Satoshi Hata

Investigation of Corrosion Fatigue Phenomena in Transient Zone and Preventive Coating and Blade Design against Fouling and Corrosive Environment for Mechanical Drive Turbines

For mechanical drive steam turbines, the investigation results of corrosion fatigue phenomena in the transient zone are introduced, including basic phenomena on expansion line and actual design and damage experience. These results were analyzed from the standpoint of stress intensity during the start of cracking. In order to resolve such problems, preventive coating and blade design methods against fouling and corrosive environments are developed. Detailed evaluation test results are given for coating performance using a unique test procedure simulating fouling phenomena and washing conditions. Finally, the results of the successful modification of internals and on-line washing results on site are introduced.

Measurement Of Dynamic Performance Of Large Tilting Pad Journal Bearing And Rotor Stability Improvement

Capacities at today’s modern ethylene and refinery plants have steadily increased, giving rise to a growing demand for larger compressors and more powerful drivers all of which require larger rotating parts. In keeping with this trend, it is critically important to optimize the design of rotors, impellers and journal bearings for improved rotor dynamics and high performance fluid dynamics. Rotor stability itself can be greatly influenced by maintaining shorter bearing spans through careful impeller design and the proper selection of journal bearings, such as load-on-pad (LOP) or load-between-pad (LBP) types, and determining the correct number of pads. In order to achieve a robust compressor design, case studies can be important tools in understanding the actual behavior and dynamic characteristics of large journal bearings. In this paper, the authors will present the results of a unique test to measure and compare the oil film profile, pressure and temperature along the bearing pad surface as well as the pad movement vibration for several types of journal bearings under rotating conditions. The dynamic data are compared with 3D finite element analysis/computational fluid dynamics (FEA/CFD) results for each type of journal bearing including rotor response comparison with experiment and analysis. The design and performance of improved impellers to create higher shaft rigidity and shorter bearing spans are also discussed. Finally, the authors will present their findings on optimum designs for large journal bearings and make recommendations on how to model journal bearings by separating each pad in the vibration system.

New On Line Washing Technique for Prevention of Performance Deterioration due to Fouling on Steam Turbine Blades (1st Report, Fouling Phenomena, Conventional Washing Technique and Disadvantages)

Mechanical-drive steam turbines have the heavy deposition of fouling materials on blade and nozzle path surfaces due to contaminated materials such as silica and sodium in steam. As a result, turbine performance tends to be deteriorated gradually. This first paper introduces this fouling phenomena and actual conventional washing procedure in order to prevent the fouling problem and its practical disadvantage by showing thermodynamics analysis. In the second report, the new online washing technology by water injection nozzles is introduced and the most important design factors of this washing system are discussed by showing the results of detail analysis and online washing test results.

Repair Technologies Of Mechanical Drive Steam Turbines For Catastrophic Damage.

Mechanical drive steam turbines play an important role as core equipment in petrochemical plants, and these turbines are protected for safe operation by an antioverspeed trip device, as well as other monitoring and protection systems. However, in some cases, a turbine will suffer severe mechanical damage due to improper operation or failure to activate the protection system as a result of human error. For urgent plant recovery and to minimize the duration of risky operation with no spare rotor, a damaged turbine has to be repaired in as short a time as possible. This paper introduces actual experiences in repairing and reviving catastrophically damaged turbine rotors through special welding procedures, based on element tests to find the optimized welding conditions, detailed strength calculations to confirm the integrity, and heat transfer analysis for proper heat treatment process conditions. These basic procedures are discussed to show useful data. The revived rotor of the extraction condensing turbine was placed back into the casing and operated. The turbine was uniquely modified in order to balance the required amount of power and minimize the repair time, to restart the plant as quickly as possible. The case study for this optimization is discussed by showing thermodynamic calculations, performance, and repair schedules. Root cause analysis for the process of the catastrophic failure is explained, for the integrated control system governing the control and operation positioner systems. INTRODUCTION Mechanical drive steam turbines play important roles in petrochemical plants. For safety in operation, these turbines are protected by an overspeed trip device, as well as other monitoring and protection systems. However a turbine still can suffer severe mechanical damage from improper operation or failed activation of protection systems, caused by human error and improper control of steam purity. When rotor damage does occur, a rotor is normally replaced with a spare rotor and the plant continues to operate with the running risk of having no replacement rotor. For urgent plant recovery and to minimize the operating time with no spare rotor, a damaged turbine has to be repaired in as short a time as possible. However, in cases where the damage is catastrophic and existing technology cannot repair the damaged rotor, it has to be scrapped and a new rotor must be fabricated. Consequently, the end user has to wait a minimum of six months to one year for a new rotor. In order to repair and revive a catastrophically damaged turbine rotor in emergencies in response to end user requirements, a new welding technique has been developed based on risk analysis of repair and laboratory element tests. In addition, to optimize welding conditions, the authors studied detailed strength calcula15 REPAIR TECHNOLOGIES OF MECHANICAL DRIVE STEAM TURBINES FOR CATASTROPHIC DAMAGE by Manabu Saga Manager, Turbine Design Section Shugo Iwasaki Acting Manager, Materials Laboratory Yuzo Tsurusaki Mechanical Engineer, Turbine Design Section and Satoshi Hata Manager, Turbine Design Section Mitsubishi Heavy Industries, Ltd. Hiroshima, Japan tions to confirm integrity, and performed heat transfer analysis for finding proper heat treatment process conditions. The authors introduce typical experiences in rotor repair by discussing useful results of the above analysis and the test results. FAILURE MODE OF STEAM TURBINES The failure damage modes of mechanical steam turbines are classified into main components for steam flow paths, rotating components such as rotors, grooves, disks, and blades, as well as stationary parts such as control valve bearings (Table 1). The basic root causes for each damage mode are listed. Severe damage modes include destruction of blades due to excessive centrifugal force, blade corrosion fatigue failure, and rotor bowing due to interference/rubbing in transient operations such as initial start up. Table 1. Failure Damage Mode. In Figure 1, a typical damage condition is shown in the steam turbine cross section. The first stage nozzle profiles are eroded at the trailing edges, due to contact with hard solid particles. The flow path of the diaphragm and blade profiles at the leading edges in the low-pressure (LP) high moisture section are eroded by water droplets. In some cases, the welded zone of the nozzles are affected by a combination of erosion and corrosion. Corrosion fatigue failure will occur in the blades of the LP section at the wet and dry enrichment zone under corrosive conditions, if proper water treatment is not performed during steady and transient operation, or if a corrosive chemical leakage occurs at a heat exchanger. Excessive contact friction at the rotor thrust collar will induce melting damage of thrust bearing pads, due to excessive thrust force from drain invasion. In other cases, lubricant oil additives may generate oil sludge contaminants on pad lubricating surfaces, and this will reduce bearing durability. If lubricant oil is not selected properly, in the worst case the rotor will rub against the bearings. TYPICAL FAILURE EXPERIENCE Rotational equipment manufacturers design, manufacture, and deliver steam turbines to customers based on well-proven technologies and supply experiences, and therefore they do not experience catastrophic accidents. However, this paper introduces typical catastrophic damage in using steam turbines. Figure 2 shows trends in rotation speed and key events from start to excess speed rotor damage, during the site-based solo running test. This extraction condensing turbine for driving a charge gas compressor is equipped with a position control backup system. The turbine was coasted up smoothly to a maximum continuous speed of maximum continuous rate (MCR) 10,279 rpm. Rotating speed was increased for a moment to electric overspeed trip speed (EOST); however, the trip interlock did not activate and speed Figure 1. Failure Damage Map. continued to increase, exceeding EOST speed. After the operating governor function key and the turbine control were shifted to the backup system, the governing valve suddenly opened from 12 percent to 60 percent in a no load condition and the turbine rotor was accelerated to 170 percent of MCR. Eventually, the turbine rotor disks and blades became damaged, resulting in oil leakage. Figure 2. Typical Failure Experience (Overspeed Burst). The control system for this turbine is shown in Figure 3. The control system has backup modules operating by position control, and this position control is used to supply the actuator output signal instead of the electric governor in the case of a governor failure. The backup system monitors the actuator output signals from the governor and controls two signals to switch the actuator signal source from governor to position control. Two backup modules are utilized for governing and extraction control valve actuators. As a result of detailed investigation of the system and signals, it was found that circulating current from the distributed control system (DCS) into the signal system of the backup modules caused the supply signal to the actuator to increase, thereby opening the valve. This caused a large amount of steam flow leading to the abnormal increase in rpm, and the interlock that should have performed an emergency valve close did not operate properly. Circulating current causes a 12 percent to 60 percent deviation of signals between the governor and governor backup module. The actual damage conditions are shown in Figure 4 and Figure 5. The second (high-pressure section) and third stage blades (lowpressure section) have broken off from the rotor grooves, and the disks and grooves are deformed at the first stage and other stages PROCEEDINGS OF THE THIRTY-FOURTH TURBOMACHINERY SYMPOSIUM • 2005 16 Components Damage Mode Root Causes Stationary Parts Rotating Parts Flow Path Parts Control Valve

New Technique For Online Washing Of Large Mechanical-Drive Condensing Steam Turbines.

Engineer for ExxonMobil Chemical Company, in Baytown, Texas. As Lead Specialist, he acts as the focal point for the ExxonMobil Chemical Worldwide Machinery Network and is involved with the development of machinery strategies for new and upgrade projects. He is also involved in the selection, operation, maintenance, and troubleshooting of machinery systems. Mr. Bhat received his B.S. degree (Mechanical Engineering) from Karnataka University in India, and an M.S. degree from West Virginia College of Graduate Studies. He is a member of ASME.

New Technologies Of Synthesis Gas Compressor Drive Steam Turbines For Increasing Efficiency And Reliability.

Recently, synthesis gas compressor drive steam turbines have required upgrading to increase efficiency and reliability for saving both operation and maintenance costs in many ammonia plants. This paper introduces the latest practical technologies to achieve very high performance. Examples include a highly unique assembly of integral shrouded blades, a new profile design procedure for both fluid loss reduction and increased strength against high-speed and high-stage power. Finite-element and computational fluid dynamics analysis results of new blades and nozzles are discussed while comparing experimental data from a cascade test and a rotating blades shaker test. These results are shown in terms of actual loss distribution, efficiency measurement, and vibration/stress mode on rotating blades including design criteria. Other useful applications of new technologies to reduce steam leakage and increase last stage blade performance are introduced. These involve modification of the exhaust casing and a new turning device. In particular, high speed and high loading are inevitable in synthesis gas compressor drive steam turbines. In order to improve operation reliability considering these factors, a special cooling design is applied for the thrust bearings to reduce the pad metal temperature. The results of this analysis and basic experimental data are discussed in detail. Furthermore, examples of actual job applications are explained, and high-speed balancing, mechanical running test, and site performance test results are shown. INTRODUCTION Synthesis gas compressor drive steam turbines are the most important rotating equipment in the field of methanol and ammonia plants. They are specially designed to cope with high speeds (exceeding 10,000 rpm) and high output powers (up to 40,000 kW) and have been applied as both end drive machines for high-pressure (HP) and low-pressure (LP) compressors. In the process of these plants, efficiency improvement is achieved through such means as a chemical catalyst, and as a result the required maximum power tends to decrease to less than 30,000 kW. Thus the efficiency of these turbines is focused on the design of the plant in order to minimize the margin on heat and flow balance for the most cost effective solution. In contrast, large capacity plants for methanol or new fuel are under consideration in a case study. For these mega plants, the synthesis gas compressor drive steam turbines with large output powers (exceeding 50,000 kW) will be required and realized in the near future. In this sense, these synthesis gas compressor drive steam turbines have to be continuously improved and upgraded to increase their efficiency and reliability for saving both operation and maintenance costs. As a starting point to this improvement, the performance of several existing extraction-condensing turbines actually in operation undergoes detailed analysis of their high-pressure and 75 NEW TECHNOLOGIES OF SYNTHESIS GAS COMPRESSOR DRIVE STEAM TURBINES FOR INCREASING EFFICIENCY AND RELIABILITY by Tomoyoshi Sasaki Manager, Turbine Design Section Satoshi Hata Manager, Turbine Design Section and Kyoichi Ikeno Mechanical Engineer, Turbine Design Section Mitsubishi Heavy Industries, Ltd. Hiroshima, Japan low-pressure sections. According to the analysis results, practical countermeasures are considered including the application of newly developed nozzles and integral shrouded blades (ISB) for speed control stage having mostly high-stage power. In this paper, the process of key components development is introduced by showing the results of finite-element analysis (FEA), computational fluid dynamics (CFD) analysis, lab evaluation tests, actual application, and performance evaluation based on onsite data. STRATEGY OF MODIFICATION The cross section of synthesis in a gas compressor drive steam turbine and the key features for improvement are shown in Figure 1 to make the concept of modification clear. The smooth flowpath from the inlet governing valve diffusers through HP and LP sections to the exhaust casing is designed by CFD in order to minimize losses. The first stage generates a maximum 12,000 kW and accounts for the greater part of the total output power. For this stage, the combination of nozzle and ISB with developed profiles is applied to increase stage efficiency dramatically, as explained later in this paper. The ISB with advanced profile is used for all other stages. In particular, the last stage has a bow nozzle to decrease secondary flow losses. In addition, a slant labyrinth seal is applied in the high-pressure side and extraction portion. This special seal can decrease the leakage by about 30 percent. The journal and thrust bearings have large thrust forces, high-pressure intensity, and heat load due to high-speed friction losses. For the purpose of decreasing metal temperature, back metal cooling for pads and copper back pads are applied. The latest material coating technology is used for improving reliability for long-term operation. A special coating is applied to the first stage nozzles and LP section blading to prevent solid and drain erosion. Figure 1. Strategy of Modification. DEPTH ANALYSIS OF PERFORMANCE A synthesis gas compressor drive steam turbine in actual operation at site was chosen for a case study, and a detailed performance analysis was carried out to make a loss map, considering the HP and LP sections separately. Loss of Flowpath Through Nozzle and Blade The calculated loss distribution for each stage is shown in Figure 2. From these analysis results, in the case of conventional nozzle and blade, the first stage of speed control stage accounts for a large part of the total loss, which consists of leaving loss, tip leakage loss, nozzle, and blade loss related to their profiles. The third stage of extraction pressure control stage loss is smaller than the first stage, but stage loss distribution ratio is almost the same—and these kinds of losses have to be minimized. For efficiency improvement, these control stages will be highlighted and the matching of nozzle and blade will have to be improved to prevent flow separation, flow velocity deceleration, and tip leakage. This will be achieved by profile modification and reaction control as shown in Figure 3. For decreasing losses effectively, the secondary flow loss of the nozzle and blade is considered as shown in Figure 4. The conventional blades shrouded by tenons have very high centrifugal forces for high-speed synthesis gas compressor steam turbines, and the nozzles are designed to have large gauging in order to minimize the blades height. For these large gauging nozzles, the profile cannot be optimized, and the nozzle exit velocity angle into the blade is so large that the stage overall efficiency tends to decrease. In the case of large stage power and large steam flow, this height restriction becomes critical, and to increase the blade strength, the application of ISB is one of the most important countermeasures. Figure 2. Actual Loss Analysis. Figure 3. Conventional Nozzle and Blade. Casing Internal Leakage Except for nozzle and blade losses, internal leakage through the split surface of diaphragms inside the casing will be considered in order to evaluate the turbine performance practically. The expected leakage ratio for each stage and related portion is described in Figure 5. According to leakage flow rate and energy level, the leakage from the HP section and extraction portion apparently affects the overall turbine efficiency. Based on the results of the above loss and performance analysis, reaching the target of performance improvement is addressed as shown in Figure 6. PROCEEDINGS OF THE THIRTY-FIRST TURBOMACHINERY SYMPOSIUM • 2002 76 NEW SEAL HIGH EFFICIENCY NEW NOZZLE NEW BLADE BOW NOZZLES SMOOTH PATH CFD DESIGN SMOOTH PATH CFD DESIGN

Technical Challenges for Compressors and Steam Turbines for Efficient and Sustainable Operation in Mega Ethylene Plants

Changing markets, industry demands for increased efficiency and long term operation, and availability of new technology have all contributed in development of more efficient and reliable turbomachines. The authors present ethylene plants trends, demonstrate the challenges faced by the turbomachinery equipment manufacturers and highlight various advancements in the turbomachinery technology. History maps are introduced for design advancements, verification tests, and application results in terms of transient fluid dynamics, thermodynamics, rotor dynamics, and blade vibration strength evaluation. In addition, after recognizing the need for long term operation and related typical damage and deterioration modes, the authors explain various practical technologies (such as effective on-line washing, flow path surface treatment, combination of anti-corrosion and erosion prevention, stage performance enhancement by partial component replacement, NDE techniques for both compressors and steam turbines, and a unique casing replacement technique on the same footprint for increasing capacity) used to provide more efficient and reliable machines.

Investigation of Steam Turbine blade failure

Blade failure was observed on a backpressure steam turbine (driving a centrifugal compressor) after it was in service for more than one year. This paper presents details of observations, inspections carried out and root cause analysis of the turbine blade failure.