plant maintenance.pdf

7/27/2019 PLANT MAINTENANCE.pdf

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PLANT MAINTENANCE & WORKS SERVICES

(CME 315)


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TABLE OF CONTENTS

PLANT MAINTENANCE AND WORKS SERVICES Page

Course Overview

Unit 1 MAINTENANCE FUNCTION..........5

Section 1 The Role of the Maintenance Department.5

Section 2 Types of Maintenance...7

Section 3 Centralised or De-Centralised Maintenance Department? ..9

Section 4 Maintenance Stores and Inventory Control.........10

Section 5 Scheduling OF Maintenance Work..12

Section 6 Operational Policies for Effective Maintenance Department ..15

Unit 2 PUMPS AND COMPRESSOR.........17

Section 1 Types of Pumps....17

Section 2 Performance of Pump ......28

Section 3 Installation of Pump ....31

Section 4 Compressors.....34

Section 5 Maintenance of Pumps and Compressors ...38


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Unit 3 VALVES & PIPE CIRCUITS46

Section 1 Types of Valve46

Section 2 Installation ofValves..52

Section 3 Maintenance Pipe Circuits .54

UNIT 4 BOILERS...57

Section 1 Classification of Boilers.57

Section 2 Structure of a Boiler..61

Section 3 Feedwater System of A Boiler..65

Section 4 Combustion and Draft Systems of A Boiler65

Section 5 Steam Distribution System of A Boiler68

Section 6 Troubleshooting of A Boiler.70

UNIT 5 STEAM TRAPS, FILTERS AND STRAINER...73

Section 1 Types of Steam Traps...73

Section 2 Installation of Steam Traps...75

Section 3 Types of Filter And Strainer.....76

Section 4 Maintenance of Steam Traps , Filters And Strainers79


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UNIT 6 REFRIGERATION AND HEAT PUMPS..81

Section 1 Types of Refrigeration.81

Section 2 Performance of Refrigerators..86

Section 3 Heat Pumps..87

Section 4 Maintenance of Refrigerators..88


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Unit 1 MAINTENANCE FUNCTION

Section 1 The Role of the Maintenance Department

THE MAINTENANCE FUNCION

Refers to the set of operations undertaken to solve the day to day problems inherent in keeping

the physical facility (plant, machinery, buildings, services) in good operating order. In terms of

activities and responsibilities, the maintenance function can be classified as PRIMARY

FUNCTIONS or SECONDARY FUNCTIONS.

Primary Functions: require daily attention by the maintenance department. These are core to

the department and can be done by no one else.

Secondary Functions: are objectives and responsibilities assigned to the maintenance

department for reasons of technical knowhow, precedent and expediency.

Responsibilities of a Maintenance Dept

To extend the useful life of plant assets To assure the optimum availability of a stored equipment for production and obtain the

maximum possible returns on investment.

To ensure operational readiness of all equipment. To ensure the safety of personnel using the facilities.

Duties of a Plant Engineer

Maintenance of fixed and mobile plants Selection, control, and maintenance of work services The installation and commissioning of plant and services Budgetary control of maintenance and work services The selection of services, plants, equipment and consumable stores necessary for the

maintenance of fixed and mobile plants

Control of staff and operatives necessary for the maintenance of fixed and mobile plants Control of operations of fixed and mobile plants


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The design of plant to ensure optimum operating efficiency and the reduction ofmaintenance

Training of potential plant engineers Provision of consultancy services.Structure of Maintenance Department

Objectives:

To minimize bureaucracy To establish firm lines of authority, responsibility and accountability minimum overlap. To minimize operational cost To keep vertical lines of authority and responsibility as short as possible

To maintain an optimum number of staff reporting to the individual [1 : b/n 36]

Factors Affecting Structure

Type of Operation Continuity of Operations Geographical Situation Size of the maintenance department Scope of the maintenance department Workforce level of training and reliability


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Section 2 Types of Maintenance

Based on the point in time when repairs or maintenance work is carried out, there are three main

types of maintenance:

Breakdown Maintenance Corrective Maintenance Preventive Maintenance

Breakdown Maintenance (BM)

Reactive to breakdowns and therefore lacks adequate planning Cost much more than other types of maintenance Repairs tend to be incomplete as focus is placed on symptoms rather than rootcause of

problems.

Corrective Maintenance (CM)

Corrective repair tasks are schedules to correct specific problems that have beenidentified in the plant system.

Characteristics of CM Reacts to and deals with the first signs of the problem, and does not wait till the system

breakdown.

Life cycle cost of maintenance dictates the frequency of service. Complete repairs of presenting problems are made only when required. Repairs are well planned.

Preventive Maintenance (PV)

Maintenance tasks are implemented before a problem is evident. Characteristics of PM Proactive in by design Uses productive tools to detect potential problems and immediately schedule tasks to

prevent further degradation in the system.

Maintenance tasks are timedriven


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Maintenance tasks are thoroughly executed. Typically all types of maintenance activities are effectively, and complementarily

utilized.


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Section 3 Centralised or De-Centralised Maintenance Department?

Definition:

Centralisation is the process of bringing the activities of an organisation, particularly those

regarding planning and decision-making, become concentrated within a particular locationand/or group.Advantages of Centralisation

Easier dispatching from a more diversified craft group. The justification of more and higher quality equipment. Better relationship between craftsmen More specialized supervision Improved training facilities

Advantages of Decentralized Maintenance Department

Reduced travel time to and from job Better equipment knowledge through repeated experience Improved maintenanceproduction relationship More effective implementation of preventive maintenance due to local knowledge

Ideally a hybrid of centralized and decentralized department is the optimum. Depending on

circumstances, decide which aspects to be centralized or not. As circumstance changes adapt to

changes.

Training provision should be need based. In house training may save money, but may

compromise on quality.


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Section 4 Maintenance Stores and Inventory Control

Maintenance Stores and Inventory Control (INVI)

Inventory Item: Refers to any resource that is held in stock for future use (spares, equipment etc.)

Maintenance cost is generally made up of three components:

Maintenance Labour Cost Materials and Spare Parts Cost Cost of Production downtime when breakdown occur

Having too much inventory is a problem because it increases cost associated with keeping

inventory.

E.g. Storage Space Cost

Interest on cash used in purchasing excess spares and materials

Insurance Cost (against theft and fire)

Cost of obsolete or expired materials

Not having enough inventory is a problem because is increased both cost of production

downtime and also maintenance labor cost. How?

How much is Too Much?

Major Categories Inventory Items

1) Major Spare Partsshortage of these do cause prolonged downtime. e.g. high costcomponents render only repairables, difficult to acquire.

1) Minor Spare Partse.g. pipes, bolts, belts, carbon brushes2) Janitor / Housekeeping Supplies and Consumablese.g. lubricants, tissues, light bulbs,

filters


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3) Tools and Instruments4) Non maintenance itemse.g. excess produce from production

Factors that call for Increase in Inventory

High cost of production downtime Excessive maintenance scheduling Discounted bulk purchasing Unnecessary variety in plant equipment Decentralisation of maintenance stores Supplier location and dependability

Factors that call for decrease in Inventory

Lack of cash Supplier reliability Obsolesce of stock Storage cost

Have a database of inventory and make sure it is regularly updated.

Facility Register


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Section 5 Scheduling OF Maintenance Work

SCHEDULING

When to Schedule: Generally when staff number is more than ten, and also crafts number is

more than two. The larger the department, the more scheduling needs to be done.

Reason for Scheduling: Can result in improved efficiency of department

Ensure essential jobs are performed when monitored.

Helps in monitoring employees performance

How much Scheduling: 6080% ofemployees time, depending on nature of work

environment. May also be 0%. Monitor effectiveness!

Steps required in scheduling:

a) Choose a work unit (e.g. mins. manhours, man day, fractions of standard time)b) Size the job to be scheduledc) Decide how many employees are not to scheduled (i.e. emergency response teamd) Decide on lead time for scheduled job (e.g. a week, biweekly, 3day, etc.)

SELECTION AND IMPLEMENTATION OF SCHEDULING SYSTEM

a) Method of Requesting Work or Flow of Work Request: E.g. Work description, jobticket, work sheet. A staff should be dedicated to receive these orders. Maintenance

staff to redirect orders to this person.

Job no. to be allocated

Job

No.

Time /

Date

Requested

Requested

by

Description Location Contact

No.

Comment

/ Remark

Enough detail information must be recorded. Must also include work previously

scheduled, but not completed.


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b) Coordinating and Dispatching:Awareness of individual employees performancerating, motivation is vital. The foreman must not assume all personnel have his work

rate. This will help avoid incomplete work, idling of craftsmen. Early communication

of schedule to responsible staff will help their preparation towards work, leading to

improved efficiency. Cancellations and other changes should be relayed.

c) Determination of Priority: Necessary when work load exceeds resources, (i.e.human, equipment, materials). Maintenance must liase with production manager to

determine priority. If there are more than one production unit, be fair to all.

Remember the plant manager should have the final say and take responsibility for his

decision. NB: Health and Safety always a priority.

Produce a Priority System chart similar to (Page 1.64) and publish and distribute to all concern.

Example of Scheduling Control Sheet

Dept/ Site: Name:----------------------------

Week Ending---------------------------------------------- Emp No.------------------------

Assignment, Schedule, Check of List and Performance Record

Location Operation Oper.

Time/mins

Sched.

Compl.

Mon Tue Wed Th Fri

A Service

filters

45min 10:00

C Change

oil

90min 11:30

D Clean

condenser

75min 12:15

B R E A K 13:15

E 45min 14:00

K Boiler 45min 14:45


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Maintenance Work Order

Maintenance planningis a mechanism within the maintenance department for coordinating the

work to be assigned. This usually carried out by the maintenance planning group.

Steps:

a) Work order receivedb) Planner starts planning by assembling (Supervision + crew of craftmen to execute job)c) Planner determines the tools, equipment, and materials needed to complete the job.d) Planner estimates time required.e) Planner checks availability of all requisite resources and then schedules the work after

checking priority.

f) Revises schedule if necessaryg) Planner may assign cost to the job to determine whether it is worth doing.


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Section 6 Operational Policies for Effective Maintenance Department

Policy guidelines must be developed to take care of:

Work allocation Workforce recruitment and development Intra-plant relations Control

Work Allocation Policy Considerations

Dayto day allocation of work load must be planned. The larger the department, themore thorough this planning should be.

Ideally no more than 6080% of a maintenance personnels work load should bescheduled due to the inevitability of emergency work. Decide on % of priority of these

scheduled tasks should be indicated.

Incentive pay to be introduced where possible Choose a suitable work unit. This may be in manhours, standard time in hours, half

manday, manday, manweek.

Major works are schedules with suitable lead time, stating number and type of skilledworkers required, and also the length of time required. Small jobs tend to be unscheduled.

Decide on lead time for scheduling. A weekly or biweekly schedule with a 2to 3day lead time is a good idea.

Intra-plant Relations Policy Considerations

To what extent maintenance staff should be involved in selecting production equipment. Their involvement likely to result in reduced maintenance cost. Who should have authority to shutdown the plant for maintenance? This should be stated

clearly.

Who has responsibility for safety? Should there be a health and safety department?.


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Control Policy Considerations

Decide on the channels of communication Emphasize organizational structure Communication should be reduced to minimum. Feedback systems should be

incorporated to ensure that orders are not being ignored, and that policies are being

adhered to.

Cost control system should be covered.

Workforce Policy Considerations

Own Workforce or Contractors? Depends on cost Cost of maintenance work and cost of downtime. Quality of work required, availability of

specialist, skilled workers, retention rates. Own staff to handle normal load, peak load

can be deferred or handled by contractors. Contractors may be used for major projects.

Attitude of staff. Absenteeism, militant trade union. How many of the various specialties should be required. For example how many

chemical engineers, mechanical engineers, electrical engineers, etc. and also their level of

training.

How many full time and parttime roles to be created. Number of shifts to operated 1,2, or 3 shifts? 24hrs/7days service? By which craftsmen?

Is there a need for oncall service? To be carried out by who? How this should be paid.

Should the department be centralized or decentralized?


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Unit 2 PUMPS AND COMPRESSORS

Section 1 Types of Pump

Definition:

A pump is a device that transfers a specific volume of liquid at a particular pressure from a fixed

source to a final destination.

Types of Pump

Pumps are normally classified according to their structure. Broadly they are classified as Kinetic

(or Rotodynamic) Pumps or Positive Displacement Pumps.

Displacement Pump is a pump which imparts energy to the pumped liquid by trapping a fixed

volume at suction (inlet) conditions, and pushing it into a discharge (outlet) line.

Kinetic Pump, example of which is a centrifugal pump forces the liquid being pumped into a set

of rotating valves which constitute the impeller, discharging the liquid at a higher pressure and

higher velocity to the outlet.

There are many different types of pumps based on the structure and mode of operation. Fig. 1

below shows a classification diagram of pumps, listing the most common types. Fig. 2 below

shows the structures of some of the common pumps (pages 24)


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Centrifugal PumpsFig 2.1.1 to Fig 2.1.6 show images of

centrifugal pumps. A centrifugal pump

consist of a stationary pump casing and an

impeller mounted on a rotating shaft. The

pump casing has suction and discharge

connections for the main flow path of the

pump and normally has small drain and

vent fittings to remove gases trapped in

the pump casing or to drain the pump

casing for maintenance. Fig 2.1.1 depicts

the following:

Pump casing Pump shaft Impeller Volute Stuffing box Stuffing box gland Packing Lantern Ring

Impeller wearing ringPump casing wearing ring Fig 2.1.1 Centrifugal Pumps


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The pump casing guides the liquid from the suction connection to the centre of the impeller. The

vanes of the rotating impellerimpart a radial and rotary motion to the liquid, forcing it to theouter periphery of the pump casing where it is collected in the outer part of the pump casing

called the volute. The volute is a region that expands in cross-sectional area as it wraps around

the pump casing. The purpose of the volute is to collect the liquid discharged from the peripheryof the impeller at high velocity and gradually cause a reduction in fluid velocity by increasing theflow area. This converts the velocity head to static pressure. The fluid is then discharged from

the pump through the discharge connection.

Some centrifugal pumps containdiffusers. A diffuseris a set of

stationary vanes that surround the

impeller. The purpose of the

diffuser is to increase theefficiency of the centrifugal pump

by allowing a more gradual

expansion and less turbulent areafor the liquid to reduce in velocity.

The diffuser vanes are designed in

a manner that the liquid exiting the

impeller will encounter an everincreasing flow area as it passes

through the diffuser. This increase

in flow area causes a reduction inflow velocity, converting kinetic

energy into flow pressure. Fig 2.1.2 Centrifugal Pump Diffuser

Packingmaterial provides a seal in the area where the pump shaft penetrates the pump casing.Wearing rings are replaceable rings that are attached to the impeller and/or the pump casing to

allow a small running clearance between the impeller and pump casing without causing wear of

the actual impeller or pump casing material.

The lantern ringis inserted between rings of packing in the stuffing box to receive relativelycool, clean liquid and distribute the liquid uniformly around the shaft to provide lubrication and

cooling to the packing.

Multi-Stage Centrifugal PumpsA centrifugal pump with a single impeller that can develop a differential pressure of more than

150 psi between the suction and the discharge is difficult and costly to design and construct.

A more economical approach to developing high pressures with a single centrifugal pump is toinclude multiple impellers on a common shaft within the same pump casing. Internal channelsin the pump casing route the discharge of one impeller to the suction of another impeller.

Figure 9 shows a diagram of the arrangement of the impellers of a four-stage pump. The water

enters the pump from the top left and passes through each of the four impellers in series, going

from left to right. The water goes from the volute surrounding the discharge of one impeller tothe suction of the next impeller.


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Fig 2.1.3 Single Stage Centrifugal Pump

Fig 2.1.4 Single and Double Volute Centrifugal Pumps


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Fig 2.1.5 Multi Stage Centrifugal Pump

Types of Centrifugal Pump

Based on the direction of flow of the pumped liquid, there are three main types of centrifugal

pump, namely:

Axial Pump Radial Pump Mixed Pump

Fig 2.1.6Axial Flow Pump


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Fig 2.1.7Radial Flow Pump

Fig 2.1.8Mixed Flow Pump

Positive Displacement Pumps

Positive displacement pumps physically entrap a fixed quantity of liquid at the suction of the

pump and push that quantity out through the discharge of the pump. For example, in a single-

acting plunger pump (Figure 2.1.10) the swept volume created by piston movement is the

quantity delivered by the pump for each piston stroke, and total flow rate is related to the number

of strokes per unit time. Similarly, the gear pump (Figure 2.12) traps a fixed quantity in the spacebetween adjacent teeth and the casing, and total flow rate is related to the rotational speed of the

gearwheels.

The positive displacement pump delivers liquid in separate volumes with no delivery in between.They differs from centrifugal pumps, which deliver a continuous flow for any given pump speed

and discharge resistance.

Positive-displacement pumps are inherently low-capacity, high discharge-pressure pumps. Theyare the preferred choice in the pumping of more viscous liquids like wastewater and sewage.


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Principle of Operation ofPositive Displacement Pumps

All positive displacement pumps operate on the same basic principle. This principle can be most

easily demonstrated by considering a reciprocating positive displacement pump consisting of asingle reciprocating piston in a cylinder with a single suction port and a single discharge port as

shown in Figure 2.1.9. Check valves in the suction and discharge ports allow flow in only onedirection.During the suction stroke, the piston moves to the left, causing the check valve in the suction

line between the reservoir and the pump cylinder to open and admit water from the reservoir.

During the discharge stroke, the piston moves to the right, seating the check valve in the suction

line and opening the check valve in the discharge line. The volume of liquid moved by thepump in one cycle (one suction stroke and one discharge stroke) is equal to the change in the

liquid volume of the cylinder as the piston moves from its farthest left position to its farthest

right position.

Figure 2.1.9 Reciprocating Positive Displacement Pump Operation

Type of Positive Displacement Pumps

Based on their design and operation, positive displacement pumps can be grouped into three

types:

Reciprocating pumps Rotary pumps Diaphragm pumps


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Reciprocating pumps

A reciprocating pump consist of a reciprocating piston or plunger in a cylinder with a suction

port and a discharge port as shown in Figure 2.1.9. Check valves in the suction and dischargeports allow flow in only one direction. The swept volume created by the piston or plunger

movement is the quantity delivered by the pump for each stroke.

Fig 2.1.10 Schematic Diagram of a Plunger Pump

Fig 2.1.11 Plunger Pump


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Rotary PumpsRotary pumps operate on the principle that a rotating vane, screw, or gear traps the liquid in the

suction side of the pump casing and forces it to the discharge side of the casing.

Fig 2.1.12 Gear Pump

Fig 2.1.13 Lobe Pump


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Diaphragm PumpsDiaphragm pump will function when a diaphragm is forced into reciprocating motion by

mechanical linkage, compressed air, or fluid from a pulsating, external source. The pump

construction eliminates any contact between the liquid being pumped and the source of energy.

This eliminates the possibility of leakage, which is important when handling toxic or very

expensive liquids. Disadvantages include limited head and capacity range, and the necessity ofcheck valves in the suction and discharge nozzles.

Fig 2.1.14 Diaphragm Pump

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