bluuebunny/crossref_metadata_2025 huggingface dataset:
Adhesion Effect on the Ultimate Strength of Sandwich Pipes
Authors: Castello Xavier , Estefen Segen F.
Published: October 2008

Sandwich pipes composed of two steel layers separated by a polypropylene annular can be used for deepwater oil&gas transportation. They combine high structural strength to resist external pressure with thermal insulation to prevent blockage by paraffin and hydrate. In this work, experimental tests and numerical models were employed to verify the influence of the inter-layer adhesion on the ultimate strength under external pressure and longitudinal bending of a sandwich pipe prototype. The maximum shear stress obtained from sandwich pipe specimens bonded with a specific adhesive indicated the adhesion levels to be adopted in the numerical simulations. Two contact models were employed to simulate the bonding and slipping conditions between layers, one adopting a friction model and the other including non-linear springs between metal and polymer nodes. The latter is an adapted solution to simulate both tension and shear loads. As expected for a sandwich structure, the structural strength is strongly dependent on the interface stickiness. The analyzed geometry is able to withstand a water depth up to 3,000 meters with a bonding strength corresponding to only 10% of the idealized perfect adhesion condition.
Fatigue Testing of Out-of-Plane Bending Mechanism of Chain Links
Authors: Rampi Lucile , Vargas Pedro
Published: October 2008

Three years ago, several mooring chains of an off-loading buoy failed after only 8 months of service. These chains were designed according to conventional fatigue assessment using API RP 2SK T-N curves to a fatigue life or 20 years with a factor of safety equal to 3 on life. Of particular interest is that the mooring chain failure underwent significant mooring chain motions that caused interlink rotations. Although traditionally neglected, these interlink rotations, when combined with significant chain tensions can cause bending stresses in the chain links (See Figure 1). This recently identified phenomena, Out-of-Plane Bending (OPB), explains the extensive fatigue damage causing the mooring chains of the off-loading buoy to fail [3][4][5]. References [3] and [4] document full scale tests of the OPB mechanism using a full scale test frame with the ability of applying inter-link rotation to a pre-tensioned chain. This testing confirmed that interlink rotations with a constant tension load can result in significantly high stresses. OPB stresses were measured on four different chain sizes of various grades: 1) 81 mm Studded Grade R3S, 2) 107 mm Stud-less Grade RQ3, 3) 124 mm Stud-less Grade R4, and 4) 146 mm Stud-less Grade RQ4, Grade R3 in [3] and [4], but no actual fatigue tests were performed. References [3] and [5] document analytical and computational efforts to explain and quantify the OPB stresses. In this paper, special focus is placed on obtaining actual fatigue failures of chains from OPB loading. Smaller chain sizes (40 mm) are used to accommodate the load limits of the testing frame. To mimic the actual loading as close as possible, sub size models of actual chainhawses were used in the testing. Two chainhawses were used: 1) the chainhawse has internal curvature where a link rests on the intrados, similar to offloading buoy that failed in eight months, and 2) a straight chainhase, a design that is in use today with demonstrated improved fatigue performance over the curved chainhawse. OPB stresses are measured and reported. Fatigue loading in the OPB mode was applied for several configurations. The two chainhawse exhibit very different stress levels and fatigue performance. An empirical relationship previously reported in [3][4][5] is compared to the measured OPB stresses with mixed results. Although limited in number, the fatigue tests indicate that overall the chain fatigue performance is at or above the B1 DnV curve. The BS B1 curve is also compared.
Model Testing of Ultra-Deepwater Floater Systems: Truncation and Software Verification Methodology
Authors: Baarholm Rolf , Fylling Ivar , Stansberg Carl Trygve , Oritsland Ola
Published: October 2008

Model tests for global design verification of floating production systems in depths beyond 1000m–1500m cannot be made directly at reasonable scales. Truncation of mooring line and riser models, software calibration, as well as extrapolation and transformation to full depth and full scale, are required. Here, the first two of the above three items are addressed. The paper emphasizes the important matters to be taken into account. The choice of proper procedures for the set-up and the interpretation, and consistent and well documented methods, are essential. A case study with a deep-water semisubmersible is presented. In general, good agreement between model test results and analytical results from time-domain coupled analysis of the floater system responses is found.
Laboratory Wave Modelling for Floating Structures in Shallow Water
Authors: Stansberg Carl Trygve
Published: October 2008

The analysis of moored floating vessels in shallow water requires special attention, when compared to similar problems in deep water. In particular, low-frequency wave drift forces need to be studied. Model testing is essential in validation of numerical prediction tools for these problems. Wave-group induced low-frequency wave components is an important part of the problem. Their reproduction in laboratories needs special attention. In general, two types of low-frequency waves are present: “bound” waves following the wave groups, and “free” waves propagating with their own speed. The former is included in second-order numerical codes for floater is included in second-order numerical codes for floaters, while the latter is normally not. Therefore, identification and possible reduction of the free components is of interest. A practical way to do this in a large wave basin is described in this paper. Results from generation of bi-chromatic waves without and with correction are presented. Corrected results show a clear reduction of the free wave component.
Independent Design Verification of SCRs for Ultra Deepwater IHF Development
Authors: Song Ruxin , Mekha Basim , Sebastian Abhilash
Published: October 2008

Steel catenary risers (SCRs) have been selected as the production riser solution for the Independence Hub Facility (IHF) in water depth of 8,000 ft in the Atwater Valley region of the Gulf of Mexico. This is the deepest water depth for SCRs to date. Initially, the gas production riser system consists of two 10-inch SCRs and four 8-inch SCRs attached to a deep draft semisubmersible as the host platform. Technip was selected to conduct independent engineering design verification for the production SCRs to verify the feasibility of their design and to identify potential design problems. This paper describes the design extreme challenges and uniqueness due to the ultra deep water, in addition to presenting the design verification methodology, procedure, selection of hydrodynamic parameters, pipe soil modeling, computer modeling, findings, and technical discussions. ABAQUS was the primary tool used for this design verification in association with other in-house riser analysis tools. Comparisons were made with the results from Flexcom. The independent verification analysis included storm analysis, motion fatigue analysis, semi-submersible heave-induced vortex induced vibration (HVIV) fatigue analysis, semisubmersible vortex induced motion (VIM) fatigue analysis, and riser interference analysis. Sensitivity study was carried out to demonstrate the accuracy of the simulation results and the robustness of the design. The independent verification shows that the riser top design is governed by the strength criterion due to large tension force. Fatigue governs the riser touchdown point (TDP) region, especially for the larger diameter SCRs. Among fatigue damage sources, fatigue caused by semisubmersible motion and VIM dominate. This paper concludes that the IHF SCR design meets the API RP 2RD design code requirements.
The Consideration of Welding Profiles in Fatigue Evaluation of Structure Design
Authors: Zhang D.
Published: October 2008

Structural fatigue plays a very important role in plating structural design. There are a lot of efforts in finding effective ways to improve the fatigue life of the plating structure. One of the means is to use welding profile. Welding profile is widely used in fatigue sensitive areas to improve the fatigue life of offshore platforms. How to evaluate the impact of welding profile to fatigue life calculation has always been the topic of engineering design. This paper will study the impact of different shapes of welding profiles to the fatigue life of structure through a real project example, and discuss its application in platform design. Different welding profiles have large impact on fatigue life; and an achievable good welding profile can improve the fatigue life dramatically. With the help of welding profiles, offshore engineers can achieve a more efficient design of the structure.
Wind Waves in East China Sea
Authors: Yan Yixin , Gao Jiayun , Tong Chaofeng
Published: October 2008

To know more about the hydrodynamic environments either in extreme conditions or in normal conditions, numerical simulation becomes more important due to insufficient field data. For large open sea, numerical models based on momentum balanced equation as mild slope equation or Boussinesq equation seems to be impractical. The third generation spectral numerical model was used in this discussion WAVEWATCH and SWAN to forecast wave conditions. Each model itself was nested and offered boundary conditions for smaller scale computation. WAVEWATCH provided extern boundary conditions for SWAN model computations. So wave parameter of different scale could be described so to offer wave parameters for engineering concerning. At the same time, some characteristics of third generation spectral wave model were depicted. Input winds were from NCEP analyzed data and QSCAT data respectively. The comparisons of computation with these data would show the spectral model characteristics of typical dependence on the wind condition. The output of WAVEWATCH under cyclone was also discussed in the paper.
Application of ADCPs for Long-Term Sediment Transport Monitoring in Arctic Environments: Examples From the Laptev Sea
Authors: Wegner Carolyn , Ho¨lemann Jens A. , Klagge Torben , Timokhov Leonid , Kassens Heidemarie
Published: October 2008

For offshore constructions the knowledge on sediment transport dynamics is essential and the quantification of suspended particulate matter (SPM) is of major importance. The Laptev Sea shelf is one of the largest Siberian shelf seas and ice-covered for about nine months a year. In order to use indirect measuring devices for the quantification of SPM concentration on the Laptev Sea shelf, optical (turbidity meter) and acoustic (ADCP; Acoustic Doppler Current Profiler) backscatter sensors were compared to assess their potential for the investigation of SPM dynamics in an arctic environment. To estimate SPM concentrations from optical backscatter signals, these were converted using the linear relation between the backscatter signals and SPM concentrations derived from water samples. Applying the theoretical interaction of sound in the water with SPM the acoustic backscatter signals were transformed adapting a previously established approach. SPM concentrations estimated from the backscattered signals of both sensors showed a close similarity to SPM concentrations obtained from filtered water samples. While the ADCP offers distinct advantages over the turbidity meter in that it allows measurement of the complete concentration profile, bottom location, and currents, co-deployment of both sensors are recommended for improved SPM measurements.
Implementation and Validation of Wave Watch III Model Offshore the Coastlines of Southern Italy
Authors: Benassai G. , Ascione I.
Published: October 2008

The spectral third-generation ocean wind-wave model WAVEWATCH III (WW3), operational since January 2005 at the Department of Applied Sciences of the University “Parthenope” (Italy), was adopted for simulating wave propagation in the Gulf of Naples. The model was coupled with PSU/NCAR mesoscale model (MM5), which gives wind forcing at 1-h intervals. The model was implemented using a four-nested grid configuration covering the Mediterranean Sea until the Gulf of Naples, the inner mesh with higher resolution (1 km × 1 km). The simulated directional spectral waves were compared with APAT storm wave data recorded in winter 2000 offshore the Gulf of Naples and with wind and wave data collected by Servizio Idrografico e Mareografico offshore the mouth of river Sele in the Gulf of Salerno. The implementation of the wave model with reference to the December 2004 storm on the coastlines of the Gulf of Naples gives evidence of the need of a regional wind-wave model for this orographically complex area.
Effect of Reeling on Welded Umbilical Tubing Fatigue
Authors: Buitrago Jaime , Doynov Krasimir , Fox Allen
Published: October 2008

One key component of umbilicals is the steel tubing carrying the pressurized fluids. During manufacturing and deployment of the umbilical, the tubing is subjected to a series of reeling and unreeling operations, resulting in a cumulative amount of plastic strain. For conventional design, this plastic strain is thought to limit the fatigue performance of the tubing, thereby limiting the number of such operations. This paper discusses an experimental program aimed at assessing the effect of the cumulative reeling strain on the fatigue life of girth-welded, super duplex steel tubing. In particular, the reeling simulation and fatigue testing equipment used are described and the experimental procedures are presented. Interpretation of fatigue tests indicate that (1) reeling degrades the fatigue performance of the welded tubing, (2) 75% of the B design curve may represent the 97.5% survival bound for tubing reeled up to 12% cumulative reeling strain, and (3) the fraction of the B design curve reduces to 40% for the same bound when the data from the 20% reeling strain tests are included. However, given the uncertainties involved, project-specific applications will require a fatigue qualification program for the specific tubing size, reeling history, and welding procedure at hand.
A Practical Algorithms on Health Monitoring of Submarine Pipeline and Its Application
Authors: Jin Wei-Liang , Shao Jian-Wen
Published: October 2008

Submarine Pipeline plays an important role in the development of Oil and Gas, especially when the field extends into the deep water. There is over 4,000 kilometers submarine pipeline in China Sea, and some of them encountered failure, and the accidents lead to loss of property and pollution of environment. Health Monitoring is a new concept and economical way to ensure the safety of pipeline. In the paper, a practical algorithm which includes abnormality detector, remaining fatigue life counter and vibration analysis, and its practical application program based on DELPHI, are both introduced. An AR (Auto-Regression) Model is adopted as a statistical tool to detect the abnormity of time-history signals, if the abnormity comes up, the vibration analysis is started up to give out the vibration information, which is the effective evidence to alarm the owner where the danger is and how the danger is. With the abnormity detector module, a remaining fatigue life counter always runs to counter the remaining life of pipeline, especially the welding of pipeline. The system is all developed based on Distributed Optical Fiber Sensor (DOFS). The system in the paper is now used on QK17-1 Oil field Submarine Pipeline in Bohai Sea, China.
Finite Element Modeling of the Failure Behavior of Pipelines Containing Interacting Corrosion Defects
Authors: de Andrade Edmundo Q. , Benjamin Adilson C. , Machado Paulo R. S. , Pereira Leonardo C. , Jacob Breno P. , Carneiro Edna G. , Guerreiro Joao N. C. , Silva Rita C. C. , Noronha Dauro B.
Published: October 2008

This paper describes the application of solid finite element models in the analysis of five tubular specimens containing interacting corrosion defects. Each of these specimens has been submitted to hydrotest up to failure as part of a previous research project. The specimens were cut from longitudinal welded tubes made of API 5L X80 steel with a nominal outside diameter of 457.2 mm (18 in) and a nominal wall thickness of 7.93 mm (0.312 in). The analyses accounted for large strains and displacements, stress-stiffening and material nonlinearity. The failure pressures predicted by the solid finite element models are compared with the failure pressures of these specimens measured in the laboratory burst tests carried out previously. Also the failure behavior of each specimen is described and illustrated by contour plots of stresses.
Model Tests: LNG-Carriers in Ice
Authors: Hellmann Jens-Holger , Rupp Karl-Heinz , Kuehnlein Walter L.
Published: October 2008

Approximately on third of the world’s known and not yet exploited reserves of natural gas are in Russia. The overwhelming majority of these reserves are in Artic and Subarctic areas. But not only in Russia, also in other areas like Canada and USA, natural gas reserves are found in harsh and ice covered environments. As a consequence, the LNG ship technology is going towards Arctic LNG-Carriers. New developments in ice navigation, winterization and ship sizes are generating a new exiting challenge for shipping and ship building industries all over the world. Existing ice class regulations should be only considered as a first guide for designing ice-going vessels. Because the future performance in ice covered waters of new developed LNG-Carriers needs to be investigated in much more detail, therefore ice model tests are imperative. It is common practice guiding ships in ice-covered waters by using one or two icebreakers for wider LNG-Carriers. The LNG-Carrier is following in the broken channel of about 1.25 to 2 times the widths of its beam. For the model tests a parental level ice sheet of target ice thickness will be prepared according to HSVA’s standard model ice preparation procedure. In order to obtain a defined friction coefficient between the ice and the model hull, HSVA applies a special paint composition to the models of ice-going vessels. The channel will be broken with the help of two stock icebreakers towed through the level ice generating the most realistic wide ice channel. The prime objectives of such ice model tests are: • Evaluation of the icebreaking performance in a wide ice channel, • Propeller-ice-interactions and • how the ice is transferred aside and below the vessel.
Abandon and Recovery Wire Rope Torsion Prediction
Authors: den Haan Joost , Krutzen Martijn P. M.
Published: October 2008

Adverse weather conditions during a pipelay operation may be a reason to abandon the pipeline and recover it when weather conditions allow it. The aim of the analysis presented in this paper is to predict the residual torque in steel wire ropes during abandon (pay-out) and recovery (pay-in). The basis of the analysis is the derivation of the stiffness coefficients when torque and tension are coupled by a torque factor. Based on a theoretical model a computer program is written to simulate in an incremental way the torsion in the ropes during pay-in and pay-out. The model includes transport of torsion as well as slip. The calculated residual torque allows for a risk assessment with respect to hockling.
Directional Return Period of Severe Storms Off Italian Coasts
Authors: Arena Felice , Meduri Saveria , Pavone Diego , Romolo Alessandra
Published: October 2008

The paper proposes the directional analysis of the severest storms recorded by the Italian Wave Measurement Network (RON). For this purpose the buoy data have been processed and all the storms have been selected; for the strongest storms, the direction of the sea states, which form them, has been analyzed. The directional return period of sea storms in which the maximum significant wave height exceeds a threshold is then obtained, by applying the ETS model. It is found that, for the prediction of extreme storms off Italy, it is possible to assume the duration of storms constant, with an error smaller than 4%.
Are There Different Kinds of Rogue Waves?
Authors: Liu Paul C. , MacHutchon Keith R.
Published: October 2008

Inasmuch as there is as yet still no universally accepted definition for rogue waves in the ocean, we think there might just be more than one kind of rogue waves to contend with. While the conventional approach has generally designated waves with Hmax/Hs greater than 2.2 as possible rogue waves, based on Rayleigh distribution considerations, there is conspicuously no provision as to how high the ratio of Hmax/Hs can be. In our analysis of wave measurements made from a gas-drilling platform in South Indian Ocean, offshore from Mossel Bay, South Africa, we found a number of cases that indicated Hmax/Hs could be valued in the range between 4 and 10. If this were to be the case these records could be considered to be “uncommon” rogue waves, whereas a record of Hmax/Hs in the range between 2 and 4 could be considered to comprise “typical” rogue waves. On the other hand the spikes in the Hmax data could have been caused by equipment malfunction or some other phenomenon. Clearly the question of whether or not there are different kinds of rogue waves can not be readily answered by theoretical considerations alone and there is a crucial need for long-term wave time series measurements for studying rogue waves.
Influence of Chord Stress on Axial Strength of Circular Tubular TX-Joints
Authors: Shi Yongjiu , Zhu Lei , Wang Yuanqing , Chen Hong
Published: October 2008

Normally the chord stress has a remarkable effect on the static strength of tubular joints and some research has been done on planar tubular joints such as X-joints. This paper analyzes the influence of chord stress on axial strength of multiplanar circular tubular TX-joints with FE package ANSYS. The numerical analyses conclude that the chord compression and tension both reduce the strength but in different extents. The chord in compression always reduces the strength. A low chord tension may not reduce the strength but a high chord tension may reduce the strength significantly.
Analysis of a Wedge Wave-Maker in a Tank of Finite Depth
Authors: McCormick Michael E. , Kraemer David R. B.
Published: October 2008

The analysis of the performance of a wedge-type wavemaker in a tank of finite depth is presented. The analytical technique is somewhat different than those applied previously to performance studies of wave-makers. Those techniques include the assumption of a product solution of the Laplace equation. This assumption leads to combinations of sinusoidal and hyperbolic functions of the wave number. Here, following Yeung (1981), both product and summation solutions are assumed. This assumption is based on the fact that the fluid beneath the wave-make is confined by the wave-maker, the backwall and the tank floor. From potential-flow theory, the streamlines of the oscillatory flow of this confined fluid are well defined. Yeung (1981), in a three-dimensional analysis of hydrodynamic coefficients of a heaving, vertical, circular cylinder, makes this assumption without stating so. Using the experimental data of Wang (1974) for comparison, results of the analysis are presented for various combinations of wave-maker draft, breadth and water depth for a triangular wedge. The results show that the effects of the evanescent waves are of second-order. Close to the wedge, results are presented resulting from the inclusion of four evanescent waves. The technique is of value because of its relatively simple form and its versatility.
Wave Loads of Slender Marine Cylinders Depending on Interaction Effects of Adjacent Cylinders
Authors: Sparboom Uwe , Oumeraci Hocine
Published: October 2008

Within a basic research programme at the Coastal Research Centre (FZK) in Hannover large-scale wave experiments were performed with single vertical and inclined Cylinders (Oumeraci, 2004). Additionally, cylinder groups were investigated with special reference to shelter and amplification effects depending on cylinder spacing. Nonbreaking regular and irregular waves as well as breaking freak waves were generated. The test set-up and some first results of the experiments looking to the maximum wave loads are reported in the paper.
The Application of Reliability Assessment Techniques in the Offshore Industry
Authors: Morandi Alberto C.
Published: October 2008

This review paper is a part of the Douglas Faulkner Symposium within OMAE 2006. It is structured along the following main topics: a) the potential for combining advanced numerical modeling of structures with structural reliability techniques, b) the need for better understanding the risks associated with abnormal environmental events and their potential impact on marine structures, particularly for offshore operations in the Gulf of Mexico. These are fields where Professor Faulkner’s pioneering efforts continue to be very relevant and an inspiration for future academic and industry research.
The Northern Sea Route in Focus
Authors: Schwarz Joachim
Published: October 2008

For many years researchers, oil- and shipping companies and governmental bodies in Russia and other northern countries have been working on the development to use the Northern Sea Route (NSR) for shipping oil and other resources out of the Russian Arctic. The EU-funded project ARCDEV (Arctic Demonstration and Exploratory Voyage), in which gas-condensate was transported in winter 1998 by an icebreaking tanker escorted by two icebreakers from the river “Ob” to western Europe did show the technological feasibility but also economical drawbacks. Due to the effects of the climate change, i.e. the significant decrease of the ice thickness and coverage in the Arctic, the Northern Sea Route has gained attention by potential users around the world. Further research on various topics of Arctic Transport Systems such as Route Optimisation, Navigation in Ice, Ship Design, Environmental Protection is being intensified and will help transport along the NSR to be profitable and environmentally safe. In a few years ship-transport of oil from the western part of the Russian Arctic will start year-round. The experience gained by these activities will be used to develop also the cargo transport along the entire Northern Sea Route from the Kara Gate to the Bering Strait as part of the 40% shorter sea way between Europe and East Asia.
Deviations in Predicted Condenser Performance for Power Plants Using HEI Correction Factors: A Case Study
Authors: Sunder Raj Komandur S.
Published: October 2008

The Heat Exchange Institute (HEI) Standards for Steam Surface Condensers are used to design and predict the performance of condensers for power plant applications. Since their inception, the Standards have undergone numerous changes to incorporate technological advances and revisions to various factors based on testing and operating experiences. Admiralty and copper-nickel (CuNi) tubes were very popular until the 1970’s. Subsequently, increasing concerns with the use of copper-based alloys in nuclear power plants as well as other factors led to specification and use of stainless steel (SS) and titanium. The first condenser designed with titanium tubes was put into service in 1977. In 1978, the HEI published the seventh edition of the HEI Standards for Steam Surface Condensers. The eighth edition was issued in 1984 followed by Addendum 1 in 1989. The ninth edition was issued in 1995 and Addendum 1 to the ninth edition was published in 2002. Notable differences between the ninth and seventh editions include: higher circulating water inlet temperature correction factors below 70.0 °F; for Admiralty, higher tube material and gauge correction factors for tube wall gauge below 16 BWG and lower values above 20 BWG; for 90/10 CuNi and 304 SS, higher tube material and gauge correction factors for tube wall gauge between 12 BWG and 24 BWG; and, for titanium, higher tube material and gauge correction factors for tube wall gauge above 18 BWG. Depending upon the tube diameter, material, wall gauge and the correction factors used for a specific condenser application and its operating range, there could be substantial deviations in predicted condenser performance and associated impact on output. Using a case study, this paper examines the use of the correction factors from the seventh and ninth editions in power plant condenser performance predictions. It provides recommendations for developing proper benchmarks and for ensuring optimum condenser performance.
A Study of a Single Stage Centrifugal Compressor
Authors: Xu C. , Amano R. S.
Published: October 2008

A low flow coefficient unshrouded centrifugal compressor would give up clearance very large in relation to the span of the blades, because centrifugal compressors produce a sufficiently large pressure rise in fewer stages. This problem is more acute for a low flow high-pressure ratio impeller. The large tip clearance would cause flow separations, and as a result it would drop both the efficiency and surge margin. Thus a design of a high efficiency and wide operation range for a low flow coefficient centrifugal compressor is a great challenge. This paper describes a new development of high efficiency and large surge margin low flow coefficient (0.145) centrifugal compressor. A viscous turbomachinery optimal design method developed by the authors for axial flow machine was further extended and used in this centrifugal compressor design. The new compressor has three main parts: impeller, a low solidity diffuser and volute. The tip clearance is under a special consideration in this design to allow impeller insensitiveness to the clearance. A three-dimensional low solidity diffuser design method is proposed and applied to this design. This design is successful to extend the low solidarity diffusers to high-pressure ratio compressor. It is demonstrated that the design is in a great success. The design performance range of the total to static efficiency of the compressor is about 85% and stability range is over 35%. The experimental results showed that the test results are in good agreement with the design.
L-0 Blades Failure Investigation of a 110 MW Geothermal Turbine
Authors: Mazur Zdzislaw , Herna´ndez-Rossette Alejandro , Garci´a-Illesoas Rafael
Published: October 2008

A last stage (L-0) turbine blades failure was experienced in a 110 MW geothermal unit after one year of operation period. This unit has two tandem-compound intermediate/low-pressure turbines (turbine A and turbine B) with 23-inch/3600 rpm last-stage blades. There were flexible blades continuously coupled 360 degrees around the row by loose cover segment at the tip and loose sleeve and lug at the mid-span (pre-twist design). The failed blades were in the L-0 row of the LP turbine B connected to the generator. The visual examination indicated that the group of 12 L-0 blades of rotor B on the generator side was bent and another group of 5 blades at 140 degrees from the first damaged group was also bent. The cover segments were spread out from the damaged blades and had cracks. Laboratory evaluation of the cracking in the cover segments indicates the failure mechanism to be high cycle fatigue (HCF), initiating at the cover segment holes outer fillet radius. The L-0 blades failure investigation was carried out. The investigation included a metallographic analysis of the cracked cover segments and bent blades, Finite Element Method (FEM) stress and natural frequency analysis (of blades/cover segments), fracture mechanics and crack propagation analysis. This paper provides an overview of the L-0 blades failure investigation, which led to the identification of the blades vibrations within the range 250 Hz to 588 Hz induced due to unstable flow excitation (stall flutter) as the primary contribution to the observed failure.
Innovative Approach to Leak Detection Solves Several Problems for Plant Operators
Authors: Speranza John
Published: October 2008

Power plants operating hydrogen cooled generators face a few challenges regarding the safe and reliable supply of hydrogen to their electric power generators. The mode of hydrogen supply differs from plant to plant depending on such things as distance from the central hydrogen supply or permit restrictions on the amount of stored hydrogen. There are number of plants that utilize single cylinders or transportable cradles of six, twelve, or eighteen cylinders. Others utilize large bulk systems that are either stationary high or low pressure tanks or transportable high pressure tube trailers. Subsequently the volume of hydrogen on a particular power plant site can vary from a couple hundred cubic feet to over a hundred thousand cubic feet. One of the chief safety concerns that many plant operators are faced with is the possibility that a major generator casing leak or facility piping leak occurs while a large volume of hydrogen is “lined up” to continuously feed hydrogen to the generator. The operator is faced with few options to mitigate this safety risk. One method used to mitigate this risk is to isolate the hydrogen supply and manually feed hydrogen into the generator when monitored closely by plant personnel. Other approaches include the implementation of mass flow meters to monitor the flow of hydrogen and alarm if a prescribed limit is exceeded and excess flow valves that are designed to limit the amount of hydrogen flow going through them. An alternate and innovative approach has been implemented at a handful of power plants recently utilizing a Proton Exchange Membrane (PEM) hydrogen generator. The generator not only makes the hydrogen needed to maintain pressure and purity within the generator casing, but also has the inherent ability to monitor demand and alert plant operators if a hydrogen leak occurs.
Second Law Analysis and Optimization of Organic Rankine Cycle
Authors: Somayaji C. , Mago P. J. , Chamra L. M.
Published: October 2008

This paper presents a second law analysis and optimization for the use of Organic Rankine Cycle “ORC” to convert waste energy to power from low grade heat sources. The working fluids used in this study are organic substances which have a low boiling point and a low latent heat for using low grade waste heat sources. The organic working fluids under investigation are R134a and R113 and their results are compared with those of ammonia and water under similar operating conditions. A combined first and second law analysis is performed by varying some system operating parameters at various reference temperatures. Some of the results show that the efficiency of ORC is typically below 20% depending on the temperatures and matched working fluid. In addition, it has been found that organic working fluids are more suited for heat recovery than water for low temperature applications, which justifies the use of organic working fluids at the lower waste source temperatures.
Low BTU Fuels Operation in Heavy Duty Gas Turbines: Ansaldo Energia Experience
Authors: Bonzani Federico , Maali Richard
Published: October 2008

The ever increasing energy demand on conventional natural gas and oil fuels has made the need much more important to use low BTU fuels to the maximum possible both in terms of economics as well as environmental well being. To this extent, Ansaldo Energia has made a major contribution to the development of advanced technology to burning various low BTU fuels in heavy duty gas turbines. Currently, Ansaldo Energia has four major low BTU projects dealing with IGCC technology as well as various steel mill gases. Each of these projects has its own features which all in all give a wide range of experience in development and operation of gas turbine fired with low BTU fuels. The gas turbines used in the projects were all manufactured by Ansaldo Energia and were of the V94.2K type. To date the units have accumulated over 150,000 EOH on low BTU fuels. The paper illustrates the design characteristics of the combustion systems installed at ISAB Priolo 500MW IGCC plant (Italy) and Elettra Servola 180MW (Italy) as well as the development of the systems to allow the successful operation of the plants. The paper will also touch up on: • The Eni Power Ferrera Erbognone 250MW IGCC plant (Italy) where the syngas burner development test campaign has shown very promising results and the plant is expected to start operation in December 2005. • The experience achieved on Buggenum Power Plant where at the request of the customer Ansaldo has improved the current burner to operate on uniquely available syngas fuel only. Ansaldo developed a new design of the current burner. The paper focuses on the main critical aspects of the development were overcome and to highlight the state of art achieved by Ansaldo Energia in this field.
Effects of Hydrogen Enrichment on Confined Methane Flame Behavior
Authors: Tuncer Onur , Acharya Sumanta , Uhm Jong Ho
Published: October 2008

Many land based power generation units presently operate on natural gas, whose major constituent is methane, and many of them would need to tackle the challenges due to a fuel switch towards synthesis gas in the near future. Operating conditions and stability of a pre-mixed gas turbine combustor is quite sensitive to the changes in the fuel composition. Behavior of a premixed confined hydrogen enriched methane flame is studied with regard to thermo-acoustic instability induced flame flashback, emissions, flammability limits and acoustics over a wide range of operating conditions. However, most emphasis is put on lean combustion, which is an industry standard method used to lower pollutant emissions by reducing adiabatic flame temperatures. Hydrogen addition extends the flammability limits and enables lower nitric oxide emissions levels to be achieved at leaner equivalence ratios. On the other hand, increased root-mean-square pressure fluctuation levels, and higher susceptibility to flashback is observed with increasing hydrogen volume fraction inside the fuel mixture. This phenomenon is mostly attributed to much higher burning speeds of hydrogen in contrast to pure methane. A semi-analytical model has been utilized to capture the flame holding and thermo-acoustically induced flame flashback dynamics for a pre-mixed gas turbine combustor. A simple linearized acoustic model, derived from the basic conservation laws, and a front-tracking algorithm based on the Markstein’s G-equation are coupled together in order to track the flame initiation front, which in turn yields in an understanding of dynamic flame holding characteristics. A limit cycle behavior in the flame front movement is observed during simulations due to a non-linearity in the feedback term that relates acoustic velocity to heat release. Sets of experiments including flashback speed measurements have been performed at varying fuel composition. Phase locked CH radical imaging measurements have also been performed in order to track the flame initiation front in time with respect to the dominant instability cycle. Computer simulations are performed to study flashback and combustor acoustics together numerically and it is observed that these are in good qualitative agreement with the experiments.
Coal Pulverizer Monitoring and Analysis: A Case Study
Authors: Zhang George Q. , Thulen Paul C.
Published: October 2008

This paper describes a case study of coal pulverizer monitoring and analysis. It represents the partial work of a project called “Mill Advisor” which investigated the common operational and maintenance problems of the coal pulverizer. Combining vibration monitoring and operational parameters such as flow rate, pressure drop and temperature measurement as well as grinding process modeling, this project intends to develop a system which closely monitors the operating condition of the pulverizer online, extracts the operational and maintenance knowledge, estimates the health condition of the equipment, and schedules maintenance based on the operation condition of the pulverizer and power generation demand. Specifically, this case study covers the following topics: 1)coal mill operational and maintenance problem identification; 2)sensing and data acquisition system design and implementation; 3)mill roller wear modeling and life span estimation; and 4)mill health indicator or availability proposition. On-site tests were conducted on a CE843RS pulverizer in a power plant.
Natural Gas Decarbonisation Technologies for Advanced Power Plants
Authors: Gambini Marco , Vellini Michela
Published: October 2008

In this paper two options for H2 production, by means of natural gas, are presented and their performances are evaluated when they are integrated with advanced H2/air cycles. In this investigation two different schemes have been analysed: an advanced combined cycle power plant (CC) and a new advanced mixed cycle power plant (AMC). The two methods for producing H2 are as follows: • steam methane reforming: it is the simplest and potentially the most economic method for producing hydrogen in the foreseeable future; • partial oxidation of methane: it could offer an energy advantage because this method reduces energy requirement of the reforming process. These hydrogen production plants require material and energetic integrations with power section and the best interconnections must be investigated in order to obtain good overall performance. With reference to thermodynamic and economic performance, significant comparisons have been made between the above introduced reference plants. An efficiency decrease and an increase in the cost of electricity has been obtained when power plants are equipped with a natural gas decarbonisation section. The main results of the performed investigation are quite variable among the different H2 production technologies here considered: the efficiency decreases in a range of 5.5 percentage points to nearly 10 for the partial oxidation of the natural gas and in a range of 8.8 percentage points to over 12 for the steam methane reforming. The electricity production cost increases in a range of about 41–42% for the first option and in a range of about 34–38% for the second one. The AMC, coupled with partial oxidation, stands out among the other power plant solutions here analysed because it exhibits the highest net efficiency and the lowest final specific CO2 emission. In addition to this, economic impact is favourable when AMC is equipped with systems for H2 production based on partial oxidation of natural gas.
Considerations for Ultra-Low NOx Operation in Combined Cycle Plant Retrofits
Authors: Fadda Dani , Reis Tom , Buzanowski Mark
Published: October 2008

High efficiency selective catalytic reduction (SCR) systems are designed as retrofits for heat recovery steam generators (HRSG) to comply with increasingly more stringent environmental standards. The retrofits are designed for continuous combined cycle plant operation with ultra low NOx emissions. These retrofits require special design considerations. Maldistribution (non uniformity) in the velocity profile within a high efficiency SCR system is one consideration which is the focal point of this paper. With a specified velocity profile (having a slight maldistribution), high and low efficiency retrofits are compared. It is demonstrated that, while the slight maldistribution in the velocity profile may significantly impact the performance of a high efficiency retrofit, it may be unnoticeable for a low efficiency retrofit.
Turning NGCC Into IGCC: Cycle Retrofitting Issues
Authors: Gutierrez Juan Pablo , Sullivan Terry B. , Feller Gerald J.
Published: October 2008

The increase in price of natural gas and the need for a cleaner technology to generate electricity has motivated the power industry to move towards Integrated Gasification Combined Cycle (IGCC) plants. The system uses a low heating value fuel such as coal or biomass that is gasified to produce a mixture of hydrogen and carbon monoxide. The potential for efficiency improvement and the decrease in emissions resulting from this process compared to coal-fired power plants are strong evidence to the argument that IGCC technology will be a key player in the future of power generation. In addition to new IGCC plants, and as a result of new emissions regulations, industry is looking at possibilities for retrofitting existing natural gas plants. This paper studies the feasibility of retrofitting existing gas turbines of Natural Gas Combined Cycle (NGCC) power plants to burn syngas, with a focus on the water/steam cycle design limitations and necessary changes. It shows how the gasification island processes can be treated independently and then integrated with the power block to make retrofitting possible. This paper provides a starting point to incorporate the gasification technology to current natural gas plants with minor redesigns.
Combined Cycle Performance Test Uncertainty Validation by Comparing Monte Carlo Analysis With Monovariate Perturbation Results
Authors: Spencer Kerri L. , Friedman Jeffrey R. , Sullivan Terry B.
Published: October 2008

This paper focuses on the calculation of the test uncertainty of an ASME PTC 46 [1], overall plant performance test of a combined cycle by two separate methods. It compares the combined cycle corrected plant output and heat rate systematic uncertainty results that are generated using monovariate perturbation analysis with the Monte Carlo method. The Monte Carlo method has not been used widely in power plant performance testing applications. It offers insights into the results of the Monte Carlo analysis method, which is less intuitive than the conventional method. This study shows that utilizing two distinctly different methods of calculation of test uncertainty serves to corroborate assumptions, or to isolate flaws in one or both methods. In developing the method for calculation of test uncertainty, the authors conclude that it is prudent to validate the calculation method of choice of test uncertainty, and to consider the correlations in measurement uncertainties. Also discussed in detail are the impact of correlated uncertainty assumptions, and recommendations on their application. Correlated uncertainty has not been extensively discussed in the literature concerning specific applications in performance testing, although it should be a critical consideration in any uncertainty analysis. Details of determination of instrumentation uncertainty, measurement uncertainty of a parameter, and calculation of sensitivity factors are included in this paper.
Mitigating Manganese-Induced Pitting Failures on a Stainless Steel Surface Condenser
Authors: Mellon Brian , McCain Douglas R. , Post Raymond M.
Published: October 2008

In early 2005, the 4-unit, 1200 MW Cottonwood Energy facility on the Sabine River in Deweyville, TX experienced a sudden increase in condenser tube failures and eddy current pit indications. Metallurgical analysis of failed tube specimens revealed the presence of a thin, hard manganese-rich coating, with intense pits propagating at breaks in the deposit. Successful mitigation of manganese-induced pitting and repassivation of the condenser tubes requires that the surface and pits first be thoroughly cleaned prior to implementing a manganese deposit control program. This paper reviews the successful cleaning process developed and implemented by Cottonwood Energy to remove manganese deposits from four stainless steel surface condensers. The cleaning procedure employed several novel features to ensure complete manganese removal, minimize environmental impact, reduce costs, control attack on the base tube metal, and ensure personnel safety. The paper also includes a discussion of corrective actions taken to prevent re-occurrence.