment expert is absolutely necessary for such
a study.
Because of the large study team required for a rotating
equipment package, and also the complex nature of a meeting
that involves diverse experts, managing and controlling a
HAZOP study of this nature is difficult. The situations, if not
controlled and managed properly, might tend to adversely
affect the HAZOP meeting dynamics and effectiveness. Some
experts are nominated to attend the HAZOP meeting on a part
time basis to deal with specific issues. Some others might be
“on call”.
The HAZOP study team members should have the
relevant experience, knowledge and authority so that they
can make firm commitments and decisions in their areas of
responsibility on the issues and matters that will be discussed
during the HAZOP meeting. The stability in decision is
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World Pipelines
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SEPTEMBER 2014
