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RBI, Risk Based Inspection Results and experience from a Pilot study
within the Swedish Pulp and Paper Industry
PED Workshop 07, Bucharest
Annika Haglund, Inspecta Technology
Introduction to RBI
23-04-19
Page 3
The definition of Risk
R = P × C
P = the probability of failure for a component, over a given time period into the future. (Not constant with time for time dependent degradation)
C = the consequence, given that the failure has occurred. (For example measured by probable costs, fatalities, discharge volume, or core damage probability.)
R = the risk level (for the analyzed event), the expected value for the consequence. The metric of the risk (”the probable consequence”) is the same as the metric of the consequence.
23-04-19
Page 4
Risk types
Three main types of risk measures:
Risk measure Denotation Example of unit
Personal risk (safety) Rs “probable fatalities per year”
Environment risk Rm “expected value for discharge volume per year”
Economic risk (loss of production)
Re “probable cost per year”
23-04-19
Page 5
10-5
10-4
10-3
10-2
10-1S
an
nolik
he
t fö
r fe
l , P
10-5
10-4
10-3
10-2
10-1
0.1 1 10 100
Konsekvens , C [106 SEK]
Typical selections of components to inspect:
i) based on plant experience (statistics)
Consequence of failure, C [M€]
Pro
babili
ty o
f fa
ilure
, P
[1/y
ear]
ii) based on analyses of risk level, (probabilities, consequnces)
23-04-19
Page 6
10-5
10-4
10-3
10-2
10-1
0.1 1 10 100
Sannolik
het fö
r händ
els
en
, P
s
Konsekvens vid händelsen, Cs[106 SEK]
100
1000
100 000R = 10 000
Changes in risk level due to different actions
consequence reduction; safety systems, redundancy, protection, …
rebuild
inspection, change of material, load monitoring, …
Consequence of failure, C [M€]
Pro
babili
ty o
f fa
ilure
, P
[1/y
ear]
The reduction at inspection is dependent on interval and the detection capability.
23-04-19
Page 7
Why should the Industry use RBI?
The current inspection planning is in practice based on rough thumb rules. There is a need to utilize more analytical approaches in order to focus inspection on high risk items and prioritise the efforts.
Inspection planning by Risk Based Inspection (RBI) methods imply a systematic assessment of all components in a system. For each component the damage mechanisms are analysed in detailed, based on the chemicals, material and loadings.
The safety consequence and economic consequence at failure of each component is analysed.
23-04-19
Page 8
Why should the Industry use RBI?
Inspection intervals are determined based on the development of the damage mechanisms, the risk level, and the inspection effectiveness. Cost-benefit analyses are made for the economically driven inspections.
The industry will take benefit by developing more detailed and optimised inspection programs. The number of failures reduce and reliability increase. Savings are also made by the better optimisation of the inspection efforts and reduction of planned downtime.
23-04-19
Page 9
Why should the Industry use RBI?
Traditional inspection according to Swedish regulations will give fixed intervals; 3 years, 6 years etc. Will not consider differences in materials and details for damage mechanisms for the equipment.
An example:
- Pressure vessel A made from SS and pressure vessel B from CS - Both contain White liquor
- Shall the inspection intervals be the same?
NO!
23-04-19
Page 10
Where will the risks apear – An example
% Total Risk compared with % Piping ComponentsThe Ethylene factory, 1958 Piping Components
0%10%
20%30%
40%50%60%
70%80%90%
100%
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
% Piping segment
% o
f th
e to
tal r
isk
10% of the equipment
stands for almost 100% of the risk
RBI pilot studySmurfit Kappa Kraftliner
23-04-19
Page 12
RBI – The project
Part 1 RBI Screening
Rough assessment of possibilities by RBI for different systems
Improved safety (lower economic consequence in case of failure, improved personal safety)
Cost savings (increased intervals between planned shutdowns)
Part 2 Implementation of detailed RBI
Implementation of RBI in a selected system
23-04-19
Page 13
Part 1 – RBI Screening
The three systems evaluated:
Pulp production line (digestery, bleachery)
Recovery systems (evaporator, causticising plant, lime sludge burning)
Energy plant (soda recovery boiler, bark boiler, steam system, feed water tanks, condensation cleaning and gas destruction)
The Piping systems were excluded.
The paper mill was excluded.
23-04-19
Page 14
Data acquisition
Component data (material, pressure and temperature)
Chemicals
Present inspection intervals and history
Consequences from a failure (production stop, personal injury)
23-04-19
Page 15
Data acquisition for the assesment of:
The probability of failure
The consequence in case of failure
The potential with RBI (Cost savings, increased safety)
23-04-19
Page 16
Results from the RBI ScreeningA potential to prolong the inspection Intervals in the bleachery
(because of the low pressure and therefore low utilizations)
A potential to prolong the intervals for the evaporation plant. Especially for the Liquor vessels due to redundancy and favorable environment.
A potential to prolong intervals for parts of the pulp production line, introduce inspection for other parts as the pressure diffuser and the vessel for depressurization of pulp in L2 (non-pressurised equipment)
A potential to prolong the interval for the recovery boiler from 1 year to possibly 2 years. Most components have already today 3 years NDT intervals.
23-04-19
Page 17
… 2 weeks later, The vessel for depressurization of pulp in L2 The corrosion had
gone throw the shell of the vessel!
The vessel carries the pressure diffuser. Reinforcements are necessary.
The RBI sreeening identified the equipment as a high risk object.
With RBI as a base for the inspection program this would never have happened.
23-04-19
Page 18
Del 2 – Implementation of the detailed RBI
Was implemented for one of the pulp production lines, L1(digester with associated piping, chip feeding systems etc)
What changes would RBI give to the current inspection program?
Include the whole system, also equipment that don’t have demands for in-service inspection from authorities.
23-04-19
Page 19
Method
Collection of data
1) Categorisation of components:- Existing ID-numbers for pressure vessels and tanks- Grouping of piping systems (ID-nr missing)- The Digester was split into three parts; top, middle and bottom end
2) Collection of data (pressure, temp, chemistry etc)
3) Estimate the cost for inspection, building of scaffoldings, removal of insulation from equipment, cleaning / per component
4) Estimate the consequence
- stop in the production- repairs- personal injury
23-04-19
Page 20
Method
Assessments
1) Identify all causes of damage:- corrosion, erosion- internal Stress corrosion cracking (SCC) - corrosion under the insulation, external SCC- Fatigue; thermal and mechanical
2) Judge the rate of corrosion (general data, thickness measurements)
3) Damage tolerance analysis for the digester (LBB)
23-04-19
Page 21
Method
Analysis
Time to failure calculated with simplified models
Damage factors calculated based on- The materials susceptibility to damage- Variations in the process (chemistry, temperature etc)- History of breakdowns
Prepare an inspection program based on:- Equipment with high personal safety risk - Equipment with high risk cost per year- A broad cost-/benefit analysis
23-04-19
Page 22
Results
The highest personal safety risk level is for:
The digester
Steaming vessel
Some piping to/from the digester
Inline-mills (in-service inspection not mandatory)
The highest financial risk level is for:
The digester
Some piping systems to and from the digester
23-04-19
Page 23
Result – risk matrix for present inspection
Very high
High
Medium
Low
Risk matrix (financial) - present inspection
1,00E-04
1,00E-03
1,00E-02
1,00E-01
1,00E+00
100 1000 10000 100000 1000000
Consequense (kSEK)
Pro
bab
ilit
y (1
/yea
r)
23-04-19
Page 24
Result – risk matrix for alternative inspection
Very high
High
Medium
Low
Risk matrix (finansial) - alternative inspection
1,00E-04
1,00E-03
1,00E-02
1,00E-01
1,00E+00
100 1000 10000 100000 1000000
Consequence (kSEK)
Pro
bab
alit
ity
(1/y
ear)
23-04-19
Page 25
Result - financial
Total yearly expected cost with different inspection programs
0 879 1067
42706
75033512
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
1 2 3
Inspectionprograms
kS
EK
/ye
ar
RiskcostInspectioncost
Inspectionprogram
1: No inspection
2: present inspection
3: alternative inspection
23-04-19
Page 26
Result – personal safety risk
Personal safety risk
4,34
0,31 0,31
4,05E-034,49E-03
7,46E-04
0,0001
0,001
0,01
0,1
1
10
1 2 3
Inspection programs
Pro
bab
le f
ata
litie
s pe
r ye
ar
Digester included.
Digester excluded
Inspection program
1: No inspection
2: Present inspection
3: alternative inspection
23-04-19
Page 27
Results - reflections
Digester
High risk level due to the very high consequence → requires other actions in addition to inspection
LBB will decrease the consequence considerably. One has to have leakage supervision to be able to able to gain from LBB.
Piping systems
Often high risk level due to financial consequence and lack of previous inspection
23-04-19
Page 28
Conclusions
The new proposal for inspection program
Fulfills the Swedish Regulations for personal safety
Will decrease the risk cost considerably and give improved total profitability for the plant
Leads to new inspections for most piping systems. A lot can be inspected during operation.
Leads to some new inspection methods to find ”new” causes of damage (for example EC/UT for internal SCC)
Leads to prolonged interval for some pressure vessels
23-04-19
Page 29
Experiences from Smurfit Kappa KraftlinerKappa thought that their documentation
was complete
Specifically documentation from reconstruction seems to be missing.– Obtain information from the suppliers– Material data was not always correct
A new way of working, first time– More detailed analysis reviled new
knowledge for the systems– Initially many new concepts
23-04-19
Page 30
Experiences from Smurfit Kappa KraftlinerLimited need for internal resources
– From each division: engineers from operation and engineers from maintenance, in risk identification sessions and data gathering
A new inspection plan was developed
Focus on some new equipment.– For example Vessel for pressurization of pulp and
Pressure Diffuser in L2. No demands for in-service inspection according to Swedish Regulations. These were pointed out in the RBI study to be high risk objects.
23-04-19
Page 31
Quotation: Lennart Nordström, Pulp line manager, Smurfit Kappa Kraftliner Piteå
”Could we in the Pulp and Paper Industry
afford not to use RBI?”
www.inspecta.com