RBI in Major Plants

Presented by Eur.Ing. R.T.Canaway, B.Sc., F.I.Chem.E.,

Managing Director of Suregrove Limited
+44-1737-813605
enquiry@suregrove.com

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Risk Based Inspection
An Overview
Introduction:-
Risk Based Inspection, or RBI, is increasingly
being promoted in the process industries as
a means of optimising the costs of
complying with statutory and other HSE
obligations.

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What is the Purpose of Inspection?
♦ Check the plant is ‘fit for purpose’
♦ Monitor the deterioration of vessel or piping
thickness
♦ Assess the REMAINING SAFE
OPERATING LIFE ………say 5 years left
♦ Retire plant which is deemed not usable
♦ Examine failure mode

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The Inspector Must Be/Have
♦ Able to undertake
his/her work without
interference
♦ Competent
♦ Tools
♦ Records
♦ Able to trend thinning
Or tolerances

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Why use RBI ?

Focus on Critical Plant to ensure the business

is in a safe and profitable state

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Inspection Methods
Visual Penetrant Dye Magnetic
Testing – finds Particle – Flux –
surface flaws Field Distorted
Eddy Current - Radiography - Ultrasonic
AC – near volumetric Testing – planar
surface flaws and volumetric
ACFM/ACPD – Ultrasonic TOFD Time of
size of flaw – Testing - size of Flight
Alternating Current Field
Measurement or Potential Drop flaw Diffraction – all
details from 2 probes
ultrasound from upper and lower
extremes of flaw

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Failure Modes
Corrosion/Erosion, Creep > 350oC Fatigue
Water, Chloride, High Temp Cracking –
High Temperature Cyclic stressing
Sulphidation, V/L
Damage >
Impingement 450oC - e.g. Toe of
- Cracks grow welds
Embrittlement – Stress Corrosion Brittle Fracture
Caustic with T>70oC, Cracking – OK if T > 0oC
H2 Partial P>5 bar, Ammonia, Chlorides
But not if T < 0oC
H2S Partial P>0.05 psia
HCN/HF promotes

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Can use RBI to focus on:
♦ Corrosion/Erosion ♦ Condition Monitoring
– If conditions are severe – Machine reliability not
e.g. high PP of adequate
contaminant – Critical to
– Thereby eliminating production/safety
“lower” risk areas? – Mechanical failure
– Ignore systems where could lead to VCE?
conditions are outside – Ignore safe systems
concern range? E.g. such as potable water
low T and no or low pumping?
Contaminant PP

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Objective
The main aim of RBI, if properly carried out,
is to manage the “Risk” of plant failure at
an acceptable level.

“Risk” = Likelihood x Consequence

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If the risk of failure of a
component has an effect:
Assess the Risk in terms of:
- Safety (Personnel? Fire?Toxicity?……..)
- Loss of Production?
- Failure to meet Legislation?
Then cost the risk of failure and its probability
Or likelihood
- Set Inspection Requirement and Frequency

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Then we can :

♦ Eliminate unnecessary work?

♦ Reduce inspection work load
♦ Increase/Decrease Frequency of Inspection
♦ Save Time and Money

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The HSE will accept:
♦ Goal setting safety legislation (UK in 1989
& 2000) has enabled a move towards
inspection strategies based on the risk of
failure. This legislation allowed a
user/owner together with a nominated
“Competent Person” the flexibility to decide
a “suitable” written inspection regime based
on system information and good
engineering practice.

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Application:
♦ The evolution to a risk-based approach has
been supported by specific process plant
operating experience together with better
knowledge of material degradation
mechanisms and availability of fitness-for-
service assessment procedures.
Also, developments in NDT technology
have improved inspection ability,
performance and consistency.

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Major Plants
♦ Industry considers there are benefits from
more informed inspection, particularly in
refining & petrochemicals where they are
now setting inspection priorities on the
specific risk of failure. Benefits include:-
♦ Improved inspection screening for high risk
areas;
♦ Prioritising inspection based on measured
risk;

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♦ Cost savings by stopping ineffective
inspection, extending inspection intervals
and greater plant availability;
♦ Systematic management of risks associated
with equipment failures.

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But!
♦ Inspection is usually only one part of a
site’s integrated integrity management
strategy which also normally includes
routine and preventative maintenance and
they are usually linked within a common
framework.

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What is Risk Based Inspection?
“Risk Based Inspection” is a systematic process that
involves planning an inspection on the basis of the
information obtained from a Risk Analysis of the
equipment concerned.

The purpose of the “Risk Analysis” is to identify the

potential deterioration mechanisms and threats to
the integrity of the equipment and to assess the
consequences and risks of failure.

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Risk Analysis
Risk Analysis usually contains the following
6 stages:-
♦ Identification of equipment failure scenarios
♦ Identification of potential deterioration
mechanisms and modes of failure
♦ Assessment of the probability of failure
from each mode/mechanism

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Risk Analysis
♦ Assessment of consequences resulting from
failure
♦ Determination of the risks from failure
♦ Risk ranking and categorisation.

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Types of Risk Analysis
♦ Qualitative;
♦ Semi-Quantitative;
♦ Fully Quantitative.

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Measuring Risk
♦ Qualitative risk analysis is based primarily
on objective engineering judgements made
by an RBI “team”. The Likelihood and
Consequences of Failure (LoF & CoF) are
expressed in relative terms, as below:-
♦ Risks are usually expressed within a Risk
Matrix.

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Measuring Risk
L.o.F:- C.o.F:-
♦ Very unlikely ♦ High
♦ Possible ♦ Moderate or
♦ Reasonably probable ♦ Low
and
♦ Probable

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Typical Risk Matrix
5 Medium-High Risk High
High Risk
Risk

LIKELIHOOD
CATEGORY
4 Med. High Risk

2 Medium Risk
Medium Risk
1 Low Risk
A B C D E
CONSEQUENCE CATEGORY

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Measuring Risk
♦ Semi-Quantitative risk analysis determines
single numerical values for the probability
of failure and the consequences from every
cause and effect. Analysis of failure is more
numerically based and detailed than the
Qualitative approach, but may still include a
large element of engineering judgement.

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Likelihood and Consequence
X-Y Plot

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Measuring Risk
♦ For a fully Quantitative risk analysis, the
likelihood and consequences of failure are
determined for each scenario using standard
reliability analysis methods with the total
probability of failure evaluated using
methods such as survival statistics. Results
are normally presented on logarithmic
probability-consequence plots.

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 Iso Risk Lines

10-1
Likelihood

10-3
Risk = 10
10-5
Risk = 1
10-7

10 102 103 104 105

Consequence

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Measuring Risk
♦ Whilst all these approaches to Risk
Analysis may be valid, the process and the
data needs to be transparent and the use of
non-validated software may be restricted.
The risk analysis & measuring process must
be consistent and able to be independently
assessed.

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Definitions
“Risk” – The risk of failure of an item combines the
probability or likelihood of failure with a measure
of the consequences of that failure:-
Risk = Probability x Consequence
The “Consequence” of failure through the
unintentional release of stored energy and/or
hazardous material is the potential for injury,
damage, lost production, pollution, reputation etc.
These can be measured in a variety of ways –
fatalities, fines and compensation payments,
bankruptcy, higher insurance premiums…..

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Definitions cont.

“Inspection” in RBI is the planning,

implementation and evaluation of
examinations to determine the physical and
metallurgical condition of equipment or a
structure in terms of fitness-for-service. It is
usually part of a company, site or facility
“Integrated Integrity Management Strategy”
for managing risk of failure which should
still include conventional routine and
preventive maintenance.

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Process of Risk Inspection
♦ Risk Based Inspection is defined as a
logical and structured process of planning
and evaluation as shown in the following
flow chart for plant integrity management
by RBI:-

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Definitions etc
“In-service” inspection is most valuable
where there is uncertainty about the process
operating conditions, their effect on
materials, particularly where the conditions
are such as to promote “deterioration”.

“Deterioration” is defined as damage, defects

or degradation from the design intent or the
as-manufactured condition.

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Guidelines on Inspection
Frequency
Guidelines have been published by various
organisations giving guidance on good
practice for setting intervals between
statutory inspection of pressure equipment,
3 of these are:-
♦ SAFeD (Safety Assessment Federation) - In
1997 SAFeD produced guidelines on
extension of existing intervals.

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Guidelines on Inspection
Frequency
♦ CEOC (European Confederation of
Organisations for Testing, Inspecting,
Certification and Prevention - recognised
inspection intervals varied significantly
within the EEC and basis is not one of risk
and that it would be desirable to inspect on
a variable throughout cycle life.

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Guidelines on Inspection
Frequency
♦ Institute of Petroleum – In the IP Code of
Safe Practice proposed two interrelated
concepts – Grade Allocation and Sampling
examination procedures. - allocation of
grading depends upon assessment following
1st examination – if rapid deterioration item
is allocated a low grade (i.e. high failure
risk). If reasonable deterioration and
predictable then given less severe grade.

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Guidelines on Inspection
Frequency
This is a semi-quantitative method for
assessment of risk and recognises the
importance of good information. The
periodicity (in months) between inspections
is set according to type of vessel and
allocated grading as follows:-

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IoP Guidelines on Inspection
Equipment Grade Grade Grade Grade
0 1 2 3

Pressure 36 48 84 144
Vessels & Heat
Exchangers
Pressure 60 72 108 144
Storage
Vessels
Protective 24 36 72 ~
Devices
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Guidelines on Risk Assessments
♦ The UK HSE published a Guide to Risk
Assessment Requirements in 1996 intended for
employers which set down 5 steps:-
1. Look for Hazards;
2. Decide who might be harmed and how;
3. Evaluate risks and review precautions;
4. Record findings;
5. Review assessment & revise if necessary.

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Guidelines on Risk Assessments
♦ In 1999 the UK HSE published a discussion
document which described the assessment
of risk process adopted by the HSE.

♦ It also introduced the important concept of

tolerability – i.e. the willingness of society
to live with a risk etc

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Guidelines on Risk Assessments
♦ CEOC produced guidelines* on a
Qualitative & Quantitative approach
including historical and analytical
approaches to estimating probability of
failure – they noted weaknesses of both
methods and concluded improvement of
both methods should continue and also
building of data bases required.

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Guidelines on RBI
♦ The UK HSE Hazardous Installations
Directorate issued an internal circular in
1999 as guidance for HSE inspectors for
auditing plant inspection systems which
adopt RBI.

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Guidelines on RBI
♦ ASME issued an overview of RBI
principles in 1991 recommending a four-
part process:-
1. Definition of the System;
2. A Qualitative Risk assessment;
3. A Quantitative Risk Analysis;
4. Development of inspection programme

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Guidelines on RBI
This ASME document mainly considered the
theoretical approach to the problem
detailing actual analysis methods i.e.
FMECA (Failure Modes Effects Criticality
Analysis), Structural Reliability & Risk
Assessment (SRRA) and Probabilistic Risk
Analysis (PRA).

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Guidelines on RBI
♦ API 581 designed for the petroleum and
chemical industries was published in draft
form in May 2000. It followed the same
overall approach as ASME, aiming to:-
1. Define & measure level of risk;
2. Evaluate safety, environmental and
Business Interruption risks;
3. Reduce risk of failure by effective use of
inspection resources.

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Guidelines on RBI
The level of risk is assessed following the
same procedure as ASME – quantitative
analysis applied after initial qualitative
analysis.
The qualitative analysis assesses each plant
item in a 5 x 5 risk matrix.
The likelihood of failure is determined from
the sum of 6 weighted factors viz:-

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Guidelines on RBI
♦ Amount of equipment within item;
♦ Damage mechanism;
♦ Usefulness of inspection;
♦ Current equipment condition;
♦ Nature of process;
♦ Safety design and mechanisms.

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Guidelines on RBI
The consequence of failure is divided into
only two factors:-
1. Fire/Explosion;
2. Toxicity

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Guidelines on RBI
Risk is then calculated as the product of each
consequence and likelihood for each
damage scenario, the total risk for an item
equated as the sum of all the scenario risks:-
Risks = Cs x Fs
where:- S = Scenario
Cs = Consequence of Scenario
Fs = Failure frequency of Scenario

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Guidelines on RBI
RiskItem = Σ Risks
The inspection programme is then developed
to reduce that risk. To do that one needs to
establish:-
1. What type of damage to look for;
2. Where to look for damage;
3. How to look for damage;
4. When to look for damage.

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Guidelines on RBI
What and Where is established from design &
process data and equipment history. How to
look for damage by reviewing the damage
density and variability, sample validity,
sample size, detection capability of method
and validity of future based on past
observations. When to look for damage is
related to estimated remaining life of item.

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Software Packages for RBI
There are many commercial software
packages which vary in complexity but
generally follow the semi-quantitative risk
assessment methodology. 5 of these
packages are listed below but a report
prepared for the UK HSE did not
specifically endorse any one and noted none
of the methods used have been validated.

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Software Packages for RBI
They also noted their practical application is
limited and they should only be used as a
guide and not to replace risk assessment and
inspection planning.
♦ Akzo Nobel;
♦ Det Norsk Veritas (DNV);
♦ The Welding Institute (TWI);
♦ Tischuk;
♦ LMP Technical Services.

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RBI Team
In all but the simplest situations situations, RBI is
best undertaken as a team activity similar to
Hazop. Technical knowledge and experience
should encompass;-
♦ Risk assessment;
♦ Process hazards and failure consequences;
♦ Plant safety and integrity management;
♦ Mechanical engineering/metallurgy/design;
♦ Plant operation, maintenance & inspection history;
♦ Inspection methods/NDT effectiveness etc.

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RBI Team
♦ Where there are significant Health & Safety
implications arising from equipment failure,
the qualifications and competence of team
members needs to be to a recognised
professional standing. Where not available
in-house “duty holders” will need to take
advice from appropriate external experts
and consultants.

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RBI Team
♦ Ideally, the Team Leader should be independent
from the direct pressures of the site production
function and should have appropriate seniority and
authority.
♦ Good records need to be kept on how qualitative
judgements and decisions were kept.
♦ In many cases the information required for a
quantitative risk assessment either does not exist,
or is not sufficiently accurate.

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Assessing Requirements for RBI
♦ What reference has been made to published
information?
♦ What are the reasons/drivers for the risk-based
approach?
♦ Is the availability and accuracy of information
sufficient?
♦ Does the approach reflect the plant complexity
and potential catastrophes?
♦ How do Integrity Management & Inspection link
to plant operations?
♦ How is the documentation managed & controlled?
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Auditing the RBI Process
♦ How often is the Management Process
audited and reviewed?
♦ Who carries out the audit and review?
♦ What aspects of the Management Process
are covered;
♦ Is documentary evidence available to
support each aspect?
♦ How has the Integrity Management process
changed?

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RBI should not be used to:
Reactively spot check a Try to satisfy the
system which has just Authorities
been involved in a major
accident

Purely extend the period Just produce computer

between maintenance output which is not
turnarounds without good relevant to the job
reason

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RBI will not solve:
Inadequate Deliberate
Design/Operation beyond damage/External factors
intention/incorrect such as storm, hurricane
manufacture – these are which exceed the design
under Quality Assurance case
Failures caused by Wrong selection of
presence of unforeseen materials or PMI failure
presence of contaminants
or pollution (perhaps
intermittent occurrence)

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No Plant May Implement RBI if:

They have no records They have a poor loss

They cannot display the record
trends of the last
inspections

They are looking to save Their Maintenance is

money only inadequate

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RBI is useful:
In work prioritisation – to Feedback in industry to
focus on areas where highlight failure modes
business outage could be and educate other plants
significant before failure

As a tool to help the To assess the risk to the

company focus its business (in terms of loss
resources of production)

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