Abstract of Papers:- - Malaysian Gas...

Abstract of Papers:-

Managing the integrity of a pipeline system aims to improve the health, safety and

environment (HSE) of pipeline systems and to allocate operator resources effectively to

provide a structural, easily communicated means for selecting and implementing risk

reduction activities.

This paper gives a general introduction of recently research in pipeline integrity

management around the world, and will address subjects such as QRA, ECA, EFFS and QRBI.

• QRA based RBI is a quantitative analysis both in PoF and CoF for different pipeline

sections.

• Engineering Criticality Assessment (ECA) based on fracture mechanics can be used to

determine the flaw acceptance and inspection criteria in fatigue and fracture design of

risers and flowlines.

Abstract of Papers (cont’d) :-

• The extended-fitness-for-services (EFFS) assessment may be applied to evaluate the

integrity of an in-service pipeline section containing damages.

• A QRBI is mainly used to do a quantitative assessment in infant mortality phase for a

new pipeline, based on which to determine the major degradation mechanisms, high

risk locations and establish optimized inspection schedule to ensure pipeline don’t fail in

the burn-in phase.

Then integrity management software based on the aforementioned theories will be

introduced briefly.

Key words: Integrity Management, QRA, ECA, EFFS, QRBI

Dr. Yong Bai

Mohd Ashri

Vincent Hui Shao

OFFSHORE PIPELINES & RISERS

Enhanced

Regular Pipeline Integrity Management Defect Assessment (Remaining Strength)

Free-Span Assessment

On-bottom Stability

Corrosion Rate

Risk-Based Inspection (RBI)

Fitness For Service (FFS)

Structural Reliability Analysis (SRA)

Enhancement of PIM OFFSHORE PIPELINES & RISERS

Enhanced Pipeline Integrity Assessment

Specific PARLOC Data Base

QRA Based RBI

Extended Fitness For Service (QRA/SRA based FFS)

Engineering Critical Assessment (ECA)

1. Specific PARLOC Data Base


Pipeline Database

Contents of Database

Sources of Data

Data Collection

Data Collation and Verification

Incident & Defect Database

Contents of Database

Sources of Data

Data Collection

Data Collation and Verification

Loss of Containment Incidents

Causes and Consequences of Incidents

Analysis of Loss of Containment Incidents

Factors affecting Leak Frequencies

Incidents to Safety Valves

Incidents to Umbilical, Jumpers and Hoses

Assessment of Incidents to Pipelines

Causes of Incidents

Tabulation of the Frequency of Loss of Containment

Pipeline Failure Database PARLOC OFFSHORE PIPELINES & RISERS

To develop and update databases that collect all of the failure incidents occurred to and some selected corrosion defects in the offshore pipelines and static steel risers owned or operated by a certain area:

Sources of Data:

Specific Pipeline Information, e.g.:

• Pipeline No. 1 (12in, X60, 2Km)

• PL No. 2 (10 in, X50, 9km, etc.)

PARLOC 90

PARLOC 96

Journal articles, published papers etc.

Pipeline Operators

UK Health and Safety Executive

(HSE) pipeline database, 1992

Other database


Incidents Database


Analysis of Loss of Containment Incidents

• The specific databases will collect information and data for the pipelines and risers owned/operated by a

certain area, e.g. Asia.

• The UK PARLOC databases have shown us how useful these databases are in risk assessment and

management. We may however, compare our specific PARLOC databases with the UK PARLOC databases.

• Once the specific PARLOC databases are established, they may be used effectively for the extended

assessment of FFS and RBI of pipelines and risers.

OFFSHORE PIPELINES & RISERSPipeline Failure Database PARLOC

2. QRA Based RBI


To provide a visual QRA platform to standardize the process of risk assessment so that engineer can save the time needed for risk calculation and modeling and report preparing.

• QRA Modules includes:

Module 1: Data Gathering

Module 2: Hazards Identification

Module 3: PoF Assessment

Module 4: CoF Assessment

Module 5: Risk Evaluation

QRA ModulesOFFSHORE PIPELINES & RISERS

Module 1: Data gathering

Pipeline design data

Pipeline operating data

Pipeline inspection data if any

Environmental data

Geographical data

Emergency response mechanism

Inspection and monitoring scheme

Marine traffic statistics

Module 3: PoF assessment

Internal corrosion

External corrosion

Erosion

Welding & materials

On bottom stability

Free-span

External impact

Module 5: Risk evaluation

Risk Modification / Evaluation

Module 2: Hazards identification

Trawling

Anchoring

Wreck

Dropping objects

Marine growth

Wave, wind and current

Internal corrosion

External corrosion

Erosion

Welding & materials

On bottom stability

Module 4: CoF assessment

Emergency response assessment

Source emission simulation

Oil dispersion simulation

Gas dispersion simulation

Fire simulation

Explosion simulation

Consequence calculation

QRA ModulesOFFSHORE PIPELINES & RISERS

Pipeline failure usually takes the form of leakage, which is the initiate event resulting to serious consequences.

Probability of Failure (Pof) is estimated as failure frequencies of different types of degradation mechanisms operating in the pipeline component.

The failure frequency is calculated based on different damage causes. The main damage causes identified for subsea pipelines are listed below:

Internal Corrosion

External Corrosion

Erosion

External Impact

Free-span

On-bottom Stability

The specific PARLOC database is proposed to be used for pipeline Pof assessment.

Probability of Failure PofOFFSHORE PIPELINES & RISERS

Consequence of failure can be expressed as number of people affected (injuredor killed), property damage, amount of a spill, area affected, outage time,mission delay, money lost or any other measure of negative impact for thequantification of risk.

It is usually divided into three categories of Safety, Economic andEnvironmental consequence to be analyzed respectively by qualitatively orquantitatively way.

The consequence analysis is an extensive effort covering a series of stepsincluding:

Accident scenario analysis of possible event sequences (Event Tree Analysis for instance)

Analysis of accidental loads, related to fire, explosion, impact

Analysis of the response of systems and equipment to accidental loads

Analysis of final consequences to personnel, environment, and assets

Each of these steps may include extensive studies and modeling.

Consequence of Failure CofOFFSHORE PIPELINES & RISERS

Theoretically, a Life Cycle Cost-Benefit assessment should be a perfect method for determining the optimum target reliability.

The selection of target reliability is based on consequences of failure, location and contents of pipelines, relevant rules, access to inspection and repair, and QRA results, etc.

When conducting QRA based RBI analysis, target reliability levels in a given reference time period and reference length of pipeline should be selected. Reliability

Cost

Optimum Reliability

Failure Cost

Initial Investment

and Maintenance

Cost

Total Cost

Target ReliabilityOFFSHORE PIPELINES & RISERS

Limit StatesSafety Classes

Low Normal High

SLS 10-1~10-2 10-2~10-3 10-3~10-4

ULS 10-2~10-3 10-3~10-4 10-4~10-5

FLS 10-2~10-3 10-3~10-4 10-4~10-5

ALS 10-3~10-4 10-4~10-5 10-5~10-6

1. 5x5 Risk Matrix in Initial Assessment

2. Risk level at analysis year

3. Next Inspection year


( , , )CoF f manned condition ouside diamter product analysis year analysis yearRisk PoF CoF

( )next inspection analysis step high analysisY Y Y PoF PoF ( ) ( ) ( ) ( ) ( )CoF A or B or C or D or E

Q-RBI: Initial Assessment

4. Calculation of Annual Probability of Failure for Corrosion defect

where

5. How to judge failure (inspection is needed)?

(1) The allowable corroded pipe

pressure exceeds MAOP

(2) The defect depth exceeds 85%

of the nominal wall thickness

(3)

1 ( )PoF


( ) Normal accumulative distrubution x 2 2( ) ( )

corr

Pcorr corr OP

P OP

StD P StD OP

Q-RBI: Detailed Assessment

/ [ / ] 1d dmeasd t StD d t

3. Extended Fitness For Service (QRA/SRA Based FFS)


The risk and reliability based fitness-for-services (FFS) assessment addressed in this paper isa Quantitative Risk Assessment (QRA) based FFS study on subsea oil or gas pipelines.

The main purpose of SRA is to determine the target reliabilities for different pipeline segments.

Structure Reliability Analysis (SRA) method is used to calculate the maximum safe operatingpressure, which indicates the pipeline retaining pressure capacity.

QRA and SRA results will be used to conduct traditional FFS, which indicates whether thepipeline is fit for service or not by a comparison of pipeline retaining pressure capacity withgiven MAOP.

EFFS To portray pipeline present risk

picture and define the target reliability

of every pipeline segment;

EFFS: IntroductionOFFSHORE PIPELINES & RISERS

This risk and reliability based FFS studyprocess will focus on pipeline corrosiondefect.

Initially, QRA will be performed to derive thepipeline target reliability.

Using target reliability and SRA method, thepipeline retaining pressure capacity Psafe willbe obtained as the preparation of FFS.

Finally, traditional FFS will be conducted toindicate whether the pipeline is fit for serviceor not by a comparison of pipeline retainingpressure capacity with given MAOP.

Operating data

Develop defects to

remaining design life

Psafe > MAOP?

Yes

Inspection data Design data

QRA

Corrosion rate Target reliability

Pipeline

Segmentation

Defect assessment one

by one based on SRA

method

No

Psafe >MAOP?

Calculate remaining

design life capacity

Remaining life to

current MAOP

Yes

No

Calculate de-

rated capacity

EFFS: MethodologyOFFSHORE PIPELINES & RISERS

This section intends to perform quantitative risk assessment (QRA) to establish the pipeline structure target reliability taking into account pipeline safety, environmental, and economic consequences.

The Quantitative Risk Assessment process will bring benefits to the following directions:

Pipeline Segmentation - Much more precise pipeline segmentation

Probability of Failure (Pf) - Much more precise pipeline failure consequences calculation

Consequences of Failure (Cof) - Much more detailed calculation of corrosion rates

Target Reliability - Much more beneficial choice of pipeline target reliabilities

EFFS: QRA and Target ReliabilityOFFSHORE PIPELINES & RISERS

Limit StatesSafety Classes

Low Normal High

SLS 10-1~10-2 10-2~10-3 10-3~10-4

ULS 10-2~10-3 10-3~10-4 10-4~10-5

FLS 10-2~10-3 10-3~10-4 10-4~10-5

ALS 10-3~10-4 10-4~10-5 10-5~10-6

g(Z)<0 represents a failure state where loads S exceeds the strength R.

g(Z)>0 represents a safe state since strength R is larger than loads S.

g(Z)=0 represent the limit state line (or surface).


SR)Z(g

EFFS: SRA Limit State

The structural failure probability Pf can be calculated as

And the reliability R is

The safety index β (API 2A-LRFD) is the most popular measure of reliability in industry. The safety index is related to the corresponding failure rate by formula:

Where, (.) is the standard normal distribution function.


0zg

Zfdzzf0)Z(gPP

0)Z(gPP1Rf

1fP

EFFS: SRA Failure Probability

The uncertainties are measured in terms of standard deviation and variance from mean values and combine to give an uncertainty in the predicted pipeline safe operating pressure.

An example of the mean bias (B) and COV (Coefficient of Variation) of the burst prediction model is (Bai et al 1997) in Table 2:

A bias factor X is introduced to reflect the confidence in the criterion in prediction of burst strength.

Normalized random variables in the design equation can be expressed as in Table 3:

OFFSHORE PIPELINES & RISERSEFFS: SRA Uncertainties


For normalized defect length , the normalized mean Rm (Pburst) is given by:

FM

ALL

A

XX

XAXLXL

XA

fm BBBXBXBX

BX

D

tR

5.02 ))(003375.06275.01(1

12

For normalized defect length , the normalized mean Rm (Pburst) is given by:

FM

AL

A

XX

XAXL

XA

fm BBBXBX

BX

D

tR

1)3.3032.0(1

12

Psafe is the operating pressure that gives an acceptable/desirable safety index (β) i.e. probability of burst for the individual defect considered

Pburst = r * Psafe

The mean load Sm is given by:

m safe XfS P B

502

Dt

LX L

502

Dt

LX L

EFFS: SRA Longitudinal Corrosion


The safety index is calculated as:

RSmm SR ln/)/ln(

))1()1ln(( 22

ln SmRmRS VV

Where:

2 2 2 2 0.5( )Rm A L F MV V V V V

The CoV for the load (Sm), VSm is taken from Bai’99 as 0.02.

The variance of the mean resistance is estimated from the variances of XA, XL , Xf,

XM.

The safety index β is related to the corresponding failure rate (Target Reliability) by formula:

1fP

EFFS: SRA Longitudinal Corrosion

Following item will be considered when doing assessment:

• Zone 1 and zone 2 (different safety class value)

• Internal and external (different corrosion rate)

• Submerged and atmospheric (different corrosion rate)

• Defect type

• Defect Dimension (d/t vs L)

• Defect Orientation (Clock position vs KP)

SRA Based Remaining Strength

• Reliability based corrosion capacity (SRA Approach)

OFFSHORE PIPELINES & RISERSEFFS: Corrosion Capacity & Remaining Life

Corrosion Rate

• de Waard Model

• Norsok Model

SRA Based Future Corrosion Capacity

QRA Based Target Reliability Level

SRA based Remaining Life Calculation

• DNV RP F101 Part A Criteira

• ASME B31G Criteria

Degradation Tendency

EFFS: Examples

4. Engineering Critical Assessment (ECA)


To supplement the traditional S-N approach and determine the flaw acceptance and inspection criteria in fatigue and fracture design of risers and flowlines.

Assessment is generally made by means of a failure assessment diagram (FAD) based on the principles of fracture mechanics.

• ECA includes:

Data Gathering and Preparing

FAD Determination

Stress Assessment

Factor Calculation (e.g. Stress Intensity Factor)

Fracture Ratio and Load Ratio Determination

Fatigue Assessment

Remaining Strength

ECAOFFSHORE PIPELINES & RISERS

Level 1, a preliminary FAD based on the CTOD design-curve method, is the basis of the elastic–plastic fracture assessment procedure in BS7910.

ref

r

Y

L

ref

r

flow

S

ECA – The FAD MethodOFFSHORE PIPELINES & RISERS

Level 2 is an alternative FAD based on the lower bound of many curves obtained from experimental data on general austenitic steel.

Level 3 requires the value of reference strain, εref , of the target region including the flaws. Since εref is defined as a corresponding true strain obtained from the tensile curve at a true stress, the tensile curve of the target region must be determined before.

I refK Y a 2

2

1

YIC

EK

ECA – The FAD MethodOFFSHORE PIPELINES & RISERS

Here,

ζY and E are the yield stress and elastic modulus ,

Lr and Kr are the load ratio and the fracture ratio,

ζref , KI and KIC are applied stress, stress intensity factor, and fracture toughness, respectively.

Additionally, δ is the calculated CTOD value.

API X65-graded natural gas pipeline of diameter 762mm and thickness 17.5mm

ECA – APL X65 Pipeline testOFFSHORE PIPELINES & RISERS

Locations of tensile specimen sampling in: (a) weld metal and (b) HAZ


Schematic diagrams of (a) CTOD specimen geometry; notch

locations of (b) weld metal specimen and (c) HAZ specimen


Abstract of Papers:- - Malaysian Gas...

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