RISK ANALYSIS METHOD FOR THE RELIABILITY OF AN EXPERIMENTAL APPARATUS

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RISK ANALYSIS METHOD FOR THE RELIABILITY OF AN
EXPERIMENTAL APPARATUS
UNIVERSITÀ DEGLI STUDI DI PISADiparimento di
Ingegneria Meccanica, Nucleare e della Produzione
Speakers Dr. ing. Davide Mazzini Dott. ing.
Calogero Sollima
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Introduction

• In the framework of the research program KM3NeT,
  Design Study for a Deep Sea Facility in the
  Mediterranean for Neutrino Astronomy and
  Associated Sciences, the Dipartimento di
  Ingegneria Meccanica, Nucleare e della Produzione
  (DIMNP) of the University of Pisa is
  collaborating with INFN and LNS to conduct the
  following Work Package
• WP7, Risk assessment and quality assurance
• quality assurance of the telescope parts and the
  assembly procedures
• risk analysis of design and operation of the
  telescope

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Introduction

• As a preliminary activity it was planned to
  collaborate with the NEMO staff (as this
  apparatus will be included in the future
  telescope) to study the design and the existing
  processes set up for the realisation of the
  prototypical facility
• Planned actions
• To collect useful data for the comprehension of
  the project (conceptual design and construction
  of fundamental parts, procedures for document
  management, selection of suppliers, etc.)
• To develop a QA manual to be shared between the
  involved organisations
• To apply methods to assess its reliability

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Risk Analysis conceptual elements

• The apparatus has a foreseen functionality
  (Mission)
• The Efficiency of the apparatus is the
  probability to reach the required operation
  during the designed lifetime and operating
  conditions
• Reliability, represented by the Mean Time
  Between Failures (MTBF)
• Maintainability, represented by the Mean Time to
  Repair (MTTR)
• The Entity is each part of the facility that can
  be considered individually

• Possible subdivision of the Tower Floor
• Structure
• Four Optical Module
• Floor Control Module
• Floor electro-optical cables

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Risk Analysis conceptual elements

• The failure (or damage) is the event causing the
  loss of the functionality of the entity
• The damages may be classified on the base of
• the nature of the failure, e.g.Overload
  (pressure, impact, temperature), Fatigue, Ageing,
  Corrosion, etc.

• Possible failures of the Tower Floor entities
• Structure
• pressure, overload for impact, miss of the trim,
  corrosion
• Optical Module
• Failure for mechanical and electric reasons,
  miss of structural constrain
• Floor Control Module
• Failure of electronic components, water
  infiltration
• Floor electro-optical cables
• Connections, bending

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Risk Analysis conceptual elements

• The damages may be classified on the base of
• the time in which they occur
• Defining the failure rate l(t) as the failure
  frequency of the components, it is possible to
  recognize thee different periods in their lifetime

BATHTUB CURVE
Early failures
Wearout failures
Useful life
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Risk Analysis conceptual elements

• In the first part of the component lifetime, an
  Early Failure or Infant Mortal Failure occurs,
  usually, a damage related to manufacture and QA
  (lack of control during the phases of production
  and assembly)
• e.g. welds, joints, connections, wraps, dirt,
  impurities, cracks, insulation or coating flaws,
  incorrect adjustment or positioning
• An Early failure may be caused by
• Miss or poor quality controls and functionality
  tests
• Poor materials
• Minimal maintenance
• Poor productive processes
• Poor assembly procedures
• Human errors
• Non-adequate methodologies for packing and
  transport

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Risk Analysis conceptual elements

• The second part of the Bathtub curve is the
  useful life of the compoment in which
  stress-related failures, referred as Random
  failures or Stochastic failures, may occur. That
  is, random fluctuations (transients) of stress
  exceeding the component strength respect to the
  Early Failures, a greater intensity is needed
• (e.g. increases of voltage for an electrical
  equipment,
• an impact for a structure, an exciting
  vibration, etc.)
• The third part a Wearout Failure occur, owing to
  corrosion, oxidation, breakdown of insulation,
  atomic migration, friction wear, shrinkage,
  fatigue, etc.

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Risk Analysis methodologies

• How to prevent the different failures?

• A Quality Assurance program should be adopted
• Functionality tests should be conducted in order
  to test the components and to assess their
  manufacture (Running-in)

Early Failures

• Defence in depth concept
• Improved design technique and appropriate
  selection of materials and suppliers
• Prevention of damages in the packing, transport
  and assembly phases
• Skill and training of the involved personnel (in
  particular, operators of service suppliers)

Random Failures

• Improved design technique and appropriate
  selection of materials
• Maintenance

Wearout Failures
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Risk Analysis methodologies

• How to know if the produced effort of the design
  staff is adequate for the prevention of the
  different failures?

Assessment of the apparatus Reliability and
Availability by the Risk Management Methodologies
A measure of the potential for loss in terms of
both the likelihood of the incident (event/year)
and the consequences of the incident
(effects/event)
Risk
The development of a quantitative estimate of
risk based on engineering evaluation of incident
likelihood and consequences
Risk Analysis
The process by which the results of a risk
analysis are used to make decisions (either
through relative ranking of risk reduction
strategies through comparison with risk targets)
Risk Assessment
The planning, organizing, leading an controlling
of an organization or activity in ways, which
minimize the adverse operational and financial
effects of accidents
Risk Management
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Risk Analysis methodologies
Risk Assessment Process

• Advantages
• provides a systematic approach for ranking risks
  and making decisions
• represents a powerful tool to help in design and
  management activities

• Disadvantages
• Care for correct initial assumptions and correct
  interpretation of results
• Modelling represents a drastic simplification of
  what really happens in nature
• Need of accurate data

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Risk Analysis methodologies

• The reliability of the systems is evaluated by
  various methodologies classified in
• Qualitative methods it is studied the
  interconnections between the failures of the
  different entities, and how they affect the
  functionality of the overall system
• Quantitative methods it is built up a
  mathematical model to predict the reliability of
  the system in time
• Some of them
• Event Tree analysis
• Failure Mode and Effects Analysis (FMEA)
• Failure Modes, Effects and Criticality Analysis
  (FMECA)
• Fault Tree analysis (FTA)
• Hazard and operability Analysis (HAZOP)
• What-If analysis

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FMECA

• The Failure Modes, Effects and Criticality
  Analysis is a methodology designed to
• identify potential failure modes for a product or
  process
• assess the risk associated with those failure
  modes
• rank the issues in terms of importance
• identify and carry out corrective actions to
  address the most serious concerns
• FMECA is normally a bottom up process that looks
  at how component failures can affect the larger
  systems as defined in a system description and
  block diagrams
• It can therefore be particularly detailed and is
  normally applied to very high valued systems
  where failure (breakdown) causes major
  difficulties

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FMECA

• The basic steps for performing an FMECA analysis
  include
• Assemble the team
• Establish the ground rules
• Gather and review relevant information
• Identify the item(s) or process(es) to be
  analysed
• Identify the function(s), failure(s), effect(s),
  cause(s) and control(s) for each item or process
  to be analysed
• Evaluate the risk associated with the issues
  identified by the analysis
• Prioritize and assign corrective actions
• Perform corrective actions and re-evaluate risk
• Distribute, review and update the analysis, as
  appropriate

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FMECA

• Major ground rules are
• The analysis procedure has to be applied
  methodically to each entity of the apparatus to
  avoid omissions
• The analysis has to be standardised in its
  different phases with this aim, a table may be
  adopted including the different items to be
  investigated
• Risk Priority Numbers (RPN) is adopted to
  evaluation the risk associated with the potential
  problems. The analysis team must
• Rate the severity of each effect of failure
• Rate the likelihood of occurrence for each cause
  of failure
• Rate the likelihood of prior detection for each
  cause of failure
• Calculate the RPN by obtaining the product of the
  three ratings
• RPN Severity x Occurrence x Detection

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FMECA

• The FMECA analysis procedure is a tool that has
  been adapted in many different ways for many
  different purposes. The process is well
  established, but can be customized based on
  specific objectives
• It can contribute to improved designs for
  products and processes, resulting in
• higher reliability
• better quality
• increased safety
• enhanced customer satisfaction
• reduced costs
• It provides a knowledge base of failure mode and
  corrective action information that can be used as
  a resource in future troubleshooting efforts and
  as a training tool for new engineers