Mid-term exams
There are many reasons to evaluate the performance of a plant beyond meeting contract guarantees. For example, a performance test might be conducted on an old plant to verify its output and heat rate prior to an acquisition to conclusively determine its asset value. Other performance tests might verify capacity and heat rate for the purpose of maintaining a power purchase agreement, bidding a plant properly into a wholesale market, or confirming the performance changes produced by major maintenance or component upgrades.
Performance tests are also an integral part of a quality performance monitoring program. If conducted consistently, periodic performance tests can quantify nonrecoverable degradation and gauge the success of a facility's maintenance programs. Performance tests also can be run on individual plant components to inform maintenance planning. If a component is performing better than expected, the interval between maintenance activities can be extended. If the opposite is the case, additional inspection or repair items may be added to the next outage checklist.
Whatever the reason for a test, its conduct should be defined by industry-standard specifications such as the Performance Test Codes (PTCs) published by the American Society of Mechanical Engineers (ASME), whose web site—www.asme.org—has a complete list of available codes. Following the PTCs allows you to confidently compare today's and tomorrow's results for the same plant or equipment. Here, repeatability is the name of the game.
The PTCs don't anticipate how to test every plant configuration but, rather, set general guidelines. As a result, some interpretation of the codes' intent is always necessary. In fact, the PTCs anticipate variations in test conditions and reporting requirements in a code-compliant test. The test leader must thoroughly understand the codes and the implications of how they are applied to the plant in question. Variances must be documented, and any test anomalies must either be identified and corrected before starting the test or be accounted for in the final test report.
A performance test involves much more than just taking data and writing a report. More time is spent in planning and in post-test evaluations of the data than on the actual test. Following is a brief synopsis describing the process of developing and implementing a typical performance test. Obviously, the details of a particular plant and the requirements of its owner should be taken into account when developing a specific test agenda.
Planning for the test
The ASME PTCs are often referenced in equipment purchase and/or engineering, procurement, and construction (EPC) contracts to provide a standard means of determining compliance with performance guarantees. The ASME codes are developed by balanced committees of users, manufacturers, independent testing agencies, and other parties interested in following best engineering practices. They include instructions for designing and executing performance tests at both the overall plant level and the component level.
Planning a performance test begins with defining its objective(s): the validation of contractual guarantees for a new plant and/or the acquisition of baseline data for a new or old plant. As mentioned, part of planning is making sure that the plant is designed so it can be tested. Design requirements include defining the physical boundaries for the test, making sure that test ports and permanent instrumentation locations are available and accessible, and ensuring that flow metering meets PTC requirements (if applicable).
After the design of the plant is fixed, the objectives of testing must be defined and documented along with a plan for conducting the test and analyzing its results. A well-written plan will include provisions for both expected and unexpected test conditions.
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