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Novel Construction Initiative Meeting November 4-5, 2015, Paris

Development to cope with large Wall Thickness Variaties when inspecting Pipeline Girth Welds

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Safety first, Safety always

Alarms

Emergency numbers

Emergency exits

Gathering point

Health and Safety of people is our number one priority.

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Agenda

1. Application Offshore New Construction Pipeline Operation

2. Owner and Standards requirements for Wall Thickness variations

3. Consequences for AUT inspection

4. Feasibility study Rotoscan Adaptive Focal Law Settings (AFLS) program

5. Feasibility Test results

6. Qualification of AFLS methodology by Third Party

7. Statistical results

8. Conclusion

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Offshore New Construction Pipeline Operation (Ultrasonic Inspection of Pipeline girth Welds)

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Owner Specification & Standard Requirements

• Many Owner Specifications and Standards for the Offshore Industry have strict requirement for large tolerances on pipe wall thickness variations.

• Many projects contain pipe material (seamless) in excess of 2.5mm wall thickness variations

• Examples are given in view of the Total Specification and DNV standard Norway

DNV-OS-F101- Appendix E section B 107

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Typically dimension tolerances

• Overview of a typical Pipeline Project pipe diameter dimensions and associated nominal Wall thicknesses

• On the basis of the requirements for wall thickness variations, the number of reference blocks can be determined

Example Scope of Work Overview applicable dimensions

OD (inch) OD

(mm) WTnom

(mm)

10.75 244.5 16.5

10.75 280.0 20.4

10.75 266.2 26.9

12.75 298.5 17.4

12.75 310.5 25.1

12.75 323.9 31.0

14 339.7 17.4

14 365.1 24.3

16 426.0 28.4

18 456.3 22.8

As for many large pipeline projects there are several diameter/wall thickness

configurations being subject to wall thickness variations outside tolerance boundaries.

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Consequences for AUT inspection

• The impact on wall thickness variation(s) in view of the AUT inspection concept

Weld Configuration and Zonal Inspection Concept

Probe targets are dispositioned within the weld bevel configuration

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Consequences in view of Reference blocks

• When a standard Rotoscan PA system would be utilized, the number of reference blocks required to fulfill the most Owner Specifications & Standards requirements could be significant (in example below calculated to be 290)

• The number of reference blocks can be drastically reduced (to save cost and operational barge time) when the AUT system can be enhanced with a SW module (making use of Adaptive Focal Law Settings) that controls the ultrasonic beam steering in function of the (online) wall thickness measurements

• A feasibility study has been performed to investigate whether the System hardware, in combination with the SW module (from now on called: AFLS), can be used to comply with the Standards & Owner specifications.

∆ WT

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Content Feasibility Study AFLS

• As an input for the AFLS feasibility study it is important to know;

• Diameters and wall thickness involved

• Weld bevel configurations used

• Feasibility based on AFLS concept depends on;

• PA AUT system Software & Hardware capabilities

• Type of Phased Array probe(s), Frequency, number of elements and pitch used

• Wall thickness range(s) to be covered from the pipe-mill

• Requirements of Owner Specifications & Standards in view of:

• Maximum allowable zone heights (dividing the weld volume in dedicated areas)

• Reference reflector(s) used for the overall inspection sensitivity

• Allowable wall thickness variation as per Specification & Standards

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Feasibility Study AFLS

• Work Preparation Module is used to determine whether the combination of PA 128 system and PA probes is able to steer the focal laws within the given wall thickness range in compliance with AUT inspection requirements

• Work Preparation Module; • Based upon Mat Lab code

• Provides Sequence information for each inspection function

• Provide optimal Set-up parameters based upon Inverse Focal law calculations

• Beam visualization and beam paths (inspection coverage)

Focal Law = Set of Time

Delayed pulses to create an

ultrasonic beam configuration

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Feasibility Study AFLS

Create average setup Check whether element

shift can cover WTR Create lookup table

Adjust

1. Probe offset

2. Angle of tandem paths

3. Add skips

4. Use larger pitch

Finetune on calblock

no

yes

Modifications? yes

no

Done

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Feasibility Study AFLS

bevel\WT 16.5 17.4 20.4 25.1 26.9 31.0

J1

J7

V25

NA

0.85mm pitch PA-probe 1.5mm pitch PA-probe

Feasible for ±10% Wall Thickness Range

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Functionality Tests & Settings

• The Focal Law functionality test is performed using the following settings;

• 10% Wall Thickness Range of nominal wall thickness

• Reference reflectors of Ø2.0mm FBH and 1.0mm Square Notches

• Zone height max 3.0mm

• Overtrace adjacent zone between -6dB and -12dB.

• Amplitude response 80% FSH within +/- 2dB

• Transit Distance measurement within +/- 0.5mm

• The online wall thickness measurements is steering the PA inspection configuration in steps using;

• Adaptive Focal Laws Settings (AFLS)

• Weld bevel configuration

• Elements shifts

• Gate Start shift settings

• Field calculation (visualization) of the above

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Weld Bevel Configuration

• Weld bevel and zone configuration changes in view of wall thickness variation

• Within the AFLS configuration for all Set-ups the following definition is followed;

• Cap, Last Fill, HP and Root zone height are fixed

• Wall thickness variations is distributed over the zone heights of the remaining Fills

• Due to the wall thickness variations repositioning for reflector positions within the zones are automatically calculated

Bevel change for increasing thickness

ΔWT

Black cross = Target points

Red circles = -10% WT

Blue circles = +10% WT

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Elements shifts

• For increasing (degreasing) wall thickness the active elements move towards the upper or lower end of the array

• Analysis have been performed for all Set-ups and involved inspection functions whether the wall thickness range can be handled using the available elements within the PA probe array

• Example output J7-bevel, 30.5mm WT identifying the boundaries of the system

• Vertical axis : PA probe elements / Inspection functions

• Horizontal axis : WTR range

• 0 = middle of beam

• Green lines = Beam array boundaries

Elements shift 0-5°

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Adaptive Focal Laws

• Without changing the focal laws, using the element shifts only, the focal spots will not end-up exactly on the bevel configuration

• To this end delay times are altered, in function of wall thickness variation, to position the focal spots on the correct position on the bevel for every inspection function

• See figure showing the Delay change (vertical axis) in function of the element(s) in the array

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Gate Start shift settings

• The shift in the gate settings as a result of a change in the active elements will be compensated based upon the measured wall thickness.

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Field calculation (visualization)

• Beam plots: PA 128 : no Element shift, no AFLS

• Beam plots: PA128: Element shift & AFLS

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AUT System Configuration: Single data display (WTR corrected) presentation:

• The Final inspection result screen is a composition of the (L), (H) and reference (M) inspection results

• The L, M and H scans are all separate recorded and stored within the Rotoscan program

Feasibility Test Results

M(reference) 1.5mm WTR H(AFLS) 1.5mm WTR L(AFLS) 1.5mm WTR

Input Wall thickness

depending the WT

reading

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Feasibility Test results

• Reference calibration scan on block “M” (WTR corrected) • Calibration result when switched to “WTR-L”

• Calibration result when switched to “WTR-H”

• This is illustrating the effect when the “L” or “H” related settings are projected on the “wrong” measured wall thickness.

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Feasibility Test results (Example)

• Calibration result “M” reference block

• Green color identifies overtrace within -6dB / -12dB boundaries

• Red color identifies overtrace outside -6dB / -12dB boundaries

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Feasibility Test results

• Amplitude responses reference blocks M – L - H

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Feasibility Test results

• Transit distance responses reference blocks M – L - H

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Qualification of AFLS methodology

• Test on Welds having Welding Imperfections, applying the Adaptive Focal Law Settings;

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Qualification of AFLS methodology

• The AFLS methodology has been subject to independent DNV qualification

• Qualification in compliance with:

• DNV-OS-F101-2013 Appendix E

• DNV-RP-F118 2010

• Weld scanning has been performed on welds

• Ø 16” x 26.9mm

• Ø 12” x 26.9mm

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Statistical Results

The Probability of Detection (90 at 95% Confidence) has been calculated using the AFLS methodology at a threshold of 20% FSH to be 0.61mm

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Statistical Results

The Height Sizing accuracy (5% against under sizing) has been calculated using the AFLS methodology a to be -1.02mm

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Statistical Results

The Depth Sizing accuracy (5% against under sizing) has been calculated using the AFLS methodology a to be -0.6mm

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Conclusion

• Wall thickness variations of pipelines has a significant effect on the AUT inspection methodology when working in compliance with pipeline Owners specification and International standards

• This normally results in a high number of reference blocks and multiple scanning activities during the lay-barge campaign, resulting in a high cost figure and impact on pipeline lay rates

• The qualified AFLS functionality is capable to handle large wall thickness variations being in compliance with the Specifications and Standards resulting in;

• Less Lay barge time

• Less Reference blocks

• Resulting in a significant cost reduction

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