PLANT MAINTENANCE.pdf

PLANT MAINTENANCE & WORKS SERVICES (CME 315)

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

Unit 3

VALVES & PIPE CIRCUITS ……………………………46

Section 1

Types of Valve………………………………………………46

Section 2

Installation of Valves………………………………………..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 Boiler………………65

Section 5

Steam Distribution System of A Boiler……………………68

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 Strainers………79

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

Unit 1

Section 1

MAINTENANCE FUNCTION

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 know – how, 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

 The design of plant to ensure optimum operating efficiency and the reduction of maintenance  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 3 – 6]

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

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 root – cause of problems. Corrective Maintenance (CM)  Corrective repair tasks are schedules to correct specific problems that have been identified 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 time – driven

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

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 location and/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 maintenance – production 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.

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 Parts – shortage of these do cause prolonged downtime. e.g. high cost components render only repairables, difficult to acquire. 1) Minor Spare Parts – e.g. pipes, bolts, belts, carbon brushes 2) Janitor / Housekeeping Supplies and Consumables – e.g. lubricants, tissues, light bulbs, filters

3) Tools and Instruments 4) Non maintenance items – e.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

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: 60 – 80% of employee’s 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. man – hours, man day, fractions of standard time) b) Size the job to be scheduled c) Decide how many employees are not to scheduled (i.e. emergency response team d) Decide on lead time for scheduled job (e.g. a week, bi – weekly, 3 – day, etc.) SELECTION AND IMPLEMENTATION OF SCHEDULING SYSTEM a) Method of Requesting Work or Flow of Work Request: E.g. Work description, job ticket, 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

Time /

Requested

No.

Date

by

Description Location

Contact

Comment

No.

/ Remark

Requested

Enough detail information must be recorded. Must also include work previously scheduled, but not completed.

b) Coordinating and Dispatching: Awareness of individual employee’s performance rating, 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.

Sched.

Time/mins Compl. A

Service

45min

10:00

90min

11:30

75min

12:15

EAK

13:15

45min

14:00

45min

14:45

filters C

Change oil

D

Clean condenser

B

R

E K

Boiler

Mon

Tue

Wed

Th

Fri

Maintenance Work Order Maintenance planning is 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 received b) 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 necessary g) Planner may assign cost to the job to determine whether it is worth doing.

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 

Day – to day allocation of work load must be planned. The larger the department, the more thorough this planning should be.



Ideally no more than 60 – 80% of a maintenance personnel’s work load should be scheduled 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 man – hours, standard time in hours, half man – day, man – day, man – week.



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



Decide on lead time for scheduling. A weekly or bi – weekly schedule with a 2 – to 3 – day 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?.

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 part – time 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 on – call service? To be carried out by who? How this should be paid.  Should the department be centralized or decentralized?

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 2 – 4)

Centrifugal Pumps Fig 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 ring Pump casing wearing ring

Fig 2.1.1 Centrifugal Pumps

The pump casing guides the liquid from the suction connection to the centre of the impeller. The vanes of the rotating impeller impart a radial and rotary motion to the liquid, forcing it to the outer 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 periphery of the impeller at high velocity and gradually cause a reduction in fluid velocity by increasing the flow area. This converts the velocity head to static pressure. The fluid is then discharged from the pump through the discharge connection. Some centrifugal pumps contain diffusers. A diffuser is a set of stationary vanes that surround the impeller. The purpose of the diffuser is to increase the efficiency of the centrifugal pump by allowing a more gradual expansion and less turbulent area for the liquid to reduce in velocity. The diffuser vanes are designed in a manner that the liquid exiting the impeller will encounter an ever increasing flow area as it passes through the diffuser. This increase in flow area causes a reduction in flow velocity, converting kinetic energy into flow pressure. Fig 2.1.2 Centrifugal Pump Diffuser Packing material 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 ring is inserted between rings of packing in the stuffing box to receive relatively cool, clean liquid and distribute the liquid uniformly around the shaft to provide lubrication and cooling to the packing.

Multi-Stage Centrifugal Pumps A 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 to include multiple impellers on a common shaft within the same pump casing. Internal channels in 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 to the suction of the next impeller.

Fig 2.1.3

Single Stage Centrifugal Pump

Fig 2.1.4

Single and Double Volute Centrifugal Pumps

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

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 singleacting 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 space between 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. They are the preferred choice in the pumping of more viscous liquids like wastewater and sewage.

Principle of Operation of Positive 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 a single 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 one direction. 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 the pump 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

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 discharge ports 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

Rotary Pumps Rotary 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

Diaphragm Pumps Diaphragm 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 of check valves in the suction and discharge nozzles.

Fig 2.1.14

Diaphragm Pump