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Threat Based Flexible Riser Inspection, Monitoring and Life Extension

5th May 2016 Gilles Gardner Technical Manager


Agenda - Overview

(Re)Introduction to Un-Bonded Flexible Pipe

Overview of Installed Base

Flexible Riser Threats

Failure Modes

Detection/Inspection

Monitoring

Repair

Life Extension

Event Based Re-Assessment

Extending Service Life


Introduction to Un-Bonded Flexible Pipe

Annulus – Space between the two extruded polymer fluid barriers

Protects the Carbon Steel Wires which are not Corrosion Resistant

ARMOUR

ARMOUR

ARMOUR


Flexible Riser Configurations

FREE HANGING LAZY WAVE STEEP WAVE

TETHERED LAZY WAVE STEEP S LAZY S


Introduction to Un-Bonded Flexible Pipe - Statistics

> 3,300 flexible pipes in service

> 39,000 flexible pipe operational years

58% of flexible pipes installed are risers

76% of all flexible pipe have design pressure below 345 bar (5,000 psi)

90% of all flexible pipe is below 10-inch (ID)

70% pipes are used for design temperature less than 80° C (176° F)

70% of all flexible risers in water depths less than 1,000 m WD

Source: Subsea UK


Flexible Riser Threats Failures UK and Norway

Loss of Integrity = Loss of Containment Source: UKOOA Learn more at www.2hoffshore.com

Flexible Riser Threats Operations

Pressure

Rapid Changes

Collapse Carcass

Blistering Pressure Sheath

Temperature

Polymers

High – Loss of Structural Capacity or Creep

Low – Reduced Elasticity

Read the Manual! Learn more at www.2hoffshore.com

Flexible Riser Threats

Each Layer Has Failure Modes -> Threats

Failure Modes Highlighted at Design Stage

Develop Inspection or Monitoring Strategy Early

Implement in Operation

Refine Frequency

Experience and Results Incorporated


Flexible Riser Threats Outer Sheath

External – Environmental Barrier

Robust - Polymer Extruded Layer ~8-14mm

Breach = Flooded Annulus ~ Reduced Life

Breach = Carbon Steel Layers in Seawater

Multiple Outer Sheaths


Flexible Riser Threats Outer Sheath - Detection

Post Installation Annulus Test

Regularly Scheduled Annulus Tests (Yearly)

Test Integrity of Layer

Fluid Volume in the Annulus

Confirms Correct Venting Operation

Positive Pressure or Vacuum

Low Pressure


Flexible Riser Threats Outer Sheath - Inspection

Only Layer to be Inspected Directly

General Visual Inspection – In Air and Subsea

Close Visual Inspection – Subsea

Focus on Damage

Can be Combined with Annulus Testing

Ancillary Items Can be Included

Clamps / Buoyancy /Tethers


Flexible Riser Threats Outer Sheath - Monitoring

Topside Vent Pressure

Automated Annulus Testing

Tracks Change in Annulus Environment

Drop in Pressure ~ Breach

Gas Sampling – Chemical Content


Flexible Riser Threats Outer Sheath - Repair

Static Clamp

Dynamic Clamp (Articulation)

Stop Fresh Seawater

Stop Oxygen

Arrest Corrosion


Flexible Riser Threats Tensile Armours

Provide Tensile Capacity

Two/Four Helically Crosswound Layers

Carbon Steel Wires

Material Selected H2S or CO2 Content

Corrosion - Fatigue


Flexible Riser Threats Tensile Armours - Inspection

Direct Inspection Not Possible

Non Destructive

Ultrasonic – Narrowband or Wideband

Proven – Extensive Track Record

Narrowband Requires Couplant – Confirms Flooding

Wire Thickness Measurements

Wideband (ART) No Couplant Required


Flexible Riser Threats Tensile Armours - Monitoring

Acoustic – Detect Break Signatures

Motion – Detect Small Torsional Changes

Strain Sensing

Optical Fibres


Flexible Riser Threats Pressure Armour

Provides Burst Capacity

Two Helically Wound Overlapping Wires

Carbon Steel

Unlocking - MBR

Corrosion - Fatigue


Flexible Riser Threats Pressure Armour - Inspection

Non Destructive

Magnetic Field and Eddy Current Lines

Magnetic Stress Measurement

Defect Detection

Do Not Require Couplant

Stress Level

Range of Reach - Patterns


Flexible Riser Threats Pressure Armour - Monitoring

Strain Sensing

Optical Fibres

Limited Track Record


Flexible Riser Threats Pressure Sheath

Pressure Retaining Layer

Continuous Extruded Polymer Tube

Polyamide / Polyvinylidene Fluoride (PVDF)

Polyethylene (PE) / Cross Linked Polyethylene (XLPE)

Collapse / Burst

Ageing


Flexible Riser Threats Pressure Sheath - Inspection

Coupon Sampling

Removed from Fluid Stream

Destructive Testing – Mechanical Properties

Must be Considered at Design Stage


Flexible Riser Threats Carcass

Provides Collapse Resistance

Single Helically Wound Shaped Wire

Stainless Steel – 316L


Flexible Riser Threats Carcass – Inspection/Monitoring

Reduced Bore Detection – Gauging

Internal Visual Inspection

Production Halted


Flexible Riser Threats Non Destructive Inspection –

Alternatives Computerised Tomography (CT)

Wall Thickness Map

Including Contents

Wire Damage / Unlocking

Deposits or Hydrates

Limited Inspection Experience


Life Extension

Event Based Re-Assessment

Identified Through Integrity Assessment

External Event may Result in Limited Life

Repair or Re-Instatement may Extend

Update Global and Local Models

Assess Remaining Life

Source: NORSOK Learn more at www.2hoffshore.com

Life Extension

Reassessment of Original Design Assumptions

Identified Through Inspection and Monitoring

Reduced Conservatism Based on Conditions

Environment

Operating

Annulus

Update Global and Local Models

Assess and Extend Life

Source: NORSOK Learn more at www.2hoffshore.com

Summary - Conclusions

Understand Threats at Design Stage

Initial Engineering Review and Risk Assessment Evaluated Against Need for Action

Clear Plan for Inspection/Testing/Monitoring

Refine Strategy

Continuous Process

Mitigation, Intervention or Repair Can Extend Life

Integrity Data Beneficial to Performing a Life Extension

Analysis Based on Gathered Data to Reduce Conservatism

New Inspection Techniques Improving Information Available

Life Extension Possible – Use Information Gathered


Questions?



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Threat Based Flexible Riser Inspection, Monitoring and Life Extension

01 First Issue for DNV GL Seminar 03 May 2016 G Gardner

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