MAINTENANCE STRATEGY
COURSE ASSESSMENT 2
Student Name: Dave Phelan
Student Number: 7495538
Assignment Reference No. MSTR/July10/1
Date Submitted: 25/10/10
Question
Answer these questions in the form of an essay (2000 - 2500 words)
Figure 1 shows a manufacturing process and Figure 2 shows a batch chemical reactor unit within this process. Table 1 shows the life plan for the batch chemical reactor with an indication if the task can be done with the reactor on-line (i.e. working) during a plant shutdown or during a short gap in production between batches – which is called a production window. There is a separate Microsoft Excel spreadsheet which gives details of all of the closed maintenance jobs which have been carried out on this reactor unit. This is called “Worklist for MSTR Assignment2.xls”
a) Explain why you would regard this batch chemical reactor as a plant unit.
b) Explain your reasons for concluding that this unit is critical for production.
c) Extract any user requirements for this designated unit from the plant description. Are there any production ‘windows’?
d) Extract any corporate requirements for this unit from the plant description.
e) Extract any legislative requirements for this unit from the plant description.
f) Having described the requirements for this unit, comment on whether you believe any other of the tasks in Table 1 could be completed during a production window in addition to the visual inspection.
g) Comment on whether you think any maintenance tasks are missing
h) How do you think this maintenance strategy could be improved?
Answer: 2499 words (word limit 2000-2500)
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Table of Contents
Section 1 - Introduction ...........................................................................................3
Section 2 – Questions
2.1 Explain why you would regard this batch chemical reactor as a plant unit ......3-4
2.2 Explain your reasons for concluding that this unit is critical for production ......4-5
2.3 Extract any user requirements for this designated unit from the plant
description. Are there any production ‘windows’?...................................................5-7
2.4 Extract any corporate requirements for this unit from the plant description .....8-9
2.5 Extract any legislative requirements for this unit from the plant description .....8-9
2.6 Having described the requirements for this unit, comment on whether you
believe any other of the tasks in Table 1 could be completed during a production
window in addition to the visual inspection .............................................................8-9
2.7 Comment on whether you think any maintenance tasks are missing...............8-9
2.8 How do you think this maintenance strategy could be improved......................8-9
Section 3 – Conclusions ....................................................................................9-10
References .....................................................................................................................................................19
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1. Introduction
This short essay answers a list of specific questions that pertain to a bulk
pharmaceutical manufacturing process (Figure 1) that includes a batch
chemical reactor unit (Figure 2). These questions broadly cover a view of the
criticality of the reactor, consideration of legislative, corporate and user
requirements derived from the plant description, a view of possible
opportunities to expand maintenance activities during a production window,
and consideration of how the existing maintenance strategy could be
improved.
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Raw Material
StorageCentrifuges
CentrifugeFeed
Vessel
Batch Reactor
Unit
Figure 1: Manufacturing Process
88
T1TIC
LP Steam
CV1
V1
P1
M1
SV1
SV2
Raw Materials
Figure 2:
Batch Chemical Reactor
Condensate
Trap
2. Questions
2.1 Explain why you would regard this batch chemical reactor as a
plant unit
The reactor clearly forms an integral and substantive part of the
manufacturing process, itself comprising of a number of ‘sub-level’
plant assets (e.g. P1) and control loops (e.g. LP steam TI/TIC/CV1).
Moubray (1997, Appendix 1) provides guidance on how to develop a
plant asset register as a foundation to apply a maintenance
management strategy, in his case a reliability centred maintenance
(RCM) programme. The ultimate aim of such a programme is to
ensure that the physical assets targeted do what the user wants
them to do in their present operating context. A list of equipment,
vessels, buildings etc. forms the plant asset register and, Moubray
asserts, should be constructed as a hierarchy that makes it possible
to identify any system or any asset at any level of detail, down to
individual components.
Moubray recommends (1997 p.81) that the level at which RCM is
best applied in a hierarchy, known as the level of indenture, is that
which leads to a reasonably manageable number of possible events
that could cause a functional failure. Starting too low down in the
hierarchy will often lead to too many unhelpful complexities including
difficulties dealing with control loops that cross sub-system
boundaries and can lead to the same function being analysed
multiple times. Equally, starting at the top of the hierarchy may lead
to many failure modes being overlooked. Moubray states that
identification of the optimum level to apply RCM becomes intuitively
obvious with practice (Moubray: 1997,p.86).
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After consideration of the factors outlined above and in conjunction
with personal experience and intuition, the author believes that the
batch chemical reactor should be regarded as a plant unit and should
be captured as such within the plant asset register.
2.2 Explain your reasons for concluding that this unit is critical for
production
In any maintenance programme resources will be finite, therefore a
quantitative analysis of business impact should be carried out to
identify the equipment which has the biggest impact on safety and
plant throughput (Wheelhouse: 2010, p.38).
Kelly (2006: p.170) agrees that it is important to rank the identified
plant unit according to its impact on production and safety. He bases
such rankings on the consequences of unit failure multiplied by the
likelihood of unit failure (see Figure 3).
Criticality
Ranking
Consequential
Production Impact
Consequential Safety
Impact
Level 1 (high)
criticality
Failure causes an
immediate and high
production loss
Failure causes an
immediate and high-
risk safety hazard
Level X (low)
criticality
Failure causes no
immediate or potential
production loss
Failure causes no
safety hazard
FIGURE 3 – TYPICAL CRITICALITY RANKING OF PLANT UNITS BASED
ON FAILURE CONSEQUENCES
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Here, in terms of operating context the primary function of the
manufacturing process is to produce 13,000 te/year of a bulk
pharmaceutical product. At the next level down in the plant asset
register hierarchy, the primary function of the batch reactor is to
produce 18 tonne of product within the required specification every
10 hours. This equates to 7,222 hours of operation at 1.8 tonne/hour
production rate, which, after allowing for the 16-hour annual
shutdown, requires that the reactor is available to run for 82.6% of
the year. This means that there is 17.4%, or 1525 hours per year of
spare reactor capacity.
From the process description provided there is no built-in redundancy
(i.e. no spare reactor). It is also stated that the centrifuges are the
process bottleneck. Therefore, if an unplanned reactor breakdown
occurs it wouldn’t necessarily immediately impact production.
However, a significant amount of reactor downtime may compromise
the primary function of the manufacturing process. The centrifuge
feed vessel will provide some buffer capacity to safeguard against
reactor breakdowns and keep the centrifuges supplied with feed. The
amount of buffer capacity available will determine the maximum
duration of reactor outage that can be tolerated before plant
throughput is adversely impacted. On the other hand, a breakdown
on the centrifuges will immediately impact plant throughput.
The author concludes that the reactor unit is clearly critical for
production, but it is logical that in a production criticality ranking list
the centrifuges might be ranked higher, perhaps as a Level 1,
whereas the reactor unit might be ranked slightly lower as a Level 2.
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2.3 Extract any user requirements for this designated unit from the
plant description. Are there any production ‘windows’?
A user specification requirement (USR) is defined as a description of
what the user wants from a unit or system that he believes will deliver
a business advantage. The USR should include details of the
functionality required of the unit/system, capacities, processing
details etc. Functional requirements usually specify what the system
is to accomplish rather than how it is to be accomplished.
Here, based on information included within the process description,
the USR for the reactor unit includes:-
The reactor must be capable of receiving 18 tonne of raw
materials from storage (details not specified although pumped
fill perhaps via P3 is likely to be required to minimise batch
cycle time).
The reactor must be sized to produce an 18 tonne batch of
product with a batch cycle time of 10 hours that meets the
required product specification.
The reactor must be constructed from materials that are
compatible with the chemicals/products used (i.e. no adverse
affect on product quality or safety), plus capable to withstand
the temperatures and pressures required for the process. It is
stated that the reaction materials are benign and do not pose
a corrosion concern. The author postulates that a glass-lined
vessel is required because it has a smooth, anti-stick surface,
is easy to clean, and does not introduce impurities to the
process materials.
The pipe-work must be fabricated from stainless steel.
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The reactor must be agitated and jacketed with a LP steam
supply to the jacket.
The reactor must be capable of being sealed to fully contain
its contents throughout the reaction.
The reactor must be fitted with a temperature control system
that has the capability to control the reactor contents through
a defined temperature/time profile with a high temperature
alarm at 125°C. Additionally, the control system must be
configured to protect the glass lined vessel from being
damaged by thermal shock.
The reactor contents must be transferrable through an
automated discharge valve at the base of the reactor to the
centrifuge feed vessel via a pump.
Production Windows
Production window is defined as a short gap in production between
batches, during which it may be possible to carry out asset
maintenance tasks.
Here, the life plan for the batch reactor unit (ref table 1) indicates that
the only activity that could be undertaken during a production window
is the weekly visual check on the reactor coupling which takes 5
minutes to carry out.
The author suggests that there may be additional production
windows if the overall batch cycle is considered. The batch cycle time
may be defined as from “reactor-empty to reactor-empty”. This
equates to the time taken to fill the empty reactor with raw materials
(fill step) + the 10 hour temperature profile time (reaction step) + the
time taken to transfer the entire contents of the reactor to the
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centrifuge feed tank (empty step). As the fill and empty steps have
not been defined it is not possible to specify the batch cycle time
precisely. However, intuitively the author suggests that some
maintenance activities could be carried out on specific items during
the fill step (e.g. steam trap), during the reaction step (e.g. P1) or
during the empty step (e.g. CV1). The buffer capacity in the
centrifuge feed tank will also effectively create a production window.
2.4 Extract any corporate requirements for this unit from the plant
description
Corporate requirements include: the need to license the
pharmaceutical product by the FDA and British Pharmaceutical
Society; the need for all production and maintenance activities to
comply with Good Manufacturing Practice (GMP); the registration of
the manufacturing process to the quality standard ISO9002; the need
for all company activities to conform to the environmental standard
ISO14000; the need for maintenance activities to comply with the
company permit-to-work system; in line with company guidelines the
reactor must be maintained to achieve a 25 year life and gearboxes
maintained to achieve a 15 year life; the facility must be kept well-
painted, clean and tidy for possible visits from pharmaceutical
inspectors at any time or visits from key customers.
2.5 Extract any legislative requirements for this unit from the plant
description
The reactor and the reactor jacket are rated as a pressure vessel and
a registered steam receiver respectively and are therefore subject to
the Pressure System Safety Regulations (PSSR) 2000 (Lloyds
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British: 2010). The aim of PSSR 2000 is to prevent serious injury
from the hazard of stored energy as a result of the failure of a
pressure system or one of its component parts.
The Regulations require users to:
establish the safe operating limits of the plant
have a suitable written scheme drawn up or certified by a
competent person for the examination at appropriate intervals
of:
- pressure vessels
-all safety devices
-any pipework which is potentially dangerous
A reactor failure may result in an immediate and high risk safety
hazard, therefore the reactor unit should be rated as safety critical
(see Figure 3). The reactor and jacket must both be fitted with a
certified safety relief valve.
2.6 Having described the requirements for this unit, comment on
whether you believe any other of the tasks in Table 1 could be
completed during a production window in addition to the visual
inspection
The author believes that in view of the frequency and duration of the
specified tasks in Table 1, that a production window is effectively
created by the buffer capacity in the centrifuge feed tank, and that
there is 17.4% or 1525 hours/year of spare reactor capacity, that all
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tasks included within Table 1 and all secondary tasks if required
could be undertaken during a production window.
2.7 Comment on whether you think any maintenance tasks are
missing
Maintenance tasks on the reactor system that the author believes are
probably missing include:
The integrity of the glass lining on the reactor could be compromised
either due to mechanical damage resulting from impact, or by thermal
shock caused by heating or cooling the vessel too quickly. A typical
maintenance checklist for glass-lined equipment should include:
visual inspection of the lining; spark testing for signs of glass-lining
failure; glass-thickness readings; inspection of tantalum repair plugs
and patches, if installed; vessel nozzle connections; and vessel
jacket connections (Goliath: 2007). The inspection frequency may
range from once every two years to continuous testing depending on
the severity of service or if damage is suspected.
Performance monitoring of the agitator motor and drive (i.e. establish
baseline amps being pulled by the agitator motor then instruct
operator to check periodically, say 1 / week).
Performance monitoring of the pump motor and drive (i.e. check
delivery performance versus pump curve; establish baseline amps
being pulled by the pump motor then instruct operator to check
periodically, say 1 / week).
Visual check on reactor seals – perhaps consider changing out
periodically prior to failure.
Visual check on pipe-work flanges and joints for leaks, say daily, and
consider changing out gaskets periodically prior to failure.
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Visual check of condition of lagging on the reactor jacket, steam and
condensate pipe-work.
Check calibration of thermocouple and the performance of the
temperature control loop. Replace conductive fluid in the temperature
pocket periodically (say every 6 months).
Thickness test pipe-work (establish baseline then check, say
annually).
From the completed work-list spreadsheet for the reactor system
there have been 10 reactive/breakdown tasks, of which 50% are
repeat failures that pertain to the following two issues :
Centrifuge P2 mechanical seal replacement:
- on 18/01/1997 (took 3hrs to complete v 2hrs standard)
- again on 29/03/99 (4hrs actual v 2hrs standard)
- and again on 18/05/99 (2hrs actual v 2hrs standard)
Recalibration of reactor T1 temperature sensor
- on 01/09/98 (took 3hrs to complete v 2hrs standard)
- and again on 17/04/01 (2hrs actual v 2hrs standard)
It is proposed that T1 be recalibrated annually and that P2 is visually
checked for condition and signs of leakage, say weekly.
2.8 How do you think this maintenance strategy could be
improved?
The author believes that the existing maintenance strategy appears
to be quite reasonable as the data provided in the completed work-list
indicates that there are a relatively very few breakdown maintenance
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tasks compared with preventive tasks (i.e. 2.9%). However, it is
asserted that improvements could be achieved by applying the RCM
approach referenced earlier including a rigorous failure mode and
effects analysis (FMEA). Use should be made of the equipment
history and known failure modes, plus the missing tasks itemised
earlier in Question 2.7.
The FMEA approach seeks to identify the failure modes that are
reasonably likely to cause each functional failure, and to ascertain the
failure effects associated with each failure mode (Moubray: 1997,
p.53). This should be developed by a cross functional team that
includes an operator, fitter, electrical/instrument technician and
chemical engineer who ideally know the facility and process well, and
have been trained to identify root causes in connection with the
analysis of failures. Their combined knowledge and skills coupled
with expert advice from vendors where needed should lead to the
creation of an effective preventive maintenance programme designed
to avoid expensive unplanned breakdowns that could otherwise
impact safety or production.
The author also strongly advocates the application of total productive
maintenance – TPM (Plant Maintenance Resource Center: 2010).
Some elements of this already exist (e.g. operator first line
maintenance routines). Further improvement could be derived from
better use of data, KPIs, visual management and industry
benchmarking. Operators could also be trained to carry out basic
preventive maintenance routines. Application of a structured
methodology to effectively manage the workplace, such as 5S, is also
advocated as this creates genuine plant ownership amongst the plant
team and sets high standards that the team members themselves
strive to maintain and improve upon.
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3. Conclusions
An analysis of the process description for a bulk pharmaceutical
manufacturing process was carried out to identify the key elements of the
USR and maintenance strategy for one of its major component parts, namely
the batch chemical reactor unit (BCRU).
It was concluded that it is appropriate to consider the BCRU as a plant unit
within a plant asset register hierarchy, and that it is critical to safety and
production within the operating context of the manufacturing process. A
number of tasks thought to be missing from the existing maintenance
programme were itemised and recommendations were provided to improve
the maintenance strategy, principally through the use of FMEA as a core
feature of RCM.
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References
Goliath (01 July 2007); Business Knowledge On Demand – Maintenance and repair of glass-lined equipment: a customized inspection and maintenance program will minimize operational and performance problems, http://goliath.ecnext.com/coms2/gi_0199-6800697/Maintenance-and-repair-of-glass.html
Lloyds British (2010): http://www.lloydsbritishtesting.co.uk/legislation3.php
Kelly, Anthony (2006): Strategic Maintenance Planning, Butterworth-Heinemann
Moubray, John (1997): Reliability-centred Maintenance, Industrial Press Inc New York
Plant Maintenance Resource Center (2010): An Introduction to Total ProductiveMaintenance (TPM), http://www.plant-maintenance.com/articles/tpm_intro.shtml
Wheelhouse, Paul (2010), Maintenance Strategy Study Guide, Manchester Business School MBA
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