Q1

In Mazoon Electricity Company, from maintenance department:

The structure:

Objective: The prime objective of maintenance is to keep the equipment in good condition to maximize lifetime productively.

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Responsibilities:

a. Supervisor:

1. Anticipates all work hazards and ensures that all safeguards areutilized.2. Ensures that all employees are properly trained and instructed in thesafe operation of electrical equipment and aware of all hazardsassociated with the use of these electrical devices.3. Initiates any necessary administrative action required to enforcesafety practices.4. Requests assistance from Health, Safety and Environment Sectionon equipment and devices, which require unique safety practiceinstructions.

b. Employee:

1. Follows MZEC HSE policy, related procedures and instructions ofresponsible supervisor and/or Health and Safety Staff.2. Brings to the attention of the supervisor and/or Health and SafetyStaff potential hazardous situations such as discrepancies betweeninstruction, procedures, policies and manual, faulty equipment,misapplication of device, etc.3. Electrical equipment known to be malfunctioning must be repaired orreplaced before use. The repair must be initiated as soon aspossible after the malfunction is noted.

c. The following practices are to be followed by all employees:

1. The user (MZEC and contactor staff) is responsible for obtainingnecessary tools and safety equipment from the designated storagearea, checking it for discrepancies, returning it to storage area ingood condition and reporting any faulty equipment to his/hersupervisor. It shall be the supervisor's immediate responsibility toreplace any faulty safety equipment and notify the Health and SafetySection.2. Eye protection is required during any electrical hardware repair,installation and/or during electrical operation.3. Electrical safety shoes, shirts, pants and proper gloves will be wornwhen operating or testing electrical equipment.4. Protective apron will be worn over polyester or other highlyflammable clothing during soldering operations.5. Jewelry such as rings and metal watches should not be worn whileperforming electrical repairs.

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Q2

a) What are the various types of maintenance strategies that can be adopted for a process industry?

There are many maintenance strategies can be adopted by the maintenance department in process industry, each maintenance strategy has its advantages as well as the disadvantages.

The six types of maintenance strategies going to be listed below can all be used in the process industries and some of them can be used together.

1) Beak down maintenance. - where the maintenance is started only after the device fails to finish a certain job-

In this type of maintenance the industry won’t have to recruit lots of maintenance employees and will not stop working unless the device stops the job finishing, at the same time it sometimes costs the company the price of the whole device, and might stop the production for many hours that the industry can’t handle.

2) Planned maintenance. – the maintenance will be starting depending on the structure from the manufacture usually depending on the working hours of the machine-

In this type of maintenance since the manufacture provides the planning of maintenance of the machine and that how you make sure that the machine will work in a very high performance percentage for a very long time, at the same time you might change some parts and components and sometimes even the lubrication even if it can work for one more month, so this how you are going to pay and change for something doesn’t needs to be changed.

3) Preventive maintenance. – to avoid failure making the maintenance before the failure time-

In this case the machine will perform well in a very high rate, but at the same time it might fail before the maintenance time due to any reasons that may happen, at the same time you might change the parts before the time they need to be changed (spending more money).

4) Scheduled maintenance. – putting a time table for each device maintenance time depending on the history and experience of the machine-

In this case the machine will be well performed, but it needs lots of man power at the same time, the industry will loss many of working hours on the due to the maintenance schedule which will cost lots of money.

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5) Corrective maintenance. – to avoid repeated maintenance of equipment redesigning some of the components and modifying the machine-.

In this type of maintenance the industry won’t have to stop much for maintenance especially for regular cases of failure due to component shape errors, but it will cost the company much to spend on the development and research of the maintenance and design.

6) Condition based monitoring. – maintenance done based on condition of machine-

The machine will be loaded with lots of sensors that are operated by operators, which gives the operator the whole information of the device and component conditions, where the industry won’t have to stop unless something is really going on, at the same time they won’t change any part before the actual changing time, at the same time it will cost the company a very big amount of many to establish this type of maintenance, that’s why it is only recommended for high capital industries.

b) What is work order? In Al-Quram desalination plant, Muscat, feed pump is creating noise, design a suitable work order form to above problem. With whole details planner, crew, supervisors … etc.

- Work order is a form in which written instructions are detailed for work to be carried out. The purpose of work order is to enable the following:

1) To make the request in writing the work to be carried by maintenance.

2) Ascertaining the work requested by operation.

3) Assigning the best method and the best qualified workers for the job.

4) Reducing the cost through the most effective utilization of resources.

5) Maintaining and controlling the maintenance work.

6) To improve the planning and scheduling of maintenance activities.

7) To collect data of the work carried and the feed back to improve future work procedure.

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Steam turbine

Steam turbines are is used in many industries to impel process and chiller compressors, boiler fans, boiler feed and water pumps, sugar mill grinder, paper mill line shafts and generators in different of industries and applications especially in power plants. Accordingly, steam turbines can be designed/constructed simple and small to large and complex designed/constructed.

To specify the desired maintenance and overhaul times for steam turbines, the design/construction of the steam turbines as well as the industry and application using the turbine for must be taking under consider.

Fig.1 210MW Steam Turbine

TECHNICAL SPECIFICATION OF 210 MW STEAM TURBINESerial No. Description Parameter1 RATED CAPACITY 210 MW2 PRESSURE AT STOP VALVE 150 KG/CM23 TEMPERATURE AT STOP VALVE 535 C4 MAX. STEAM FLOW AT S.V 641 TONNES /HR5 REHEAT/NON REHEAT REHEAT6 TYPE OF GOVERNING THROTLLE CONTROL7 TURBINE SPEED 3000 RPM8 EXHAUST PRESSURE 76 MM HG.ABS9 NUMBER OF CYLINDERS H.P-1,DOUBLE FLOW IP-

1,DOUBLE FLOW LP-110 NUMBER OF STAGES HP-25, IP-20 +20,LP-8+811 HEIGHT OF LAST STAGE BLADE 676 MM12 LAST STEAGE MEAN DIA 2132 MM13 SPECIAL FEATURE -DOUBLE SHELL HP WITH BARREL

TYPE OUTER SHELL – DOUBLE SHELL DOUBLE FLOW IP – HYDRAULIC BARRING –

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ELECTRO-HYDRAULIC GOVERNING

14 WEIGHT OF TURBINE 425 TONNES15 LENGTH OF TURBINE 14.1 METERS16 TYPE OF TURBINE REACTION17 COLLABORATOR SIEMENS, GERMANY

Table.1 Specification of 210MW steam turbine

The type of maintenance was applied in this industry is condition based monitoring, since the amount of equipment depends on the complexity of the steam turbine, the minimum acceptable turbine parameters that should be monitored by turbine size/type are shown below:

Steam Turbine Parameters to be Monitored Continuously

SmallSingleStageUnits0.5-2MW

MediumSize

MultistageUnits1.5-10MW

Admission/Extractionand Non-ReheatUnits

100 MW

CombinedCycle

ReheatUnits

LargeReheat

Subcriticaland

SupercriticalUnits

Speed (RPM) X X X X XPower (MW or SHP) X X X X XSteam Turbine Inlet Pressure

X X X X X

Steam Turbine Inlet Temperature

X X X X X

Steam Turbine 1st Stage Pressure

X X X X

HP Turbine Outlet, IP Turbine Inlet, IPTurbine Outlet/LP Turbine InletPressures and Temperatures

X X

Admission Steam Inlet Pressure andTemperature (As applicable)

X X

Extraction Steam Outlet Pressure andTemperature (As applicable)

X

Turbine Exhaust Steam Pressure

X X X X X

Turbine Exhaust Steam Temperature

X X X

Sealing Steam Pressures X X X X XSealing Seal Exhauster Vacuum

X X X X

HP and IP Turbine Shell/Steam ChestTemperatures/Differentials

X X X

Rotor/Shell Differential X X X

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ExpansionsRotor Eccentricity X X XHP and IP Stress XExtraction Line and Drain LineThermocouples

X X X

Lube Oil Supply Pressure X X X X XLube Oil Supply Temperature

X X X X

Lube Oil Sump Level X X XBearing Metal or Drain Temperatures

X X X X

Thrust Bearing Wear/Temperatures

X X X X

Thrust Bearing Wear/Temperatures

X X X X

Hydraulic Fluid Pressures andTemperatures

X X X X

Cooling Water Supply Pressures andTemperatures for Lube Oil andHydraulic Fluid Heat Exchangers

X X X X X

Water and Steam Purity Monitoring

X X X X

Control Valve Position (%) Indication

X X X X

Admission and Extraction ValvePosition (%) Indication

X X

Table.2 Parameters should be monitored in steam turbine based on the size and type

Fig.2 online Steam Turbine monitoring

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The history of the steam turbine maintenance will be shown and discussed below:

Fig. 3 history of failure causes for the steam turbine lost availability in MW-Hrs per year from 1998-2002

The loss of lube oil incidents had the highest frequency of failure. These have happened in sizes ranging from 10MW to 400 MW for the variety of the reasons shown in Table.3. From the history we can understand that many of the failures due to these problems have resulted in turbine rubs in addition to damage to applicable bearings. Over speed events had the highest severity failure. While some of the failure causes due to improper checkout during commissioning or losing control during testing of steam turbine with uncoupled boiler feed pump, the others are due to component failures. Most of the blade failures have been in the low pressure (LP) section of the turbine, where the blades have experienced stress corrosion cracking or excessive erosion and FOD.

Component Failure Mechanism

Cause(s) Frequency Rank Severity Rank

Turbine Rotor andBearings

Loss of lube oil

1. Pressure switches did not work.2. Backup lube oil pump did not work.3. Duplex filter switching problem4. Oil supply valve leaked5. Ruptured bearing oil line

1 3

Bucket or BucketCover Failure

Fatigue,corrosion,erosion,rubbing, andSCC

1. Blade and/or cover cracked, pitted,thinned or eroded and finally broke.2. Corrosive chemicals in the steam3. High backpressure for last turbine

2 2

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stage.4. Water induction5. Resonance sensitive bucketdesign6. Bowed rotor and/or humped shell

Turbine RotorOverspeed (OS)with or withoutWater induction

1. NRV stuck open during shutdown.2. Mechanical OS device did notwork.3. Main Steam Stop/T&T valve stuckpartly open.4. Lost control of test5. Controls – OS did not work

3 1

Turbine RotorMajor rubbing,high vibration

1. NRV stuck open during shutdown.2. Mechanical OS device did notwork.3. Main Steam Stop/T&T valve stuckpartly open.4. Lost control of test5. Controls – OS did not work.

2 2

Nozzle andBuckets, HP andIP Stages

Solid particleerosion

1. Exfoliation – boiler inlet piping.2. Main Steam Stop/T&T valve inletstrainer broke.

3 4

Nozzle andBuckets, LPStages

Droplet erosion

1. Saturated steam in the LP turbine.2. Poor turbine design.

3 4

Nozzles andBuckets, AllStages

Foreign orDomestic ObjectDamage(FOD/DOD)

1. Debris in inlet line to turbine.2. Main Steam Stop/T&T valve inletstrainer broke.3. Parts adrift inside turbine, orbroken nozzle partitions or bucketshrouds.

4 3

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Table.3 Steam Turbine Failure – Mechanisms and Causes (1=highest, 4=Lowest)

Fig.3 operation of a steam turbine generator system

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