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Root Cause Analysis Of A Gas Turbine
Page 1
"FAILURE ANALYSIS OF GAS TURBINE BLADES FRACTIONATION PLANT AND
OFFICE JOSE"
Case: Nuovo Pignone PGT5 model of D4-81 001 Turbocharger Plant Division and Office Jose.
This work was the development of Root Cause Analysis for
Gas Turbines Nuovo Pignone, PGT5 model of D4-81 001
Turbocharger Plant Division and Office Jose, to find the roots
of physical, human and induced latent the critical flaw.
Author: Ing. Manuel López Anuel Co-Author: Ing. Manuel García
AÑO
2009
Root Cause Analysis Of A Gas Turbine
Page 2
ABSTRACT El presente trabajo consistió en el desarrollo del Análisis Causa Raíz a la turbina a gas marca Nuovo Pignone, modelo PGT5 del Turbocompresor D4-81001 de la Planta de Fraccionamiento y Despacho Jose, con el fin de encontrar las raíces físicas, humanas y latentes que indujeron a la falla crítica. This work was the development of Root Cause Analysis for Gas Turbines Nuovo Pignone, PGT5 model of D4-81 001 Turbocharger Plant Division and Office Jose, to find the roots of physical, human and induced latent the critical flaw. Para el logro de este objetivo se describió el contexto operacional del equipo para diagnosticar los parámetros de funcionamiento y de diseño de la turbina a gas. To achieve this objective, the operational context described to diagnose equipment operating parameters and design of the gas turbine. Seguidamente se realizó un Análisis de Criticidad para identificar los modos de falla más críticos que tienen lugar en el equipo; se procedió a realizar el Análisis Causa Raíz propiamente dicho, estructurado por un Árbol Lógico de Fallas basado en la información obtenida de entrevistas no estructuradas al personal operativo; las hipótesis obtenidas fueron validadas mediante una exhaustiva investigación que incluyó la revisión de registros de fallas y la realización de una prueba no destructiva de materiales (PMI), deduciéndose como raíz física de la falla crítica, a la desviación en la selección del material constituyente del tornillo de cierre de la pieza de transición del eje de alta presión de la turbina, derivándose de este hecho las acciones pertinentes para minimizar la ocurrencia de dicho evento. Then made a Criticality Analysis to identify critical failure modes that take place in the team, was performed Root Cause Analysis proper, structured by a Fault Tree Logic based on information obtained from unstructured interviews to operational staff, the hypotheses obtained were validated by an exhaustive investigation that included review of records of failures and the realization of a non-destructive testing of materials (PMI), less as a physical root of the critical flaw, the deviation in the selection of constituent material of the screw shaft transition piece high-pressure turbine, as a result thereof the relevant action to minimize the occurrence of the event.
Root Cause Analysis Of A Gas Turbine
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NOMENCLATURE % Percentage ° C Degrees Celsius ° F Degrees Fahrenheit AC Criticality Analysis Accro Extension of Cryogenic Complex East ACR Root Cause Analysis ANSYS Swanson Analysis Systems BD Barrels Daily CADAFE Management Company Limited and Electrical Development Cr Chrome Eq Equation CN F Correction factors Faith Iron FEM Finite element techniques Fig Figure GCV Gas Control Valve HMI Human Machine Interface Hp Horsepower HP High Pressure hrs hours I Class Range IGV Gas Inlet Vane In Inches ISO International Standard Organitation KV Kilovolt LGN Natural Gas Liquids LP Low Pressure LVDT Linear variable differential transformer MCC Reliability Centered Maintenance MmHg Millimeters of mercury Mo Molybdenum MPa Mega Pascal N Number of Classes Or Nickel
Root Cause Analysis Of A Gas Turbine
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P Pressure PCD Speed Axial Compressor PDVSA Petroleos de Venezuela Sociedad Anónima P I ISO Power PMI Positive Material Identification P N Corrected net power Psia Pound per square inch Rpm Revolutions Per Minute s Seconds S Entropy SAO Management Systems and Data Processing SIAH Industrial Safety, Environmental and Occupational Hygiene SRV Speed Ratio Valve TFS Time Out of Service You Titanium T Temperature STPP Average Time Out of Service V Volume Va Highest value Vb Lowest value
Análisis Causa Raíz de una Turbina a Gas
Page 710/05/2010
INTRODUCTION The gas turbines are teams of great importance within the oil industry. They are
responsible for delivering the power required to drive generators, pumps and
compressors which are used in generating electricity, necessary for operation of
processing plants, and maintaining production flows with order to obtain final products
that produce wealth to the nation.
The country has many oil and gas plants, which have turbines from different
manufacturers and models, such is the case of the Fractionation Plant and Jose
Office that as primary industry in the Venezuelan economy seeks to maintain its
facilities in optimum condition and production processes that ground is available to
absorb change according to security needs, hygiene and environment which it faces.
Turbomachinery Management has a staff trained in the maintenance area and a fault
log history of the teams he owns. Currently the organization has implemented
maintenance policies in order to preserve the assets involved in production systems,
reducing the risk of equipment failure, resulting in security for both facilities, the
environment and human resources inherent operational process.
Maintaining a significant contributor in reducing the risk of failure in industrial
systems, to improve the status of the different frequency components under defined
intervention. These may be recommended by the manufacturer, custodians of the
equipment or the expertise of professionals in the field.
The specific application of this work focuses on identifying the root physical, human
and latent induced a real failure in a gas turbine. As a point of departure was
necessary to be aware of the operating principle of the equipment, how to identify the
variables and operational parameters of the same. After determining the critical
flaws, to know the impact generated at the operational, safety and environmental, in
order to identify the root physical, human and latent critical failure through the
Análisis Causa Raíz de una Turbina a Gas
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development of a Fault Tree Logic. These techniques helped to create and propose a
set of actions and strategies to ensure increased effectiveness of the machine.
THE PROBLEM Geographic Location
Cryogenic Complex East is located in the states of Anzoategui and Monagas,
consists of three floors of natural gas extraction, one of them is located in San
Joaquin, 12 km west of the city of Anaco, Anzoátegui state, the second located in
Santa Barbara and 65 miles from the city of Maturin, Monagas State and a plant
found in Jusepin, Monagas State, these plants process natural gas to produce LNG.
Cryogenic Complex East also has a Fractionation Plant and Office, located in the
Jose Antonio Anzoategui Petrochemical Complex (Jose) on Highway Rómulo
Betancourt Píritu between the cities of Barcelona and north of the state of
Anzoategui, See Figure 1.1. Its operating philosophy is to receive via pipelines from
the NGL extraction plant in San Joaquin, Santa Barbara Jusepín divided up in:
Propane, Normal Butane, Isobutane, Pentane, residual fuel and naphtha, stores and
dispatches the national market and International.
Figure 1.1. Geographic location of the Cryogenic Complex East.
Source: Office Fractionation Plant and Jose. (2009)
Análisis Causa Raíz de una Turbina a Gas
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Mission, Vision & Quality Assurance Company
Mission. Transporting, fractionate, store and ship safely, timely and reliable Natural
Gas Liquids (NGL), supported by competent human capital within an organizational
environment favorable in harmony with the environment, with updated technology,
adding maximum value to the business of Natural Gas Liquids (NGL)
Vision. To be the organization that values the business of Natural Gas Liquids
(NGL), applying global best practices in harmony with the environment, and
contributing to socioeconomic development of the country.
Quality Policy. The Division and Office Management bases its Quality Policy in the
commitment to split the Natural Gas Liquids, storage and dispatch promptly to the
quality required by our customers and meeting the requirements of Safety, Health
PDVSA and Environment, through effective quality system and continuous
improvement of processes.
PROBLEM
PDVSA is one of the biggest companies in the country for its economic contribution
and their international infrastructure consists of a large organized by functions whose
primary objective is exploitation, management and marketing of oil and its derivatives.
The gas fractionation plant can be defined as an operations center that receives the
gas liquid extraction plants of San Joaquin, Santa Rosa, Santa Barbara and Jusepín
to split into different products such as gasoline, propane, butane (normal and
isobutane ) and pentane. Within its operational part are the following areas: area 250
A train, train B area 260, area C fractionation train 270 and the refrigeration area 380.
The area 380 has five operating turbochargers, turbines powered by Nuovo Pignone
® brand PGT5 model. The turbines are responsible for providing electrical energy
necessary for the proper functioning of the plant, while consisting of different
Análisis Causa Raíz de una Turbina a Gas
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components are considered vital because failure of one of them generates a possible
shutdown of the plant. Currently, the D4-81 001 turbo has presented problems to the
level of the turbine component failures, characterized by high temperatures, vibration,
corrosion, among others, causing unplanned downtime of that set of equipment,
leading to failure of scheduled tasks by the company, production losses, high costs
and waste of the life of your components.
For these reasons the company has been in charge of proposing the implementation
of root cause analysis in order to identify the root causes physical, human and latent
failures that lead to criticism of the turbine and thus to propose actions to reduce the
occurrence of the same in the machine. To obtain this result, it was necessary to
apply a criticality analysis methodology, which allowed rank the failures of major
impact at the operational, environmental and / or safety. Then performed Fault Tree
Logic, through a set of hypotheses generated by a multidisciplinary team composed
of staff for Operations, Technical Management and Maintenance Staff.
Consequently, the development of this research allowed the generation of feasible
actions to improve the operation of the turbine under study in order to maximize
profitability gas field and to comply with the strategic plans of PDVSA GAS.
OBJECTIVES
General Purpose
Analyze the root cause of a gas turbine model brand Nuovo Pignone PGT5 D4-81
001 Turbocharger Plant Division and Office Jose, PDVSA GAS.
Specific Objectives
Análisis Causa Raíz de una Turbina a Gas
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1. Describe the operational context of the gas turbine PGT5.
2. Applying the analysis of criticality to the gas turbine PGT5 to identify the failure
of major impact at the operational, environmental and / or safety.
3. Identify the physical roots, and latent human failures that lead to criticism from
the gas turbine PGT5.
4. Propose actions for reducing the occurrence of the failings of the gas turbine
PGT5.
Análisis Causa Raíz de una Turbina a Gas
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THEORETICAL FRAMEWORK Turbomachinery
Turbomachines are a class of fluid machines. Fluid machine means all mechanical
devices allowing for an exchange of mechanical work between the outside and the
fluid passing through the machine (called working fluid). As an example, include the
rocket motor, the internal combustion engine, pumps, turbines, among others.
In the turbomachinery (Latin turbare, "whirlwind", "whirlwind") there is ongoing
communication between the input and output of fluid. As a result part of the so-called
flow machines. The exchange of mechanical work with the outside world is achieved
through a shaft to which it is attached a piece appropriately called the rotor. This
makes these machines generally have a morphology with rotational symmetry.
Examples of turbomachinery are the turbines, turbochargers, the turbo pumps, turbo-
generators, among others. The exchange of power with demands that it rotates shaft
and to transmit a pair. Not always, but very often the existence of a stator or part not
rotating, whose mission is to deflect the current. Only with the concurrence of the
stator and rotor can be an efficient operation. Another basic feature is the production
of a pressure difference between input and output [6].
Gas turbine
It is an internal combustion engine, where the energy contained in hot gases is
converted into mechanical energy to move a team, whether it's a pump, compressor
or generator. Any device that generates power cycles operates a gas turbine Brayton
cycle operates under constant pressure or cycle. A gas turbine can be shown in
general outline in Fig 2.1.
The gas turbines can be classified as follows:
According to his design philosophy:
Análisis Causa Raíz de una Turbina a Gas
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Aeroderivative. This turbine model comes from the adequacy of the turbines
used in aviation and has the following characteristics:
• They are of small size.
• The parts are cooled by air.
• Lightweight materials
• Its maintenance is not in place, is done in external workshops.
• It has increased efficiency.
Industrial. These turbines were designed for industrial developments and
their characteristics are:
• The materials used are robust.
• Are large.
• Maintenance was done on site.
• The time between maintenance is higher than aeroderivative.
Depending on the number of axles:
Simple. Generally used for loads to a single speed (generators).
Double or multi-axis. For loads at various speeds (pumps and compressors)
[7].
Análisis Causa Raíz de una Turbina a Gas
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Figure 2.1. Gas turbine.
Source: Manual Nuovo Pignone. (2004)
Brayton Cycle
Any device that generates power cycles operates a gas turbine Brayton cycle
operates under constant pressure or cycle. To facilitate the study of Brayton cliclo
eliminates some real situations such as:
• Pressure drops. It is considered that there is no friction, so that the fluid
maintains its pressure as it flows from one place to another.
• Heat loss. Considered all isolated teams and there is heat exchange with the
environment.
The compression and expansion processes are isentropic.
These considerations mean that there is a moderate difference between the actual
cycle and ideal cycle, but allows an effective analysis of the processes occurring. The
diagrams of temperature vs properties. Entropy (TS) vs pressure. Volume (PV) have
been very helpful for the study of cycles. In Figure 2.2. Shows an example of the
Brayton cycle in a TS diagram and shows the differences between the ideal cycle and
actual cycle.
Análisis Causa Raíz de una Turbina a Gas
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Figure 2.2. Brayton cycle or cycle of constant pressure.
Source: Workshop PGT5 gas turbines. (2005)
In the TS and PV diagrams, the area enclosed within the curves of the process
represents the net work produced during the cycle and is equivalent to the net heat
produced in that cycle. See Figure 2.3.
Figure 2.3. PV and TS diagrams for an ideal cycle.
Source: Workshop PGT5 gas turbines. (2005)
Figure 2.3. represents the ideal behavior of gases within the turbine. At one point
the air is taken in atmospheric temperature and pressure and is compressed to point
2, this process is considered isentropic and the air volume decreases due to
compression. Then there is an increase volume at constant pressure from the point 2
to point 3 (combustion process), from point 3 to point 4 gases are expanded through
an isentropic process, before being discharged into the atmosphere 1.
Below is a diagram of the Brayton cycle, in open cycle mode, for a turbine axle:
The gas turbine shown in Figure 2.4, is composed of a compressor, a combustion
chamber, turbine wheel and an axis that is attached directly to the load. In this setup,
Análisis Causa Raíz de una Turbina a Gas
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all components rotate at the same speed and is used in power generation, as it must
maintain a constant frequency (60 Hz) that depends directly on the speed.
Figure 2.4. Simple axis turbine.
Source: Workshop PGT5 gas turbines. (2005)
There are other settings where there are two axes, which rotate independently and is
known as gas turbine dual axis, the first axis is called the axis of low pressure (Low
Pressure, LP) and delivers the power needed to move the compressor raises the
pressure air required for combustion, this axis is maintained at a constant speed
during operation of the turbine. The second axis is called the axis of high pressure
(high pressure, HP) and which transmits power to the load, this configuration is used
to move equipment requiring vary its speed depending on process requirements
where they are. Figure 2.5. represents a double axis turbine.
Análisis Causa Raíz de una Turbina a Gas
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Figure 2.5. Double axis turbine.
Source: Workshop PGT5 gas turbines. (2005)
Each manufacturer has its own turbine design and configuration in order to improve
the efficiency of the cycle, the two previous schemes are open loop, but there are
others such as:
• Closed loop: The combustion gases are recycled and reused continuously.
• Regenerative cycle: The exhaust gases are used to heat the air before
entering the combustion chamber
• Regeneration cycle: The exhaust gases are used to heat another system.
ISO Power
ISO Power (International Standard Organitation) is the net power output of the
turbine, working under specific conditions, which are:
• Ambient temperature: 15 ° C
• Atmospheric pressure: 750 mmHg
Análisis Causa Raíz de una Turbina a Gas
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• Humidity: 60%
To make a good selection, it is important to know the net power output at the site
where the turbine will be operational and for this we must know the conditions of
temperature, altitude above sea level, relative humidity, pressure drops in ducts and
the manufacturer's correction factors. So the net power corrected for the workplace,
is given by:
(2.1)
Where
P N: Net power corrected.
P I: Power ISO.
F CN: Correction factors needed to more accurately calculate the net power.
In other cases, the manufacturer provides certain tables, where data is entered to
obtain the corrected power
Maintenance levels of gas turbines
Each of the turbine components are in continuous operation, subject to mechanical
and thermal fatigue for that reason the manufacturer recommends replacing each of
them to have certain hours of operation. This will have different levels of
maintenance, which are denominated as follows:
cNccN fffPP ...: 211 ×××
Análisis Causa Raíz de una Turbina a Gas
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Combustion zone. It is known as Level I maintenance is performed every 8000 hrs.
At this level of maintenance is inspected and replace components of the combustion
chamber and nozzle transition piece.
Hot Steps. Level II is known as maintenance is performed in 20000 hrs. At this level
of maintenance are inspected and replaced components of the combustor, transition
piece, nozzles and performs inspection of the turbine wheel.
Mayor. Is known as Level III maintenance is done every 40 000 hrs. At this level of
maintenance are inspected and replace components of the combustor, transition
piece, nozzles, turbine wheels, compressor, axial, shafts, bearings and exhaust
plenum.
The three levels mentioned above are satisfied for most models of existing turbines,
but not the recommended operating hours for it, which depend on each manufacturer.
In PGT5 turbines there is a last type of maintenance which replace: housing, axle
and axle high low pressure, this type of maintenance was named Mayor of elders.
In Figure 2.6. is a summary of the types of maintenance and operating hours
required for their implementation.
Análisis Causa Raíz de una Turbina a Gas
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Figure 2.6. Maintenance levels.
Source: Workshop PGT5 gas turbines. (2005)
Main components of a gas turbine PGT5
Axial compressor. Its function is to raise the pressure of the air entering the turbine
and is composed of the stator vanes and rotor blades. The stator blades are secured
in an enclosure and does not rotate, the rotor blades are in the shaft and have a
velocity turn. A set of rotor and stator blades form a compression stage.
In the gas turbine PGT5 are 15 stages of compression.
In Figure No. 2.7. shows the axial compressor and the various parties that are
forming.
Análisis Causa Raíz de una Turbina a Gas
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Figure 2.7. Axial compressor.
Source: Workshop PGT5 gas turbines. (2005)
IGV. The IGV (Inlet Gas Vane) are stator blades that are in the early stages of axial
compressor, whose main function reducing turbulence to the axial compressor inlet.
In the units there is a stage PGT5 IGV.
Combustion Chamber. It's where combustion occurs in the turbine and it generated
the hot gases, which contain the energy that is transformed into mechanical energy.
It is composed of:
• Combustor casing.
• Spark Plug (Spark Plug).
• Flame detector.
• Injector gas.
• Combustor basket.
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In Figure 2.8. shows the combustion chamber and the different parts that compose
it.
Figure 2.8. Combustion chamber.
Source: Workshop PGT5 gas turbines. (2005)
Spark plug. Produce the necessary spark to initiate combustion of the gas / air
mixture generates an electric arc 15 000 KV. See Figure 2.8.
Flame detector. Da confirmation to the onset of the combustion process control
system of the machine. See Figure 2.8.
Fuel gas injector. Its function is to evenly distribute the gas within the basket so that
the combustion process is consistent in all areas.
In Figure 2.9. shows the fuel gas nozzle of a gas turbine PGT5.
Análisis Causa Raíz de una Turbina a Gas
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Figure 2.9. Fuel gas injector.
Source: Workshop PGT5 gas turbines. (2005)
Combustor basket. The gas is a mixture of fuel and air to make way for the
combustion process. The final design of this component is the product of many
assessments, including her, movement, chemical reactions and thermodynamics of
combustion. See Figs. 2.10. and 2.11.
Figure 2.10. Combustor basket of a gas turbine PGT5.
Source: Workshop PGT5 gas turbines. (2005)
Análisis Causa Raíz de una Turbina a Gas
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Figure 2.11. Scheme of the air entering the combustor basket.
Source: Workshop PGT5 gas turbines. (2005)
Transition piece. Transfer the hot gases and combustion products to the first stage
nozzles. Given the configuration of the turbine, is designed to distribute the flow
evenly through the nozzles.
In Figure 2.12. shows the transition piece of the gas turbine PGT5.
Figure 2.12. Part of transition from a gas turbine PGT5.
Source: Workshop PGT5 gas turbines. (2005)
Análisis Causa Raíz de una Turbina a Gas
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Nozzles. They consist of a series of blades that form a passage where the hot gases
from the combustion products are accelerated and directed to the turbine wheel. In
the turbine model PGT5 there are two (2) nozzles
The 1st-stage nozzles are the components that are subject to greater thermal stress
across the section of the turbine.
As PGT5 model turbines are dual-axis of the nozzle opening is variable, with the aim
of controlling the high shaft speed between 98% and 105%
In Figure 2.13. shows the nozzle of a gas turbine PGT5.
En la Fig. 2.13. se muestran las Toberas de una turbina a gas PGT5.
a) nozzle 1 st step b) Variable nozzle vanes
Figure 2.13. Nozzle of a gas turbine PGT5.
Source: Workshop PGT5 gas turbines. (2005)
Rotor Shaft or high pressure (HP). This area generates the power to move the
compressor axial bearing rotates on two bearings, called bearings 1 and 2. It consists
of the axial compressor rotor and turbine wheels. PGT5 model has only one turbine
Análisis Causa Raíz de una Turbina a Gas
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wheel (1 st stage). Each turbine wheel consists of a series of blades, the hot gases
passing through these blades, there is a change of power to turn the shaft.
In Figure 2.14. shows the rotor shaft or a high pressure gas turbine PGT5.
Figure 2.14. Axis or high-pressure rotor of a gas turbine PGT5.
Source: Workshop PGT5 gas turbines. (2005)
Rotor Shaft or Low Pressure (LP). Is the power generated to move the load. In
PGT5 drives turbines and centrifugal compressors rotates on two bearings bearing,
called bearings 3 and 4. As the axis high, this shows a wheel (2nd stage).
In Figure 2.15. shows the rotor shaft or a low pressure gas turbine PGT5.
Análisis Causa Raíz de una Turbina a Gas
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Figure 2.15. Axis or low-pressure rotor of a gas turbine PGT5.
Source: Workshop PGT5 gas turbines. (2005)
Blades of gas turbines
The blade is an airfoil that is the path exposed to the passing of gas. The blades are
highly stressed fatigue when working in extreme conditions which support large
vibratory forces.
The design and machining of the blades is very complicated because it must adapt in
order to withstand the working conditions to which it is subjected, and therefore must
have high rigidity and an adequate geometry to distribute all efforts when operating in
resonance.
The blades are airfoils that receive the gas and do change speed and pressure, thus
absorbing energy. Are secured to the shaft, forming the so-called wheel [8].
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Mechanism of failure in turbine blades
A component failure in service or parts may be caused by one of the following factors
or combination of them: improper design, poor material selection, material
imperfections, deficiencies in the manufacturing process, deficiencies in the process
assembly and appropriate service conditions [8].
Failure
Occurrence is unpredictable, inherent element of a computer that prevents it fulfills
the mission for which it was designed, also defined as the onset of permanent
deformation, which changes the dimensions and mechanical properties of a
component.
Any failure has direct and indirect effects on the system (operation or security) which
depend on the operational context of performance standards and the physical effects
of each failure mode.
Fault Types
According to their scope:
Partial: causes deviations in the performance characteristics of a team outside
specified limits, but does not provide complete inability to fulfill its function.
Total: causes deviations or losses of the operating characteristics of a team, so that
causes an inability to perform the function for which it was designed.
According to their rate of appearance:
Progressive is one in which there is degradation of device performance and may be
determined by a previous examination of the characteristics.
Flashing: is that which is presented alternately by limited periods of time.
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Sudden is what happens instantly, and can not be predicted by a previous
examination of the characteristics of the equipment.
According to their impact:
Minor: is one that does not affect production targets or service.
Mayor: This is the part that affects production targets or service.
Review: is this completely affects production targets or service.
According to his office:
Independent: These are faults whose causes are inherent in the same computer.
Dependent: they are the origin of which equipment failure is attributable to an
external cause [9].
Failure Modes
The failure mode causes each functional failure, is what causes loss of function of all
or part of an asset in its operating context (each functional failure may have more
than one failure mode) [10].
Effects of faults
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These are the events or facts that can be observed if a particular failure mode, ie to
define what happens when each failure mode occurs [10].
Operating Environment
Some of the important factors to be considered are:
• If physical activity is part of a continuous or batch process.
• The presence of redundancy or alternate modes of production.
• Quality parameters required of the particular product.
• The operational context and environmental standards.
• Security risks.
• Shifts.
• Volumes of stock of finished goods and work in process.
• Repair time.
• Policy spares in stock.
Equipment Criticality
It is a classification that is set to highlight the importance (hierarchy or priority), with a
particular equipment or system within the process to which it belongs [11].
Criticality Analysis (CA)
It is a methodology to rank systems, facilities and equipment, depending on their
overall impact, as determined by the weighted evaluation criteria operational,
environmental and security in order to facilitate decision making. It performs the
following steps:
• Defining scope and purpose for the analysis.
• Establishing the criteria of importance.
• Selecting an evaluation method for ranking the selection of the systems being
analyzed.
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The criteria used are: safety, environment, production, cost, frequency of failures,
mean time between failure, among others. The criticality analysis must be applied
when present the following needs: priority setting in complex systems, managing
scarce resources, determine impact, apply other methodologies such as: failure
analysis, root cause analysis, among others. This kind of analysis applies in any set
of processes, plant, systems, equipment and / or components that need to be ranked
according to their impact on the process. Their common areas of application are:
maintenance, inspection, materials and spare parts, availability of facilities, personnel.
The statistical tools are commonly used in this type of analysis and information
usually found in the records of the plant.
Root Cause Analysis (RCA)
It is a methodology to systematically identify the root causes physical, human and
latent problems, and then apply corrective measures (solutions) to decrease their
impact by identifying the conditions conducive to the event [12].
The Root Cause Analysis is a fundamental tool Fault Tree Logic, which is an aid in
solving problems, leading to the discovery of the causes of problems through logical
thoughts related to the event of failure. Its construction is due to:
• Describe the event.
• Describe how or possible modes of failure.
• Formulate hypotheses.
• Validate hypothesis.
• Determine natural causes, human and latent.
Logical tree structure for ACR faults
The 2.16 shows the logical tree structure of a fault.
Definición
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Where:
Physical Evidence: Are all real evidence found after the unwanted event occurs.
Hypothesis: They are all possible mechanisms that cause failure events.
Physical roots: They are all situations or events that directly affect the physical
origin of the operational continuity of equipment or systems, eg minimum flow by
blocking a pipe, bad connections, defective parts, among others. Usually at this level
will not find the root cause of the failure, if not a starting point to locate it.
Human roots: They are all those mistakes made by the human factor which directly
or indirectly in the occurrence of a failure, for example, improper installation, design
errors, failing to properly implement the relevant procedures, among others.
Figure 2.16 Fault Tree Software for ACR.
Source: own. (2009)
La Caja Superior del problema
EvidenciasFísicas
Hipótesis
Raíces Físicas
Raíces Humanas
Raíces Latentes
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Latent roots: All those problems but never have occurred, are feasible its
occurrence, for example, lack of procedures to start or put out of service, improper
operating procedures, untrained personnel, among others [12].
Benefits Generated by Root Cause Analysis
• Reduced number of incidents, failure and waste.
• Reducing costs associated with failure.
• Improved reliability, security and environmental protection.
• Improving the efficiency, profitability and productivity of processes.
Impact After the implementation of an RTA
There have been cases in which the completion of the ACR in a plant is a starting
point for the improvement of other plants and the entire company, because the root
causes of catastrophic failures discovered in a plant, after studies have found that
generally are the same causes of the other plants. This means that in the future the
same mistake will not occur in the area, unit or facility or any other study for that
reason some people call the RTA tool for "Learning to Learn" [12].
Diagnosis Process
The diagnosis, is an analysis performed to determine the situation and what are the
trends of it. This determination is made on the basis of information, data and facts
collected and arranged systematically, which allows to evaluate better what is
happening [13]. In other words, the diagnosis is the starting point for designing
Análisis Causa Raíz de una Turbina a Gas
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operations and actions that can address the problems and needs identified in the
same [14].
Generally to make a diagnosis, you must meet the following steps:
• Observation.
• Description (you need a language).
• Classification.
• Association.
• Identification of meaningful relationships.
• Critical observation of the attributes (features).
• Selection of priorities.
• Development of a criterion.
• Diagnose.
In the maintenance, diagnosis of equipment or systems for the state in which they
are at the same time allows to know how many teams have as well as the location
and function of each within the system, in this sense, for this This analysis efficient
results, you must meet certain requirements, among which are:
• Location of equipment within the company:
At this stage, should answer questions such as, What is the role of the team,
"What benefits and costs generated by the team," among other questions to
define the use of equipment and the relevance of it in the production process in
which is involved.
• Machines Status:
For this phase, we analyze the external aspects of equipment, such as the
level of cleanliness and order of equipment, state of oxidation of some
components, among others.
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• Maintenance Amount applied:
For this stage we study aspects of the planning and execution of maintenance
tasks that are applied to study computers.
Weighting factors
The weighting is a method that serves to underline the importance of various factors
which contribute to an event by assigning appropriate coefficients [13], ie the
weighting of factors is balanced and equal consideration given to some arguments or
values proportion to their importance. The weighting can be quantitatively assigning
each factor a value that is commonly expressed in percentages.
Positive Material Identification (PMI)
With Positive Material Identification (PMI) can clearly determine the composition of
the alloy material and therefore its identity. If a material non-certification or it is not
clear, this technique can be known with certainty its membership.
PMI is used particularly for high-quality metals such as stainless steel and high alloy
metals. Now the engineers are carrying capacities of the materials to design limit, it is
extremely important to be sure you are using the right material.
There are two methods for PMI: The principle of X-ray fluorescence is one of the
methods. The equipment contains radioactive sources, which emit radiation. The
exposed material sent back by element specific radiation, generating energy. Since
each element has its own atomic structure, this reflection will generate a different
energy level for each item. This energy is detected and quantified by identifying the
alloy material. The radiation is emitted in such quantity as may be required additional
means of security.
The most important advantage of this method is that it can be implemented without
damaging the object. Immediately after receiving the assessment results.
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The other method of PMI is "Spark Emission Spectroscopy by." The spectroscopy is
based on optical emission. The team throws a spark that is used to vaporize the
material being analyzed. The atoms and ions in the vapor produced a spectrum that
can be measured optically and recalculate to determine the components of the
material.
Material characteristics such as structural differences and heat treatments have no
effect on the results of the measurements of PMI. However, it is important that the
surface is identical to the rest of the material. Oxides, coatings and dirt will affect the
results. The surface must also be smooth. The elements can be identified using PMI
include: Titanium, Vanadium, Chromium, Manganese, Cobalt, Iron, Copper, Zinc,
Nickel, Niobium, Molybdenum. It is important to note that radiation is low enough to
require additional security measures [15]. To perform these tests using a portable
analyzer to identify alloys, which can be seen in Figure 2.17.
Figure 2.17. Portable Analyzer to recognize alloys by PMI.
Source: Office Fractionation Plant and Jose. (2009)
Superalloys
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The superalloys are a category that goes beyond the ferrous and nonferrous metals.
Some are based on iron, some in the nickel and cobalt. In fact many of the
superalloys containing substantial amounts of three or more metals, rather than a
single metal alloying elements.
Superalloys are a group of high-performance alloys designed to meet very strict
requirements of mechanical strength and resistance to surface degradation (corrosion
and oxidation) at high operating temperatures. Conventional resistance temperature
is not usually the major criterion for these metals, and many of them have strength
properties at room temperature that are good but not outstanding. The distinguished
performance at high temperatures, tensile strength, hot hardness creep resistance
and corrosion resistance at high temperatures are the mechanical properties of
interest. Operating temperatures are often around 2000 ° F (1100 ° C) [16].
The Superalloys are normally divided into three groups according to their main
constituent iron, nickel or cobalt:
• Alloys based on iron. These alloys contain iron as the main element,
although in some cases the iron is at a rate lower than 50% of the total
composition.
• Nickel-based alloys. These alloys generally have better resistance to high
temperature alloy steels. Nickel is the metal base. The main alloying elements
are chromium and cobalt trace elements include aluminum, titanium,
molybdenum, niobium and iron.
• Cobalt-based alloys. The main elements in these alloys are cobalt (about
40%) and chromium (perhaps 20%), other alloying elements are nickel,
molybdenum and tungsten [16].
Table 2.1. shows the typical compositions of the superalloys.
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Table 2.1. Compositions typical of Superalloys. [Hoffman EG]
Nimonic 75
It is one of many superalloys available in all metals and Forge. This is a degree of
Nimonic used in applications where corrosion resistance and heat is the key. It can
withstand the enormous amount of pressure and high temperatures. Table. 2.2.
shows the properties of the superalloy Nimonic 75 [16].
Table 2.2. Superaleción Properties of Nimonic 75. [Alloywire]
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Martensitic Stainless Steels
Martensitic stainless steels (Table 2.3) are essentially only chromium steels (11-18%)
containing small amounts of other alloying elements such as nickel sometimes, but in
this case amount to not exceed 2.5%. The carbon content can vary from a minimum
of 0.08% to a maximum of approximately 1.20%. The present high temperature
austenitic microstructure, which is transformed into martensite by cooling rapidly.
They are magnetic, corrosion resistant means moderately aggressive and heat
treatment can achieve tensile strength in the order of 1400 MPa [16].
Table 2.3 shows the types of martensitic stainless steels.
Table 2.3. Martensitic stainless steel grades. [Hoffman EG]
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Análisis Causa Raíz de una Turbina a Gas
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METHODOLOGY
In this chapter of the research was developed the methodological framework as the
foundation for the development of work in order to find answers to questions and
stated objectives.
It should be noted that the methodology was as follows:
TYPE OF RESEARCH
The level of study and evaluation refers to the degree of depth that addresses the
issue. According to this, the study referred to Root Cause Analysis of a gas turbine
case: Nuovo Pignone PGT5 turbocharger model D4-81 001 Fractionation Plant and
Jose Office is defined as follows:
According to the strategy
The project used a mixed research because we used two types, as was done in the
following manner:
Documentary research. Because it is subject to the consultation of bibliographic
documents, manuals and catalogs of equipment, all of these focused on the
procedures and methodologies of the maintenance area.
Field research. Which allowed us to obtain the necessary information directly from
the area in which the machine is located in the studio, where they could observe the
actual physical needs of the activities that were raised.
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According to its purpose
According to the results obtained during the investigation, it can be classified as
applied, as they used the knowledge related to the maintenance area, which were
adjusted to the context of activities designed and implemented by the turbine
currently under study.
Depending on the level of knowledge
The study is descriptive because it was aimed to collect information regarding the
actual state of people, objects, situations or phenomena as presented at the time of
collection. Descriptive studies seek to specify the important properties of individuals,
groups, communities or any other phenomenon to be tested.
The whole process of this study was strategically targeted from the technical point of
view, from data collection to analysis and interpretation thereof; is to identify causes
that prevent the proper functioning of the system under study and discuss
improvements which will support the turbine operation in a reliable working
environment in order to increase reliability, maintainability and availability.
STAGES OF THE RESEARCH
The completion of this work was divided into six stages, which are described below:
Description of the operational context of the gas turbine PGT5
In this phase, observed the operation of the turbine as well as the different
components that conform to it, through the reading of the various operating
parameters reflected in the HMI screen.
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The HMI screen provided in outline form, all necessary information on how to operate
the machine. This screen is located in the control panel cooling area 380 (see Annex
B). We also used information from the records of failure and performance parameters
obtained in the previous stage. Within the data obtained in the histories of failure are
the downtimes and the description of each failure by the machine.
Criticality analysis of the gas turbine PGT5
To rank the faults of the machine under study, data were based on criticality matrix
weights attributable to the various parameters involved in it. The matrix enabled the
evaluation of the overall impact of faults, formed by the degree of involvement at the
operational level, environmental and security generated by the occurrence of the
same to the context in which the unit operates.
The weighting matrix was developed under the statistical principle of frequency
distributions of grouped data for the creation of class intervals or ranges (Eq. 3.1), in
which they have been discriminated against different parameters considered.
Depending on the degree of impact on this parameter, this was assigned a value that
increases as it generates an adverse or negative, and vice versa.
NVbVaI )( −
= . (3.1)
Where
I: Interval class.
Va: Highest value.
Vb: Lowest value.
N: Number of classes.
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Downtime
It is the time elapsed since the failure of the equipment until restart. The value used
in the analysis of criticality is the sum of all downtimes of the failures occurred in the
period under review (January 2007-December 2007), as shown in Equation 3.2.
. (3.2)
Where
TFS: Time out of the total in a given period.
Tf SN: Time out of service failure occurred.
Operational Impact
This impact is made up of operational parameters inherent flaws that presented the
equipment, these being the number of times to repeat the event (number of failures)
and the average time that elapses the computer out of service for purposes of failure
(Mean Time Out of Service (STPP)).
The data needed to determine these parameters were obtained from log failures in
2007 that has major maintenance management (Appendix C).
To determine the number of failures were classified the same as the name of the
alarm that said the panel of the unit, and joined the number of times it was generated
during the study period and the downtime is the time elapsed since the computer
failed, until re-boot. For its part, Time Average Out of Service (STPP) was obtained
through Equation 3.3.
NTfsTfsTfsTFS +++= ...21
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fallasdeCantidadServiciodeFueraTiempos
TPFS
) (∑= (3.3)
Then, as indicated at the beginning of section 3.5.3, it was determined ranges for the
classification of the number of failures and STPP, using the Ec.3.1 for each case.
Impact on safety
To obtain a security impact on staff interviews Comprehensive Security Environment
and Occupational Hygiene (SIAH) in order to identify safety risks for workers in the
presence of faults discussed above. It attributed a value for each fault, resulting:
• If the answer is "Yes" = 1.
• First answer "No" = 0.
Environmental impact
To obtain the environmental impact proceeded the same way as for estimating the
impact on safety, including staff interviews Comprehensive Security Environment and
Occupational Hygiene (SIAH). The question in this particular case was as follows:
Does the environment through noise, generation of high temperatures or greenhouse
gases? It attributed a value to each response as follows:
If yes, "Yes" = 1.
For negative replies, "No" = 0.
Global Impact
To obtain the overall impact is made a sum of the weights obtained at the operational
level, environmental and security and then under the statistical principle of frequency
distributions of grouped data were classified and grouped by range of involvement in
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high-criticality, intermediate low and generating a fault in the gas turbine PGT5, in
2007.
Identification of the physical roots, and latent human failures that lead to more criticism from the gas turbine PGT5
To identify the real physical, human and latent root cause analysis used to find the
real cause actual fault that caused the most critical of the machine under study. This
technique required the establishment of a multidisciplinary team with expertise in the
areas of operational maintenance, reliability, turbomachinery, major maintenance,
industrial safety, occupational health and environment, which facilitated the collection
of information associated with the evidence of the event and possible Causes of
failure from non-structured interviews.
Formulation of hypotheses and construction of the Fault Tree Logic
The scenarios represent the way in which he gave the failure mode. For this
research, the hypotheses were stated in terms of failures occurred and obtained
through unstructured interviews with staff in Operations and Maintenance
Management.
After you selected the critical failure or event to analyze, we proceeded to define the
modes of occurrence and how these could have occurred, in other words, the
hypothesis. Then made Logical Fault Tree roots defining physical, human and latent
presented at the event.
Each of the hypotheses were validated or discarded by means of the following tests
or analysis:
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Positive Material Identification
Technique that involved the identification of the elements of the alloy under study, to
rule out differences in the characteristics of the materials used in the assembly, with
respect to the technical design. To develop this analysis we used the commercial tool
available to the organization (Portable Analyzer to recognize alloys (see Annex D)).
Comparison of current operational conditions with operational context
Corroboration consisted of the operational conditions presented by the team at the
time of the fault with respect to corresponding normal operating conditions, failure to
exclude evidence at the operational level.
Proposed actions for reducing the occurrence of faults
At this stage, guidelines, and conducted training programs for operators, according to
the results obtained in the logical tree so failure to solve the root causes that give rise
to the event under study.
Análisis Causa Raíz de una Turbina a Gas
DEVELOPMENT AND ANALYSIS OF RESULTS
OPERATIONAL CONTEXT DESCRIPTION GAS TURBINE PGT5
PGT5 gas turbine (Fig. 4.1) subject to study belongs to train a cooling area 380. The
cooling system of the area 380 is formed by a closed circuit cooling of three levels
and four stages that uses propane refrigerant. The compression of the gas from the
initial pressure of 8 psia at the final pressure of 257 psia is done using centrifugal
compressor driven by gas turbines such as technical specifications listed in Table 4.1,
which transmit the motion to the compressors through a coupling joint and operate in
parallel forming two compression trains each consisting of two teams, and equipment
attached to an auxiliary role to the other trains.
The study team has been operating since 1992 in the refrigeration area 380, for 24
hours a day, fulfilling the date maintenance plans 40000 hours of operation for major
maintenance, the latest being implemented during 2007.
The turbine studied and described in Chapter II has control devices during operation
to minimize the risk of damages to the atmosphere by emission of greenhouse gases
and temperatures above those recommended.
The risks to safety in normal operation is limited on a global level to falls, injuries
touch of elements subjected to high temperatures and suction of gas leakage from
the staff. The faults that can register the team are contained in Annex C.
To increase production levels, reliability, improve operating conditions and / or just for
obsolescence of spare parts in 2005 was reloaded the turbine under study. This
consisted in the replacement of parts and pitch control system in order to increase
overall efficiency. The unit under study had a power of 6800 Hp and ISO was
increased to 7300 hp, power currently used, as shown in Table 4.2.
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Figure 4.1. PGT5 gas turbine turbocharger belonging to the D4-81 001.
Source: Office Fractionation Plant and Jose. (2009)
Table 4.1. Technical Information of the turbine under study. [Nuovo Pignone]
Function Transforming the energy of hot gases into mechanical
energy to move the centrifugal compressor
Fuel Type Propane Gas
ISO Power (Hp) 7300
Manufacturer Nuovo Pignone
Model PGT5
Compressor Type Axial
Compressor No. stages 15
N ° stage turbine 2
HP shaft speed (rpm) 11 140
LP shaft speed (rpm) 10 290
Rotation Counterclockwise
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Table 4.2. Current values of the turbine under study. [Fractionation Plant and Office Jose]
Inlet oil temperature to the bearings (° F) 90.94 Speed High pressure rotor (rpm) 11 143 Speed Low pressure rotor (rpm) 10 692 Percentage of opening of the SRV (%) 57.93 Percentage of opening of the GCV (%) 69.77 Intervalvular fuel gas pressure (psi) 163.13 Higher value of Vibration (in / s) 0.24 Average exhaust temperature (° F) 924.50 Air discharge temperature in the axial compressor (° F) 669.69 Discharge pressure of air in the axial compressor (Psi) 96.75
APPLICATION OF CRITICAL ANALYSIS OF A GAS TURBINE PGT5
To rank the faults of the machine under study, data were based on criticality matrix
weights attributable to the various parameters involved in the same as explained in
Chapter III of this work.
For criticality analysis application proceeded to locate the fault data of the machine
and maintenance work.
The organization has a record of failure of the machine, these are shown in Table
No. 4.3 and in this we can see the faults made by the turbine in 2007, Time Average
Out of Service (STPP) in hours and the number of repetitions for the period under
study.
To calculate the average time out of the Item 2 (failure by loss of vibration
acceleration and high speed shaft) of Table 4.3, Equation 3.3 was applied and
obtained the following:
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For each of the faults was also carried out this procedure, which can be seen in the
other items in Table 4.3.
Then, as indicated at the beginning of section 3.5.3, it was determined ranges for the
classification of the number of failures and STPP, using Eq 3.1 for each case.
Table 4.3. STPP for failures made by the gas turbine PGT5, in 2007. [Self]
ITEM
EVENTS N ° SHOOTING
STPP (hours)
1 Maintaining the fuel gas valve and cabin filter 1 159.50
2 Loss of high acceleration and high shaft
vibration
3 3630
3 Overspeed Trip 1 1.00
4 Correction of air leakage / off by leaking fuel
gas line
2 23.50
5 Falla, bearing thermocouples 2 and 4 2 5.00
6 False Trip signal fire 2 0.85
7 Mtto. filter house IV / V output air seals 1 7.00
8 Check PCD and configuration constants,
specialist
1 90.00
As for the STPP parameter in Table 4.3, we obtain the following:
As the number of failures in Table 4.3, we obtain the following:
These intervals were obtained from the difference between the highest and the lowest
we want to evaluate the number of classes. In this case, three classes are
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considered, these being associated with a low impact, intermediate and high, as
appropriate. We proceed similarly for the classification of the number of failures.
Table 4.4 presents the results of class intervals for the parameters considered for
operational-level assessment of the impact that generated the fault.
Table 4.4. Class interval of the parameters of impact assessment at the operational level of faults made by the gas turbine PGT5, 2007. [Self]
Number of failures STPP (hours / year) Weighing
1 to 1.67 0-1209 1
1.67 to 2.34 1209-2419 2
2.34-3 2420-3630 3
The purpose of obtaining the weighting of different faults presented in the period
under review is that the same could determine the degree of involvement of each
failure at the operational level, since this was an important contribution to the time of
measuring the impact overall the machine generates.
In Tables 4.5. and 4.6. different weightings are designated for each failure according
to the impact at the operational level by the STPP and the number of faults, using the
previously estimated range.
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Table 4.5. Weight designated to failure as to the impact at the operational level by the STPP in the gas turbine PGT5. [Self]
EVENTS STPP (hours)
Weighing
Maintaining the fuel gas valve and cabin filter 159.5 1
Loss of high acceleration and high shaft vibration 3630 3
Overspeed Trip 1 1
Correction of air leakage / off by leaking fuel gas
line
23.5 1
Falla, bearing thermocouples 2 and 4 5 1
False Trip signal fire 0.85 1
Mtto. House filter IV / V output air seals 7 1
Check PCD and configuration constants, specialist 90 1
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In Table 4.7 we can see the weighting corresponding to the various faults made by
the turbine during the study period, the amount of faults and the STPP, in addition to
the total weight that generate these parameters.
Table 4.6. Weight designated as failures at the operational impact caused by the number of failures in gas turbine PGT5. [Self]
EVENTS Fault No. Weighing
Maintaining the fuel gas valve and cabin filter 1 1
Loss of high acceleration and high shaft vibration 3 3
Overspeed Trip 1 1
Correction of air leakage / off by leaking fuel gas line 2 2
Falla, bearing thermocouples 2 and 4 2 2
False Trip signal fire 2 2
Mtto. House filter IV / V output air seals 1 1
Check PCD and configuration constants, specialist 1 1
Source: own. (2009)
These values allowed to determine the impact generated by each failure at the
operational level. In the following sections of this chapter will identify safety and
environmental impacts, which together with the operational impact, allowed the
ranking of the failures and the identification of those in the highest degree detrimental
to the turbine under study.
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Table 4.7. Weight designated to failure as to the impact at the operational level in the gas turbine PGT5, in 2007. [Self]
EVENTS STPP (hours)
Weighing
No Fault
Weighing
Total
Maintaining the fuel gas valve and
cabin filter
159.5 1 1 1 2
Loss of high acceleration and high
shaft vibration
3630 3 3 3 6
Overspeed Trip 1 1 1 1 2
Correction of air leakage / off by
leaking fuel gas line
23.5 1 2 2 3
Falla, bearing thermocouples 2
and 4
5 1 2 2 3
False Trip signal fire 0.85 1 2 2 3
Mtto. House filter IV / V output air
seals
7 1 1 1 2
Check PCD and configuration
constants, specialist
90 1 1 1 2
1.
Impact on safety
To obtain the impact on security were interviewed maintenance personnel and the
Department of Comprehensive Security Environment and Occupational Hygiene
(SIAH) in order to identify safety risks for workers in the presence of faults discussed
above. It attributed a value for each response, resulting:
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• If the answer is "Yes" = 1.
• First answer "No" = 0.
2.
Environmental impact
To obtain the environmental impact interviewed maintenance personnel and the
Department of Comprehensive Security Environment and Occupational Hygiene
(SIAH) similar to the previous section, in order to identify the risks to the environment
in the presence of faults outlined above. It attributed a value for each response,
resulting:
• If the answer is "Yes" = 1.
• First answer "No" = 0.
In Tables 4.8 and 4.9 we can see the weights that were each presented by the
turbine failure at the level of security and to the environmental impact respectively.
Table 4.8. Weighting attributed to fail under the impact generated a level of safety in the gas turbine PGT5, in 2007. [Self]
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EVENTS Does it affect? Weighing
Mtto. gas valve fuel and cabin filters If 1
Loss of high acceleration and high shaft vibration If 1
Overspeed Trip Not 0
Correction of air leakage / off by leaking fuel gas line If 1
Falla, bearing thermocouples 2 and 4 Not 0
False Trip signal fire Not 0
Mtto. House filter IV / V output air seals Not 0
Check PCD and configuration constants. Not 0
Table 4.9. Weighting attributed to fail under the impact generated at the environmental level in the gas turbine PGT5, in 2007. [Self]
EVENTS Does it affect? Weighing
Mtto. gas valve fuel and cabin filters If 1
Loss of high acceleration and high shaft vibration If 1
Overspeed Trip Not 0
Correction of air leakage / off by leaking fuel gas line If 1
Falla, bearing thermocouples 2 and 4 If 1
False Trip signal fire Not 0
Mtto. House filter IV / V output air seals Not 0
Check PCD and configuration constants. Not 0
Table 4.10. Weighting of each failure with respect to the overall impact of the gas turbine PGT5, in 2007. [Self]
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Impact
EVENTS
Operational
Security
Environmental
Global
Maintaining the fuel gas valve
and cabin filter
2
1 1 4
Loss of high acceleration and
high shaft vibration
6
1 1 8
Overspeed Trip 2 2
Correction of air leakage / off by
leaking fuel gas line
3
1 1 5
Falla, bearing thermocouples 2
and 4
3
1 4
False Trip signal fire 3 3
Mtto. House filter IV / V output air
seals
2
2
Check PCD and configuration
constants, specialist
2
2
From Table 4.10 it can be seen that the failure of greater criticality corresponds to
Item 2 "loss of vibration acceleration and high speed shaft", as corresponds to the
fault that has the highest overall impact (in operation, environment and security) the
study period.
Was then applied Eq 3.1 and won the class interval to weigh the overall impact, as
follows, allowing then to identify the level of criticality of each event.
In Table 4.11 we can see the level of criticality obtained from the overall impact that
generated a fault.
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Table 4.11. Identification of criticality from the overall impact created by the failure of the gas turbine PGT5, in 2007. [Self]
Global impact Criticality level
(2 to 3.9) Under
(4 to 5.9) Intermediate
(6-8) High
In Table 4.12 we can see the level of criticality that represented each failure during
the study period.
Table 4.12. Criticality of the flaws in the gas turbine PGT5, in 2007. [Self]
Item
EVENTS
Weighing
Criticality Level
1 Maintaining the fuel gas valve and cabin
filter
4 Intermediate
2 Loss of high acceleration and high shaft
vibration
8 High
3 Overspeed Trip 2 Under
4 Correction of air leakage / off by leaking
fuel gas line
5 Intermediate
5 Falla, bearing thermocouples 2 and 4 4 Intermediate
6 False Trip signal fire 3 Under
7 Mtto. filter house IV / V output air seals 2 Under
8 Check PCD and configuration constants,
specialist
3 Under
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Failure of high criticality. Criticality analysis of PGT5 applied to the turbine was
found that the failure of senior or criticality was called "loss of high acceleration and
high shaft vibration, resulting primarily defined by the number of failures and STPP
that comprise the operational impact.
Note that these parameters constitute the matrix limits made for the assessment of
criticality at the operational level, as adopted in the same weights that they attach
greater value.
Intermediate criticality failures. Within the criticality failures were found
downstream approximately 37.5% of total failures in the study, observing the impact
at the operational level as a factor to the impacts on environment and security.
Some failures of this level of criticality had low overall impact, because according to
these studies did not result in safety and environmental impact, or alternatively, these
were of low weight.
Minor flaws criticality. Half of the failures were presented in this line, reasoned that
the overall impact was only operational impact, which showed low values compared
with the rest of the faults studied, because these failures had STPP few repetitions
and relatively short study period.
IDENTIFICATION OF THE ROOTS physical, human and latent induce critical bugs PGT5 GAS TURBINE
To identify the main causes that prevent the proper functioning of the machine
subject to review the methodology Root Cause Analysis (RCA) as defined in Chapter
II of this project, which was obtained Logical Fault Tree more able to show below and
described below.
Problem
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The problem that motivated the present study is the presence of critical flaws in the
turbine, and considered by the interruption of service at the same undesirable events,
which lead to high STPP and therefore low availability and reliability operational,
aspects that harm the continuity and operational condition of assets, and the image
and credibility of the organization.
Failure Modes
The failure modes were represented by different fault events or demonstrations turn
evaluated by the criticality matrix presented in the previous section, which was
defined more failure criticality itself, which consisted of called "loss of acceleration
and high shaft vibration high."
Hypotheses and their validation
The critical failure mode in turn led to two possible causes or hypotheses, these
being:
a. Failure of high-shaft vibration.
b. Failure of high-shaft rotor.
As to the failure by vibration of the shaft high, we proceeded for validation and / or
evaluation with the revision of history and record fault operating conditions at the time
of the event or critical strike (See Annex C) of what was found that vibration values
were elevated over the allowable range of operation, because the rotor deceleration
showed rupture of the blades of the turbine first stage nozzle first stage and other
areas (Fig. 4.2.) as following the interruption of the closed screw transition piece, fails
evident from the report of inspection made by the dynamic teams section of the
organization.
Análisis Causa Raíz de una Turbina a Gas
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It is known that the breakdown of these elements leads to the same segments
remain in motion inside the turbine, hitting the environment and creating instability in
that part of the team, so the vibration sensors that area caught these disturbances in
the form waves that are sent through signals to the computer control system, which
neutralize or suppress the function of that component.
Figure 4.2. Broken blades belonging to the gas turbine PGT5.
Source: Office Fractionation Plant and Jose. (2009)
. Below is the logical fault tree (Fig. 4.3), which shows the structure that was used to
identify the root causes physical, human and latent that caused the failure.
Análisis Causa Raíz de una Turbina a Gas
Page 63
Figura 4.3 Tree logical flaws. Source: own. (2009)
Pérdida de aceleración y alta
vibración en el eje de alta
Corrección de fuga de aire/Paro por
fuga en la línea de gas combustible
Falla, termocuplas de los
cojinetes 2 y 4
Mantenimiento de la válvula gas
combustible y caseta de filtros
Fallas críticas de la Turbina PGT5
Ruptura del tornillo de cierre
de la pieza de transición
Falla por vibración del
eje de alta
Material
Criterio de selección
inadecuado
Falta de adiestramiento de
personal sobre los
procedimientos adecuados
Problema
Modos de Falla
Hipótesis
Causa Raíz Física
Causa Raíz Latente
Causa Raíz Humana
Falla en el rotor del eje
de alta
Disponibilidad de
repuestos
Carencia/incumplimiento
de procedimientos de
trabajo
Análisis Causa Raíz de una Turbina a Gas
In turn, on the failure of the rotor shaft high, as described above, it was the
breakdown of vanes of the turbine, caused by the rupture of a screw the piece of
transition, as shown in Figure 4.4.
Figure 4.4. Screw closure of the transition piece PGT5 Turbine.
Source: Office Fractionation Plant and Jose. (2009)
From the above, it follows that the hypothesis that is consistent with the origin of the
critical flaw is a broken screw piece of transition.
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Physical root cause
As a physical root cause of the fault, we proceeded to conduct research as the main
point that led to the validation of the material used in the manufacture of screw
fractured transition piece, quoted in section 4.3.3.
The study consisted of performing a non-destructive testing of chemical composition
of the material called Positive Material Identification, which were revealed
components of the alloy that is made the screw.
When comparing the results of this test with the technical specifications of the turbine
manufacturer, differences could be observed on the alloy composition, as the
manufacturer requires that the material is called Nimonic 75 superalloy and the screw
which was found a martensitic stainless steel.
Below are the different screws studied (Figs. 4.5 and 4.6) with the tables (4.13 and
4.14) for the chemical composition thereof.
Figure 4.5. Exhibit A silver screw (PART NUMBERT: RVR20649).
Source: Fractionation Plant and clearance Jose (2008)
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Table 4.13. Chemical composition of the sample A as Positive Material Identification (PMI). [Fractionation Plant and clearance Jose]
The analysis used the chemical composition of the screw found in the transition piece
describes the type of steel is a martensitic stainless steel.
Figure 4.6. Sample B screw black (PART NUMBERT RVU22079).
Source: Fractionation Plant and clearance Jose (2008)
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Table 4.14. Chemical composition of the sample B as Positive Material Identification (PMI). [Fractionation Plant and clearance Jose]
Chemical composition (%)
Or 68
Faith 1.87
Cr 25.95
You 3.91
Type of steel according to analysis: Nimonic 75 (steel alloy resistant to high
temperature super-alloy considered.)
.
The outcome of the chemical composition, it is concluded that the sample B exceeds
in quality and service conditions (high temperature) sample A In other words that the
screw was found in the turbine (sample A) did not have the necessary properties to
withstand the high temperatures at which they are subjected by the hot gases. On
the other hand if the B sample has such properties.
Root cause human
One of the reasons why a physical faults are incurred as the one indicated in the
previous section is oriented to the search criteria by inadequate equipment or labor
involved in assembling the unit, and the personnel involved stock maintenance.
4.3.6. Latent root causes
The human root cause shown above was motivated by underlying causes such as:
at) Availability of parts: in turn is caused by delays in the process of procurement and
stock selection of materials for assembly and / or replacement.
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b) Lack and / or non-working procedures: the root cause is motivated by possible
lack of supervision of staff during the installation process and / or assembly, which
allows procedures to ensure compliance with work, and sometimes the lack a safe
working procedure for carrying out such work, which does not guarantee that at the
time of assembling the unit count with materials and / or right tools.
c) Lack of staff training in the area: one of the fundamental latent roots corresponds
to the lack of staff training and updating in terms of operation and maintenance of
equipment considered for the study, as well as foundations in metallurgy, all this will
personnel involved have the appropriate technical criteria for making assertive
decisions, once they submit the underlying causes described above.
PROPOSITION OF ACTION FOR THE REDUCTION OF THE OCCURRENCE OF THE SHOOTING OF A GAS TURBINE PGT5.
After performing Fault Tree Logic and analyze the physical roots, human and latent,
we proceeded to the proposal of actions to minimize the occurrence of faults and
improve the availability of the turbine.
... ... ... The realization and implementation of proposed actions and to achieve
improved to minimize the occurrence of faults studied both for the turbine to the
others that are located in the study area.
The following actions are proposed to decrease the occurrence of critical failure
obtained from this research.
Análisis Causa Raíz de una Turbina a Gas
Table 4.15. Actions for reducing the occurrence of the failings of the gas turbine PGT5.
Item
Actions Responsible
1 Tracking the processes of seeking input and turbine parts.
2 Optimization of spare parts in inventory.
Maintenance
3 Supervision of staff working in maintenance actions and / or assembly of the unit. Maintenance, SIAH
4 Develop manuals to permit compliance of appropriate work. Maintenance: supervisors,
operators and maintainers
5 Training of staff of operations and maintenance departments in the areas of
metallurgy and material resistance, as well as operation and maintenance of the
turbines in the study.
Maintenance: supervisors
Source: own. (2009)
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Table 4.16. Continuation of actions for reducing the occurrence of the failings of the gas turbine PGT5.
Item
Actions Responsible
6 To track the status of the team on the vibration to predict potential failures.
7 Review compliance inspection program predictive electronic analysis, among
others.
8 Promote the creation of a unit to train personnel at the system requirements. and
in turn keep a record of events and components most critical issues facing the
turbine.
Maintenance
9 Start the presentation of projects and proposals for reducing dependency on
external services.
Maintenance: supervisors,
operators and maintainers
10 Implement a program of planning for the timely production of parts prior to the
appearance of active faults to ensure the availability of critical spares.
Maintenance: supervisors
Source: own. (2009)
Análisis Causa Raíz de una Turbina a Gas
These actions should focus on the basis of the experience of qualified personnel and
be discussed by the same through various group dynamics such as panels,
brainstorming, inter alia, to turn delegate functions and to execute the departments.
With the implementation of the proposed actions are aimed at improving the
performance of the machine, reducing the causes of failures, high downtimes,
increase the maintenance personnel training in addition to operators to proactively
implement activities and give greater continuity to the process, minimizing the
dangers on the ground for those who work there and for the environment.
Análisis Causa Raíz de una Turbina a Gas
CONCLUSIONS In closing this segment of the research are presented the conclusions reached, in line
with the objectives pursued.
1. The operational context served as a starting point for research, to provide
general information regarding the function of turbine operating conditions,
frequency of maintenance and modifications thereof.
2. Criticality analysis applied to the turbine PGT5 was found that the failure of
senior or criticality is called "loss of high acceleration and high shaft vibration."
3. The criticality of some of the flaws evaluated showed low overall impact
criticality or not critical, because according to these studies did not result in
safety, and environmental impact, or alternatively, these were of low weight.
4. The validation of the hypotheses in the Fault Tree Logic guided the
formulation of a new hypothesis, concluding that the critical physical failure
corresponds to the rupture of a locking screw of the transition piece high
pressure shaft.
5. NDT fractured screw indicated that the material used to manufacture
consisted of a martensitic stainless steel, which diverges from the same
material recommended by the manufacturer, which is an alloy steel, heat
resistant superalloy considered known (Nimonic 75), the first being an alloy
with lower capacity to withstand the conditions of service, with respect to the
material recommended by the manufacturer.
6. The actions and strategies will support proposals for decision-making plant in
Jose Division and Office.
Análisis Causa Raíz de una Turbina a Gas
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Análisis Causa Raíz de una Turbina a Gas
RECOMMENDATIONS
The suggestions arising from the research process are aimed at organizational levels
PDVSA GAS, whom he will be taking appropriate and timely decisions on the
following points:
• Implement and include actions and strategies proposed in this research in
order to avoid or minimize the occurrence of critical failure studied.
• To monitor the implementation of the criticality analysis methodologies and
root cause analysis in the area of turbomachinery in order to continue the
timely improvement in the maintenance of equipment.
• Avoid the use of spare parts out of technical conditions recommended by the
manufacturer.
• Provide the definition of policies, plans and maintenance programs and
cleaning the turbo placed permanently in the refrigeration area 380.
• Finally, it is recommended to continue the upgrading in the other turbines that
are in the area as belonging to the extraction plant Santa Barbara in order to
increase overall efficiency.
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REFERENCES [1] M. Cabello. "Criticality Analysis of the plant equipment Fractionation Refinery Catalytic Puerto la Cruz (RPLC)." Graduate job. Universidad de
Oriente (2006).
[2] M. Gonzalez. "Failure Analysis for tape cutting machines used in the Horizontal type saw. In this research, an analysis of flaws in the weld seam tape cutting machines used in the horizontal saw. "Graduate job. Universidad
de Oriente (2004).
[3] JJ Lopez. "Failure Analysis of First Stage Blades of the turbogenerator No. 7 MS-7001E General-Electric Generating Plant CADAFE-gloves." Graduate
job. Universidad de Oriente (2003).
[4] C. Jimenez, L., Carmona. "Criticality Analysis and Economic Evaluation of programs for maintenance of rotating equipment assigned to the maintenance area of the San Joaquin extraction plant PDVSA GAS." Graduate
job. Universidad de Oriente (2002).
[5] JM. L., Ching Q. "Failure analysis and feasibility of replacement after major maintenance of compressors in gas plants in PDVSA, San Tome Southern District." Graduate job. Universidad de Oriente (2000).
[6] Lecuona, and JI Nogueira. "Turbomachinery. Processing, analysis and technology, "Editorial Ariel, SA, 1st edition. Barcelona, Spain (2000).
[7] J. Gonzalez. "Workshop for gas turbines and PGT5 PGT10," National
Institute of Educational Cooperation. Monagas. (2005).
[8] Sawyers GAS TURBINE ENGINEERING HANDBOOK, "Theory & Design", Volume 1 Gas Turbine Publications Inc. Stamford, Connecticut (1976).
Análisis Causa Raíz de una Turbina a Gas
Page 76
[9] SUAREZ, D. "Mechanical Maintenance," Theoretical and Practical Manual of the Universidad de Oriente, Anzoátegui (2001).
[10] confirms & Consultants. "Reliability-Centered Maintenance." Puerto la
Cruz. Venezuela (2007).
[11] SUAREZ, D. "Using Equipment Criticality Methodology DS" Universidad
de Oriente. Venezuela (2005).
[12] "Solving Problems through the use of Root Cause Analysis Tools (ACR), ACR Education Workshop, PDVSA INTEVEP, (2004).
[13] University of Salamanca. "Encyclopedias Viewer." Plaza & Janes Editores,
Spain (1999)
[14] ANIORTE N. "Epistemological Analysis", Mexico (2008).
[15] SGS. "Positive identification of materials." Peru. (2009)
[16] HOFFMAN, E. "Fundamentals of Tool Design, 2nd ed., Society of Manufacturing Engineers, England (1984).
[17] R. Huerta Mendoza "Criticality Analysis, a Methodology for Improving Operational Reliability." Maintenance Club (2003).
[18] E. Avallone, "Mechanical Engineering Handbook", Ninth Edition, McGraw-
Hill Publishing, Mexico, Volume II, (2001).
[19] RJ, and KC Zawoysky, Tornroos "GE Generator Rotor Design, Operational Issues, and Refurbishment Options" GE Power Systems (2001).
[20] C. Torres "Service Manual for Gas Turbines MS-5000 Heavy Duty"
Fractionation Plant Meneven Jose SA (1994).
Análisis Causa Raíz de una Turbina a Gas
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[6] Balestrino M, "How to Develop a Research Project" Consultores Asociados,
Spain (1998).
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