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$Page 1: 19 17 Failure analysis Gas turbine blades fractiont Jose ... · PDF fileRoot Cause Analysis Of A Gas Turbine Page 1 "FAILURE ANALYSIS OF GAS TURBINE BLADES FRACTIONATION PLANT AND$
Root Cause Analysis Of A Gas Turbine

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"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


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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.


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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


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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

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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


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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)


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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


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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


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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.


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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:


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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].


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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.


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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.


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,


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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.


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.


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Figure 2.5. Double axis turbine.


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


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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 ×××


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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.


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Figure 2.6. Maintenance levels.


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.


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Figure 2.7. Axial compressor.


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.


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.


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Figure 2.9. Fuel gas injector.


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.



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Figure 2.11. Scheme of the air entering the combustor basket.


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.



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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.


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


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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.


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.


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Figure 2.15. Axis or low-pressure rotor of a gas turbine PGT5.


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


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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.


Page 36

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.


Superalloys


Page 37

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.


Page 38

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]


Page 39

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]


Page 40


Page 4110/05/2010

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.


Page 42

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.


Page 43

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.


Page 44

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


Page 45

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


Page 46

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:


Page 47

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.


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.


Page 49

Figure 4.1. PGT5 gas turbine turbocharger belonging to the D4-81 001.


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


Page 50

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:


Page 51

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


Page 52

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.


Page 53

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


Page 54

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.


Page 55

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:


Page 56



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:



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]


Page 57

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]


Page 58

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.


Page 59

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


Page 60

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


Page 61

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.


Page 62

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.


. 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.


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


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.


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.

65

Page 65

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)

66

Page 66

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)

67

Page 67

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.


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)


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.


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.


Page 73


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.


Page 75

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[3] JJ Lopez. "Failure Analysis of First Stage Blades of the turbogenerator No. 7 MS-7001E General-Electric Generating Plant CADAFE-gloves." Graduate

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[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

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[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).

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