(05) Christian Bucherie, BV

LIFETIME EXTENSION OF AGEING FIXED OFFSHORE PLATFORMS

AND SUBSEA ASSETS

AIM FORUM – KUALA LUMPUR 17-18th SEPTEMBER 2013

2 KUALA LUMPUR AIM FORUM – 17-18th SEPTEMBER 2013

ABSTRACT

► 3rd party Life Extension Certification :

The approach to integrity by key O&G players is changing, actions being more directed towards predictive processes than corrective actions.

In the same period the identification of “critical elements” became a commonly admitted pre-requisite to any integrity strategy.

The critical steps may be summarized as follows :

• What to measure where how when ?

• Do the sets of measurement allow to totally trace the “ life “ .

• Critical steps towards life extension .

Exploring offshore structures and other critical subsea systems like flexibles risers, path to 3rd party Life Extension Certification

CONTENT 1 Context / BV approach 2 Platform inventory /

Site conditions 3 Structural assessment /

Strength & fatigue analyses 4 Inspections program /

Lifetime extension 5 Conclusions / current

developments: SIM, etc.


CONTEXT / BV APPROACH

1970 1980 1990 2000 2010

► The situation: Offshore Fixed platforms are more intensively

loaded than before, and may present local overstressing or damage.

Oldest installations have reached their original design lifetime and therefore require life extension assessment.

► The experience of the Certification Authority: BUREAU VERITAS

certification activities in the Southern North Sea:

• 1974: First certification

• 1994: First recertification First issue of our Procedure GEP n°305 - Fixed Offshore Installations Condition Appraisal of Ageing Structures

Service life lifetime extension


CONTEXT / BV APPROACH

Phase 1 SCREENING:

- Platform inventory - Site conditions

Phase 2 RE-ANALYSIS:

- In-place / Pushover - Fatigue

Phase 3 SURVEY

PROGRAM

Phase 4 CONCLUSIONS

► The objectives: Such re-appraisal has to give an up to date and "State of the Art“ picture of the

platform data and strength, with respect to data assumed and to methods used initially, at the time of building.

Then this picture is used to assess if the existing platform is still “fit-for-purpose”, and to decide the in service inspections for the forthcoming period.

► Our services for structures: BUREAU VERITAS scheme of RECERTIFICATION for LIFETIME EXTENSION

includes four phases:


Platform inventory

The inventory mainly includes the data collection from: initial building documents (as-built) with all follow-up reports, periodical inspection reports,

1. Platform arrangement reassessment from initial (as-built) and follow-up reports: Topside arrangements (initial design data and fabrication records, historical record of revamping, and present situation → weight assessment), Appurtenance arrangements (conductors, risers, boat landing, and fenders).

2. Platform conditions reassessment from inspection reports: Damage, accident, with subsequent repairs, Corrosion, anodes maintenance Records of marine growth thickness & cleaning operations, scour & debris observations.

Phase 1 SCREENING:



SITE CONDITIONS

Review of initial reports for environmental & soil conditions with if possible more recent data: measurement of water depth (the relative deck level elevation), measurement reassessment of wave and other environmental data (wind, etc.), soil investigation at a later built adjacent platform.

1. Deck clearance reassessment:

Possible air gap reduction (or platform subsidence) and wave-in-deck risk.

2. Metocean loads reassessment:

to improve the accuracy of the 20-year old description of meteocean conditions

3. Soil resistance reassessment from soil investigations:

more recent techniques of investigations and analyses may be available.

Phase 1 SCREENING:



EXAMPLE OF RECERTIFICATION

Wellhead platform installed in the 80’s (Southern sector of North Sea) Initially designed for survival waves: Hmax =17 m (air gap of 1.5 m) 2005 : Recertification for lifetime extension

with the addition of a new topsides module (weight increase of 20%):

• Climate worsening: the design wave becomes Hmax =19 m

• Measurements concluded that deck elevations are 0.75 m below design values.

• No damage recorded during in-service inspection.

As the air-gap became negative, BUREAU VERITAS recommended:

• Relocation of all equipments necessary for the platform process integrity.

• Reinforcement of secondary equipments support which have not been relocated.

• Re-analysis of the new topside arrangements and environmental conditions (i.e. to check the piles compression due to weight and wave increases)

Phase 1 SCREENING:



DAMAGES EXAMPLES

Dented members:

• Boat impact / dropped objects (The size of local indentation with possible member misalignment needs to be measured. Both joints of the impacted brace are to be inspected)

Fatigue Cracks:

• Unexpected cracks generally in the first horizontal level below sea level. (local wave effect not properly modelled in fatigue calculation)

• No crack in area of low fatigue life estimation due to the conservatism of analysis procedure (joint flexibility, number of cycles estimation, etc.)

Phase 1 SCREENING:



LOSS OF INTEGRITY CAUSES Phase 1 SCREENING:


Jacket failures modes:• Load increase:

» Design ● Environment worsening: - underestimation of design waves- unexpected marine growth- hurricane, tsunami, freak wave, etc.

● Soil: variation of soil design capacity

» Operation ● Topsides loads increase / Centre of gravity shift (revamping)● Addition of conductors or risers

» Accident ● Ship impact / Dropped objects

• Strength reduction:» Design ● According to out of date codes

● Water level variation (Air-gapreduction / subsidence)

» Operation ● Insufficientinspections / maintenance

● Lack of repairs

» Degradation ● Corrosion● Scour● Fatigue cracks


THE PRINCIPLES Phase 2 RE-ANALYSIS:


The re-analysis of the platform should be carried out:

to give an up-to-date picture of platform strength, to confirm the suitability of structures for an extended lifetime,

In-place structural strength reassessment: Conventional in-place analysis (components checks: members, joints & foundations) may be complemented by more advanced methods (i.e. push-over analysis).

Jacket fatigue strength reassessment: Fatigue re-analysis should be carried out in accordance with the latest State of the Art and when relevant, "past" and "future" conditions should be considered separately.


IN-PLACE STRENGTH Phase 2 RE-ANALYSIS:


Traditionally, the strength is expressed the maximum of all unity checks (UC’s in case of components check),

but it can be also measured by the reserve strength ratios (RSR’s in case of system check)

CONVENTIONAL CHECKS (storm)

MEMBERS CHECK

FOUNDATIONS CHECK

CONNECTIONS CHECK

YIELD CRITERION

PUNCHING CRITERION

BUCKLING CRITERION

FOUNDATION CRITERION

CRITERIA FOR SAFETY FACTOR EVALUATION OF

EACH COMPONENT

RECERTIFICATION BASED ON CONVENTIONAL ANALYSES RECERTIFICATION BASED ON PUSHOVER ANALYSES

Phase 1 SCREENING:


Phase 2 RE-ANALYSIS: In-Place analysis

Fatigue analysis

Pushover analysis Higher analysis level

PUSHOVER

PLASTIFICATION

JOINT STRENGTH

GLOBAL & LOCAL STABILITY

FAILURE MODES TO BE ACCOUNTED FOR JACKET

PUSHOVER ANALYSIS

FOUNDATION STRENGTH


FATIGUE STRENGTH Phase 2 RE-ANALYSIS:


The fatigue re-analysis based on the extended lifetime should be carried out

in accordance with the latest state of the art for all tubular joints:

Updated wave distribution if new measurements are available

For Hot-spot Stress Approach: A more refined assessment of local stresses using local joint flexibility (LJF) or FE meshes when parametric stress concentration factor (SCF) are no longer applicable.

Fatigue loads that describes all phases (i.e. dynamical response may changed consequently to topsides weight increase)


DIFFICULT ASSESSMENTS Phase 2 RE-ANALYSIS:


In case of pushover for strength assessment:

• The RSR values are generally greater than 2.0 due to load redistribution. A criterion between 2.0 and 1.5 (safety factor of pile capacity for storm conditions) is still under discussion in offshore industry, and may be specified by the operator or regulatory authority.

Fatigue in splash zone and in upper level in water:

• The correlation between Hot-Spot Fatigue lifetime calculation and joints inspections (unexpected cracks or absence of cracks) is not always satisfactory.

Assessment with damage

• The member strength reduction can be assessed by simple equations for extreme conditions, but regarding loads redistribution, and its consequence on fatigue lifetime estimation needs to be improved.

Approximate section resistance


SPECIAL SURVEY

A special survey inspection should be performed after the re-analysis, in order to complete the evaluation of platform conditions, and to correlate this actual condition with the finding of re-analysis.

1. Inspection of overall conditions of the platform (annual inspections):

GVI: General Visual Inspections to check the presence and condition of members Scour surveys Marine growth measurements in order to plan platform cleaning inspections of anodes

2. Structural inspections of the damaged areas:

Dents, straightness, flooded members, thickness/corrosion, etc.

3. Specific inspections of appurtenances:

Potential readings at several locations Riser attachments (bolt clamp check)

4. Critical joints inspections

Phase 3 SURVEY

PROGRAM


CRITICAL JOINTS

The underwater inspection strategy is based on: previous inspection results known damage re-analysis results BUREAU VERITAS recommends to select for the inspection plan:

1. Joints with earlier cracks or other recorded anomalies (boat impact for example)

2. Joints not covered by earlier inspections

3. Joints found critical by re-analysis low fatigue life (< twice the extended lifetime) High stressed areas For program definition BUREAU VERITAS is developing a Risk Based approach for underwater inspections. It integrates the likelihood of failure, the evolution of marine growth, and the member failure consequence, etc.

Phase 3 SURVEY

PROGRAM


based on weighting factors which represent a criticality ranking of joints CRIT = f ( LoF, CoF) where:

LoF = Likelihood of Failure CoF = Consequence of Failure

SIM Risk Assessment

Objective: Providing a qualitative or quantitative risk based inspections of joints for the lifetime extension.

Reliability Research

works

Phase 3 SURVEY

PROGRAM

Conventional Inspections Plan 1 Joints with earlier cracks

2 Joints not in earlier inspections plan 3 Joints found critical by re-analysis

Structural Integrity

Management (SIM)

Probabilistic

RBI

Levels of inspection strategy

LoF

CoF

High Criticality

Medium Criticality

Low Criticality

Phase 2 RE-ANALYSIS: In-Place analysis

Fatigue analysis

Pushover analysis

Phase 3 SURVEY PROGRAMME:

STRATEGY PROGRAM Phase 1 SCREENING:

Platform Inventory Site conditions

INSPECTION & SIM


The in-service inspections with the resulting data update is a key step of SIM mainly based on a continuous (or at regular interval) process of the fitness-for-purpose control.

Phase 3 SURVEY

PROGRAM

Phase 1 SCREENING:




Phase 3 SURVEY PROGRAM

- Strategy - Program

DATA UPDATE

UPDATING PHASE


The conclusion for the lifetime extension includes: 1. Platform mitigations: overall load reduction, etc.

2. Repair or reinforcement work, as considered in the final run of re-analysis

3. Maintenance & inspections: marine growth cleaning, joints inspections, etc.

→ TARGET: recertification for 5-years extension.

Target 5-years possibly renewable lifetime extension confirmed by a Certificate of Fitness with the approval of the Inspection Program

Phase 3 SURVEY PROGRAM:

- Strategy - Program

Phase 4 CONCLUSIONS

Phase 1 SCREENING:




Phase 4 CONCLUSIONS

DECISION PHASE


•Deep Sea Facilities Pipelines, risers & subsea Equipment

• Offshore Facilities

• Pipelines & risers

• Fixed Platform structure

• Topsides equipments

• Onshore Facilities Onshore pipework & pipelines Refinery

• LNG Terminal

• Ageing and lifetime extension : a challenge for O&G industry • How to manage existing ageing assets and extend their life beyond their initial intended design-life

FROM ONSHORE TO DEEPWATER


•1.1 Data collection

• General Design Data

• As built documentation

• Historic of inspection

• Structural Analysis with FE model

•1.2 SIM evaluation

•.jcm file •SIM Engine

•Risk Matrix

•Inspection frequency

•Inspection scope

•2.1 Inspection planning

•CAMPAIGN

•2.2 Inspection results assessment

•SMR & anomalies

•Management of change

ASSET LIFE CYCLE APPLIES


•ISO 13628

•API 17N, 17B, 17J, 17E …

WHAT DEEPWATER ASSETS ?


Integrity = Resistance vs Loads balance,

with enough margin on «R» side •Resistance

•Design / Initial •Grade

•Thickness

•Allowances

•Deterioration versus time

•Loads •Fluid loads •Pressure

•Temperature

•Density

•Sand content

•Corrosivity

•Environment loads •Wind

•Wave

•Current

•Sea bottom interaction

•Inspection / Monitoring

•Data •Evaluation •Strategy •Program

•But what ?

•Where ?

•Design Conservatism ?

INTEGRITY


•Data •Evaluation

•Strategy •Program

•Configuration analysis & other specialised

Software :

•Hot spot Forces, Moments

•Soil interaction and Buckling sensitive spots

CONFIGURATION ANALYSIS (FORCES, MOMENTS)


•Refined stress / fatigue analysis for complex structures •Data •Evaluatio

n •Strategy •Program

•Defect assessment / FFS analysis

STRESS ANALYSIS (MAX STRESS, FATIGUE)


►Margins for Life extension are created through :

Assessment of possible design conservatism (fluid or environmental loads)

Controlled safety margins reduction beyond design life

Use of inspection/monitoring tools/methods with increased reliability

Reduction of uncertainties, which reduces probabilities of failure

Use of efficient integrity management system

LIFE EXTENSION

(05) Christian Bucherie, BV

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