PED Workshop 07, Bucharest Annika Haglund, Inspecta Technology

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

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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.

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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”

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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)

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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.

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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.

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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.

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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!

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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

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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

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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.

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Data acquisition

Component data (material, pressure and temperature)

Chemicals

Present inspection intervals and history

Consequences from a failure (production stop, personal injury)

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Data acquisition for the assesment of:

The probability of failure

The consequence in case of failure

The potential with RBI (Cost savings, increased safety)

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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.

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… 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.

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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.

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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

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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)

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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

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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

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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)

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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)

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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

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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

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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

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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

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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

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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.

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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

PED Workshop 07, Bucharest Annika Haglund, Inspecta Technology

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