Magazine article Risk Management

An Approach to Screening Faulty Plant Machinery

Magazine article Risk Management

An Approach to Screening Faulty Plant Machinery

Article excerpt

An Approach to Screening Faulty Plant Machinery

A significant portion of fires and explosions result from machinery failures, which can often be traced to deficient operational practices. Unfortunately, lost operating experience resulting from recent staff reductions in the refining and chemical industries have made it difficult for process plants to address these deficiencies. In addition, the assessment shows that some plants are incurring additional operating risks by improperly applying predictive maintenance concepts that delay inspections of critical machines.

A comprehensive reliability evaluation, which includes assessing operational, maintenance and organizational practices, is normally required to fully assess operational risks. However, a screening test can determine fire and explosion risks in process plants. Applying this test to plants that have undergone reliability evaluations indicates that those with passing grades have had significantly lower rates of machinery failures and fires than those that failed.

The screening approach consists of five questions that deal with operational procedures. Process plant operators should be able to provide specific written details on how the various functions are performed. Although the following screening questions and their underlying issues have been primarily applied in large refining and chemical facilities, they can also be used to evaluate operating risks in power plants and other process industries.

What are the testing procedures for alarms and shutdowns and how often are they performed?

Every plant has monitors that alert operators when its process exceeds allowable levels. The monitors also activate an automatic shutdown if these excessive levels endanger the plant. These vital alarm and shutdown systems are almost always tested when the plant undergoes general maintenance, but plant operators are usually reluctant to perform these tests while the plant is operating. Experience has shown that these alarm and shutdown functions should be tested at least every four to six months, which would require that these tests be performed while the plant is operating.

Unfortunately, plant operators often do not perform these tests during operation for fear that they will inadvertently cause a plant shutdown. This should not be a concern as long as the testing procedures are properly engineered and implemented. With the trend toward longer periods of uninterrupted operation and the existence of lower available levels of operating experience, systematic testing of these safety systems is even more imperative.

What surveillance procedures are utilized for evaluating the operating condition of machinery?

Surveillance procedures are an active function and so differ from conventional monitoring functions. Surveillance requires operators and technicians to test and evaluate machinery support and safety systems to assure they operate properly. Conventional monitoring, performed by most operators, is basically a passive function since it emphasizes transcribing instrument readings onto a log sheet. In recent years computerized process control systems have improved manual monitoring methods, but they still do not replace a comprehensive surveillance program.

Surveillance involves performing a physical inspection of possible leaks, loose components, unusual noises and the like; a log sheet analysis comparing values with defined safe ranges and identifying deterioration trends; tests of standby and emergency lubrication and sealing systems; and machinery operation analysis, which includes performance tests and vibration analysis. Operators who consistently perform these functions are more likely to identify and avoid problems before they endanger their plants.

What provisions exist to ensure that operators are using the proper procedures for starting and shutting down equipment?

A key part of an operator's training involves using proper start-up and shutdown procedures. …

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