CT Fatigue Life

7/23/2019 CT Fatigue Life

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SPE Distinguished Lecturer Program

The SPE Distinguished Lecturer Program is funded principally

through a grant from the SPE Foundation.

The society gratefully acknowledges the companies that support

this program by allowing their professionals to participate as

lecturers.

Special thanks to the American Institute of

Mining, Metallurgical, and Petroleum

Engineers (AIME) for its contribution tothe program.

Society of Petroleum Engineers

Distinguished Lecturer Programwww.spe.org/dl


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Why Coiled Tubing Works and How to

Make Sure it Works on Your Job

... in Your Well

Why Coiled Tubing Fails and How to

Avoid Failure on Your Job... in Your Well

or

Steven M. TiptonThe University of Tulsa

Society of Petroleum EngineersDistinguished Lecturer Programwww.spe.org/dl


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The Oilfield is a Rough Place


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Outline

Introduction / Mechanics Primer

CT Fatigue Research TU Coiled Tubing Mechanics

Research Consortium

Surface Defects Analytical Modeling

FlexorTU5 Inspection

3D laser imaging


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Background

1989 - developed CoilLIFE Schlumberger

1994 - JIP to revise CoilLIFE and developCT test machine

1995 - developed coiled tubing fatigue module for

NOV-CTES (Achilles) 1996 - 2000 University of Tulsa JIPs to study

CT mechanical and fatigue behavior

2000 present: University of Tulsa Coiled TubingMechanics Research Consortium


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What is Coiled Tubing

Exactly what it sounds like

Continuously Milled Tubing

Rolled from Flat Strip Resistance Welded Seam

HSLA (High Strength Low Alloy)

55-120 KSI CRA

Chrome Alloys, Titanium

Diameters: 0.75 4.5 Thicknesses: up to 0.25

Lengths > 30k ft

10K 20k ft most common

Courtesy Quality Tubing
http://../Tipton%20Stuff/For%20Dr.%20Tipton%20from%20Blount/Why%20CT%20Fails%20Global%20Symposium08/CTManufacturing.wmv


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Typical CT Rigup

Coil Tubing

Reel ~ 10-20K ft

Gooseneck

Guide Arch

Injector

What is it used for?

Anything jointed

tubulars are used for!

Drilling

Completion

Servicing

Courtesy ICoTA


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Coiled Tubing Units


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Coiled Tubing

2009 SAE Baja Vehicle


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Bending Strains

Bottom material in

COMPRESSION

Top material in

TENSION

Strain defined as % material stretches

in Tension or shortens in Compression


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repeats each tripspool

straight straighthole

arch arch

spool

Bending Cycles

time

strain


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Bending Strains Lead to

ULTRA-Low Cycle Fatigue

e.g., lives 10 100 cycles to failure

Normal Low Cycle >103 Cycles to Fatigue

Engine Parts >106 Cycles to Fatigue

Ballooning >30% even when pressure is


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Huge Cyclic Plastic Strains (>2%!)

Bending Strains

Ratcheting

Incrementaldiametergrowth >30%

Lives < 10 cycles!

Even withpressure below50% of yield

Wall Thinning

bending axis


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Permanent Elongation


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Bending Strain Distribution

Strain


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Strain

x,m = r/R

r

R

Bending Strain Distribution


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Bending Stress Distribution

StressSy

-Sy


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Bending Stress Distribution

Stress

Sy

-Sy


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Causes Permanent Elongation

Stress

F


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CT Fatigue

Research

CoilLIFE

FatigueTest

Machine


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CT Fatigue

Research

CoilLIFE

FatigueTest

Machine


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CT Fatigue

Research

CoilLIFE

FatigueTest

Machine


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TU CT Fatigue Test Facility


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Accelerated CT Fatigue Test Machine

F i C k D l


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5 4 3 2 1 1 2 3 4 5 6 7 8

NUMBER OF

FAILURESNUMBER OF

FAILURES

Fatigue Crack Development

F i C k D l


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Fatigue Crack Development

MOST fatigue

cracks initiate

at the inner surface

Fatigue behavior of CT

defies engineering logic!

Appears as

a pinhole

failure

cross sectionthrough tubing wall


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120 ksi, 1.5" x 0.134" x 48"R

0

50

100

150

200

250

300

350

400

450

500

0 2000 4000 6000 8000 10000 12000 14000 16000

Pressure (psi)

Cycle

sto

Failur

e

CT Life Prediction Routine

50% (mean) prediction

95% confidence prediction


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Factors that influence life:

Diameter

Pressure

Wall Thickness

Bending Radius

Spool

Gooseneck

Material Grade

CT Life Prediction

70 120 ksi

Larger diameter larger bending strains

Thinner walls higher tangential stresses

Higher pressure higher tangential stresses

Smaller radius larger bending strains


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Effect of Tubing Diameter


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Gooseneck Radius of Curvature


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Material Selection


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Fatigue Life Estimation

f , b , f, S=f(h, Sy, x)

E, K, n

LCFTesting

Constant PressureFixtureTesting

FittingRoutine

Plasticity / Fitt ingRoutine

MATERIAL DATA SETLCF Data

CT Fatigue Model

x

x

time

ComplexField Loading

time

P

Coil Tubing Parameter

time

D

inputinput

output


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0

100

%

LifeExpe

nded

Distance along String

Fatigue Life Profile

Implemented with String Management Software:

CT Life Prediction

warning level

Fatigue eliminated as a primary failure mode!

Wh t Ab t D f t ?


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What About Defects?


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Means of Imposition

Milling (cut into surface)

Impressing Corrosion Pits (chemical milling)

EDM Different shapes possible

a b fd ec g h i

d wx

M f I iti


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Means of Imposition

Milled Ball Impressed Ball


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Influence of Surface DefectsLow Pressure Impressed vs Milled 1/8" Balls

0

0.2

0.4

0.6

0.8

1

1.2

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45

d/t

%D

efectLifetoBaselineLife

Impressed (t=0.156)

Milled (t=0.156)

Impressed (t=0.204)

Milled (t=0.204)

scatter

Depth / Wall Thickness Ratio

Ratioof

DefectLifetoBaselineLife

2.375 80 ksi tubing, tested on 72 radius fixture


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Repairing Defects

What happens after a

defect is discovered? Scrap / Replace string

(expensive)

Cut and splice (welding

expensive)

Grind repair

R i i D f t


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Repairing Defects

One Option: Butt Welding

Unfinished inside of the butt

weld constitutes a severestructural discontinuity!


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Butt Welding Fatigue Data

0

10

20

30

40

50

60

70

80

90

%o

fUnweldedS

ampleLife

Manual Welds:

average = 38%

std. dev = 18%

Orbital Welds:

average = 41%

std. dev = 11%

Manual AverageOrbital Average


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Grind Repairing

replaced with

smooth, gradual thickness change

Abrupt, localized discontinuity

Technique is important and grind repair

guidelines have been developed


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Fatigue Life Predictive Model

No defect:

229

Cut defect:

76

Repaired:

129

Impressed:

214


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Defects Must be FOUND

Visual Inspection

Magnetic Flux Leakage Most popular approach for CT inspection

MFL can only DETECT defects

Cant provide any information about defect

size or severity

3D Laser Imaging for NDE Complete geometry of defect is captured

digitally

3D Laser Imaging S stem


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3D Laser Imaging System

(Low-Cost)

Longitudinal Milled Defect


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Commercial Laser System

Sawcut

ImpressedballMilled ball

MilledCylinder


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Impressed ball Machined ball

Color-coded Digital Data


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w

d

Ap

Automated Defect Measurements

rmax

rmin

C l d d Di it l D t &


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Color-coded Digital Data &

Photographic Image

Useful todistinguish

cut or

impressed


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Sour and Corrosive Environments

Similar effects: CT to Pipe

H2S

HIC (Hydrogen Induced Cracking)

SSC (Sulfide Stress Cracking)

SCC (Stress Corrosion Cracking)

Residual Stresses

Accelerates Corrosion

Manufacturing and Materials


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Manufacturing and Materials

defects/flawsFrom 7 to 20 reels per

1,000 reels (~last 3 yrs)0.7 to 2%

Only Those Reported

Failures occur that are

not fully investigatedEspecially later in CT Life

Courtesy BJ Services

Cold Weld


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Conclusions

Fatigue is inherent to the use of CT Large CT Bending Strains Cause

Fatigue, diameter growth, elongation Scatter is Associated with Fatigue Data

Fatigue Software can Predict Influence of Material, diameter, wall thickness, bending radius,

internal pressure, statistical scatter, defects, grind

repairs

Field Monitoring Software used to Assess

Every Section of Tubing Along the EntireString Avoids failures in the field


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Conclusions

Defects can have first order influence (cut)

Or negligible influence (impressed) Repairing by Grinding is a viable option

Software helps to quantify defect severity(and effectiveness of a grind repair )

3D Laser Scanning

Holds the potential to detect defects

Capable of measuring every detail about their

geometry

C l i


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ConclusionsTo Avoid Failures on Your Job

.... or In Your well:

Control the Factors that Contribute toFatigue Damage Accumulation

Minimize tubing diameter

Maximize spool andgooseneck sizes

Select material mostsuited for application

Minimize tripping

Minimize tubing movementwith high pressure

C l i


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Conclusions

Avoid Defects Eliminate sources of

defects - handling,injector debris

Monitor/Inspect

EnvironmentallyInduced Cracking

Storage corrosion

Repair shallow defect

using grind repair

techniques


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Why Coiled Tubing Fails and How to

Avoid Failure on Your Job... in Your Well

Steven M. Tipton

The University of Tulsa

[email protected]

918-850-0252

www.coiledtubingutulsa.org

Why Coiled Tubing Succeeds and How

to Assure Success on Your Job... in Your Well


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CT Fatigue Life

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