Improving the reliability of the compressed air supply to the blast furnaces at Tata Steel IJmuiden - Het verbeteren van de bedrijfszekerheid van de persluchtlevering aan de hoogovens van Tata Steel IJmuiden

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Delft University of Technology

FACULTY OF MECHANICAL, MARITIME AND MATERIALS ENGINEERING

Department of Marine and Transport Technology Mekelweg 2 2628 CD Delft the Netherlands Phone +31 (0)15-2782889 Fax +31 (0)15-2781397 www.mtt.tudelft.nl

Specialization: Transport Engineering and Logistics

Report number: 2015.TEL.7937

Title:

Improving the reliability of the

compressed air supply to the blast

furnaces at Tata Steel IJmuiden

Author:

R.M. Draisma

Title (in Dutch) Het verbeteren van de bedrijfszekerheid van de persluchtlevering aan de hoogovens van Tata Steel IJmuiden.

Assignment: Master thesis

Confidential: Yes (until July 1st_{, 2020)}

Initiator (TU Delft): prof.dr.ir. G. Lodewijks Initiator (Tata Steel): ir. F. Kuiper

Supervisor: Dr. ir. H.P.M. Veeke

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Student: R.M. Draisma Assignment type: Master thesis

Supervisor (TU Delft): Dr. ir. H.P.M. Veeke Creditpoints (EC): 35 Supervisor (Tata Steel): Ir. F. Kuiper Specialization: TEL

Professor (TU Delft): Prof. dr. ir. G. Lodewijks Report number: 2015.TEL.7937 Confidential: Yes

until July 1st_{, 2020}

Subject:

Improving the reliability of the compressed air supply to the

blast furnaces at Tata Steel IJmuiden

Tata Steel IJmuiden

Tata Steel produces, processes and distributes quality steel. The company is the fifth largest steel company in the world and the second largest producer in Europe. In IJmuiden more than 9000 people are employed and more than 7 million tons of high quality steel is produced every year. The business park is 750 acres and is located directly on the North Sea.

Problem definition

The blast furnace blowers at the Energy Department (END) at Tata Steel IJmuiden produce large quantities of compressed air which are necessary for the operation of the blast furnaces. Since the blast furnaces are the bottleneck of the IJmuiden facility, they must operate at maximum capacity. In the last three to four years the blast blowers have suffered from a higher unplanned downtime than is acceptable for the END. This situation leads to a decrease in the reliability of the compressed air supply to the blast furnaces, endangering their reliable and efficient operation. Consequently the failing blowers form a great financial risk for the company, making it a top priority to ensure a reliable compressed air supply through the reliable operation of the blast blowers.

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Research goal

The goal of this assignment is to improve the reliability of the compressed air supply to the blast furnaces at Tata Steel IJmuiden.

Execution

 Analyse the processes concerning the operation and maintenance of the blast blowers using Delft Systems Approach

 Acquire & analyse data concerning the availability and failures of the blast blowers  Analyse the root causes of the unplanned downtime

 Identify and evaluate possible solutions and/or improvements  Design a solution for the optimization of the maintenance strategy  Design a model for optimization of the operational strategy  Analyse relevant literature

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Preface

This report is written as the deliverable for a thesis, performed as part of the master program Transportation Engineering and Logistics at Delft University of Technology. The research that is covered in this report was carried out at the Asset Management and Development department at Tata Steel IJmuiden.

Performing the research at Tata Steel IJmuiden has been exciting for me, as it would be for every Mechanical Engineering student. The sheer size of the factories, machinery, energy consumption and material flow combined with all the accompanying challenges are fascinating. It is an environment that I have enjoyed to be in for every day during my research.

First of all I would like to express my gratitude towards my supervisor at Tata Steel IJmuiden, Folkert Kuiper, who has freed up a lot of time to provide guidance, advice and to serve as a sparring partner whenever necessary. The discussions we have had concerning the research were sometimes

passionate, but always fair, very useful and in a good atmosphere. All this has certainly helped to improve the quality of the research.

Furthermore, I would like to thank my supervisor from the TU Delft, Hans Veeke, for all of his advice and input during the meetings we have had. Hans has also functioned as a source of positive thinking when necessary, for which I am grateful.

Finally, I would like to thank professor Lodewijks for his input and advice during the meetings we have had, which for instance has led to the valuable idea of the introduction of custom variables in the performance model.

Robert Draisma,

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Summary

The blast furnace blowers, consisting of steam turbines that power large air compressors, at the Energy Department (END) at Tata Steel IJmuiden produce large quantities of compressed air which are necessary for the operation of the blast furnaces. Since the blast furnaces are the bottleneck of the IJmuiden facility, they must operate at maximum capacity. In the last three to four years the blast blowers have suffered from a higher unplanned downtime than is acceptable for the END. This situation leads to a decrease in the reliability of the compressed air supply to the blast furnaces, endangering their reliable and efficient operation. Consequently the failing blast blowers form a great financial risk for the company, making it a top priority to ensure a reliable compressed air supply through the reliable operation of the blast blowers.

During the problem analysis the processes involved were analysed using the Delft Systems Approach (Veeke, Ottjes, & Lodewijks, 2008). Furthermore the availability for technical systems was defined. A data analysis was performed to quantify the problem and root cause analyses led to an overview of the causes of the unplanned downtime. Several potential improvements for the maintenance and operational strategies were identified, which lead to the following research question:

“How to improve the reliability of the compressed air supply to the blast furnaces at Tata Steel IJmuiden by maximizing the availability of blast furnace blowers through revised operational and maintenance strategies?”

For the improvement of the operational strategy two topics are covered. First, standards and result measurements are introduced that are to be used for the evaluation of process performance with the goal of improving this process performance. Second, a risk assessment model is introduced that is used for the evaluation of the production planning and possible investments that can attribute to a reduction in the probability of production loss at the blast furnaces.

The four standards that are introduced are the availability, repair time, the required operational hours of the blast blowers and the reliability of the product supply. These standards have accompanying result measurements, being the availability (%), MTTR (hrs), MTBF (hrs) and production loss (€). The process performance for the processes involved is to be evaluated by comparing the measurement results to the standards, which can lead to an intervention if necessary.

A validated and verified risk assessment model was created that can be used to calculate the probability of the occurrence of a scenario that causes production loss for the blast furnaces. It is used in this research to evaluate the production planning and several investment decisions. Apart from the results that are generated for this research, the intention is that the model will also be used by the END for this same purpose in the future. From the short term risk analysis of the production planning can be concluded that, given the input used, an investment in the refurbishment of WM23 (€8 mln) or

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December 2017, with cumulative expected costs of €7.2 mln. From the long term risk analysis of the production planning can be concluded that, given the input used, the most profitable scenario in terms of the reduction in expected additional costs versus investment cost is to perform an overhaul of WM22 (€1.5 mln) in the second half of 2016, with the purpose to have it operational starting January 2017. According to the model output, the investment will be profitable within 10 months and will lead to a reduction in expected costs due to production loss of €16 mln, or 57%, over the period from January 2017 to July 2024.

The maintenance strategy can be improved in three ways. The first is by implementing operational testing for backup machines in order to verify their condition. By using the backup machines once a year, they prove to be operational and ready for use when necessary. Any defects that will come to light during this testing can be resolved while not immediately having consequences for the reliability of the product supply.

The second is to use the time slots of the operational testing of the backup machines for visual inspections of the main machines. However, for this strategy to be viable, the complexity of a visual inspection as it currently is has to be greatly reduced. It is recommended to research the possibility of using borescoping for the visual inspection of the steam turbine and compressor internals in order to prevent having to remove the housing of the machine, which currently is a costly and time consuming process. This will lead to a lower threshold for performing a visual inspection, which benefits the maintenance strategy.

The third improvement of the maintenance strategy is using the thermodynamic parameters of the blast blowers, which are currently already measured and logged, for performance monitoring. Evaluating the machine performance on a regular basis facilitates decision making on the production and maintenance planning. Performance monitoring facilitates the detection of internal wear to the blast blowers without having to perform a visual inspection. Furthermore, it can prevent consequential damages, by detecting initial damage in an early stage and taking appropriate measures. It is concluded that a thermodynamic model, as created during this study, can be used for this purpose. Using this thermodynamic model may enable the detection of wear and damage to the internals of the steam turbines and air compressors of the blast blowers, through the evaluation of deviations in the blade angle/airratio and correlation (for air compressors), the power output/steam mass flow-ratio and correlation (for steam turbines) and the isentropic efficiency (for both). The first two parameters were devised during this study were found to be possible indicators for internal damage during the validation of the model. The performance model also measures performance results concerning the availability and machine status, which can be used to compare to the standards of the use and maintain processes in order to evaluate the process performance.

Implementation of the advice and models that result from this study is believed to lead to improvements in the maintenance and operational strategies.

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Summary (in Dutch)

De zogenaamde windmachines, bestaande uit stoomturbines die grote lucht compressoren aandrijven, bij het Energiebedrijf(ENB) van Tata Steel IJmuiden produceren grote hoeveelheden perslucht welke nodig zijn voor het bedrijven van de hoogovens. Aangezien de hoogovens de bottleneck van de productieketen in IJmuiden vormen moeten zij altijd op maximale capaciteit draaien. In de laatste drie tot vier jaar zijn de windmachines aan meer ongeplande stilstand onderhevig dan acceptabel is voor het ENB. Deze situatie leidt tot een afname in de betrouwbaarheid van de persluchtlevering aan de hoogovens, hetgeen hun betrouwbare en efficiënte werking in gevaar brengt. Derhalve vormen de falende windmachines een groot financiëel risico voor het bedrijf, wat ertoe leidt dat het verzekeren van een betrouwbare persluchtlevering aan de hoogovens door het verbeteren van de bedrijfszekerheid van de windmachines de hoogste prioriteit heeft.

Bij de probleemanalysis zijn de relevante processen processen rondom de windmachines geanalyseerd met behulp van de Delftse Systeemkunde. Daarnaast is de beschikbaarheid voor technische systemen gedefinieerd. Een data-analyse is uitgevoerd om het probleem te kunnen kwantificeren en root cause analyses hebben geleid tot een overzicht van de grondoorzaken van de ongeplande stilstanden. Verschillende mogelijke verbeteringen zijn geïdentificeerd betreffende de operationele- en de onderhoudsstratgie, hetgeen leidde tot de volgende onderzoeksvraag:

“Hoe kan de betrouwbaarheid van de persluchtlevering aan de hoogovens van Tata Steel IJmuiden verbeterd worden door het maximalizeren van de beschikbaarheid van de windmachines op basis van herziene operationele- en onderhoudsstrategiën?”

Voor het verbeteren van de operationele strategie zijn er twee onderwerpen behandeld. Allereerst zijn standaarden en resultaatmetingen geïntroduceerd waarvan de bedoeling is dat ze gebruikt worden voor het evalueren van procesprestaties, met het doel deze te verbeteren. Ten tweede is er een risico-analyse model geïntroduceerd waarmee de productieplanning en mogelijke investeringen ter reductie van de kans op productieverlies bij de hoogovens geëvalueerd kunnen worden.

De vier geïntroduceerde standaarden zijn de beschikbaarheid, reparatietijd, de vereiste operationele uren van de windmachines en de betrouwbaarheid van de productlevering. Deze standaarden hebben bijbehorende resultaatmetingen, zijnde de de beschikbaarheid, gemiddelde reparatietijd, de gemiddelde tijd tussen storingen en de hoeveelheid productieverlies (€). De procesprestaties van de relevante processen dienen te worden geëvalueerd door het vergelijken van de resultaatmetingen met de standaarden, op basis waarvan eventueel actie kan worden ondernomen.

Er is een gevalideerd en geverifiëerd risico-analyse model gemaakt dat gebruikt kan worden om te berekenen wat de kans is dat er zich een scenario voordoet dat leidt tot productieverlies bij de hoogovens. In dit onderzoek wordt het model gebruikt om de productieplanning en verschillende

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gegeven de gebruikte input, een investering in de revisie van WM23 (€8 mln) of in een reservedelenvoorraad (€20 mln) niet winstgevend is in de periode van mei 2015 tot december 2017. Uit de risico analyse voor de lange termijn kan worden geconcludeerd dat, gegeven de gebruikte input, de beste investeringskeuze de revisie van WM22 (€1.5 mln) is. De revisie zou moeten plaatsvinden in 2016, met als doel om de machine in januari 2017 operationeel te hebben. Volgens de modeluitkomst zal de investering binnen 10 maanden terugverdiend zijn en een totale reductie in verwachte extra kosten door productieverlies van €16 mln, of 57%, over de periode van januari 2017 tot juli 2024 opleveren.

De onderhoudsstrategie kan op drie punten worden verbeterd. De eerste is door het implenteren van operationele testen voor de reservemachines om hun conditie te kunnen bepalen. Door de reservemachines eens per jaar te gebruiken, kunnen zij bewijzen gebruiksklaar te zijn indien nodig. Defecten die aan het licht komen kunnen gerepareerd worden zonder dat dit direct invloed heeft op de betrouwbaarheid van de productlevering.

De tweede verbetering is het benutten van de functionele testen van de reservemachines voor het uitvoeren van visuele inspecties van de hoofdmachines. Echter, voor de levensvatbaarheid van deze strategie is het van belang dat de complexiteit van de visuele inspecties zoals ze op dit moment zijn drastisch wordt teruggebracht. Het wordt aanbevolen om de mogelijkheid tot het uitvoeren van visuele inspecties met een borescoop te onderzoeken, zodat deze inspectie aan het binnenwerk van de stoomturbines en luchtcompressors uitgevoerd kan worden zonder de behuizing te hoeven verwijderen, hetgeen op dit moment een kostbare en tijdrovende bezigheid is. Dit zal de drempel om een visuele inspectie uit te voeren verlagen, hetgeen ten goede komt aan de onderhoudsstrategie.

De derde verbetering aan de onderhoudsstrategie is het gebruik maken van de thermodynamische parameters van de windmachines voor prestatiebewaking. Het regelmatig evalueren van de machineprestaties faciliteert besluitvorming betreffende de productie- en onderhoudsplanning. Prestatiebewaking vergemakkelijkt de detectie van interne slijtage van de windmachines zonder een visuele inspectie uit te hoeven voeren. Bovendien kan gevolgschade voorkomen worden door het in een vroeg stadium detecteren van de initiële schade. Er wordt geconcludeerd dat een thermodynamisch model, zoals gecreëerd tijdens dit onderzoek, kan worden gebruikt voor dit doel. Dit thermodynamisch model maakt gebruik van de evaluatie van afwijkingen in de luchtstroom / schoephoek-ratio en correlatie (voor compressoren), de vermogen / stoom massastroom-ratio en correlatie (voor stoomturbines) en de isentropische efficiëntie (voor beiden). De eerste twee parameters zijn in deze studie tot stand gekomen en zijn mogelijke indicatoren voor interne schade aan de windmachines gebleken. Het prestatiemodel meet ook resultaten betreffende de beschikbaarheid en machinestatus. Die kunnen worden vergeleken met de normen van de operationele en onderhoudsprocessen, teneinde de prestaties van die processen te evalueren.

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List of symbols

A Amplitude (μm)

f Volume flow (m3_/s)

( ) Failure probability at time

( ) Cumulative failure probability at time

h Enthalpy (kJ/kg)

h(t) Hazard rate (1/t)

̇ Mass flow (kg/s)

MW Molar Weight (g/mol)

p Pressure (bar)

P Power (kW)

R Gas constant (J / (mol ∙ K))

( ) Cumulative probability of survival at time

s Entropy (kJ/kg ∙ K) Specific entropy (kJ/kg ∙ K) T Temperature (°C) t Time x Damp fraction (-) Greek Isentropic efficiency (%)

φ Volume flow (Nm3/min)

λ Failure rate (1/t)

Subscripts

Compressor Fluid phase Gas phase

In case of isentropic process Turbine

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List of abbreviations

AMD Asset Management & Development

DSA Delft Systems Approach

END Energy Department

HO HoogOven (Blast Furnace)

IAPWS International Association for the Properties of Water and Steam

KPI Key Performance Indicator

LP Compressed air supplementation system

MTBF Mean Time Between Failures

MTTR Mean Time To Repair

OEE Operational Equipment Effectiveness

OEM Original Equipment Manufacturer

PROPER-model Process Performance model

RCA Root Cause Analysis

ROI Return On Investment

TBF Time Between Failures

TPM Total Productive Maintenance

TTF Time To Failure

TTR Time To Repair

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1 Introduction

The first part of this chapter will consist of some general information about Tata Steel IJmuiden and the department where this assignment was carried out, which is follow by an explanation of the reason for this assignment.

1.1 Tata Steel IJmuiden

At Tata Steel IJmuiden close to 9000 people are employed and more than 7 million tons of high quality steel is produced every year. The business park covers 750 acres and is located directly on the North Sea. The steel from IJmuiden is mainly used in the automotive, construction and packaging sectors. The material is also used in batteries, tubes, industrial vehicles and white goods such as refrigerators and stoves.

This research was carried out at the Asset Management & Development (AMD) department. AMD is responsible for the development of blue prints for maintenance concepts and failure reduction for all the equipment at the IJmuiden site. AMD takes on a supportive role for other departments on these subjects. This research was carried out in support of the Energy Department (END). For a better understanding, a very basic representation of the organizational structure of Tata Steel IJmuiden can be found in Figure 1.1, with the relevant departments coloured blue.

Figure 1.1: Organizational structure Tata Steel IJmuiden

1.2 Introduction to this assignment

This assignment concerns the blowers that supply the compressed air that is required for the blast furnaces. In order to be able to understand the reason for and the importance of this assignment, first an explanation of the blast furnace process and the supply of compressed air is given, followed by the problem description.

1.2.1 Blast furnace process

In the blast furnaces iron is extracted from the iron ore. Layers of fuel (charcoal or cokes) and ferrous sinter or pellets are inserted at the top of the furnace. From the bottom of the furnace huge quantities (up to 6000 m3_{/ min) of compressed hot air (up to 5.5 bar, 1200° C), which is enriched with oxygen,}

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is blasted in the furnace. The oxygen burns the coals, with temperatures in the furnace reaching up to 2000° C. In these circumstances the iron in the iron ore melts, changing into liquid iron, which finds its way down to the bottom of the blast furnace. The liquid iron, or hot iron, gathers at the bottom of the blast furnace and has a layer of slag on top of it. When enough of the hot iron has been flowing down, the furnace is opened at the bottom. The hot iron is separated from the slag, tapped into a rail car and transported to the next step in the steel making process: the steel factory. Figure 1.2 gives a visual representation of the blast furnace process. At the IJmuiden facility there are two blast furnaces, HO6 and HO7, which are the bottleneck in the entire steelmaking process, so they must operate at maximum capacity. Apart from maintenance, this process continues 24 hours a day, 7 days a week.

Figure 1.2: Representation of the blast furnace process

1.2.2 Importance of supply of compressed air

As explained, the blast furnaces need large amounts of compressed air (from now on referred to as wind) to be able to operate. When the wind demand from a blast furnace is not met, the blast furnace has to be slowed down or even shut down. A shut down of one blast furnace leads to an average production loss of over €40.000 per hour. When the wind supply is cut off unexpectedly this can also lead to serious damage to the blast furnace. These significant damages, requiring a long repair time, would endanger the existence of the company. Therefore it is critical that there is a reliable wind supply that matches the demand from the blast furnaces.

1.2.3 Equipment setup

The wind is provided by the so-called blast furnace blowers. These are compressors that are powered by steam turbines. Figure 1.3 and Figure 1.4 give an idea of the appearance and size of these machines. The Energy Department is responsible for providing the wind to the blast furnaces. To do

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four compressed air supplementation systems (LP1-LP4) that serve as supplementary capacity and (emergency) back-up systems. When all else fails, there is also the option of hiring equipment that can be connected to the emergency back-up connections to keep the capacity up, but this is a last resort. At the moment the two main blowers and one back up blower are available. An overview of the equipment status is found in Table 1.1.

Figure 1.3: Overview of an opened up WM25 with the steam turbine up front and the compressor in the background (left) and a detail shot of the compressor blades (right)

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Figure 1.5: Simplified representation of the equipment set up for wind delivery to blast furnaces

Table 1.1: Equipment status

Equipment Desirable use Status (23-9-2014)

WM21 Standby (1st backup) In revision

WM22 Standby (2nd backup) Standby (1st backup)

WM23 Not operational Not operational

WM24 Main supplier for HO6 Main supplier for HO6 (awaiting revision) WM25 Main supplier for HO7 Main supplier for HO7 (awaiting revision)

LP1 Standby, supplementary Standby

LP3,4 Standby, emergency use Standby Rental equipment Last resort back up

1.3 Initial problem

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overhauls lead to a lot of down time for the blowers. This endangers the reliability of the wind supply and thus the reliable and efficient operation of the blast furnaces. Emergency measures, such as leasing backup machinery (€10.000/day) have prevented a large impact on the blast furnace operation until now. However, the current situation is unsustainable, costs the company significant amounts of money and leads to unacceptable risks to the companies‟ survival.

 END requests that research is conducted into what has to happen in order to achieve acceptable availability of the blast furnace blowers.

 The problem interpretation by the author is that the availability of the blast furnace blowers is currently unsatisfactory, but the required availability, the actual availability and the gap between these two are unknown. Furthermore there is no clear overview of the root causes of this gap.

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2 Research scope and approach

2.1 Scope

2.1.1 Time frame

The time frame within which data and failures will be analysed lies between 1-10-2010 and 27-10-2014. This time frame is chosen due to the availability of data and because it includes the starting point for the recent problems with availability of the blast furnace blowers.

2.1.2 System boundary

Based on the assumptions above, the system boundary of this research is set around the operation and maintenance of the blast furnace blowers. The process control is also incorporated in the system boundary since it has a strong influence on the use and maintenance process. A visual representation of this system boundary is displayed in Figure 3.2, which can be found in the process analysis in chapter 3.

2.2 Approach

The research starts with a problem analysis. In order to understand the processes this research is dealing with, first a process analysis using the Delft Systems Approach (Veeke, Ottjes, & Lodewijks, 2008) will be performed. Then the availability for technical systems is defined and the factors that influence the availability will be analysed and summarized in a break down structure. Using data analysis, the gap between the actual and desired availability of the blast blowers will be established. The final step in the problem analysis is to perform a failure Root Cause Analysis (RCA) to determine the causes of the downtime that have resulted in the gap between the actual and desired availability. The method to perform this RCA is called incident mapping, which is the default RCA-method applied at Tata Steel IJmuiden.

Based on the conclusion from the problem analysis, the problem statement will be created where the required improvements to the maintenance and operational strategies are stated, from which the research question with its sub-questions will arise. Next, the solutions will be presented.

For the improvement of the operational strategy a risk assessment model will be created which can be used for the numerical substation of investments and evaluation of the production planning, facilitating decision making on these topics. The model will be verified and validated. Some investments that can possibly improve the availability of the compressed air supply to the blast furnaces and are a topic of debate within the END will be evaluated using this model. Furthermore some recommendations on the implementation of process standards are provided.

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performance model that can be used by the END to evaluate the internal state of a blast blower without having to perform a visual inspection. It will also be able to measure the operational performance of a blast blower. The model will be verified and validated, with the intention to implement the model and make it available to the END process engineer.

This is followed by advice on the implementation of these models, the conclusions of this research and the recommended topics for further research.

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3 Problem analysis

The problem analysis is divided into four stages:

1. Process analysis of the main- and relevant sub processes in order to be able to indicate the system boundary, understand the processes that are involved and determine requirements 2. Background research on availability of technical systems

3. Data analysis: Quantifying the problem by identifying the gap between the required and actual availability

4. Failure analysis of problem causes that are responsible for the gap

These analyses lead to a conclusion with the problem causes and their contribution to the main problem. Then a topic for redesign can be chosen.

3.1 Process analysis: general

3.1.1 Method: The Delft Systems Approach (DSA)

The system will be mapped using the Delft Systems Approach (DSA) (Veeke, Ottjes, & Lodewijks, 2008). This scientific method is used to gain insight into a system or process in a structured way. It is a tool that can be used to identify the influences on a system and thus the possible problem causes for a system or process. This method does not necessarily provide answers, but it enables asking the right questions.

3.1.2 Level 0: Main process

First the main process is mapped at the highest level using the steady state model. The main process of a blast furnace blower is pictured in Figure 3.1. The function of this process is to create compressed air with certain requirements. The requirements and performance will be elaborated on later in this chapter.

Figure 3.1: Level 0 representation of a blast furnace blower

This figure displays the production process, but not the use and maintenance of the resources, the blast furnace blowers, which is the main focus for this assignment. That is why the PROPER (Process Performance) model is introduced in the next paragraph.

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3.1.3 PROPER level 0: model & system boundary

The PROPER model is used to map the supporting functions of the production process. In Figure 3.2 the top level PROPER model of this system is displayed. The production process is the centre part of the model. It is given tasks by the order performance process and is supported by the use and maintenance process for the resources. The process control is responsible for all processes that lay beneath and is formed by the upper management of the END.

The blast furnaces have certain requirements to the product. These requirements should lead to standards for the entire process of handling orders, producing compressed air and using and maintaining the resources.

The system boundary concerns the processes that have a direct effect on the availability of the blast furnace blowers. That is why the boundary is set around the process control and the use and maintenance of the blast furnace blowers, as indicated in Figure 3.2.

Figure 3.2: Basic PROPER - model for the system

3.1.4 PROPER model level 1

The interest of this research lies in the use and maintenance processes of the blast blower and how these processes are controlled. In this light the order handling process and the execution of the production process are irrelevant, so those processes are removed from the PROPER model. Adding more detail to the processes that remain leads to the model displayed in Figure 3.3.

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Figure 3.3: PROPER model of processes within scope in first level of detail.

This model forms the basis for the process analysis. The next step is to get an insight into the requirements, performance, standards, results and control processes that are displayed in this model and identify mismatches between theory and practice. For that purpose each process is discussed individually.

3.2 Control blast furnace blower process

The standards and required results that follow from the control process are essential to the required availability and results of the blast furnace blowers. The control process is extracted from the PROPER model and pictured as it is theoretically supposed to be inFigure 3.4.

Figure 3.4: Model for the control blast furnace blower process

3.2.1 General process

The requirements of the blast furnaces should be translated by the END into standards for the different sub-processes in such a way that when these standards are met, the requirements from the blast furnaces are met. In order to control the functioning of the system, the results that are measured have to be evaluated and should enable the determination of the Key Performance Indicator (KPI) values, which indicate the performance of the system. When the performance does not

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3.2.2 Requirements

The desired top level requirement for this process is that the wind supply has to be equal to the demand. In the Annual Plan of 2014-2015 it is stated that the goal of the END is to achieve 0% loss of production of the blast furnaces due to absence of wind. However, on the long term, even with an infinite amount of blast furnace blowers as backup, the 0% loss could be approached, but never achieved. A required reliability of the product supply of 99.9% would be more realistic.

3.2.3 Standards

The desired standard should concern the availability of the product, for the realisation of which all the resources together are responsible. From the actual requirement stated above, it can be concluded that the availability of the product should be according to demand, with a desired result of 100%.

3.2.4 Results and performance

The results that are used by the END for controlling the functioning of the system are currently limited to the available flow capacity in normalized m3_{/min (Nm}3_{/min). The result measurement should be a}

measure to which extent the standard is achieved, which is the availability of the desired product.

The reported performance should be as such that it is directly comparable to the system requirements and can be presented in the form of Key Performance Indicators (KPI‟s). In this case the KPI‟s used by the blast furnaces and the END are different. They are explained below.

Energy Department (END)

It is general knowledge at the END that preventing production loss at the blast furnaces is top priority. However, there is no KPI for the production loss. The KPI used by the END to evaluate the use and maintenance of the blast blowers is currently defined as the ratio between the available blast capacity (Nm3/min) and the maximum demand (Nm3/min). This KPI is evaluated once a month. An example is found in Figure 3.5. This KPI does not directly measure the achievement of the main requirement, which is focussed on availability of the desired product and the production loss that is caused by a lack of the desired product.

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The significance of this performance measurement is questionable since the maximum capacity of one blower cannot be divided over the two blast furnaces in normal operation, so the maximum capacities of the blowers cannot simply be added together. Furthermore, the actual demand from the blast furnaces is not always equal to the maximum demand. That is why this measurement does not result in a correct representation of the actual situation. Also, the measurement cannot directly be translated to the desired performance KPI since it does not precisely indicate the production loss suffered by the blast furnaces as a cause of a lack of availability of wind.

Blast Furnaces

The KPI that is used by the blast furnace to monitor the performance of this process is production loss due to the wind demand that is not being met. This production loss is measured and registered by the blast furnaces.

3.2.5 Conclusion on process control

1. Requirements: According to year plan 0% production loss of blast furnaces due to END. 2. Standards: 100% availability of demanded wind supply.

3. Results & performance: Evaluated once a month. However, results measured (available capacity) are not representative for the performance and cannot be translated in a KPI that is comparable to the system requirements.

3.3 Use and maintain process

A basic representation of the use and maintain process is shown in Figure 3.6. It can be divided into four main processes, which are listed below. These processes will be discussed in the next four paragraphs.

1. Control use and maintenance 2. Maintain

3. Stand by 4. Use

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Figure 3.6: Use and maintenance process

3.3.1 Control use and maintenance

The control process for the resources is shown in Figure 3.7.

Figure 3.7: Process of controlling resources

Requirements

The requirement to the use and maintenance process is an availability of the product of 100%.

Standards

One would expect the 100% availability requirement of the product to be translated into individual standards for the sub processes in terms of for instance availability, reliability and redundancy. In practice there are no clear standards known for the usage, stand by and maintenance processes which result from the system requirements.

Results

The result measurements should be used to evaluate the extent to which the standards are being met. However, since there are no standards that have to be met, there are no results that are used for evaluation of the functioning of the process. The total available capacity is the only result that is evaluated, which, as stated in paragraph 3.2.4, is not a representative result measurement of the process.

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Although there are no clear standards, recently the END started monitoring the actual status of the individual blowers. The main statuses can be extracted from Figure 3.6, being:

1. In operation (use) a. No restrictions b. Limited 2. Stand by 3. In maintenance a. Planned b. Unplanned

This data is currently not being used by the END to perform process and process performance evaluations.

Performance

With a requirement of 100% availability of the demanded wind, the expected KPI should consist of the difference between the actual delivery of wind and the demanded delivery of wind. In reality no such KPI is measured or evaluated.

Conclusion on control use and maintenance:

1. In general: No standardized/regular evaluation of results and taken action based upon these results.

2. Requirements: 100% availability of demanded wind supply

3. Standards: No clear standards regarding for instance maintenance, availability reliability and conservation. Only known standard is that there have to be two layers of backup.

4. Results: Some results are measured, but not evaluated or taken action upon. There is data available that can be used to evaluate results and performance in terms of availability, but this data is not used.

5. Performance: Available capacity is reported as performance, but that is not representable for the functioning of this system compared to its requirements.

3.3.2 Maintain

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Figure 3.8: The maintain process

Maintenance strategy

The current maintenance strategy consists of periodical preventive maintenance and condition monitoring. The compressor blades are the internal parts that are most prone to wear and have an expected lifetime of 130.000 hours. Every 65000 operational hours, or circa once every 7.5 years, revision and visual inspections alternate. For the condition monitoring several machine parameters such as vibrations and oil temperatures are monitored. Certain maximum or minimum values are set, for which an alarm goes off when they are exceeded. No active monitoring such as trend evaluation is performed.

No visual inspections or performance monitoring to the main and backup blowers is performed in between the 65000 hour maintenance interval. The reason that no visual inspections are performed to the main blowers is that such an inspection causes approximately 500 hours of downtime for the blower and added costs, making such inspections unattractive unless there is very good reason perform one. The absence of regular visual inspections and performance monitoring means that the exact condition of the machine in between revisions is unknown, which is highly undesirable for this critical equipment.

Another observation concerning the maintenance strategy is that there is an absence of the numerical substation of the risks that are present with respect to the product supply and the current equipment status. This for instance led to the situation in 2014 that the revision of WM24 was overdue since 2008. This was caused by the fact that first the revision was pushed back for budgetary reason and later it was not possible to take WM24 out of operation due to failures of WM21 and WM25. The END intended to perform the revision in 2008 in the first place, but could not sufficiently substantiate the need for it, eventually leading to a critical situation.

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Process time (MTTR)

The average time that a blast furnace blower spends in the maintenance process is of great importance for the availability of the blower, as further explained in paragraph 3.4. This duration is influenced by two things:

1. The process times: the time it costs to perform the actual maintenance 2. Waiting times: waiting for resources such as spares or man power

Especially the second one is of interest, since spares for the blast furnace blowers are expensive and are mostly build to order. That means that keeping spares is expensive and the time between ordering and receiving spares is large.

It is currently the case that expensive parts will only be ordered if it a revision is planned or it is clear they are absolutely necessary (inspection or failure). However, the internals of the turbine and compressor are not inspected in between revisions. In case of failure of the blower, first a decision on what to replace and what to replace it with (for instance: new and improved system or not?) has to be made. Then approval is needed in order to get the funds for the repair and possible improvements. After these decisions are made, the replacement parts can be ordered, produced and shipped. Especially the production time of the replacement parts leads to a high Mean Time To Repair (MTTR), having a negative effect on the availability of the blast furnace blower.

The experts from the Energy Department state that a full revision of a blast furnace blower can be performed in 2200 hours if all the replacement parts would be in stock when starting the revision, as is the case for a planned revision, and that an unplanned revision takes approximately one year, or 8760 hours.

Possibilities for improvement:

1. Prepare scenarios for different situations, eliminating decision time while blower is waiting for repairs.

2. Have spare parts ready when replacement is necessary, which can be done in two ways: a. Always keep a set of spares in stock, however this is capital intensive (€ 20 mln) b. Identify the necessity of the parts when the time to failure is still greater than the

lead time of the parts.

Requirements

There are no clearly stated requirements set on this process. The desired requirements would cover the following subjects:

1. Duration maintenance / MTTR (hrs) 2. Quality of work

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Standards

Since there are no clear requirements, there are also no clear standards. Desired standards would cover the following subjects:

1. Process times 2. Waiting times 3. Quality of work

4. Adequateness maintenance concept

Results

Inherent to the fact that there are no standards defined, there are also no result measurements that can be used to evaluate if the standards are being met. Desired result measurements would concern the same subjects as for the standards mentioned above.

Performance

For the performance measurements the same situation as for the results exists. Since no requirements are available, there are also no performance measurements for this process. The performance measurements are used to evaluate if the requirements are being met, so they should cover the same subjects as the requirements.

Concluding: observations maintain process

1. In general: No clear requirements to this process and no standards for the sub processes. No result measurements or evaluation.

2. Requirements: Not available 3. Standards: Not available 4. Results: Not available 5. Performance: Not available

3.3.3 Use process

The use process according to the Delft Systems Approach is shown in Figure 3.9.

Figure 3.9: The use-process

The blast blowers provide the blast furnaces with certain airflow at a certain pressure. The airflow is controlled by adjusting the blade angle of the compressor blades. The steam flow is controlled by a

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valve and set to keep the steam turbine RPMs equal over time. If a load increase is applied to the turbine by an increase in compressor blade angle, the steam flow will increase and vice versa.

The airflow that has to be provided varies based on the demand from the blast furnaces and whether or not a hot blast oven has to be pre-filled with cold blast air. The latter happens multiple times per hour. Since the flow to the blast furnace is to remain unaffected, this action requires extra air flow from the blower. The consequence of this load change is that the operating point of the blast blower changes several times per hour. An example of this oscillating process is shown in Figure 3.10. The required airflow is entered into the control system by the operator.

Figure 3.10: Example of load change of blast blower through time

Process

The requirements for this process consist of the following: 1. Use the blast furnace blower within its operational limits 2. Supply wind according to demand

The operating point is measured and compared to the operational limits. When a deviation is found the control system, consisting of automated systems and the operator, intervenes. When the blast furnace blower is used outside its operational limits, this is also reported as a result to the „control use and maintenance‟ process, with special attention given to the amount of minutes the compressor has been operating in the choking area, of which the significance will become clear in paragraph 3.6.4.

There are procedures for the operators that can be used under normal operating conditions, but (correct) procedures for emergency situations are not available.

Concluding: observations use process

1. Requirements: Set wind supply according to demand.

2. Standards: Operational limits and importance of not exceeding those limits are clear 3. Results: Exceeding operational limits is reported

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3.3.4 Stand by

The stand by process is displayed in Figure 3.11.

Figure 3.11: The stand by process

Process

When in standby mode, the blast furnace blower must be ready for use. A blower standing by serves as a backup and should be available in case one of the main blowers has to be taken out of operation, either planned or unplanned. There are no clear procedures on inspecting or testing the blowers.

Standards

There are no clear standards for this process. The desired standards would cover the following subjects:

1. Conservation of the blower

2. Readiness / availability for operation

Results

In order to measure the readiness and the extent to which the blower is conserved, regular blower tests and inspections would be required. No such thing is currently performed in this process.

Concluding: observations standby

1. In general: No clear procedures on conserving, inspecting or testing the blowers. 2. Standards: Not available

3. Results: Not available

4. Measurements: Not available

3.3.5 Observations in use and maintenance process

The requirement to the process of 100% availability of the product is not translated in to standards for the different sub processes. The absence of standards means that the performance of a process cannot be evaluated and controlled. This has as a consequence that the functioning of the processes cannot be managed, endangering the functioning of the entire process. Furthermore, there is an absence of the numerical substation of the risks that are present with respect to the product supply and the current equipment status.

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3.4 Availability for technical systems

An analysis on the availability for technical systems is performed to get an understanding of the factors that influence this availability. These factors, combined with the process analysis lead to several areas of interest, of which the performance can be evaluated and if necessary improvements can be applied.

Definition

According to (Smit, 2010) the inherent availability, which only considers unplanned downtime, is defined as:

( )

With:

MTBF Mean Time Between Failures MTTR Mean Time To Repair

From the definition can be deducted that the availability approaches 100% under two circumstances, which is when the MTBF goes to infinity, thereby eliminating the influence of the MTTR, and when the MTTR approaches zero.

This leads to the conclusion that improving the availability can be done in two ways: 1. Increasing the amount of operational hours in between failures

2. Reducing the repair time

3.4.1 Mean Time Between Failures (MTBF)

The mean time between failures is defined as the average time between two blower failures over a certain period. In other words, the MTBF is the average time the blower spends in the processes „stand by‟ and „use‟ from Figure 3.6 before a failure occurs. An increase in MTBF is achieved by reducing the number of failures. Preventing blower failure can be done in two ways:

1. Using the equipment within its operational limits

2. Performing the necessary maintenance, correctly and in a timely fashion.

Usage within operational limits

In order to be able to use the equipment within its operational limits, these limits should be known, given as input standards and controlled in the usage process from Figure 3.9. Furthermore, exceeding the operational limits can be prevented by making sure the product demand matches the blower capacity. The use within operational limits is applicable to the standby and the use processes from Figure 3.6.

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Maintenance

The impact of maintenance on the MTBF is obvious. The goal of the maintenance process is to prevent failures by replacing parts before they fail. The maintenance has to be performed conform a maintenance concept. Following the maintenance concept must lead to a timely and correct execution of the maintenance. To make sure the necessary tasks are performed, there must be standards for the desired state of the equipment and awareness of the actual state of the equipment.

3.4.2 Mean Time To Repair (MTTR)

The mean time to repair is the average time the blower spends in the „maintain‟ process from Figure 3.8. A reduction in MTTR can be achieved by reducing the process and waiting times in that process. As is concluded in the process analysis, there is no standard known for the MTTR and currently there is also no control mechanism for improving this MTTR.

3.4.3 Breakdown structure realization main goal

Based on the information gained from the process analysis and this paragraph, a breakdown structure of the requirements and standards that are necessary to realize the main objective of this process is created, as displayed in Figure 3.12. This structure provides a framework for realizing the main goal: improved reliability of the compressed air supply.

3.5 Data analysis

On the subject of availability there are no up to date and reliable performance figures available at the Energy Department. In order to get insight into the size and nature of the problems, a timeline of the events in the last four years was created. Using this timeline, performance figures can be calculated and the gap between the current and required availability can be determined. Consequently, an analysis of the problem causes can be made.

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3.5.1 Timeline

The timeline forms the basis for the data analysis. It describes the period from 3-10-2010 until 27-10-2014 and displays the blower status per day, an explanation when downtime occurs and whether or not the situation is within scope. An example can be found in Figure 3.13.

The following data was used to construct the timeline:  Condenser vacuum measurements (%)  Wind flow measurements (Nm3_/min)

 Operator logbooks  Blast furnace logbooks  SAP notifications

 Failure reports from MAN (OEM)

 END reports and internal communications

Figure 3.13: Example of timeline

3.5.2 Requirements

Due to the absence of clear formulated standards for the availability, MTBF and MTTR of the individual blast furnace blowers, an assumption on these values will be made based on the information that is

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Availability

In 2012 a manual analysis was performed by the END concerning the availability of the blast blowers over the period 2002-2012. The results are displayed in Table 3.1.

Table 3.1: Availability blast blowers period 2002-2012

Availability

Main (WM24&WM25)

96,8%

Backup (WM21&WM22)

91%

These numbers are based on SAP notifications, in which downtime of the blower and the duration are entered manually. A large amount downtime of WM25 that took place in 2011-2012 was left out of the occasion because it was decided that that would not give a realistic representation of the actual situation. Since over this period, with the failure of WM25 excluded, the availability of the blast blowers was deemed acceptable, the availability figures from Table 3.1 will be assumed the required availability.

MTTR

Experts at the END argue that a complete overhaul of a blast blower can be performed in three months (ca. 2200 hrs) if the replacement of parts can start immediately after taking the blower out of operation. Furthermore it is known that an unplanned overhaul takes approximately one year, or 8760 hours. However, these numbers are not used as a requirement for the repair time.

MTBF

There is no clear requirement for the operational hours, which can be monitored with the Mean Time Between Failures (MTBF). Since the preventive maintenance of the blast blowers solely consists of a major overhaul alternating with a visual inspection once every 65000 operational hours, the MTBF should at least be equal or greater than 130000 hours.

3.5.3 Measured availability, MTBF and MTTR

The availability figures resulting from the timeline can be found in Table 3.2. Here the availability data over the past four years is summarized. The required availability is compared to the total availability and the availability only considering the downtime within scope in order to show ratio between those two.

Table 3.2: Current availability of the blast furnace blowers

Required Actual total

Availability Availability Availability Gap MTBF (hrs) MTTR (hrs) wm25 96,8% 40% 40% -57,1% 4720 7168

wm24 96,8% 93% 96% -0,4% 11456 432

wm22 91,0% 91% 93% 2,2% 11080 808

wm21 91,0% 58% 74% -17,3% 26280 9384

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Failure nr.WM25 Start Duration (hrs) Impact on availability Production cost (mln €) Repair cost (mln €) Total cost

(mln €) Part Problem area Symptom Root cause

1 12-8-2011 8520 -24% n/a 3,45 3,45 Turbine

Production error /

maintenance Liberated blade in steam turbine

Blade production error / wear not detected 2 1-8-2012 7752 -22% 1,3 1,33 2,63 Compressor Use Multiple liberated blades in compressor Choking 3 13-11-2013 5232 -15% 3,1 1,8 4,9 Compressor Use Multiple liberated and damaged blades in compressor Choking

21504 -60% 4,4 6,6 11,0 WM21 Start Duration (hrs) Production cost (mln €) Repair cost (mln €) Total cost

(mln €) Part Problem area Symptom Root cause

4 2-10-2013 9384 -26% n/a 6,4 6,4 Turbine Conservation, Use

Multiple damaged and liberated blades in steam

turbine, damage to compressor Corrosion fatigue

Total Duration (hrs) Total cost (mln €) Actual MTTR (hrs) Desired MTTR (hrs) Actual MTBF (hrs) Desired MTBF (hrs) 30888 17,4 7722 ? 10236 65000

3.5.4 Conclusion on data analysis

It can be concluded that, considering the failures within scope over the period from 3-10-2010 to 27-10-2014, the availability of blowers WM21 and WM25 is well below the assumed standard with deviations of respectively -17.3% and -57.1%, as shown in Table 3.2.

For that reason these blowers will become the focus of this research from now on. Since the availability of blowers WM22 and WM24 seems to be within the requirements, these blowers will not be investigated further.

For WM25 and WM21 the lack of availability in scope over this period has been caused by four failures in combination with a high time to repair, ranging from 7 to over 18 months.

3.6 Failure root cause analysis

As shown in the previous paragraph, for WM25 and WM21 there is a significant gap between the required and actual availability that is caused by unplanned maintenance. In this paragraph the incidents that have caused unplanned downtime within the scope of this research for those blowers are listed, followed by a description of the root cause for every incident.

3.6.1 Incidents within scope

An overview of the incidents within the scope of this research with their impact on availability and cost is shown below, in Table 3.3. It is clear that these failures have had a big impact on the availability of the blast furnace blowers and have led to enormous costs. The total cost consists of the sum of additional production costs, production loss and repair costs. More detail on the origin of the failures is found in paragraph 3.6.4.

Table 3.3: Overview of incidents within scope.

3.6.2 Financial consequences

The financial consequences consist of production loss, repair costs and the leasing of backup equipment. The incidents within the scope of this research have led to €17.7 million in added costs.

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3.6.3 Method for RCA: incident mapping

The root cause analysis is performed using incident mapping. The choice for this technique is a practical one. Since it is the default technique used by Tata Steel to perform a Root Cause Analyse (RCA), using this method benefits internal communication concerning the root cause analyses.

The incident maps are based on:

 Research by National Aerospace Laboratory (fractography)  Root Cause analyses performed by MAN (OEM)

 SAP notifications  Operator logbooks

 END reports and internal communication

In Figure 3.14 an incident map of failure number 3 is shown as an example. An overview of the incident maps for all the failures listed in Table 3.3 can be found in Appendix B.

Figure 3.14: RCA of WM25 failure using incident mapping

Failure WM25 11-2013.

Repair time 7,4 months Repair cost 4,9 mln €

LEGEND

HO isn't supplied with wind from WM25

Compressor WM25 suffers from abnormal

vibrations

Blades from stage 11 damaged & liberated

Compressor suffered two surge strikes

Surge line was shifted downwards

Blades from stage 19 damaged & liberated

Compressor is running in choking area (over 90 hrs)

Back pressure of compressor is too low

Relief valve is opened by blast furnace when shut(ting) down

Machine damage detection

New training / working instructions for operators Crack formation at

blades from stage 19

Blade crack detection Consequence Known cause Event Possible barrier Broken barrier Implemented barrier Analyzed cause Contributing circumstance Backpressure rises

Anti-surge control has wrong assumptions

due to machine damage

Anti-choking control system is turned off Operator does not

intervene WM25 is taken out of

operation

Turn anti-choking control on

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3.6.4 Root causes

The root causes as they are mentioned in Table 3.3 are elaborated on in this paragraph.

Failure 1: Blade production error and wear

After 40 years of operation, fatigue of the material lead to the failure of one turbine blade. According to analysis of MAN (OEM) and the END, the failure is caused by a rare blade production error, although according to the author it can be argued that such a failure after 40 years of operation can attributed by wear. Cracks have formed over time, which grew and eventually led to liberation of the blade. Possibly, these cracks could have been spotted during a visual inspection of the machine internals.

Failures 2 and 3: Choking

RCA‟s from MAN (OEM) and the National Aerospace Laboratory have confirmed that choking of the compressor was the root cause for failures number 2 and 3. A compressor has certain operational limits. A representation of the operational limits of WM25 including the working area that induces choking of the compressor is found in Figure 3.15. Choking of a compressor occurs when the discharge pressure is too low at a certain volume flow. The low discharge pressure results in a high airspeed through the compressor. The air in the compressor releases from the blades and that results in an unstable air flow around the blades. The consequence is that the blades start vibrating and fatigue cracks grow at the base of the blades. At a certain moment the blade will liberate from the rotor.

Figure 3.15: Operational limits of WM25

Choking could occur because the choking phenomenon and the problems it caused were not known at the END at that time. In the previous 40 years blade failure due to choking never was an issue, so the operational limit concerning choking was not guarded by a control system or by the operator. When

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change, but the resistance of the blades to choking did. This in combination with the unguarded operational limit led to failures 2 and 3. Only the compressors of WM24 and WM25 are sensitive to this problem, since the compressors of WM21 and WM22 are axial compressors that do not contain blades.

Failure 4: Corrosion fatigue

Research by MAN (OEM) leads to the conclusion that corrosion fatigue is the initial cause for the failure of the blades in the WM21 steam turbine. Since WM21 is a backup machine it is probable that often a corrosive environment exists inside the blower, since it is mostly standing still. During stand still the blower should be conserved, for instance by filing it with nitrogen, is the advice MAN provides.

According to the incident reports it is likely that WM21 already suffered damage several months before the complete failure in the form of liberated blades. The initial damage weakened other blades through foreign object damage. The machine continued operation and eventually the weakened blades also liberated, initiating a series of events that led to the enormous final damage. More information can be extracted from the incident map in Appendix B.

Overall: consequential damage

In the case of failures number 2 and 4 the failure to detect initial damage to the blower internals and the absence of adequate working instructions led to a far bigger damage to the blower than necessary. Detecting the initial damage through performance measurements and the right interpretation of the first signs of serious blower damage in the form of noise, jamming and the intervention of the anti-surge system presented themselves could have prevented the damage that was caused by the continued use of the blower. This would not have prevented the initial damage, but would have prevented consequential damage making the repair take longer and cost more.

Detecting internal blower damage through a decline in performance and a change in vibrations could be a solution. The scale of the consequential damage can be seen from the incident maps in Appendix B.

3.7 Countermeasures already taken

3.7.1 Choking prevention

Compressor choking can be prevented in two ways:

1. Anti-choking system in the form of a back pressure valve that is operated by a control system 2. Revised working instructions for the operators that explicitly prohibit the use of the

compressor in the choking area, completed with instructions on how to act if the situation does occur.

Improving the reliability of the compressed air supply to the blast furnaces at Tata Steel IJmuiden - Het verbeteren van de bedrijfszekerheid van de persluchtlevering aan de hoogovens van Tata Steel IJmuiden

Specialization: Transport Engineering and Logistics

Report number: 2015.TEL.7937

Title:

Improving the reliability of the

compressed air supply to the blast

furnaces at Tata Steel IJmuiden

Author:

R.M. Draisma

Improving the reliability of the compressed air supply to the

blast furnaces at Tata Steel IJmuiden

Tata Steel IJmuiden

Problem definition

Research goal

Execution

Preface

Summary

Summary (in Dutch)

List of symbols

List of abbreviations

Contents

1 Introduction

1.1 Tata Steel IJmuiden

1.2 Introduction to this assignment

1.3 Initial problem

2 Research scope and approach

2.1 Scope

2.2 Approach

3 Problem analysis

3.1 Process analysis: general

3.2 Control blast furnace blower process

3.3 Use and maintain process

3.4 Availability for technical systems

3.5 Data analysis

Availability

Main (WM24&WM25)

96,8%

Backup (WM21&WM22)

91%

3.6 Failure root cause analysis

3.7 Countermeasures already taken