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7/27/2019 05 - Roy Chenery

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IMarEST Conference: Condition Based Maintenance

London 28-29 September 2010

CRITICALITY ASSESSMENTS:their importance in the maintenance process

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EDCBA

consequence

l i k e l i h o o d

Roy Chenery

Marine Consultant

The importance of criticality assessments


There is no greater impediment to the

advancement of knowledge than the

ambiguity of words

Thomas Reid 1710-96

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Agenda

•What are criticality assessments and where are they used

•Criticality assessments compared to critical equipment lists

•Some examples of where the criticality assessment process could

result in improved reliability

•Questions



Criticality assessment (with respect to maintenance)

• A process for prioritising the criticality of various systems and equipment

• A risk assessment process, takes account of the likelihood and theconsequence of failures, as these vary for similar equipment depending onoperating context, design criteria etc

• Involves the concept of identifying equipment function, functional failure,failure modes, failure effects, control methods

• Provide visibility of critical areas – distinguishes between critical and

important• Prioritisation:

• Human resource

• Costs

• Focus, which enables continuous improvement

• Spares e.g. OEM or approved supplier

• Scheduling

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The process

• Stakeholder teamwork

• Experience

• Criticality process eg FMEA/FMECA/HAZID etc

• Operations

• Maintenance

• HSE

• Designer / OEM

• Subject matter expert

• Recording of results



Best practice

• The steps to achieving good maintenance management:

• Define maintenance strategy

• Create asset register

• Prioritise by criticality assessment

• Identify maintenance task and frequency

• Carry out maintenance task

• Record the results – maintenance history

• Assess effectiveness of task

• Refine task where necessary

PlanDo

CheckAct

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Criticality assessment or critical equipment?

• The regulatory framework

• ISM Code

Purpose

To provide an international standard for safe management andoperation of ships and for pollution prevention (Preamble 1)

Objectives

1.2.2 Safety management objectives of the Company should…

1.2.2.2…assess all identified risks to its ships, personnel and theenvironment and establish appropriate safeguards

Maintenance of ship and equipment

10.3 The Company should identify equipment and technical systems

the sudden operational failure of which may result in hazardoussituations




• IACS recommendation 74 – A guide to managing maintenance in

accordance with the requirements of the ISM Code

• Sect. 4 The identification and testing of “critical equipment”

The list of ‘critical’ equipment and systems will vary according to the type of

ship and the operations in which it is engaged .

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• The regulatory framework

• TMSA – Element 4

• Critical equipment and systems are defined and identified within the safety

management system.

• Management provides clear instructions on the identification of on-

board critical systems, alarms and equipment. Risk-assessment or

hazard-identification methods are documented to help the

identification of such equipment and systems.

• Critical equipment and systems are identified in the vessel’s planned

maintenance system.

• Critical equipment lists are available in an easy-to-understand format.

All items listed are identified in the planned maintenance system.




• TMSA

• Critical equipment and systems - definition

• Any vessel-based equipment, operating system or alarm that, were it

to fail, would result in the crew or the vessel being placed at risk or

that could lead to an accident.

• Critical equipment or systems should include as a minimum: cargo

pump-temperature monitors, pump-room fixed gas-detectionsystems, fire-detection and fire-fighting systems, crankcase oil-mist

detectors, steering gear, emergency generator and main-engine

shutdown alarms.

• No example of reasoning provided

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Risk Assessment in Simple Terms

•What can go wrong?

•How likely is it to go wrong?

•What happens if it does go wrong?

•Does it matter?

•What do we do if it does matter?

• Prevent it happening

• Reduce its frequency

• Mitigate its consequences



Reliability Centred Maintenance RCM

• Analysis is based on the use of seven questions:

• What is it supposed to do? Function

• In what ways can it fail? Functional failure

• What causes it to fail? Failure mode

• What happens when it fails? Failure effect• Does it matter if it fails? Failure consequence

• Can anything be done

to prevent the failure? Preventive task

• What if the failure

cannot be prevented? Redesign/run-to-fail

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“Quick” closing valves



Fire dampers

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Control of design conditions



Air pipe heads

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Criticality assessments - summary

• Distinguishes critical from important

• Provides a ranking which allows prioritisation of resources etc

• Process as important as the result

• Improves knowledge and understanding of risk and maintenance

management techniques

• Satisfies best-practice procedures

• Enables continuous improvement


London 28-29 September 2010

CRITICALITY ASSESSMENTS:their importance in the maintenance process

1

2

3

4

5

EDCBA

consequence

l i k e l i h o o d

Roy Chenery

Marine Consultant

05 - roy chenery

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