Guidelines for Drilling Riser Joint Integrity
GUIDELINES FOR DRILLING RISER JOINT INTEGRITY
by Dr Hugh Howells
2H Offshore Inc
Fry Road, Houston
Presented at the Deepwater Riser System Management Forum, Pennwell, League City, Texas, June 2000
ABSTRACT The characteristics of deepwater drilling riser systems that influence integrity requirements and loss of integrity are as follows: • Higher tensions, placing increased importance on wall thickness and which may accelerate fatigue crack growth
in the riser; • Larger curvatures, promoting the possibility of wear from drill string rotation; • Vortex induced vibrations due to severe currents, which can generate high levels of fatigue damage in short
periods of time; • Longer drill string having increased tension, increasing wear at the top of the riser; • Longer and heavier riser joints, more difficult to handle with increased scope for damage during riser running
and retrieval; • Greater internal pressures from mud head placing increased importance on wall thickness for hoop load
resistance; • Greater external pressures from water column, placing increased importance on wall thickness and dimensional
tolerances for collapse resistance; • Load sharing between riser tube and choke and kill lines placing increased importance on integrity of choke and
kill lines for overall structural integrity. The potentially greater rates of wear and fatigue damage accumulation and increased importance of wall thickness integrity for deepwater indicate that traditional inspection practices used for shallow water operations may need to be revised for deepwater drilling. When initiating a drilling programme in deep water or harsh environments, the riser inspection strategy must therefore be re-evaluated to take account of the severity of the operating conditions. As part of an industry initiative for developing guidance for drilling riser usage in deepwater, 2H Offshore Inc were contracted to develop guidelines for drilling riser joint integrity. This work consisted of the following activities: • Review of current practice for monitoring riser usage; • VIV fatigue analysis of 2 case study drilling riser; • Fracture analysis and inspection methods assessment; • Requirements for riser record keeping. The findings of this work, which form the basis of the integrity assessment guidelines being developed, are reported in this paper.
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GUIDELINES FOR DRILLINGRISER JOINT INTEGRITY
by
Dr Hugh Howells
2H Offshore Inc
Presented at the Deepwater Riser System ManagementForum,
League City, Texas, June 2000Learn more at www.2hoffshore.com
Introduction
• Characteristics of deepwater drillingrisers
• VIV - effects and implications
• Wear - reasons for concern
• Deepwater drilling riser joint inspection– Objectives, difficulties, rationalisation
• Usage logging requirements
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Deep Water v Shallow Water
• Larger tensions
• Larger internal and external pressures
• Longer, heavier riser joints
• Exposure to severe currents
• Subject to vortex induced vibrations
• Larger curvature
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Deepwater 1 Year ReturnPeriod Currents
0
500
1000
1500
0 1 2
Current Speed (m/s)
Ele
vati
on
Ab
ove
Sea
bed
(m
)
WoS
Brazil
GoM Loop
West Africa
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Effects of VIV
• High rates of fatiguedamage
• Increased dragloading
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6000ft Drilling RiserVIV Fatigue (1)21 INCH Drilling Riser - 6000ft - 12 ppg Mud
F2 CLASS WELD AND SCF 1.3
0.00E+00
2.00E-04
4.00E-04
6.00E-04
8.00E-04
1.00E-03
1.20E-03
1.40E-03
1.60E-03
1.80E-03
2.00E-03
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Location Along Riser (x/L)
Fat
igu
e D
amag
e (1
/Yea
rs)
Bin 7 Bin 9 Bin 11 Bin 13 Bin 15 Bin 17 Bin 19 Bin 21 Bin 23
Bin 25 Total
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6000ft Drilling RiserVIV Fatigue (2)
21 INCH Drilling Riser - 6000ft - 16.5 ppg MudF2 CLASS WELD AND SCF 1.3
0.00E+00
3.50E-03
7.00E-03
1.05E-02
1.40E-02
1.75E-02
2.10E-02
2.45E-02
2.80E-02
3.15E-02
3.50E-02
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Location Along Riser (x/L)
Bin 7 Bin 9 Bin 11 Bin 13 Bin 15 Bin 17 Bin 19 Bin 21 Bin 23
Bin 25 Total
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6000ft Drilling RiserVIV Drag Amplification21 INCH Drilling Riser - 12 ppg Mud - Operational Top Tension
F2 CLASS WELD AND SCF 1.3
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2
2.1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Location Along Riser (x/L)
Cd
Am
plif
icat
ion
Bin 7 Bin 9 Bin 11 Bin 13 Bin 15 Bin 17 Bin 19 Bin 21 Bin 23 Bin 25
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Wear in Deep Water
• Larger mean angles
• Larger tensions
• Higher external pressures– 2667/4445psi at 6,000/10,000ft
• Higher internal pressures– 4393/7321psi 14ppg mud, 6,000/10,000ft
• Integrity of wall more important
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Wear Hotspots
BOP
LMRP
LowerFlex-Joint
Casing
ConductorFirmSoil
SoftSoil
LOWERRISER
UPPERRISER
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Wear Control
• Flex joint angle limits– 2 degrees mean, 4 degree max (API)
• Criteria based on historical performance
• Deepwater limits?– 1 degree mean used by some drilling
contractors
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Deepwater Integrity Issues
• Increased fatigue damage from severecurrents
• Increased wear from riser curvature
• Increased susceptibility to handlingdamage from the use of longer, heavierriser joints
• Increased wall thickness integrityrequired to accommodate higher tensionsand pressures
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Purpose of Riser JointInspection
• Detect and quantify deterioration inintegrity
• Sources of deterioration:– fatigue damage accumulation
– impact / handling damage
– wear from drill string rotation
– corrosion
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Status of Drilling RiserInspection
• Shallow water– total kip-days
– 1 year usage
• Deep water– increased wear and fatigue
– limited long term experience
– strategies need to be defined
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Deepwater InspectionDifficulties
• Joint length - 75-90ft
• Joint weight - 60-70kips
• Difficult to handle - damage to buoyancy
• More remote - longer turn around
• More joints
• More expensive
• Need to rationalise
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Riser Joint Access
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Riser Joint Rack (1)
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Deepwater InspectionDifficulties
• Joint length - 75-90ft
• Joint weight - 60-70kips
• Difficult to handle - damage to buoyancy
• More remote - longer turn around
• More joints
• More expensive
• Need to rationalise
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How to Rationalise?
• In-place inspection– Calipers, pigging
• On-deck inspection– Space, equipment, personnel
• On-deck screening– Magnetostrictive method
• Selective onshore inspection
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Rationalization by Selection
• Fatigue based approach:– Severity of operating conditions
– Time in service
– Inspection detail
– Inspection frequency
– Inspection coverage
• Wear– Joint position
– Time in service
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Fatigue Crack GrowthLower Riser - Through-Thickness Crack Growth
0.0
2.5
5.0
7.5
10.0
12.5
15.0
17.5
20.0
22.5
0 10 20 30 40 50 60 70 80 90 100
Time (years)
Cra
ck D
epth
, a (
mm
)
Initial a/c = 1.0Initial a/c = 0.5Initial a/c = 0.2a = t
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Rationalization by Selection
• Fatigue based approach:– Severity of operating conditions
– Time in service
– Inspection detail
– Inspection frequency
– Inspection coverage
• Wear– Joint position
– Time in service
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Influence of OperationalPractices
• Tension and tension variation– reduced VIV, vessel capacity may limit,
increased wellhead loading
• Joint rotation– spread fatigue damage
– scope may be limited
• Flex-joint angle limits– reduced limits give less wear
– more downtime
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VIV Fatigue at Riser Base
21 INCH Drilling Riser - 6000ft - 12 ppg MudF2 CLASS WELD AND SCF 1.3
0.00E+00
2.00E-04
4.00E-04
6.00E-04
8.00E-04
1.00E-03
1.20E-03
1.40E-03
1.60E-03
1.80E-03
2.00E-03
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Location Along Riser (x/L)
Fat
igu
e D
amag
e (1
/Yea
rs)
Bin 7 Bin 9 Bin 11 Bin 13 Bin 15 Bin 17 Bin 19 Bin 21 Bin 23
Bin 25 Total
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Riser Joint Rack (2)
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Deepwater InspectionFramework
• Use time in service approach as basis
• Account for increased wear and fatigue
• Account for operational practices
• Adjust intervals with experience
• Practice can vary from contractor tocontractor and vessel to vessel
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Variables to Accommodate
• Drilling in different water depths
• Different usage of different joints– lower rated joints used more often
• Actual operating conditions– may be more or less severe than predicted
• Requires rigorous usage logging
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Usage Logging Requirements
• Operations log– riser history
• Riser stack-ups– joint position and dates
– basis for selective inspection
• Operating conditions– tension, mud-weight, drill string tension,
current and wave
– verify operation and identify extreme events
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Summary
• Current inspection practices must beextended for long term deepwater drilling
• Rationalisation dependent on:– depth and environmental conditions– time in service of each joint– operational practices
• Logging necessary to verify correctoperation and enable selective coverage
• Experience will enable refinement
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