Transcript Metodologia RBI - Donegani Anticorrosione

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
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(LoF) and Consequence
of Failure (CoF).
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
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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
Step 1.
Background to RBI
Step 2.
Assessment Personnel
Step 3.
Damage Mechanism
Assessment
Step 4.1.
Likelihood of failure-LoF
Step 4.2.
Consequence of failure-CoF
Step 4.3
Risk Assessment
Step 5.
Inspection Planning
Step 6.
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Updating RBI Assessment
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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:
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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
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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:
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Operational manual
P&ID
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 14to
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be exercised by the Study Team.
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 Σ (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
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LF1:
LF2:
LF3:
LF4:
LF5:
LF6:
LF7:
Current condition
Failure likelihood
Inspection Effectiveness
Shutdown Frequency
Operational Stability
Operation in Relation to Design
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
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CF1:
CF2:
CF3:
CF4:
CF5:
CF6:
CF7:
CF8:
CF9:
Product Loss
Pressure Factor
Explosion/Fire Damage Potential
Toxicity
Effect of Failure on Production
Location of Component
Time Taken to Rectify Failure
Threat Personnel/Environment
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
Likelihood
4
3
2
1
A
B
C
D
E
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
Start RBI
Maintenance
Shutdown
Inspection
Plan Rev.0
Shutdown/ Inspection
Inspection Reporting
Base RBI
Assessments
Inspection
Plan Rev.1
Review RBI
Assessments
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Maintenance
Shutdown
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Risk vs Time
No 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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DONEGANI ANTICORROSIONE SRL
VIA G. FAUSER 36/A
28100 NOVARA
Tel. 0321677411
Fax. 0321677444
E-mail: [email protected]
Web: www.donegant.it
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