Maintenance criticality

The procurement system database must have an adequate number of fields for accurate part description, such as specification number and dimensions. There should also be a field to indicate whether the part is process safety critical, production critical, or maintenance critical. It allows the part to be flagged for special inspections or other considerations. Many electronic procurement systems are populated with inadequate or incorrect information. Job one is to clean them up. See Figure 1-3. 

Poor maintenance—critical spares were not arranged in time. 

Operating Procedures for maintenance should be in place for every system component that requires periodic calibration or/and preventative maintenance. Critical parts should be listed and should be available at the user s site. The procedure should describe what. should be done, when and what the qualifications of the engineer performing the tasks should be. System components should be labeled with the date of the last and next maintenance. All maintenance activities should be documented in the instrument s log book. Suppliers of equipment should provide a list of recommended maintenance activities and procedures (SOPs) on how to perform the maintenance. Some suppliers also offer maintenance contracts with services for preventative maintenance at scheduled time intervals. 

The authors of this paper believe that one of the main reasons for such a situation is the missing links between the maintenance discipline and other disciplines, especially technical safety. The various analyses done by safety and maintenance engineers often do not have clear linkage and can hardly be implemented in the practical sense. Moreover, a general inconsistency in Computerized Maintenance Management Systems (CMMS) may often be observed due to the overlapping data of maintenance criticality analysis and technical safety analysis. 

The audit activities often find deficiencies in the completion of maintenance activities and missing links between equipment and the safety barriers (Ratnayake et al 2012). It is essential to know the links and interconnections between maintenance and technical safety disciplines. The safety analyses and identification of safety functions should be transferred to the maintenance engineers in order to classify specific equipment accordingly. Results of safety-related analyses performed by technical safety engineers should be prioritized over results of maintenance criticality analyses. Clear links should be established in order to ensure that one discipline s output can be used as input for other disciplines. The mandatory Performance Standards (PS) required by the PSA may be seen as a potential major link between safety and maintenance disciplines (Fig. 9). 

The failure mode of an equipment item describes the reason for the failure, and is often determined by analysing what causes historic failures in the particular item. This is another good reason for keeping records of the performance of equipment. For example, if it is recognised that a pump typically fails due to worn bearings after 8,000 hours in operation, a maintenance strategy may be adopted which replaces the bearings after 7,000 hours if that pump is a critical item. If a spare pump is available as a back-up, then the policy may be to allow the pump to run to failure, but keep a stock of spare parts to allow a quick repair. 

For some cheap, easily replaceable equipment, it may be more economic to do no maintenance at all, and in this case the item may be replaced on failure or at planned intervals. If the equipment is more highly critical, availability of spares and rapid replacement must be possible. 

Preventive maintenance includes inspection, servicing and adjustment with the objective of preventing breakdown of equipment. This is appropriate for highly critical equipment where the cost of failure is high, or where failure implies a significant negative impact on safety or the environment. This form of maintenance can be scheduled on a calendar basis (e.g. every six months) or on a service hour basis (e.g. every 5,000 running hours). 

A suitable maintenance strategy should be developed for equipment by considering the criticality and failure mode, and then applying a mixture of the forms of maintenance described above. In particular, the long-term cost of maintenance of an item of equipment should be estimated over the whole life of the project and combined with its capital cost to select both the type of equipment and form of maintenance which gives the best full lifecycle cost on a discounted basis), while of course meeting the technical, safety and environmental specifications. 

This header has undergone repair after through-thickness cracking of an assembly weld after 108.000 hours of service, it is presently in operation and periodically submitted to ultrasonic inspection during planned maintenance shutdown. Continuous on-line AE monitoring of the integrity of critical welds is expected to contribute supporting continued and safe operation of the header until its replacement, platmed to take place in 1999. 

From the standpoint of commercialization of fuel ceU technologies, there are two challenges initial cost and reHable life. The initial selling price of the 200-kW PAFC power plant from IFC was about 3500/kW. A competitive price is projected to be about 1500/kW orless for the utiHty and commercial on-site markets. For transportation appHcations, cost is also a critical issue. The fuel ceU must compete with conventional mass-produced propulsion systems. Furthermore, it is not clear if the manufacturing cost per kilowatt of small fuel ceU systems can be lower than the cost of much larger units. The life of a fuel ceU stack must be five years minimum for utiHty appHcations, and reHable, maintenance-free operation must be achieved over this time period. The projection for the PAFC stack is a five year life, but reHable operation has yet to be demonstrated for this period. 

Pressure Vessels and Piping. Some of the most critical components of a chemical plant involve pressure vessels. A thorough knowledge of the American Society of Mechanical Engineers (ASME) Pressure Vessel Code (75) is essential for design and maintenance of chemical plants. Some states have their own codes, which usually conform closely to the ASME version (see High pressure technology Tanks and pressure vessels). 

Under mechanical and environmental stresses, composites are dimensionally stable. They maintain their shape and functionaHty, a critical requirement in such appHcations as dish antennas, constmction girders, and in appHance and business machines. Color and surface texture can often be molded into an FRP product for long lasting, low maintenance permanent surface appearance. Boats are a good example. The surface color is molded in and requires minimum maintenance, an advantage in saltwater environments. 

Monitoring by Electromechanical Instrumentation. According to basic engineering principles, no process can be conducted safely and effectively unless instantaneous information is available about its conditions. AH sterilizers are equipped with gauges, sensors (qv), and timers for the measurement of the various critical process parameters. More and more sterilizers are equipped with computerized control to eliminate the possibiUty of human error. However, electromechanical instmmentation is subject to random breakdowns or drifts from caUbrated settings and requires regular preventive maintenance procedures. 

Biological Antioxidant Models. Tea extracts, tea polyphenol fractions, and purified catechins have all been shown to be effective antioxidants in biologically-based model systems. A balance between oxidants and antioxidants is critical for maintenance of homeostasis. Imbalances between free radicals and antioxidants may be caused by an increased production of free radicals or decreased effectiveness of the antioxidants within the reaction system. These imbalances can be caused by the radicals overwhelming the antioxidants within the system, or by an excess of antioxidants leading to a prooxidant functionaHty (105—118). When antioxidant defense systems are consistently overwhelmed by oxidative reactions, significant damage can... 

As in the case of highways, considerable contention results from public maintenance of the inland waterways for recreation, flood control, and other purposes, as well as for the transportation of barges and other freight-carrying vessels. Because barge transportation of chemicals is considered essential to economical distribution, governmental toUs assessed for such maintenance ate of critical interest to the chemicals industry. 

Stress Relaxation. Copper alloys are used extensively in appHcations where they are subjected to moderately elevated temperatures while under load. An important example is the spring member for contacts in electrical and electronic coimectors. Critical to rehable performance is the maintenance of adequate contact force, or stabiUty, while in service. Excessive decrease in this force to below a minimum threshold value because of losses in spring property can lead to premature open-circuit failure (see Electrical connectors). 

Incorrect information can result if the probe is made of the wrong material and is not heat treated in the same way as the process equipment (as well as because of other problems). The probe must be as close as possible to the material from which the equipment of interest is made. Existence of a critical condition, such as weldments or galvanic couples or occluded cells in the eqmpment of concern, makes the fabrication, placement, and maintenance of the probes and monitoring system or critical importance, if accurate and useful data are to be obtained. 

Has the facility established an effective critical-equipment maintenance program (also termed mechanical integrity program) to prevent failures that would cause hazardous conditions ... 

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