Case study $2$: Textile factory

A textile factory has started its operation as from $1$st July $2008.$ One of the main processes in the factory

is the steam production at the boiler plant. Coal is used as combustible.

The boiler plant operates continuously for two $(2)$ shifts per day from Monday to Saturday. Basic

maintenance work, routine inspection as well as repairs are carried out on Sundays. The factory

operates continuously three hundred and sixty$-$two $(362)$ days per year and is closed only for

Christmas, New Year $(1$st and $2$nd January$).$ The operation manager has indicated that he wants a high

level of reliability over the year since any major failure of the boiler plant normally lead to a complete

factory shutdown resulting in lost in production, and delays in the delivery of orders to customers

$($leading to penalties$).$

All the different processing units in the factory suffer from wearing leading to failure. Extracts of the

maintenance history records for some machinery within the boiler area are as follows:

$2$

$($i$).$ Replacement of double roller bearings on the Induced Draught $($ID$)$ fan of the boiler on the

following seventeen $(17)$ dates:

$18$th January $2009,20$th August $2009,11$th February $2010,30$th May $2010,6$th October $2010,21$st December

$2010,12$th August $2011,15$th December $2011,10$th March $2012,17$th December $2012,15$th April $2013,20$th

October $2013,5$th March $2014,24$th June $2014,1$st February $2015,30$th August $2015,2$nd December $2015.$

$($ii$).$ Replacement of ball bearings for the centrifugal pump for the feed water supply to the boiler on

the following twelve $(12)$ dates:

$2$nd April $2009,4$th November $2009,22$nd June $2010,15$th January $2011,25$th August $2011,8$th March $2012,$

$15$th November $2012,12$th June $2013,25$th January $2014,28$th August $2014,30$th March $2015,16$th

November $2015.$

$($iii$).$ Replacement of the driving and driven gears of the ID fan reduction gearbox. Several teeth of both

gears were severely worn out, and the gearbox is lubricated with a mineral oil. Replacement of the two

gears were done on the following four $(4)$ dates:

$15$th April $2010,25$th March $2012,5$th February $2014,30$th January $2016.$

It should be noted that replacement of the ball bearings for the centrifugal pump is done upon the

operator hearing abnormal noise from the pump $($during operation$),$ and thereby making a request to

the maintenance crew for an intervention and repair. The double roller bearings are inspected $($on a

Sunday$)$ once every two weeks $($by removing the protective bearing housing$),$ and if found to be

damaged then needful is done to immediately replace the bearings. The roller bearings are pressed fit

on the shaft of the ID fan. The ID fan is at the exit end of the path of flue gas flow, and the system is

under negative pressure in order to have the exhaust flue gas to move through to the chimney and out

to the surroundings. The ID fan is driven by a three phase motor running at $3000$ rpm with a reduction

gearbox so that the actual speed of the shaft of the ID fan is $1200$ rpm$.$ The ball bearings are mounted

by a location clearance fit onto the shaft of the centrifugal pump, and can easily be accessed for

dismantling. Each ball bearing housing is fitted with a greasing point. There is an identical standby

centrifugal feedwater pump which is connected in parallel to the other feedwater pump and the

standby pump is operated whenever the other pump has failed.

The current maintenance practice consists of the following:

Periodic greasing and lubrication of machinery.

Regular $($on Sundays$)$ check by the maintenance crew of wearing on belts, conveyors, etc.

Replacement of failed components as and when occurred.

The Management of the production plant expects a high reliability and availability of the equipment

during the weekly operating period with the minimum maintenance cost.

As a newly appointed maintenance manager, you are asked by the Management to investigate whether

the current maintenance practice is the most efficient from a technical and cost point of view. Explain

your methodology, and using any appropriate technique make your recommendations $($with

justifications$).$