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MAY-JUN 2019

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Part 2 INTECH MAY/JUNE 2019 37 SPECIAL SECTION crew, and one is conducted by the op- eration crew. Operation tasks are visual checks, visual inspections, or simple test and observation tasks. The mainte- nance crew PM tasks include detailed test procedures, calibration, and physi- cal testing that requires hand tools and communication devices. The objective of segregating the op- eration and maintenance tasks is to optimize the testing intervals and du- ration. Some tasks are simple, requir- ing a long time to prepare the work permit and the system that needs PM. Also, due to the internal mandatory re - quirements, the operations team must be involved in these PM tasks. Simple examples are stroke testing for control valves and emergency isolation valves and testing gas detectors. Analysis of PM findings There is great value in reviewing and analyzing PM findings in terms of preventing failures and maintaining equipment reliability and availability. This requirement is clearly addressed required preventive maintenance for SIS devices, do the following for each safety instrumented function (SIF): ● Review the SIL study and SIL verifi- cation report or conduct a study. ● Check the test interval (TI) for input and output devices recommended in the study report. ● Increase the TI to the maximum number (such as matching the plant total shutdown interval) and con- firm if the SIL requirement is still achieved. The preventive mainte- nance interval is based on the maxi- mum possible TI. ● For emergency isolation valves, if the TI for these valves (i.e., full stroke test) cannot meet the plant shutdown window, introduce partial stroke testing (PST) with a weight of 60 percent of the total stoke test. TI for the total and partial valve stroke shall then be clearly defined. Operator tasks versus technician tasks There should be two different PM tasks. One is conducted by the maintenance Instrument description PM task performer Online/ turnaround PM interval Task description MOV Operation Six months • Visual inspection, leak, damage, corrosion, enclosure and conduits tightness, integrity of fire-proofing. • Check handwheel, control panel, and remote-control modes. • Check alarm messages. • Conduct partial stroke, if MOV is SIS output device. Maintenance Two years • Grease per manufacturer recommendation (might be turnaround scope). • Change memory battery. Maintenance Turnaround • Full stroke • Do leak test. • Check cables/terminations connections and sealing. Process actuated Switches Operation Online Six months • Test functionality. Monitoring/ control transmitters Operation Online Yearly • Verify level transmitters' readings in comparison with local level gauges, infra- red camera, or by dip measurement. • Verify pressure transmitters' readings in comparison with permanently installed or temporary pressure gauges. • Verify temperature transmitters' readings in comparison with infrared portable device or camera or by inserting a temperature element inside a test thermowell. Flame detectors Maintenance Online Yearly • Visually inspect flame, leak, damage, corrosion, cables and connection, enclo- sure tightness. • Visually inspect cooling air and purging air. Gas detectors Operation Online Per manufacturer • Test the detector by a test gas and confirm correct alarm settings. Maintenance Online Per manufacturer • Conduct detector calibration. Study/define preventive and corrective maintenance operations Work planning Work scheduling Release assignment of the work order Carry out the work Closure of the work order Production of reports Reports analysis Figure 3. Maintenance work order Source: EN 13460 Recommended preventive maintenance for process instrumentation

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