Mechanical plant inspection

Mr. Ken Robertson, President of Exxon Chemical Americas, discussed protective programs or mechanical integrity programs in a keynote address at the Chemical Manufacturer Association s Plant Inspection and Maintenance Forum in 1990. Indicating... 

Considering the many complex forms and mechanisms of corrosion damage, the limitations of individual plant inspection and monitoring techniques are considerable. The large number of variables involved also implies that no single method can be expected to be satisfactory in all possible conditions and environments. Many of these variables are described in other parts of the book. The factors involved in the corrosive environment have, for example, been introduced in Chap. 5, Corrosion Failures. 

The "Plant Life Assessment Network" (PLAN), was started on the 1/12/1997, established around EU funded research projects working in the area of inspection, instrumentation, monitoring, structural mechanics and maintenance. 

However, it is expected that this situation will change, since a number of novel "non-invasive NDT techniques are now becoming available. With some of these techniques, the time required for a shutdown can be reduced. Other techniques make it possible to perform inspections whilst the installation is in full service. It is obvious that the availability of such techniques could support the knowledge already available on operational parameters and degradation mechanisms, in order to base shutdown intervals on actual plant condition. 

In plant maintenance, the availability of quantitative and non-invasive screening NDT methods will reduce the time needed for shutdowns and increase the intervals between them. Modem NDT methods will become just as important a tool for Risk Based Inspection approaches and maintenance planning as operational parameters and degradation mechanisms already are. 

The American Society of Mechanical Engineers (ASME) United Engineering Center 345 East 47th Street New York, NY 10017 The ASME Boiler and Pressure Vessel Code, under the cognisance of the ASME PoHcy Board, Codes, and Standards, considers the interdependence of design procedures, material selection, fabrication procedures, inspection, and test methods that affect the safety of boilers, pressure vessels, and nuclear-plant components, whose failures could endanger the operators or the pubHc (see Nuclearreactors). It does not cover other aspects of these topics that affect operation, maintenance, or nonha2ardous deterioration. 

Unit checkout Check that required mechanical work has been completed, tags and blinds pulled, and temporary piping disconnected. Plant supervision must certify completion of work. Cancel all entry and work permits. Utility system has been commissioned. Check blind list and inspect lines close bleed, drain and sample valves. 

Inherently safer principles also apply to mechanical integrity requirements. Design plant modifications for ease and reduced risk in inspections, code compliance, and maintenance. For example, if one can check the pipe thickness from a platform, it is more likely to be done than if a crane is required. 

The aforementioned reviews and assessments were assimilated to characterize the effect of dielectric, rotational, and mechanical hazards on motor performance and operational readiness. Functional indicators were identified that can be monitored to assess motor component deterioration caused by aging or other accidental stressors. The study also includes a preliminary discussion of current standards and guides, maintenance programs, and research activities pertaining to nuclear power plant safety-related electric motors. Included are motor manufacturer recommendations, responses from repair facilities to a questionnaire, in-service inspection data, expert knowledge, USNRC-IE audit reports, and standards and guides published by the Institute of Electrical and Electronics Engineers (IEEE). 

All bought-in items of plant, especially those supplied without adequate materials certification, should be subject to random inspection. Portable instruments are available for many types of non-destructive examination, chemical analysis and mechanical testing of fabricated items of plant. 

The plant was reassembled in its normal 12-kW configuration with cathode spacers fitted. To provide a worst-case operating condition, the back pressure on the catholyte system was removed so that the spacer was the only mechanism that kept the membrane from contacting the cathode. The plant was run for 24 hours under these conditions, and the cell was dismantled to inspect the membranes. There were no signs of damage to the membrane surfaces and no signs of silver deposits. 

The gas plant that was destroyed had been initially commissioned in 1969. It had not undergone a mechanical inspection for six years. Shutdowns were initially scheduled at three-year intervals, but this interval was extended to five years. The plant had not been retrofitted with modern instrumentation. Pen recorders were prevalent in the control room and operating problems had been encountered with several control valves. Three months before the incident, ice plugging in lines caused several process upsets that were not fully investigated. A defective bypass valve had leaked gas to the atmosphere and had been awaiting maintenance up until one day before the accident. 

Piping Modifications One result of the inspection of the sample locations is a list of sample locations that will require modifications. The mechanical department will be required to make these modifications before the unit test is run. It is likely that the locations that are not typically used will be plugged with debris. The plugs will have to be drilled out before the test begins. Drilling out plugs presents a safety hazard, and those involved must be aware of this and follow the plant safety protocols. 

A mechanical engineer was assigned responsibihty for operation and maintenance of this plant, as his first responsibility. A major part of his time was devoted to inspections, or mechanical work at other locations, and for the past 3 years he has devoted very little time to this plant. 

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