Hazardous or
harmless?
It happens unexpectedly and always at the wrong moment: when
the reciprocating compressor gave out in a refinery without
warning, due to major damage to the motion work, the spare
machine was, of course, in the midst of being overhauled. Due to the
failure, the hydrogen compression in the desulfurisation process was
reduced by 50% for several days. In addition to high repair costs for
the damage, the refi nery registered a substantial production loss. Emergency shutdowns of critical production machines are
always a nuisance, causing countless hours of overtime for
maintenance staff as well as often eating away at maintenance
budgets due to high repair costs. This is before one even considers
the lost production if there is insuffi cient spare capacity.
Where? What? Why?
One reason for the prolonged downtime was the extensive
troubleshooting required. The emergency shutdown was triggered by
a vibration sensor on the machine housing. Where, i.e. in which of the
four cylinders, was the root cause of the damage? What was
damaged? Can the alarm be trusted, or was it a false alarm? With the
typical single frame vibration sensor monitoring, it was not possible
to answer these questions; as such, no real informed decision could
be made. When the broken piston rod was fi nally found fi ve hours
after the shutdown, the most important question was asked: why did
the damage occur? How can such damage and related downtime be
avoided in the future?
Could the damage have been
prevented or at least minimised
so that the machine shutdown
could have been avoided? To fi nd
a solution, the operating company
immediately began evaluating
machine protection and online
monitoring systems, which
provide early damage detection
and effective protection and
thereby minimise the spread of
any damage and continuously
monitor and protect the
compressor. Ideally, it should also
be possible to record diagnostic
information in order to predict
and prevent future damage of this
sort through appropriate
measures.
Statutory requirements
All companies that operate process critical machines must set
themselves the task of evaluating the risks when operating the equipment. For the operator, a variety of laws and regulations require
the assessment and management of risks associated with the
operation of machinery, such as the international standard IEC 61511
Functional Safety: Safety Instrumented Systems for the Process
Industry Sector, as well as insurance guidelines and internal
company process standards.
Functional safety and the SIL classification
When expanding the provision of safety facilities, availability (and/or
functional safety) is an important criterion. Functional safety, i.e. the
requirement that the monitoring technology is fully operational when
required, can be certified by TUV Germany, for example. Based on IEC
61508 (functional safety) the system design is checked in detail, and/or its development process is actively accompanied by TUV experts.
The result is a certificate that is valid worldwide and documents the
safety requirements met by the monitoring system (Safety Integrity
Level (SIL)). SILs range from 0 - 4, with 0 being the lowest level of
availability.
Operators see this SIL classification as a key criterion in the
evaluation process for safety devices. In connection with this, the SIL
of protective equipment must also at least reach the required level
identified by the risk analysis (e.g. HAZOP). As such, for the user, the
scope of the certificate is worth a closer look. Have all monitoring
parameters that are necessary for effective machine safety been
classified? A SIL awarded for overspeed protection in turbomachinery
is useless in ensuring safety in reciprocating machinery. In this case,
for example, the continuous monitoring and analysis of vibrations on
the crosshead slide and the dynamic piston rod position are
important factors. In high pressure compressors in the LDPE industry,
for example, which compress ethylene to over 3000 bar, the position
measurement of the plunger is a crucial safety parameter for which
operators also allocate a higher SIL.
For operators, the expansion of machine safety facilities is only
acceptable if a guarantee is given that an increased number of
unjustified machine shutdowns will not be experienced. In order to avoid costly false alarms, plausibility checks of the measured signals
can be carried out for example. One or more checks of the analysis
results before the alarm is issued safeguard against instances where
loose cables, faulty (signal) lines or carelessness cause unjustified alarms or emergency shutdowns. These
quality characteristics are crucial for
the long term, successful application of
modern safety equipment.
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PROGNOST Systems - Intelligence on Duty
Internationally, PROGNOST Systems GmbH is the No.1 partner for companies who want to ensure safe, reliable, and economic operation of their reciprocating piston compressors. PROGNOST Systems offers Asset Performance Systems and services based on over 15 years of engineering experience in recording, analyzing and interpreting high-frequency status data for reciprocating piston machines. PROGNOST Systems offers the only system in the industry that records and analyzes status data in real time and compares them using "pattern recognition" based on actual experience. It provides machine operators with a timely analysis of the causes in the form of plain text information. This means that any reciprocating piston machine monitored by this system can be shut down fast an reliably with virtually no risk of false trips. With more than 400 current installations operating for over 80 renowned corporations around the world, PROGNOST Systems is the most successful supplier of online diagnostic systems for successful predictive maintenance strategies of reciprocating compressors. |
