Certification of Subsea Technology: ”Why Failure occur” · PDF fileCertification...

Certification of Subsea Technology: ”Why Failure occur”

Experiences from offshore failure analysis”

Gustav Heiberg, DNV Materials Technology and Failure Investigation, Høvik, Noway2005-12-05

Version Slide 205 December 2005

Outline

How are failures examined ?

Why do failures occur, root causes and project context ?

Learning from failures, Examples

How are lessons learnt incorporated in new projects and ongoing operations ?


How are offshore failures examined ?

Damage assessment based available information, system configuration and experience with relevant failure modes




Field inspection




Field inspection

Laboratory examination / testing of retrieved failed components




Field inspection


Verification of repair solutions




Field inspection


Verification

Qualification testing


Why does this happen?

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Conclusions from failure analyses:

Material selection - Qualification program for material and weldments did not reveal relevant failure modes

Fabrication - Machining of weldments reduced the area such that all straining occurred in the weldments- Critical types and locations of defects was not covered by the NDT procedure and set-up

Operation- Operational conditions differed from design basis

- Larger strains or stresses than anticipated - Not designed for the purpose- Environmental changes

“We never thought about this”, “Nobody told us”, “This has worked before”

All aspects are not covered in design basis, and changes with one supplier does not affect others

Distributed responsibility – lack of overview


How are failure modes adressed ?

Materials selection

Specification / Standard

Failure modes covered by this

Fabrication, welding, NDE

Material properties / metallurgical features

Acceptance criteria

Failure modes not covered by spec or standard

Load cases not covered in design

Operational conditions not covered by spec or standard

Choice of materials or components which has proven fit for service under slightly different conditions

Unclear interfaces / code breaks

Design basis Interface definition

Environment

Loads and stressesDesign

Definition of load cases and environmental conditions

Resistance to applied stresses / strains from selected load cases

If generic:

New JIP to establish Standard or RP

From failure mode to guideline

2 Case studies

Hydrogen Induced Stress Cracking (HISC) of duplex stainless steels


3rd largest oil spill in Norway, May 2003

• 15 MUSD capex sub-sea satellite tie-back

• 750 m3 oil spilled to sea after only 2 years of operation

• Crack in transition piece between manifold and pipeline

• Expensive repair and deferred production

• Associated costs;• Repair, procedures and training

• Emergency response operation

• Environmental impact

• Brand impact


NotchWeld

Failure Investigation

90 degreeAngle

Duplex Stainless Steel

High global tensile stresses from pipeline

Local areas with high stress concentration

No coating in the fracture area

Undesired microstructure

Material StressHydrogen/ Cathodic Protection

Hydrogen induced stress cracking (HISC)


Prevention of future failures

R&D work:

JIP on testing of Duplex and 13%Cr Stainless Steel susceptibility to HISC

JIP on development of design guideline for use of Duplex Stainless Steels exposed to cathodic protection

Partners:

Shell, Statoil, Hydro, ChevronTexaco, ConocoPhillips, Total, BP, FMC, Vetco Gray, Kværner, Technip

Project specific work

Project specific design verification work

Manufacturing follow up

Alternative solutions ?


Lined and Clad PipeOvermatching filler materials for girth welds

Non-destructive testing

Reel installation and snaking –local buckling

Pressure containment

Reel installation and snaking –fracture capacity and fatigue

Corrosion testing

Corrosion resistant alloy wall thickness requirements

Gripping force

Induction bending

Reeling of pipelines


Some Failure Modes

Local Buckling

Ductile crack growth at welds

Ovalization


Prevention of failuresR&D work:

JIP on testing related to reeling of pipelines

JIP on development of Recommended Practice for reeling of pipelines and incorporation of relevant requirements in the DNV pipeline standard DNV OS-F101

DNV OS-F101DNV RP-F108

How can lessons learnt be incorporated in new project and ongoing operations


Project Risk Management

A systematic approach to predict and manage un-certainties to reach the project goals:- Profit, cost, schedule, quality, performance, safety, environment

Assisting the project team to:- Identify, evaluate and rank project threats and opportunities- Develop strategies for risk mitigation and loss control; i.e. identify which preventive measures should

be implemented- Focus on key risk drivers, i.e. the parameters that have a make-or-break effect on the project

I.e. better decisions through:- better perception of risks and their interactions- proactive risk management


Qualification of new Technology

Make Decisions

New Concept

Introduction of New Technology

Define Qualification BasisFailure Mode Identification

and Risk Ranking

Analysis and Testing

Reliability Analysis

Concept Improvement

Selection of Qualification Methods


Deep Water TechnologyDisciplines

Coupled analysis

Failure investigation

Subsea Components

Materials Technology

Pipelines

Risk & Safety

MarineOperations

Hydraulics &Process

Inspection & Quality Surv.

Environment

MANAGING RISK

Risers

©Statoil

Structural Integrity

Laboratories

Flow Assurance

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