RBI Methodology

1
RBI Methodology
Risk Based Inspection

• API 580 581

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Introduction

• Although the term RBI has been adopted
  relatively recently, the practice of planning
  plant inspection based on the risk of failure is
  not new. Most operators base the scope and depth
  of their inspection plans on the rate of
  in-service damage and the consequence of failure,
  within a traditional time-based inspection
  programme. (Same operators can rightly claim that
  their plant inspections have always been
  risk-based).
• The term RBI refers to a structured, team-based
  assessment process with the aim of targeting
  inspection by considering the Risk of Failure
  (RoF), which is a combination of the Likelihood
  of Failure (LoF) and Consequence of Failure (CoF).

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RBI Risk Based Inspection

• Is based on the norms API 581 RP 580
• Developed by API (American Petroleum Institute)
  in collaboration with
• - DOW
• - SHELL
• - FINA
• - TEXACO
• - EXXON
• - .

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Objective of RBI Methodology

• Increase safety
• Increase the productivity of inspection
• Decrease the losses of production
• Reduce the direct costs of inspection
• Change the frequencies of inspections in base to
  the risk
• Prevent catastrophic damages

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RISK

• Definition of the Risk
• Risk (RoF)
• Likelihood of Failure (LoF)
• x
• Consequence of Failure (CoF)

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Risk Based Inspection

• Consent of
• Define the critical state for every single ITEM
• Create a priority for the Inspections basing on
  the critical state
• Focus the attention on the expected damages

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RBI Methodology

• RBI Methodology developed by different
  companies, varied in the details, but it is
  founded however on fundamental step
• Background to RBI
• Assessment Personnel
• Damage Mechanism Assessment
• Risk Assessment
• Inspection Planning and Risk Mitigation
• Updating RBI Assessment

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RBI Methodology
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Background to RBI

• RBI study is designed around the systematic,
  inductive assessment process of identifying
  historical, active or potential damage mechanism
  in each equipment. The process is a bottom up
  procedure where one damage mechanism id
  considered at a time. Once the feasible damage
  mechanisms have been identified, their
  probabilities (likelihood) of leading to
  component failure are determined and their
  effects on the components are recorder and
  analysed to yield a calculated failure
  consequence.

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Assessment Personnel

• All RBI systems have the following common
• elements
• Assessment preparation
• Information Gathering
• Damage Mechanism Review
• Risk Assessment
• Inspection Plans
• Inspection Review.

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Assessment preparation

• Since RBI is a team-based approach, the first
  step in the introduction of an RBI programme is
  to identify and assemble a competent Study Team.
  The RBI team should include staff with knowledge
  of plant operation, process hazards, risk
  assessment and inspection techniques.

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Typical RBI team

• Inspection engineer(s)
• Material and corrosion engineer(s)
• Maintenance engineer(s)
• Process engineer(s)
• Operations engineer(s)
• Safety engineer(s)
• Team leader, typically a RBI specialist(s).

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Information Gathering

• Are necessary the following information
• Operational manual
• PID
• Sketches of project of the equipment
• Pipe class
• Property of the fluids
• Design and operating conditions
• Special instructions and History inspection

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Damage Mechanism Assessment

• The Study Team will need to review the historical
  and generic date relevant to each item of
  equipment. This will include consideration of
  previous inspection reports (if available) to
  determine the known or expected damage
  mechanisms.
• The review should consider damage mechanisms
  which may lead to failure, their expected rates
  of deterioration and the general location where
  damage may arise.
• Wherever quantitative rates of damage are not
  available, an element of expert judgement will
  need to be exercised by the Study Team.

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Risk Assessment

• The failure likelihood and the failure
  consequence are calculated on the basis of
  quantitative Likelihood Factors (LF) and
  Consequence Factors (CF).

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Likelihood of Failure (LoF)

• The answers to the LF questions are assigned a
  series of values and associated weighting and the
  combination of all these determines the
  Likelihood of Failure (LoF), derived for each
  equipment in turn.
• The LoF formula is specifically of the following
  form
• LoF LF2 S (LFi)
• LF2 Failure likelihood (within a given period
  of time)
• LFi represents several factors that are
  considered to
• contribute to the overall Likelihood of
  Failure.

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LFi Factors

• LF1 Current condition
• LF2 Failure likelihood
• LF3 Inspection Effectiveness
• LF4 Shutdown Frequency
• LF5 Operational Stability
• LF6 Operation in Relation to Design
• LF7 Recurring Repairs

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Consequence of Failure (CoF)

• The answers to the Consequence Factors (CF)
  questions are assigned a series of values and
  associated weightings and the combination of
  these results is the Consequence of Failure
  (CoF), derived for each item in turn.
• The CoF formula is specifically of the following
  form
• CoF (FM x CF1 x CF2) (CF3 x CF6)
• CF4 (CF5 x CF7) CF8 CF9

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FM Factor

• In addition to other consequence factors the
  consequence calculation also consider the failure
  mode of an assigned damage mechanism. Each damage
  mechanism knowledge base is assigned one of three
  failure modes, i.e. Leakage, Leakage or
  Rupture, Rupture.

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CFi Factors

• CF1 Product Loss
• CF2 Pressure Factor
• CF3 Explosion/Fire Damage Potential
• CF4 Toxicity
• CF5 Effect of Failure on Production
• CF6 Location of Component
• CF7 Time Taken to Rectify Failure
• CF8 Threat Personnel/Environment
• CF9 Engineered Safety Systems

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Weight of Factors
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Risk Matrix

• The resultant Likelihood of Failure (LoF) is
  plotted on the vertical axis, and the Consequence
  of Failure (CoF) is plotted on the horizontal
  axis, as an assessment point on a dimensionless
  five-by-five Risk Plot. The Lof axis is grouped
  into five relative Likelihood Categories, ranging
  from 1 to 5 (approximately 10-2/yr to 10-7/yr),
  and the CoF axis is grouped into five relative
  Consequence Categories, ranging from A to E. In
  this way, the Risk of Failure (RoF) is considered
  to increase with increasing LoF and CoF.

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Risk Matrix
5
4
Risk
Likelihood
3
2
1
B
C
D
E
A
Consequence
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Inspection Planning

• After the risk assessment, the Study Team
  develops action plan based on all of expected
  damage mechanisms. The inspection plane consider
  the inspection interval and the scope of
  inspection.
• The proposed inspection plane are designed to
  provide an assurance that the residual risk of
  the equipment is in accordance with the ALARP
  principle, i.e. the aim of assessing and managing
  equipment is to reduce the RoF to As Low As is
  Reasonably Practicable (ALARP).

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Risk Mitigation

• The RBI methodology systematically leads the
  Study Team through the process of risk
  mitigation, by considering several mitigation
  action. The impact of each mitigation action can
  be evaluated, for subsequent collective appraisal
  of the benefits of the proposed action, using the
  ALARP principle. An appropriate strategy to
  manage the integrity of each equipment is
  therefore developed.

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Updating RBI Assessment

• RBI Study can be used to justify extending the
  periods between inspections. The RBI process
  relies on a feedback loop to update the
  inspection plan, such that it is relevant to the
  actual condition of the plan. The feedback stage
  provides continuing confidence that damage dose
  not exceed expectations and ensures that plan
  inspections take account of operational
  experience.
• Once an inspection plan has been developed during
  a session, future inspection of the equipment
  should be carried out to confirm that damage
  rates are within expectations and to identify any
  unexpected damage. The inspection should be
  carried out by competent staff and the results
  recorded and re-evaluated.

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FeedBack of the Study
Plant Operation
Plant Operation
Shutdown/ Inspection
Inspection Plan Rev.0
Inspection Reporting
Inspection Plan Rev.1
Start RBI
Maintenance Shutdown
Maintenance Shutdown
Base RBI Assessments
Review RBI Assessments
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Risk vs TimeNo Inspection Plan
180 months
120 months
60 months
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Risk vs Time With Inspection Plan
180 months
120 months
60 months
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