SOUTHWEST RESEARCH INSTITUTE

Rotating Machinery Technologies

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For the past several years, Southwest Research Institute (SwRI) has evaluated a substantial number of gas turbines to diagnose root cause of failure, correct operating problems, or improve component life. Brief descriptions of some of the more significant problems resolved and research programs conducted are as follows:

Reciprocating Compressor Field Performance Testing Guideline Development

The intent of this project is to produce a guideline for performance testing of reciprocating compressors. This guideline serves to summarize multiple resources available, which offer recommendations and methodology for conducting performance tests. It will also present the different methods for performance testing as well as the advantages, disadvantages, uncertainty associated with, theory, and process of each method. Also included will be a detailed description of the type of measurements and instrumentation required for the testing including calibration, uncertainty, theory of operating, installation, and types of sensors used. Lastly it will give recommendations on the processing and presentation of the testing results. This project uses knowledge on reciprocating compressor performance testing, instrumentation, uncertainty calculations, reciprocating compressor thermodynamics, and effects of pulsations on measurements.

Compressor and Pumping Station Facility Integrity Program

The objective of this project is to develop a research road map for top causes of incidents at compressor and pumping stations. This is done by collecting, organizing and statistically analyzing incident data from the stations. From this data, the top causes of incidents were determined by ranking them by consequential and frequency factors. With the top incident categories identified, SwRI engineers evaluated the causes for possible research projects which could lead towards solutions or reductions of the incidents. The road map was developed by ranking these research projects by their importance and time necessary for them to be completed. This project uses Statistical analysis, database development, knowledge on compressor and pumping stations.

Experimental Determination of Heat Exchanger Effectiveness

The heat exchanger provided by the client was set up and tested within its operating range. Multiple operating points were tested in order to develop performance curves. A theoretical model was developed and validated with the experimental data. This was used to predict the heat exchangers performance within the operating range and determine its effectiveness curve. This project uses knowledge of heat exchanger theory and thermodynamics, experimental design, instrumentation, uncertainty analysis.

Cooling Basin Analysis

Analyses are being conducted to determine the optimum location and geometry of the basin extensions for the installation of two new pumps. This involves evaluating the flow of the system using CFD to determine the best geometry to avoid vortexing and cavitations near the suction nozzles. A hydraulic analysis is also done to see if there is adequate NPSH for the pumps. This project uses knowledge in CFD, pipeline simulations software, pump operation, and cooling system operation.

R&D Testing of Scroll Compressors

SwRI is working to provide failure analysis services in this project. A possible cause of failures is that copper particles from the manufacturing process are entering the compressor casing and contaminating the lubrication oil, causing excessive wear and premature failure of bearings and other components. SwRI is performing the compressor disassembly (taking care to not introduce new particles), doing SEM examination of damaged parts, removing particles from the oil, and using sieves to separate particles into various sizes and calculate the particle size distribution by weight. The particles will be compared with particles collected at various stages from the manufacturing process to determine a possible contamination source. This project taps knowledge in failure analysis, and particle analysis.

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Characterization of Liquid and Solid Deposits in Gas Pipeline Network

This project involves modeling of an entire pipeline network using commercial software to determine the possible location of liquids hydrocarbon condensation and accumulation. Results of the pipeline modeling were combined with fundamental two-phase flow equations using as a reference average operational conditions to calculate important parameters such as liquid hold-up, estimated liquid volume, expected flow patter and probability of liquid accumulation. This project uses knowledge in pipeline operation, compressor operation, gas quality, and two-phase flow analysis.

Recycle Loop Audit of Three Compressor Stations

The project serves to evaluate the recycle loop and anti-surge system of three compressor stations. Detailed hydraulic modeling of each compressor station was performed. Steady state and transient scenarios were simulated to determine if the anti-surge routine and recycle loop were sufficient for the required operational conditions. Critical emergency shutdown and normal start-up routines were simulated. Results provided various recommendations to improve the operation of the station and avoid harsh conditions in the operation of the compressor. This project uses knowledge in pipeline operation, and compressor operation.

PRCI (Pipeline Research Council International) Orifice Plate Testing

This project involves a test program to determine accuracy of set of 10-inch and 6-inch diameter orifice plates. The project serves to determine the influence of plate parameters on performance characteristics.

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Life Management System for Gas Turbine Blades—An Industry Consortium Program

SwRI developed methods and software to predict the life of gas turbine hot section blades for GE frame gas turbines. Extensive testing of materials of new and service-exposed components was conducted to develop pertinent material properties, which were used in the life assessment algorithm and software. The consortium participants were able to use these data in their turbine fleet life management programs to realize economic gains by prudently scheduling the inspection and maintenance intervals while maintaining good availability and reliability of their engines.

Root Cause Failure Analysis of Aeroderivative Engine Blades and Vanes

Failure analyses of cracked hot section blades, vanes, and shrouds were conducted through several individual investigations to identify the damage mechanisms in the engine components of most engine manufacturers. Mechanisms of failures or degradation include high-cycle fatigue (HCF), hot corrosion, creep, high-temperature oxidation, and thermal fatigue. Most probable cause of component failure was identified and corrective actions recommended to the turbine users. Further investigative programs were recommended as needed to better understand unusual root cause of failures.

Gas Turbine Hot Section Coating Life Assessment Model

In gas turbines, the life and integrity of the coatings applied to protect the components from environmental attack and degradation govern hot section life and maintenance intervals. SwRI developed state-of-the-art coating life prediction methods for several substrate/coating systems. This model has been calibrated with service experience and can be used to predict the life of specific coatings on turbine blades in service.

Qualification of Turbine Blade Material Substitution

A turbine owner sought to improve reliability and reduce maintenance cost of its large-frame gas turbine fleet by substituting materials and coatings. Materials, coatings, and vibration data were evaluated by SwRI to qualify an alternate material and design for the first row of hot section blades. Vendors were evaluated and qualified to manufacture the blades and apply selected coatings. The turbine owner realized significant increased blade life and reduced maintenance costs as a result.

Blade Walk Research

An industry-wide compressor blade failure problem on large-frame gas turbines was investigated in a $1,000,000 EPRI-supported program. A study of turbine overhaul procedures revealed several practices that can damage blade retention devices. SwRI monitored blade tip clearance, casing distortion, and thermal-gradient sensors during a three-year period of turbine operation. This computer-controlled monitoring showed that blade tip rubbing was also a major contributor to the blade walk problem. Tip rubbing was caused by inadequate cool-down of the unit after operation. Videos were developed to train utility personnel about measures to prevent damage during both operation and overhaul.

Balancing of Aeroderivative Power Turbine for Oil Pipeline Service

A power turbine experienced excessive vibration that was diagnosed by SwRI as excessive imbalance. Correction balance weights were calculated based on data recorded on site, and the problem was resolved by attaching weights to the coupling shaft. A support pedestal crack was also discovered, and a weld was repaired during a subsequent outage.

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Bearing Failure of Aeroderivative Gas Turbine

Failure of a main roller bearing was attributed to misalignment of bearing supports caused by uneven cooling and distortion of the turbine case. Resulting malfunction of the squeeze-film damper caused excessive dynamic loads and reduced bearing life. Adjacent roller and ball bearings sustained slight consequential damage. The failure cause was documented to support revision of alignment procedures.

Audit of an Air Force Turbine Blade Thermal Spray Coating Facility

SwRI conducted a detailed audit and qualification of several coatings on various aircraft components. Technical orders, work control documents, process operation sheets, coating qualification procedures, and coating specifications were reviewed. Several anomalies were discovered in the documents, and corrective actions were recommended. Results of a round-robin metallurgical evaluation were also reviewed. The review resulted in rejection of some coatings procedures because of quality problems.

Vibration Diagnostic System for Westinghouse 501 Gas Turbines

A data acquisition and diagnostic system was developed through cooperative EPRI and utility funding. Data acquired from an unattended system is analyzed for turning gear time, critical speeds, load-time integration, and other parameters. Peak levels are trended, and an expert system diagnoses the root cause of problems when excessive vibrations occurred. A user-friendly balancing program is built into the system. Several systems have been installed on units with telephone modem access for engineering and maintenance staff data access. At one site, diagnostic systems were installed on four units that were then interconnected with a LAN.

Vibration of Aeroderivative Gas Turbine in Pipeline Compression Service

A series of forced outages caused by excessive vibration resulted in reduction in gas transmission service and excessive cost for repair and maintenance. An on-site investigation revealed severe vibration jumps because of slippage at rotor joints, nonlinearity of a main bearing support structure, and defective signal cables. A correction plan was developed to improve cables, and a closer tolerance balance criterion was established to reduce rotor excitation levels.

Rotating Labyrinth Seal Windage and Leakage Tests

A 15,000-rpm seal test facility was fabricated for a major aircraft engine manufacturer, and tests were conducted on various compressor discharge seals. The test program provided critical data to verify predictive algorithms for controlling seal parameters to improve engine performance.

Damage Assessment of Aeroderivative Turbine Combustor Section

This investigation combined metallurgical evaluation of thermal-damaged surfaces and thermo-mechanical analysis of the energy impinging on affected diffuser parts. Analyses revealed melting of critical components because of uncontrolled combustion in inappropriate chambers. The combustion was caused by incomplete purging during startup.

Fretting Problems of Aeroderivative Hot Section Blading

Visual inspection indicated that blade vibration played a significant role in the blade fretting damage. Fretting sites are consistent with the location of disk fracture initiation that had caused early rejection of expensive parts. Blade vibration damper refurbishment was recommended.

Compressor Vane Failure of Aeroderivative Gas Turbine

Examinations of failed parts revealed severe fretting of the inner shroud segments of compressor vanes and high-cycle-fatigue failure of one airfoil. Diagnosis of turbine vibration revealed that rotating stall develops at low power operation, which was a preferred operating condition. It was deduced that long periods at low-power operation leads to fretting damage accumulation. The problem was resolved by adjusting the operating schedule to avoid rotating stall.

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High-Cycle-Fatigue of Aeroderivative Fourth-Stage Turbine Blade

A recurrent fourth-stage hot section blade failure problem was traced to blade tip rubbing due to alignment and tip clearance control issues related to design and installation. Revision of the design to increase tip clearances eliminated tip rubbing and blade failure.

Aeroderivative Gas Turbine First-Stage Nozzle Failure

Visual examination indicated several nozzles had severe distortion due to thermal distress. Flow testing revealed the distorted vanes were significantly deficient in cooling flow capacity. Thermal imaging of the nozzle revealed a blockage of internal flow passages. A metallurgical examination of the section vanes revealed flow passages blocked by an accumulation of calcium and silicone deposits indicating ingestion of fine dust particles. An improved engine air filter system was recommended.

Aeroderivative Gas Turbine Booster Compressor Blade Failure

A metallurgical examination revealed corrosion pitting had lowered the effective endurance limits of the blade material. Estimated vibratory stresses were compared with various other stages, which indicated the failed blade was likely to have acceptable vibratory stresses if stress concentration from corrosion pitting can be eliminated. A corrosion-resistant coating was recommended.

Fire Damage on an Industrial Gas Turbine

A fire in the compressor section damaged variable vane bushings and prevented the rotor from running after shutdown. SwRI investigation identified the most likely cause of the fire as leakage from fuel gas nozzles in the combustor section.

Aeroderivative Gas Turbine Bearing Failures

A series of four thrust and roller bearings from different turbines was examined. All bearings showed evidence of overheating that was attributed to excessive radial and/or thrust loads and improper lubricant quantity. Some damage was a result of improper material, heat treatment, or excessively reconditioned bearings. Improved quality control was recommended, and measures were taken to prevent lube oil contamination.

Design Analysis for Lube Oil System Modifications

The owners of an aeroderivative-driven gas pipeline compressor wanted to reduce cost by separation of the synthetic lube oil system for the gas turbine from a mineral oil system for the compressor. SwRI redesigned the lube oil system to provide proper flow control to both components in the rotating train.

Hot Section Failure of Aeroderivative Gas Turbine

Severe damage was found on the first- and second-stage blades and vanes with diminished damage on third- and fourth-stage airfoils. A single first-stage turbine blade failed in a root extension section, creating massive consequential damage that included burst-through of the turbine case. The isolated blade failure is attributed to blade material deficiency and excessive excitation from first-stage nozzles.

Blade and Nozzle Integrity in Aeroderivative Turbine for Power Generation Service

Repeated blade and nozzle failures were experienced in liquid fuel-fired engines. A root cause failure analysis found that fuel or airborne contamination caused hot corrosion failures of HP and PT blades and nozzles. A coating rainbow test program provided data to support alternate vane and blade coating recommendations to mitigate the hot corrosion problem. The new coatings improved hot section reliability, which has significantly improved turbine availability.

Failure of Aeroderivative Gas Turbine Compressor

Failure was traced to fatigue of a third-stage compressor vane airfoil that had initiated in a corrosion pit at mid cord. The loose airfoil caused subsequent secondary damage to the compressor and hot sections. The extent of damage was documented, and recommendations were made for repair and replacement. Coating recommendations were provided to mitigate future corrosion damage.

Flow Validation Testing of Aeroderivative Gas Turbine Compressor Inlet Scroll

A scale model of an inlet scroll was designed and fabricated; an induced draft fan was fitted and flow velocities were profiled. Slight modifications to the inlet, based on these data, provided a substantial decrease in flow losses and improved turbine performance.

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Burner Fatigue of Industrial Gas Turbine

etallurgical examination provided evidence that a combination of high-cycle fatigue and hot spots were the primary cause of damage. An investigation was conducted using dynamic pressure transducers and accelerometers located in the combustion section. The problem was identified as a combustor rumble problem created by pulsating flow in the fuel supply line. Pulsation suppression devices for the fuel lines were recommended.

Combustor Dome Erosion

An aeroderivative turbine combustor had experienced erosion at the dome due to injection of water for NO_x control. SwRI rig testing indicated that both corrosion and erosion affect the cumulative damage process. These findings redirected the OEM approach for improved combustor redesign.

Coupling Failures of an Industrial Gas Turbine Driven Compressor Train

Problems were identified as a result of design analysis errors in calculation of torsional critical speed. A strain gage telemetry system was attached to the coupling, which showed that three torsional critical speeds of various severities were within the turbine operating speed range. An interim fix was recommended to limit operating speed to avoid excessive excitation of the most severe torsional critical speeds until a redesigned coupling could be provided.

Service Degradation and Refurbishment Assessment of Hot Section Blades

Tests of hot section blades and coatings were conducted to understand the degree of degradation and to quantify the effects of service exposure on the blades. Metallurgical and mechanical tests were conducted by SwRI to determine the quality of the refurbishment process used by the OEM to reverse the blade damage. Recommendations were made to the turbine user regarding the suitability of the components for continued service.

High Vibrations on Large Industrial Gas Turbine for Power Generation

Two turbine-generator trains experienced high vibrations in operation and failure to start problems due to excessive vibration on passing through its critical speeds. A multi-speed, multi-plane rotor balancing developed by SwRI was used to reduce vibration to acceptable levels at critical speeds and at running speed.

Heat Exchanger Shell Vibration in Air Separation Plant

High noise, vibration, and pulsation of the first-stage cooler was associated with low inlet-guide vane settings. Tests involved resonant frequency of cooler shell by impact testing, mapping of acoustic mode shape throughout the cooler and compressor, mapping of circumferential acoustic modes at the inlet guide vane, and static pressure mapping across the IGV and other compressor locations. Vortex shedding excitation from flow separation at the IGV was determined as the most likely cause. Several alternative solutions were recommended, including throttling with an alternative flow restriction, redesign of the IGV, impeller or diffuser section, or detune dominant acoustic and structural resonance away from preferred excitation frequencies.

Diagnosis of Turbo-Expander Seal and Blade Tip Damage

A turbo-expander in a process plant experienced excessive vibration that caused damage to seals and blade tip rubbing. Modal testing confirmed that shaft resonant frequencies are within the operating speed range. A diagnostic investigation revealed that the rotor casing and supports were subjected to excessive loading due to thermal expansion of the connecting piping that were inadequately isolated by expansion joints. A redesign of the expansion joints relieved the problem.

Industrial Gas Turbine Crossfire Tube Bellows Failures

A metallurgical examination revealed crossfire tube bellows had failed. High-cycle fatigue, diagnosis of vibration from sensors installed on site, and subsequent testing at the SwRI Flow Facility revealed vortex shedding excitation that corresponds with bellows structural natural frequencies.

Gas Turbine Exhaust Diffuser Vane Failure

An on-site diagnostic investigation using high-temperature strain gages on the diffuser vane showed high strain levels that corresponded to natural frequencies identified by impact modal testing. Pulsation data revealed a strong acoustic source that corresponds to strain levels in the 200-Hz frequency range. These pulsations were attributed to vortex shedding mechanisms.

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SwRI can offer you a full range of capabilities and experience in rotating machinery technologies including becoming an extension of your engineering department. For more information about rotating machinery technologies, or how you can contract with SwRI, please contact Klaus Brun, Ph.D., at kbrun@swri.org or call (210) 522-5449.

machinery.swri.org

Contact Information

Klaus Brun, Ph.D.

Gas Turbine Technology

(210) 522-5449

kbrun@swri.org

machinery.swri.org

Related Terminology

gas turbines

turbomachinery

structural dynamics

rotordynamics