PSA Norway Flexible riser seminar

Growing old gracefully - Realistic for flexible risers?

Jan Muren

Nils Gunnar Viko

Joachim Müller-Allers

Andreas Gjendal

Henning Christensen

Morten Eriksen November 2013

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Rigid risers

Wellhead

systems

Floating

wind turbinesFlexible

risers &

umbilicals

Flowlines

Steel Catenary

Risers

Offshore Loading

This is 4Subsea’s area of expertise

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Experience build-up

4subsea investigates used risers

• 28 860 m investigated in detail

• Intact and damaged

• PVDF, PA11, X-link PE pressure

sheaths

• Norway, West Africa, Netherlands, UK

• Excellent cooperation with

• Marintek Sintef DNV

• IFE NorSea Base

• Operators Vendors

• 32 engineers full time on flexibles

• Over 400 years flex-riser experience

• Over 1500 offshore annulus tests &

vent gas samples

It’s so much more on flexibles to learn

Agenda…

• Norwegian Shelf riser &

incident statistics

• Challenges &

opportunities for the future

• Strategies for growing old

with grace

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Norwegian Shelf riser & incident statistics

Flexible risers - Norwegian Continental Shelf

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0

50

100

150

200

250

300

350

1985 1990 1995 2000 2005 2010 2015

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Flexible risers - Norwegian Continental Shelf

0

50

100

150

200

250

300

350

1985 1990 1995 2000 2005 2010 2015

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Flexible risers - Norwegian Continental Shelf

Riser incidents in Norway – PSA database

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What is CODAM database?

• Database managed by PSA

• Data as reported from operators

• Data from mid – 1970’s

• Flexible riser data structured from 1995

• Damages and incidents on structures

and pipeline systems

• Focus on personnel risk

http://www.ptil.no/getfile.php/1.10.13Stigeroersskader.pdf

Flexible riser incidents reported to PSA

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Major incident• High risk of injury

• High risk of pollution

(mainly based on operators judgement)

Major incident: (typical)Observation of damaged outer coating

in riser guide tube at 12-14m below

sea level. Vacuum testing confirmed

leakage. Crack seen on video.

Most frequent riser incidents in Norway

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Carcass incidents

• Collapse

• Pull-out – PVDF interaction

• Axial failure - hydrate blocking

• Sand Erosion

• Fatigue

Abrasion / Wear

• Bell Mouth / Guide Tube

• Interfacing Structures / Ancillaries

• Seabed At Riser Touch Down

• Internal Wear

Ageing

• Hydrolysis (External Sheath, Tape Layers,

Pressure Sheath)

• High temperature (shielding/insulation)

Incident rate development

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** data to Oct 2013

5 major

incidents pr

riser year

Riser replacements in Norway

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• In total 80-100 risers replaced

• 30-50 risers replaced due to risk

assessment

• 25-30% of the 324 risers in

operation have been replaced or

re-terminated

• 60 reported major incidents in

CODAM (1995-2013)

• 49 risers reported to be replaced

• 11 risers repaired (later replaced?)

• Other replacements (flexibles)

• Flowlines

• Topside jumpers

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Any better elsewhere?

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Challenges & opportunities for the future

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Polymer ageing

• Pressure sheath

• Anti-wear tape

• Intermediate layers

• External sheath

• Bending stiffener

Wear from

• Bend stiffener

• Bell-mouth

• Subsea arch

• Clamps

• Internal in cross section

Corrosion

• CO2

• O2

• H2S

Fatigue

• Tensile armour

• Pressure armour

• Carcass

Time driven degradation processes

condensed water

+ or

seawater

Future degradation modes

• Ageing

– Failure of external sheath and tape layers of high

temperature riser operated below design temp

– Shortcomings identified in API 17 TR2 model

– Pressure sheath aging sensitive to various acids, not

only pH and humidity

– Complex chemistry, simplified models not adequate

• Corrosion (in annulus)

– Incomplete understanding of corrosion in annulus

– Significant scatter in observations

– Large variability in annulus environment (wet/dry/oil)

– Reservoir souring, low level H2S in sweet service

risers

• Fatigue of corroded areas

– Methods not validated for wires with corrosion

damage

– Tests indicate significant loss of life even with

shallow pitting

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Continuous monitoring

– Vent system function

– Annulus vent rate

– Annulus gas composition

– Annulus temperature

– Annulus liquid filling

– Sheath integrity

– Armour strain

– Bore pressure (top/bot)

– Bore temp (top/bot)

– Bore flow

– Flow induced pulsation

– Curvature / motion / twist

– Acoustic emission

Inspection / testing

– ROV general visual

– ROV close visual

– CP measurements

– Pressure test

– Bore content sampling

– Internal inspection

– Digital radiography

– Ultrasound scanning

– Eddy current

– Magnetic Stress

measurement

Growing Integrity Management tool box

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Information management in 21st century

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Wave height increase

• Yearly average significant wave

height (Hs) on the Norwegian Shelf

approx 2.0m

• UN report on climate change 2013

• North Atlantic yearly average Hs

increased 0.02m/year since 1950

• +0.5m over 25 years riser life -

important for fatigue calculations

• Norwegian research shows

increasing max and design Hs for

selected North Sea areas

Climate change

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Strategies for growing old with grace(when being a flexible riser)

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1. Learn to live with reality

• Exploit opportunities and understand weaknesses

• Use experience to modify operational restrictions

• Increase margins in new designs or retrofits

• Train personnel and provide good procedures

2. Replace risers

• Replace riser at failure, and/or

• Schedule replacement based on experience,

analysis and risk assessment

• Step-vise technology improvements

3. Condition based integrity management

• Research on degradation process

• Online monitoring of key parameters

• Processing and assessment

• Close and replace based on “real” condition

Strategy alternatives for increased regularity

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Learn to live with reality

• Systematic analysis of all

positive and negative

experiences

• Consistent handling of

uncertainties

• Improve operational procedures

• Rigorous training of operation

and project personnel

• Modify systems to cope with

operational limitations

• Include ample margins in new

designs1998 2012 and still a problem ?

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Replace risers

• Replace when risk is concluded to be

too high

or

• Run to failure

• When have a riser failed?

• Micro-leak or “extended” diffusion?

• Focus on consequence reduction

• Trust in leak rate assessments

• Schedule replacement as preventive

measure based on experienced

failures

• Assess failure cause

• Improve components, materials or

cross section design

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Moving towards condition based IM

• Visual inspection over

and under the surface

• Annulus low pressure /

vacuum test

• Offline assessment of

pressure & temperature

• Annulus gas vent

sampling & analysis

• Vent system

function

• Annulus vent rate

• Annulus gas

composition

• Annulus

temperature

• Annulus filling

• Sheath integrity

• Armour strain

• Bore pressure

(top/bot)

• Bore temp

(top/bot)

• Bore flow

• Acoustic

emission

• Flow induced

pulsation

• Curvature /

motion / twist

Campaign (yearly) Online (continuous)

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Operators checklist – Growing old gracefully

Acknowledge the complexity and

uncertainties related to flexible

risers (design, fabrication, installation, operation)

Map internal and external

competence – fill the gaps !

Facilitate communication, learning

and knowledge management

Focus on continuity (don’t redo the mistakes)

Initiate and support research and

development (much to gain by knowing more)

Improve tools and methods

Share experiences & best practices

Develop and implement strategies

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PSA checklist – Growing old gracefully

Ask the difficult questions

Facilitate efficient & consistent

reporting of all flexible pipe

anomalies

Follow up reports to CODAM

What was the end result ?

Replacement or repair ?

Additional info (retrospect)

Facilitate experience sharing

Provide rules and regulation

courses to management

personnel

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Kent Caveny

“We should not expect we are safe

because we are smart and nice people”

..or work long hours