ExxonMobil, Improving standards and technology towards achieving

Improving standards and

technology towards achieving

robust design and safe

operation of flexible risers

Krassy Doynov, EMDC. PSA Flexible Risers Seminar - Stavanger - November 26, 2013

K. Doynov. PSA Flexible Risers Seminar - Stavanger - November 26, 2013. 2

Outline

1. Safe design practices accepted by Industry for incorporation into API 17J & B (2014 editions)

2. Key API 17J & B improvement areas from lessons learned by Industry over the last 15 years

3. Technology developments priorities

ExxonMobil Experience with Flexibles


• 20 years design and operational experience

• Approximately 400km of installed risers, flowlines and jumpers

◦ Dynamic Subsea Offloading System, Risers to FPSO

◦ Dynamic Fluid Transfer Lines –TLP to FPSO, and Jumpers–

SHR to FPSO

◦ Quasi Static Surface Jumpers – Top Tensioned Riser

◦ Static Flowlines and Subsea Jumpers – Infield lines

• Geographical Spread – UK, Norway, West Africa, Canada, USA

• Water depth range: ~ 100-to-1800m

Outer sheath damage, Flooded annulus


High Probability of Occurrence

• ~ 25% of all damages reported to Sureflex JIP 2009, OTC 21524-2011

• Similar numbers & causes in some of EM fields: installation, abrasion, blocked vent

ports, dragged moorings

Repair options

Water cannot be displaced from annulus. Clamp outer sheath damage to stop O2 inflow.

Key Failure Mechanisms

Corrosion, corrosion fatigue and accelerated aging of polymer layers causing “chain-reactions”

leading to tensile, burst, and fatigue failures.

Key Uncertainties

Remnant life and time to replacement. Wire corrosion fatigue and polymer aging capacity.

Key Technology Gaps

Difficult to inspect / monitor reliably:

• annulus conditions, wire stress, and number of broken wires in inner layers

• determine corrosion & aging status from annulus composition data

Lack of Industry:

• consensus on selecting testing frequency for establishing corrosion SN curves

• design & test methodology for synergistic effects (e.g., corrosion/aging + fatigue)

Design for Flooded Annulus


EM Design and Qualification Testing Standard

• Inspection and monitoring should not be used to compensate for a lack of robust

design, even if they were both available and reliable

• Changed in 2005 to require:

◦ Design for flooded annulus conditions for the entire service life (installation

damage and repair)

◦ Design SN curve ensuring 97.5% probability of survival

2014 - 4th edition of API 17J and 5th edition of API 17B

• 2009 editions – design for dry annulus condition. Fatigue life for flooded annulus

provided for information only

• 2014 editions - design for flooded annulus condition:

◦ Condensed fluids in the annulus predicted assuming intact outer sheath

◦ Annulus flooded with de-aerated seawater (from installation damage and

repair)

◦ Annulus flooded with aerated seawater – as accidental case

◦ Impact on material selection and performance, and layer design for

associated degradation mechanisms (e.g., API17J, 5.3.2.7.4 “Antibuckling

tape structural capacity shall be defined as the minimum strength during the

pipe service life derived after accounting for aging and wear”)

Inner sheath damage – Smooth Bore


Key Failure Mode - Repetitive collapse - rupture at end fitting entry

EM Design and Qualification Testing Standard

2005: use only rough bore pipes since repetitive collapse cannot be designed for


• 2009 editions – no design requirements; recommendations for collapse calcs, erosion,

pigging, FAT

• 2014 editions - Design requirements: 1) per manufacturer’s acceptance criterion, 2)

anticollapse sheath and its end fitting sealing, FAT testing, annulus pressure testing

Corrosion Reservoir Souring


55-degree Flowline – loss of containment

• 90s design failed to predict souring of the reservoir

• Sweet wires fractured due to hydrogen sulfide

• Unsupported pressure sheath cracked

EM Design and Qualification Testing

• SSC/HIC test at 100% of actual yield / upper limit

of wire max local stress determined from FEA

• SSC/HIC test wire specimen with plastic strain and

residual stress levels representative of wires

retrieved from as manufactured pipes

Inner & outer armor wires

Inner pressure sheath


• 2009 editions SSC/HIC tests – test load = 90% of actual yield

• 2014 editions SSC/HIC tests

◦ To loads equal or exceeding calculated max local stress

◦ Test wire specimen with plastic strain and residual stress levels

representative of wires retrieved from as manufactured pipes

API 17 J&B Improvements


Maximum Operating Pressure

Incidental Pressure

Design Pressure

In

creasin

g P

ressu

re

Operating Pressure

Test Pressure

Burst Pressure

Minimum Pressure

Temperature Definition

Operating Temperature

The internal (1) temperature profile experienced by the pipe over its service life during permanent normal operation

Maximum / Minimum Operating Temperature

The maximum and minimum internal temperature to which the pipe is subjected during permanent normal operation

Design Temperature

The maximum and minimum internal

temperature to which the pipe is subjected during permanent operation

Incidental(2) Temperature

The maximum and minimum internal temperature that is unlikely to be exceeded during the life of the pipe

Lessons Learned from 15 years

• All flexibles JIPs prior to FPT JIP

• FPT JIP (2005-2012) 19 companies

• ~800 comments (2012-2013) from rest of

Industry

• All areas - manufacturing, testing, design,

analysis - improved significantly

Test pressure

Factory acceptance test (FAT)

The internal pressure applied to the pipe or pipe section during testing after manufacture to test for latent defects. Unless otherwise specified by the purchaser, the FAT pressure is 1.5 times the design pressure for flexible risers and topside jumpers and 1.3 times the design pressure for flexible flowlines and subsea jumpers. If applicable, the maximum differential pressure can be used instead of design pressure.

Offshore leak test (OLT)

The internal pressure applied to the pipe or pipe section during testing after installation to test for leak tightness. Unless otherwise specified by the purchaser, the OLT pressure is 1.1 times either (a) the design pressure of the pipe or (b) system design pressure, whichever is lower.

SIT (on-board integrity test) (3)

The internal pressure applied to the pipe or pipe section during testing on-board the installation vessel to test the structural integrity of the pipe. Unless otherwise specified by the purchaser the structural integrity test (SIT) pressure shall be as per the FAT pressure.

SIT (offshore integrity test) (4)

The internal pressure applied to the pipe or pipe section during testing in situ after installation to test the structural integrity of the pipe.Unless otherwise specified by the purchaser the SIT pressure shall be 1.25 times either (a) the design pressure of the pipe or (b) system design pressure, whichever is lower.

API 17J Design Acceptance Criteria


Layer Primary Pipe Failure Mode

Design Criteria

Operating Conditions Nonoperating Conditions

Survival Permanent

Abnormal

Temporary

Normal Extreme Normal

Extreme Installation Test

Internal carcass Collapse (1) (2) Load 0.85

Inner liner smooth bore Collapse (1) Load

For each polymer material for both static and dynamic applications, the allowable utilization for collapse shall be as specified by the manufacturer, who shall document that the material meets the design requirements at that load.

Internal pressure sheath

Rupture

Thinning (3) The maximum allowable reduction in wall thickness over the service life below the minimum design value, due to deformation into gaps in the supporting structural layer, shall be 30 % under all load combinations.

Strain

For each polymer material for both static and dynamic applications, the allowable bending strain shall be as specified by the manufacturer, who shall document that the material meets the design requirements at that strain.

The maximum allowable bending strain at nominal dimensions shall be 7.7 % for polyethylene (PE) and polyamide (PA), 7.0 % for polyvinylidene fluoride (PVDF) in static applications and for storage in dynamic applications, and 3.5 % for PVDF for operation in dynamic applications (4).

Pressure armors

Loss of interlock breakage

Stress 0.67 0.85 0.85 0.67 0.91 (9) 0.85 0.97 (5)

Collapse (1) (2) Load 0.85

Tensile armors

Breakage Stress 0.67 0.85 0.85 0.67 0.91 (9) 0.85 0.97 (5)

Buckling Load 0.85

Wire disorganization

Displacement The cumulative radial gap between each tensile armor and its adjacent layers shall not exceed half the wire thickness

Anticollapse sheath (6)

Rupture

Strain


Antibuckling tape Birdcaging (7)

Stress or strain (8)

0.67 0.67 0.85 0.85 0.85 0.85 0.91

Outer sheath Rupture Strain


The maximum allowable bending strain shall be 7.7 % for PE and PA.

Table 8—Flexible Pipe Layer Design Criteria

17J Pressure Armor Design Acceptance Criterion


• Pressure armor allowable

utilization – 0.67 instead of

0.55 for normal conditions

• FPT JIP Burst Limit State

reliability study - FORM and

1,000,000 Monte Carlo

simulations

• 3 pipes designed, and

material properties provided,

by NKT, WIL, FF

• Accounting for the residual stresses in wires due to manufacturing and FAT

• Maximum local stress is below yield

• Successful HIC/SSC tests at max local stress determined from FEA

• Strain based design when stress exceeds yield, plus full scale fatigue test

17B Local Stress of Individual Wire

API 17 J & B Testing


• Prototype, qualification, verification, validation test definitions added

• Property, testing and quality control requirements added for anti-buckling tapes

• Clarifications to FAT pressure test holding period and acceptance criteria

added to address interpretation requests received over the last 10 years

• Purpose-procedure-acceptance-criteria structure added to all FAT and

prototype tests

• Guidance on scaling/similarity assessment for qualification testing added

• 5 test levels and acceptance criteria for different test objectives added

Levels Strength Test Fatigue Test

1 FAILURE of pipe or end fitting Failure of pipe or end fitting

2 UTS of critical component Target SN curve of critical component

3 SMYS of critical component Damage Ratio=1.0 per design SN curve of critical component

4 AUF of critical component DAC (Damage Ratio=0.1) per design SN curve of critical component

5 MAX LOAD Maximum damage accumulated in the fatigue critical component in a service life

API 17 J & B Testing


Fatigue Test Objective Destructive Non-Destructive

Qualify a flexible pipe for dynamic service Validation of

failure

predictions

Validation of design

methodology and

tools with measured

component response

Verify manufacturer stated fatigue performance

Validate service life design methodology and tools

Pipe Body Calculated Failure

Tension

End-fitting Calculated Failure

Tension

Design Acceptance

Failure tension is above


Accept both pipe body and end fitting


Failure tension is below

Accept pipe body. Change the EF design or de-rate the tension capacity. End-fitting design methodology is invalidated

Failure tension is below


Accept end fitting. Change the pipe design or de-rate the tension capacity. Pipe design methodology is invalidated

EM Corrosion Fatigue


frequency

P(t)

Environment

f*

da/dN

air

environment

Industry practice Concern

Corrosion SN curves

virgin wires

Flooded annuli tend to create pits within <1year. Fatigue capacity of a pitted wire is different from the fatigue capacity of a virgin wire (>19years). This synergistic effect is not understood !

Test frequency

>0.5Hz

Faster frequencies tend to negate potential deleterious effect of environment. Loading frequency should allow for the proper interaction between material and environment to take place.

Technology Developments Priorities


Predictive Technologies

• Improve analysis methodologies for riser response predictions – fatigue,

compression, lateral buckling

• Develop testing methodologies that capture “chain-reaction” synergistic effects to

establish component capacity:

◦ Steel wire corrosion and fatigue

◦ High strength tape wear, aging and fatigue

◦ Polymers aging to different exposures – not standardized yet. Join 17TR2 JIP.

• Develop methodologies that correlate annulus sampling history to wire corrosion

and polymer aging

New Design – Expansion of Application Envelope

• Increase water depth per IDxP - weight reduction, 2014 17B Annex H composites

• Material and layer-design improvements for corrosive environments (souring

reservoirs, Black Sea)

Remnant Life Assessments

• Improve inspection technologies on layer and component level

• Develop the Predictive Technologies mentioned above

Documents

ExxonMobil, Improving standards and technology towards achieving