Pipeline2003

Conference & Exposition

IBP423 03 (a)Ultrasonic In-Line Inspection of Pipelines, New Generation of Tools

Neb I. Uzelac, Konrad Reber, Michael Belter, Otto Alfred Barbian

Copyright 2003, Brazilian Petroleum and Gas Institute - IBPThis paper was prepared for presentation at the Rio Pipeline Conference <$ Exposition 2003, held in October, 22-24, Brazil, Rio de Janeiro.This paper was selected for presentation by the Event Technical Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the IBP. Organizers will neither translate nor correct texts received. Tire material, as presented, does not necessarily reflect any position of the Brazilian Petroleum and Gas Institute, its officers, or members. It's Author's knowledge and approval that this Technical Paper will be published in the Rio Pipeline Conference <$ Exposition 2003 "brouchure"

Abstract

In-line inspection (ILI) of pipelines has established itself as the most efficient tool for evaluating the condition of a pipeline and an indispensable part of pipeline integrity management. Historically, there have been two major technologies used in in-line inspection for corrosion, the magnetic flux leakage (MFL) and ultrasonics (UT), each having their distinct properties and fields of application. Ultrasonic (UT) ILI has always provided unique quality of information about the pipelines, rendering highest accuracy and tightest measurement tolerances. In the 1990s ultrasonic tools for detection of cracks have become available.

This paper describes the new generation of ultrasonic ILI tools, both for metal loss (corrosion) and crack detection. It has been developed based on the expertise gained utilizing the first generation of UT tools combined with the advancements in electronic, hardware and software components available today.

Properties of the new tools are presented. Tool specifications and their defect detection capabilities are discussed, as well as the characteristics that make them unique. The performance of these new tools offers advantages in detection and sizing performance, increased operational convenience and improved reporting.

Based on examples from tests and inspection runs, it can be seen that the new tool technology can successfully operate in situations and pipe configurations that UT technology has historically had problems with. Examples of this are shown and it is discussed what kind of applications this technology is best suited for.

Also, assessment of defects regarding the remaining strength of the pipe is being discussed and demonstrations shown of how the new UT metal loss tools provide superior results over others in fully using the most advanced defect assessment algorithms.

Inspection of pipelines for crack and crack-like defect is another aspect where this technology offers the highest standards within the industry. Examples are shown of how cracks and crack-like defects of different kinds can be reliably detected, classified and sized using this technology. Most recent results obtained with the described technology are shown, illustrating the performance and fields of application.

Introduction

As pipeline integrity management becomes an area of increasing interest worldwide, in-line inspection (ILL also called intelligent or smart pigging) gets into the focus as one of the most efficient and straightforward ways to assess the condition of a pipeline. Several technologies of ILI are available nowadays and emerging new NOT techniques will even enhance that choice in the future.

Pipeline operators have been using several defect assessment methods to evaluate the remaining strength of their pipelines based on the input data obtained from ILI tools. Often instead of appropriate assessment calculations just a quick ranking is being done and in that case the limitations of the methods are often not considered. In the end, nevertheless, the distinction is not obvious for the pipeline operator between a calculation carried out precisely according to the code and a rough one performed to produce a quick ranking.

NOT Systems & Services

BP423 03

When planning to use ILI data for defect assessment, however, it is essential to know what kind of data needs to be acquired in the first place in order to allow for carrying out certain assessment calculations. In the usage of ILI technologies, and especially development of new ones, the knowledge of pipeline integrity assessment methods and their requirements is the key input for the specification of technical requirements of such tools [1],

Effects of tool accuracy on defect assessmentAll the data used for defect assessment, including data obtained from ILI tools, have an inherent measurement error. Usually. ILI vendors state the accuracy of tools in data sheets and final reports [2], When using defect geometry for assessment purposes, errors of measurement are usually ignored and other safety factors are introduced in assessment codes for compensation. Only the code of Det Norske Veritas Part A [3] allows for input of ILI tool accuracy and measurement technology, by introducing probabilistically calibrated coefficients. To demonstrate the effect which tool accuracy has on defect severity evaluation, we carried out sample calculations using capabilities of ILI tool available today.

Table 1 shows defect specifications of tools used for metal loss measurements, given in percent of the wall thickness for magnetic flux leakage (MFL) tools and in nun for ultrasonic testing (UT) tools, with accuracies assumed for the calculations.

Table 1 Accuracies for general corrosion of different types of metal loss (corrosion) monitoring tools. For a more realistic comparison to be feasible, measurement accuracies have all been recalculated to values at a confidence level of 80% (last column)

Tool technology Resolution Accuracy according to data sheets

Accuracy normalized to 80% confidence

MFLStandard 20 % (80% confidence) 20 %

High 10 % (80% confidence) 10 %

Ultrasonics Standard 0.5 mm (90% confidence) 0.39 mm

Figure 1 shows the curve of the Estimated Repair Factor ERF =1 for various tool technologies. ERF is the ratio of maximum allowed pressure of the flawless pipeline over the calculated safe operating pressure of a pipe with a defect. The curve is plotted in a graph of defect depth versus defect length in which every defect can be represented by a point. If the defect is below the ERF=1 curve it is not severe. Thus the lower the line the more conservative the assessment.

ERF limit line according to DNV A

- UT- - - MFL High Res.- - - MFL standard

Defect Length [mm]

Figure 1 The ERF=1 lines show the limit size of defects that are still acceptable. ERF is the ratio of maximum allowed pressure over the calculated safe operating pressure. Based on 15 mm (0.60 in.) wall thickness, MAOP of 90 bar (1300psi), pipe diameter of 812.8 mm (32 in.) and SMUTS of 530.9 MPa (77,000 psi).

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Wliile the DNV code does consider the depth measurement error, the error of length measurement is not considered. The length measurement accuracy of ILI tools has improved in the past; however, quite some differences between the available tools still exist. Length sizing accuracy ranges from 5 mm (0.2 in.) to 20 rmn (0.8 in ), as it depends on data sampling distance (typically from 1.5 mm (0.02 in.) to 10 mm (0.4 in.)), odometer sampling distance and resolution, but mostly on depth detection threshold.

Requirements for an efficient Crack Inspection tool

Among the most severe and hideous types of defects in pipelines affecting their integrity are cracks and crack-like defects. In dealing with cracks, pipeline operators have very often resorted to hydrostating testing which removes critical cracks, but does not give any information about the sub-critical ones and, in many cases, even causes them to grow (“pressure reversal”).

Liquid coupled UT ILI tools for crack inspection offer the reliability and accuracy that allows for long-term integrity assessment and management [1], since they offer:

Low detection threshold and high accuracy (small tool error)

High detection probability (low probability to miss a defect)

In comparing hydrostatic testing and ILL Kiefner [4] has looked at re-inspection intervals necessary when using both methods to assure pipeline integrity. Figure 2 shows time to failure for moderate pressure cycles of cracks all having a length of 5.5 in. (22 in. pipe, 0.344 in. wall, X46). It illustrates that a crack that survives 85% SMYS would need only 9 years to grow to a size that would fail at 72% as opposed to a crack 10% w.t. deep (detectable by a UT crack detection tool) that would need over 60 years. It means that using a dependable tool for crack detection with a detection threshold of 10% allows for a reliable long-term pipeline integrity management.

Time to Failure for Moderate Pressure Cycles for Defects of Various Depths all having a Length of 5.5 inches (22-ineh-diam., 0.344-inch-wall, X46)

Depth at which failureDepth which occurs at 72 % of SMYS ^

survives 85 % SMYS /

/Depth which survives90 % SMYS test

------ ---------------- ^

(_lLI d/t = 0.25 thresh ild /Depth which survives100 % SMYS test

9 years

i—ELI, 1 mm threshold61 years 21 yes rs

10 20 40

Years50 60 70 80

Figure 2 Re-assessment intervals for a pipeline with cracks using hydrostatic testing at different pressures and an ILI crack detection tool (from J. Kiefner, Integrity Assessment: Hydrostatic Testing and Integrity Assessment, presented at 54th Annual Pipeline Conference, American Petroleum Institute, Houston, Texas, April 29-30, 2003)

Ultrasonic In-Line Inspection Tools

Ultrasonic tools for metal loss detection, unlike magnetic flux leakage tools, provide quantitative wall thickness measurements of the pipe wall inspected. The information on metal loss (corrosion) defects comes as a grid of wall thickness measurements with a very high axial and circumferential resolution. The high accuracy and confidence level of such data, along with the fact that the “river-bottom profile” for each corrosion is provided as well, makes UT ILI data suitable for the most advanced defect assessment algorithms.

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Figure 3 illustrates the principle of operation of an ultrasonic tool for wall thickness measurement (metal loss detection).

H------ 1------ 1------ 1------ 1------ 1------ 1------ 1-------- ►800 900 1000 1100

length, mm

100 200 300 400 500 600 700 800 900 1000 1100

length, mm

Figure 3 Ultrasonic measurement principle: ultrasonic transducer slides along the internal surface of the pipe wall measuring distance to the wall and the wall thickness (top), yielding the stand-off and the wall thickness (bottom two B-scans).

Ultrasonic signal partly reflected at the internal surface of the pipe and partly at the external surface of the pipe provides a measurement of the standoff distance (distance of the transducer to the internal surface) and the wall thickness. As the tool travels through the pipeline, the sensor takes measurements at regular intervals.

Reliable detection of cracks constitutes a further challenge for the pipeline inspection industry. Depending on the type of pipeline, pipeline material and operating conditions, different types of cracks or crack like anomalies can occur; stress corrosion cracking, fatigue cracks, cracks in the weld and heat affected zone of the longitudinal or the girth weld.

Figure 4 shows the physical principle utilized by an ultrasonic tool for crack detection, where the sensors are inclined enabling the refracted wave to propagate through the pipe wall at an angle of 45°. This methodology of using ultrasonics for crack detection has long been established in other industries, but the application in pipeline enviromnent poses a range of challenges.

Figure 4 Ultrasonic principle used for crack detection: angled ultrasonic transducer generates propagation of ultrasound in the pipe wall under 45°.

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A New Generation of High Resolution Ultrasonic Inspection Tools

Ultrasonic in-line inspection tools for wall thickness and metal loss surveys have been utilized since the 1980's, and crack detection tools were first introduced in 1995 [5], Major challenge with ultrasonic tools has always been the enormous amount of collected data and major R&D efforts went into designing and applying electronics to handle it, while keeping it compact and robust at the same time.

A group of physicists and engineers who had pioneered the development of ultrasonic inspection tools has now designed and built a new generation of high resolution ultrasonic inspection tools for wall thickness measurement (metal loss inspection) and crack inspection, making use of the advancements in computer and electronics available today.

Before setting out on designing new hardware, software and firmware a detailed analysis was performed to define the requirements placed on such a new range of equipment. Major goals defined at the outset of the project are listed below:

Utilizing a minimum amount of different components in order to meet all diameter requirements from 6" to 56".

Designing hardware enabling the same basic tool to be used for wall thickness and crack detection application and an option to allow combo-runs.

Design to ensure that the tools incorporate a higher reliability and availability (less down time) than previous generation.

Using standard (industry-) components where possible instead of custom build solutions.

The new 24” crack detection tool is shown in Figure 5. The tool consists of two pressure vessels housing batteries, electronics, recording devices and a trailing sensor carrier carrying the ultrasonic transducers. Individual pressure vessels are connected through universal joints, which enable the tool to negotiate either 3D- or 1.5D-bends, depending on tool configuration.

Modular Design

Combined wall thickness and crack detection capabilities

High System Availability and Reliability

Standardization

Tool Construction

The electronic and recording unit of the tool, housed in the second unit, incorporates enough channels to cover pipeline diameters from 20" to 56" for metal loss and 20" to 42" for crack detection applications. The tool is configured for individual pipeline sizes through adaptation kits and corresponding sensor carriers, which will be available for all intermediate sizes.

Figure 5 High Resolution Ultrasonic In-Line Inspection Tool for 24" pipelines. The tool consists of two pressure vessels housing batteries, electronics, recording devices and a trailing sensor carrier with the ultrasonic transducers.

Sensor carrier

Special attention in the development of this generation of ILI tools has been devoted to the polyurethane sensor carrier. There are two different sensor carrier designs, one for wall thickness measurement (metal loss) and one for crack detection. In the metal loss version, sensors are aligned at right angles to the pipe wall (Fig. 6 - top), whereas the crack detection version has the transducers angled such to provide propagation of ultrasound within the pipe wall

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at 45° (Fig. 6 - bottom). Both sensor carriers are fitted with enough transducers to provide full circumferential coverage of the pipe (see tables with specifications).

Figure 6 Sensor carrier details: the units housing the transducers are much smaller compared to the old design (a) - corrosion, b) - crack detection unit), and the sensor carriers are much shorter and more flexible now (c) - corrosion, d) - crack detection).

New sensor carrier design, among other advantages over the previous generation of UT tools, make it very flexible enabling better detection in bends and dents. Figure 7 shows examples of detection performance in a 3D bend for both the metal loss and the crack detection tools. Figure 8 shows a scan from a metal loss inspection of a dent, illustrating clear wall thickness measurement and no losses in signal.

notch Iraus ZZ3 - HilLLiUSin - IC-Sianl. H-IH-IH

detection i >■

L&nml^WnMAOP IhBiJ/Ovp

Crack detection

23^2 23.14- Difenoa |m] 30,66IPIXJS 2.23 - NdtLiOaWll - [C-Scbfi]; 14 0MB

Ccrta- Shrd. ■ Cgnp

24” crack and corrosion inspection in a flow loop, example of pits and tight notches in a 3D bend «r

(picture above shows part of the bend).w ™ "C-scans (right) show the whole bend with detected! “

notches (upper) and corrosion pits (lower). ^ .Girth welds are indicated by vertical linesv—

Figure 7 Results from inspection in a 3D bend, performed in NDT’s flow loop with the 24” UT tool obtained from two runs; in the metal loss and in the crack detection configuration.

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OcoHD

|* M

1M@73.65 yQ/Clock

2W | 0@ 34 0 (mm)/ RWT (mm)

4 A I 0

L(min)/wn270 I 465

kV<)P(t.m.)/CM>

PipeNf./VVT (mm) 1319.0 I 66

Figure 8 C-scan of an area with a dent. Change in stand-off is visible on the C-scan, but there is no echo-loss on the wall thickness measurement. Also note the accuracy in measuring wall thickness on the upper C-scan (gray areas - representing changes in wall thickness of less then 0.1 mm)

Electronics and data processing

State of the art electronics and network technology, as used in the computer industry are applied within the tool.

This new generation of ultrasonic electronics has a dynamic ratio of 80 dB. much higher than the 20 dB on old tools, allowing for a much higher range of signal amplitudes to be measured, meaning that even highly attenuated signals can still be measured. This makes it possible for the tool to overcome thicker layers of deposited wax and perform a successful measurement.

As an example. NDT has conducted experiments with layers of epoxy internal coating and found that even 2 mm thick coatings did not compromise the perfonnance of the tool.

r BO | | H„. 1

Figure 9 C-scans of wall thickens (upper) and stand-off (lower) measurement from an “un-clean” crude oil pipeline. Note that there are no loses whatsoever at the welds.

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Figure 9 shows C-scans of wall thickness measurement in a joint of a crude oil pipeline considered not very clean. Even though there are no defects in the joint, the clearness of the scans illustrates the high signal to noise ratio, and virtually no losses at the girth and longitudinal welds.

Measurement accuracy

The new ultrasonic electronics and digital signal processing system on the tool provide improved measurement accuracy.

Contours of metal loss (river bottom profiles of corrosion) can now be followed with a greater detail as smaller changes in the wall thickness can be recorded. This also means that the length of defects will be recorded more accurately, since the starting and ending points of defects can be measured with a much better precision (see Fig. 10). Also, monitoring defect growth in subsequent inspections will be more successful since changes in corrosion will be detectable with a higher accuracy.

Common resolution NOT UTWT resolution

Figure 10 New recording procedure and digital processing of data allow for more precise recording of the shape of corrosion. B-scans of the river bottom profile of a corrosion defect with the old (left) and improved new signal processing (right)

The technology provides very high probabilities of detection in the whole pipe (full length and full circumferences), even in the region of a low frequency electro resistance welding (ERW) longitudinal weld, as illustrated in Figure 11. The crack was detected in the same way in two separate inspections, which illustrates the high reliability of the detection method.

B ox-ID

1 (Run 2]

x (m)

1,472

v n / clock184 | OG:OS

D (mm) / RWT (mm]

I iT~| oL (mm) / W D

I 27 | 5,8

MA0P (bar) / Ovp

I o ”T 74

PipeNr. / WT (mm)

IDtoLW (mm) i (*)

r~DtoGW (m) iVd

IDtoMrk (m) u/d

I

| Comment | internal & external

42Hk|PIXUS 2.21 - [C-ScanJ

C RD Ir nGW Ir Mrk |

Figure 11 Detection of a 27 mm long crack in a LF ERW longitudinal weld. Left: Photograph of MPI (magnetic particle inspection) enhanced crackRight: C-scans of two separate inspections with the UT crack detection tool

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Another big advantage of the new tool technology is that during an inspection run data is recorded and stored in such a way, that it is immediately available after the survey and readable through a lap-top computer. There is no need for complex and very time consuming translation or re-formatting routines as required until now and which took a few weeks to accomplish. In addition, the inclusion of Ethernet technology allows a vast range of additional capabilities such as remote access to the tools and long distance diagnostics. Figure 12 shows a network connection to the tool used to download data after the run while the tool is still in the receiving trap.

Figure 12 Network connection to the tool for downloading all inspection data immediately after the run, with the tool still in the launcher.

Specifications for some of the available sizes are shown in Tables 2 and 3 for wall thickness measurement tool (UTWT) and in Tables 4 and 5 for the crack detection tool (UTCT) introduced in this paper. Other tool sizes would have different lengths, weights and numbers of sensors, but defect specifications are the same for all tool sizes.

Data Analysis

After a survey, the data obtained is downloaded onto a computer. The data analysis is performed offline: usually back at the company offices. However, a valuable advantage of the data formats utilized in the new tools is the possibility to view and assess data on site. Critical areas of an inspected pipeline can be viewed immediately after a run if required. Due to the iimnense amount of data recorded, data analysis and preparation of the final report is carried out in the data analysis department.

The reports compiled are available as hard copies in a printed format, but also in electronic format. In addition, the data can be made available in a variety of different formats, which allow direct input into spreadsheets and databases, e.g. specialized GIS-based databases.

The analysis process, governed by stringent quality assurance procedures, includes the use of automated and manual routines. Specialized software was developed in-house for the analysis and visualization of survey data. The versatile software package PIXUS allows the generation of features lists, marker lists, pipe tallies, dig sheets and include special routines that allow comparisons of inspection runs.

Operational improvements

This new generation of in-line inspection tools makes full use of advancements in electronics, digital data processing and solid-state recording devices. This does not only markedly improve the performance and reliability of the tool, but also its handling and the operational performance overall. Some of the major advantages of the new generation of UTILI tools are:

Tool is shorter and lighter

Higher Inspection Speed:

Data retrieving and preparation:

Tool preparation

Fit most of the commonly used launchers and receivers, for example, the 24” toolis only 3200 rmn long(see other specifications in Table 2 and 4).

Increases possible inspection speeds at maximum axial resolution by 50% (UTCT) to 100 % (UTWT) compared to earlier tools.

Downloading and checking of data is now done immediately upon retrieving of the tool, with the data being completely ready for analysis. This means that data can be viewed and screening be made already on the site upon retrieving the tool.

All preparation and setting of parameters prior to the run is done via a laptop without opening the tool, or additional preparation of the tool in a workshop

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Back-to-back inspections: Refitting the tool from metal loss to crack detection configuration (or the otherway around, from crack detection to metal loss), can be done after the run in less than 1 hour, and so back-to-back inspection runs can be performed with minimum downtime.

Data turnaround: Time needed for interpretation of data and final report has become shorter

Data visualization software: User friendly software for data visualization is now available that operates underWindows

Table 2 Tool Specifications - 10”, 20” and 30”Metal Loss Tools

Tool size 10” 20” 30”

Inspection velocity range at full defect specs (further increase in speed affects axial resolution only)

< 2.0 m/s (up from 1 m/s)

Maximum pressure 120 bar

Standard temperature range -10 to +50 °C

Tool length 3300 mm 3000 mm 4000 mm

Tool weight 100 kg 500 kg 1000 kg

Distance range 150 km 300 km 220 km

Number of bodies (including sensor carrier)

5 3 3

Axial sampling distance 3 mm

Table 3 Minimum Defect Specifications for Metal Loss Tools

Pitting (standard configuration) (minimum diameter)

detection only with sizing

10 mm (0.40 in.)20 mm (0.80 in.)

General metal loss 1.0 mm (0.04 in.)(threshold can be lowered)

Depth sizing accuracy ± 0.3 mm

Defect location accuracy

axialcircumferential

± 15 cm from nearest girth weld ±10° (20 min.)

Internal/external/mid-walldiscrimination Yes

Confidence level 90%

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Table 4 Tool Specifications for 10”, 20” and 30” Crack Detection Tools

Tool size 10” 20” 30”

Inspection velocity range at full defect specs (further increase in speed affects axial resolution only)

<1.5 m/s (up from 1 m/s)

Maximum pressure 120 bar

Standard temperature range -10 to +50 °C

Tool length 3050 mm 3400 mm 4400 mm

Tool weight 100 kg 520 kg 1100 kg

Distance range 120 km 260 km 300 km

Number of bodies (including sensor carrier)

5 3 3

Axial sampling distance 3 mm

Table 5 Minimum Defect Specifications for Crack Detection Tools

Defect type(different configurations for axial and circumferential cracks)

Cracks and crack-like defects:SCC, fatigue, LW defects, etc.

Length 30 mm (can be set lower)

Depth 1 mm(2 mm in welds)

Axial orientation <± 10°

Radial orientation <± 45°

Length sizing accuracyfor lengths <100 mm ±10 mmfor lengths >100 mm ±10%

Depth classification< 2 mm2-4 mm> 4 mm

Defect location accuracyaxial ± 15 cm from nearest girth weldcircumferential ± 10° (20 min.)

Internal/external/mid-wall yesdiscrimination

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Confidence level 90%

Tool Sizes and AvailabilityUltrasonic Wall Thickness Measurement Tool Ultrasonic Crack Detection Tool

• 20"-56": Spring 2003 • 20"-40": Spring 2003

• 10"-18": Summer 2003 • 10"-12”: Summer 2003

• 6"-8”: Spring 2004 Sizes planned next: 14"-18"

Conclusions

Ultrasonic in-line inspection has established itself as a very reliable and advantageous method for inspection of metal loss, and recently also has set standards in crack detection. Ultrasonic metal loss ILI tools provide the advantage of direct and linear wall thickness measurements, providing river bottom profiles and highest accuracy of measurement. This makes them suitable for use in conjunction with the most advanced defect assessment methods.

Ultrasonic liquid coupled crack detection tools have demonstrated the highest reliability in crack detection; not only high probability of detection and classification, but also sizing.

A new generation of ultrasonic tools has been developed with advancements in electronic and mechanical design, which combines defect detection and sizing performances required by the most sophisticated defect assessment algorithms.

References

[1] K. Reber, M. Beller, and N. I. Uzelac, “How Do Defect Assessment Methods Influence the Choice and Construction of In-Line Inspection Tools”, ASME International Pipeline Conference, paper IPC2002-27391, Calgary, Alberta, Canada, October 2002

[2] Specifications and requirements for intelligent pig inspection of pipelines, Pipeline Operator Forum, Shell International Exploration and Production B.V., EPT-OM 1998

[3] Recommended Practice RP-F101, Corroded Pipelines, 1999, DetNorskeVeritas

[4] J. Kiefner, Integrity Assessment: Hydrostatic Testing and Integrity Assessment, presented at 54th Annual Pipeline Conference, American Petroleum Institute, Houston, Texas, April 29-30, 2003.

[5] H H Willems, O A Barbian, and NT. Uzelac, "Internal Inspection Device for Detection of Longitudinal Cracks in Oil and Gas Pipelines - Results from an Operational Experience", ASME International Pipeline Conference, Calgary, June 9 - 14, 1996.

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