Hazardous or Harmless ?
It happens unexpectedly and always at the wrong moment: when the reciprocating compressor gave out in a refi nery 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 finally found five 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 find 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.
At the end of the first decade of the 21st century, some machine safety systems already meet the advanced expectations and users can report on actual experiences with such equipment. Although machine safety systems have been recently introduced to turbomachinery, such retrofi ts are rare on typical oscillating machinery such as reciprocating compressors and plunger pumps. For these types of machine, the relevant international standards only offer operators limited information as an aid to decision making. As it is mainly reciprocating compressors that are a major cost factor in maintenance budgets, due to high repair costs, particular attention is paid to such machines.
Until now, simple machine safety switches have often been used to monitor vibrating and rotating equipment in equal measure. Experience with reciprocating compressors has shown that broken piston rods and corresponding secondary damage cannot be suffi ciently identifi ed using this equipment. ‘Run’ or ‘stop’ no longer provides a basis for the safe and effi cient operation of machinery. his especially applies to machines that are critical for production, the number of which has increased greatly in recent years due to debottlenecking programmes and the inclusion of standby machines in regular production processes.
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