Turbomachinery and Pump Symposia
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Browsing Turbomachinery and Pump Symposia by Author "Abraham, Edward A."
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Item A Systematic Approach To Case Recertification.(Texas A&M University. Turbomachinery Laboratories, 1996) Abraham, Edward A.; Coleman, Daniel E.; Bielecki, William S.; Turbomachinery Symposium (25th : 1996)Turbomachinery life expectancy, economic conditions, and plant capacity enhancements have created a need for vintage compressors to be reevaluated and re-engineered for operational parameters that may not have been incorporated in the original design. Aerodynamic revamps have been standard practice for optimizing flow conditions to today's processes. These changeouts have traditionally been limited to manipulation within designed pressure ratings. Recently, in addition to the aerodynamic enhancements, processes are requiring increased pressure levels. These new requirements and requests have posed questions and concerns which have not been of predominant importance previously. Integrity of the containment vessel, leakage of process gases, condition, and life expectancy at above design conditions must be addressed to make an informed comparison between a rerate and purchase of replacement equipment. The hazards and possible expenses of operating turbomachinery above rated pressures without a systematic and consistent verification process should be avoided. Hence, a new field has been undertaken by OEMs driven by equipment user request, to certify existing casings at increased levels in the safest and most reliable manner. The following guidelines have been produced to conduct such rerates with minimal risk to the compressor case and thus, the processes in which these machines play an intricate part: • Specific case testing history • Examine records and designs to determine if the casing has been hydrotested previously, or has been hydrotested to appropriate new condition levels. • Review of similar vintage machinery • Review designs of similar machines built in the same era to determine if ratings have ever been within appropriate levels. • Analyze the specific case design • Analyze the case with the use of modem and proven finite element methods to verify the integrity of the case design at elevated pressures based on blueprint dimensions. Review data with the user, discussing concerns of both parties and come to a consensus whether a hydrotest is feasible. • Inspect and review • Inspect the case per manufacturing blueprints to verify thickness and overall condition of the case and continuity of FEA model. With the use of magnetic particles, inspect the casing for indications and discontinuities which could endanger the casing during the hydrotest. Review the data and determine if continuation of testing is feasible. • Strain gauge casing • Place strain gauge equipment at key high stress locations based on FEA model to protest casing during hydrotesting. • Hydrotest case • With online strain readings, hydrotest casing to the appropriate levels. Carefully monitor the strain data to protect the casing from going beyond prescribed stress levels at the desired pressure levels. If stress levels appear to be approaching recommended limits, consensus should be made on whether to continue. • Recertification • After a successful hydrotest, rerate the compressor name plate and records for the new pressure level. The following paper will use a case history as a step by step example to show how case recertification has been accomplished in the safest possible manner with minimal risk to equipment.