SPE PP. Abstract

Transcription

1 SPE PP SUBSEA PEC: The NDT Diverless Robotic System For The Pipeline Corrosion Inspection E. Slomp, SPE, M. Bertelli, Impresub I.D.M.C and D. Milijanović, IDMC Overseas FZE. Copyright 2012, Society of Petroleum Engineers This paper was prepared for presentation at the Abu Dhabi International Petroleum Exhibition & Conference held in Abu Dhabi, UAE, November This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright. Abstract PEC (Pulsed Eddy Current) is an NDT system applied to many sectors, and nowadays it plays an increasingly significant role in the maintenance of the offshore structures. The operational principle is based on eddy currents created by a magnetic field induced in a metal structure. Through the reverse principle it is possible to analyze their behavior: we obtain information related to the average wall thickness and therefore of the corrosion status. Salient feature of PEC system is that it operates without removing, modifying or pre-treating the protective coating of the steel structure to be inspected. The physical human presence for the system utilization has been essential in the standard practice. In the offshore world this requirement is very expensive, risky to comply with and often even physically impossible to achieve. For these cases, the subsea technology has allowed developing systems aiming to replace the human presence if this is not achievable or economically not viable. The Subsea PEC technology has been strategically developed for deep offshore inspections; a completely diverless machine mounted on WROV is deployed on the pipeline. The machine operations are remotely controlled from the surface on board the vessel and underwater module is employed on the pipe. The system automatically performs all the placements along the pipe length in order to carry out sectional scanning and obtain corrosion status readings around entire pipe perimeter (360degree readings). A single placement of the system allows detailed scan around the targeted pipe section and includes inspection of one further meter in length along the pipe. This technology allows complete mapping of the pipeline corrosion status without production interruptions since no destruction or pre-treatment of the protective coatings is required. Subsea PEC has already achieved considerable success with encouraging results during inspections carried out in the Mediterranean Sea, Red Sea, the South China Sea and the North Sea.

2 SPE PP 2 Table of content Abstract... 1 Table of content... 2 Introduction... 3 Summary of Different Approaches and Associated Challenges... 4 Operational features of the ultrasonic wall thickness measurements:... 4 Operational features of the Pulse Eddy Current (PEC) thickness measurements:... 4 Exclusivity of Subsea PEC approach... 5 Subsea PEC - The Key Components, Results and Limitations... 6 Statement of Theory and Definitions... 7 PEC Theory... 7 Motion Technology... 8 PID control Theory Description and Application of Equipment and Processes Description Fixed structure Mobile structure Application Presentation of Data and Result Conclusions Definitions and Nomenclature References Appendix REF.1 North Sea REF.2 Gulf of Suez REF.3 Philippines Tables Figures... 21

3 SPE PP 3 Introduction The offshore Oil and Gas production heavily depends on the functional reliability of the steel structures and especially of the subsea pipelines being the literal veins of the carbohydrate transportation/production systems. As the underwater pipelines network continues to grow across the world following successful explorations in increasingly deeper waters the amount of the carbon steel embedded in the oil and gas pipelines systems reaches its all-time maximum. The accumulated wall thickness corrosion evolves as a silent, but major contributor to partial or full pipeline integrity failures. This is particularly evident across currently ageing offshore oil fields resulting in the environmental, occupational/civil safety and production stoppage risks being kept permanently to the uncomfortable high levels. The prudent and responsible offshore oilfield operators conduct regular pipeline inspections with the aim to monitor actual corrosion rates and trends, evaluate the integrity failure risks and subsequently conduct the appropriate maintenance efforts including ultimately the major capital investments associated with complete pipeline replacements abandoning in such cases further exploitation of the lines found to have exhausted their functional life. Several aspects discourage and complicate measurements of the subsea pipeline corrosion through the currently utilized inspection techniques, but the common key factor is the requirement for pipeline flow/production shutdown during the time required for the inspection to be performed. The operator naturally tends to avoid shutdown or at least to maximize operational time between shutdowns. As the end result, the compromised prolongation of the pipeline exploitation cycles, without regular monitoring of the actual wall thickness loss, boosts the pipeline failure risk with potentially catastrophic ecological, safety and economic consequences. Any new tool for subsea pipelines corrosion measurement able to widen the current bottleneck caused by inspection technologies that enforce pipelines shutdown would potentially contemplate to more reliable pipeline integrity management and thereby mitigate the above mentioned integrity failure risks and associated costs. With the principal aim to arm offshore oilfield operators with a NDT tool capable to measure the actual (remaining) subsea pipeline wall thickness without interruption of the pipeline regular function, it has been recently introduced a new inspection concept - the Subsea PEC system. This method is based on electromagnetic features of Pulsed Eddy Current (PEC) whose steel thickness measurement principles differ from ultrasonic technologies. Figure 1-Subsea PEC during Wall Thickness reading through the coating Subsea PEC is a brand name for the complete solution technology ready for the site implementation. It provides automated sectional scanning of the complete pipe segment and map corrosion status readings around the entire pipe surface. The PEC physics integrated into the Subsea PEC system also secures very important and key operational flexibility; although the wall thickness readings are taken on the pipeline outer surface, it requires no special pre-treatment to the existing pipeline coating, concrete protection shell or marine growth for achieving the accurate wall thickness readings. Hence, Subsea PEC solution is geared to work silently without disruption of the regular pipeline exploitation.

4 SPE PP 4 Summary of Different Approaches and Associated Challenges Operational features of the ultrasonic wall thickness measurements: Ultrasonic wall thickness measurement tools regularly provide reliable and accurate absolute measures of the steel/ferrous structures on land and also under the water. This is a mainstream solution of the corrosion inspection and monitoring systems found regularly within offshore oil operators. The inner side pipeline inspections are generally conducted by intelligent pigging which is highly sophisticated technique, but the line shutdown is present during the inspection time, for the pipe cleaning as precondition to conduct the inspection and it remains a permanent risk of getting the pig stacked inside the (aging) pipelines. The external side pipeline inspections are generally conducted by UT probes implementing manual point readings collection of the measurements. Given that most of the subsea pipelines are protected by a concrete coating shell, the downside of this method is that concrete cover needs to be removed and inspection pipe surface cleaned to the bear steel prior to readings would be taken by the UT probe. Again, concrete shell breaking and surface cleaning would generally require shutdown of the pipeline and the once exposed pipeline sections will remain to present a weak point for further corrosion advancement. Operational features of the Pulse Eddy Current (PEC) thickness measurements: Enabling non-contact testing of steel/ferrous structures is the embedded feature of PEC technology since electromagnetic field penetrates all other materials except metal without field intensity loss. This feature is the basis for the PEC implementation into N.D.T. inspection tools. Built on this originally promising physic various attempts have been made in the past to upgrade the core PEC features to the useful wall thickness measurement tool. In the offshore industry they have regularly ended up at the level of manually (diver) operated probes which practical implementation remains to be limited to the relatively small number of the point readings endemically exposed to the human errors or at least to the natural spread in the results collected by different probe operators. Collection of the readings/measurements, interpretation, eventual illogical measurement repetitions and presentation of the results tends to be hectic, scattered and missing systematic approach in many cases. With these deficiencies the early developed PEC tools remain to be unrecognized at the large scale implementations as a real alternative to the standardized corrosion measurements based on UT technology. Figure 2-Pipe section view with PEC concept description

5 SPE PP 5 Exclusivity of Subsea PEC approach The commonly known Pulse Eddy Current features initially also presented the starting point for Subsea PEC development, but the system itself succeeded to integrate various advanced technologies during the product s research & development life cycle. The final invention has consistently adhered to the initial development vision having all the following major operational parameters as the goals to be preserved while operating in the subsea environment: - Allow wall thickness measurements to be taken in parallel with the regular pipeline exploitation; - Applied technique to enable corrosion measurement all around pipe cylindrical surface; - Secure easy employment in both diver and diverless operational mode as the standard options, i.e. equally reliable performance in shallow and deep waters; - Develop, test and implement only the most advanced applied PEC technology granting high accuracy and reliability; - Secure fully automated, software controlled, real time measurement readings control, i.e. exclude possibilities and impact of the human errors during the measurement process; - Provide ultimate client with the intuitive and easy to understand corrosion status reporting system; To deliver a product which shall implement all the listed goals Subsea PEC development has undergone several years of extensive and vigorous design and desk studies, laboratory and field experiments & testing. The end product achieved the full integration of several research modules through profound collaboration of various technical and engineering departments. Each of the Subsea PEC components (probe, probe management software, post-processing package, machine automatisation and control system, result reporting module) was optimized to secure reliable performance on the real underwater assignment. Irreplaceable integrating support was secured by specialized marine design & build engineering manufacturer and experienced subsea sector services provider. Figure 3-Subsea PEC on pipeline during the measuring through the coating

6 SPE PP 6 Subsea PEC - The Key Components, Results and Limitations The summary of key functional and technical Subsea PEC characteristics: - Corrosion inspection conducted without interruption of the pipeline production or surface pre-treatment; - Corrosion reading access covers complete pipeline surface (360º); - Single machine placement on the pipeline covers completely automated survey of 1 m of the pipeline length; - Average net duration for 1 m of the pipeline survey is approx 2-3 hours (depending of the pipe diameter); - Opportunity to determine not only the absolute value of the corrosion but also the rate of corrosion progress; - Achieved relatively high accuracy of ± (5-10)% on the average WT measurement; - Adjustable system configuration secure no limitations to the pipeline overall diameters (6 till 46 ); - No water depth limitation; - Intuitive 3D graphical presentation report on the pipeline corrosion status. There are also several special requirements and operational limitations related to the employment of the Subsea PEC. These requirements need to be well understood in order that appropriate working procedures will be planned and ultimately the maximum possible effects achieved: - Calibration Requirement: The PEC readings depend on the electromagnetic properties of the material, which are unknown. The absolute value of a PEC wall thickness reading is therefore also unknown in advance, so the readings need to be calibrated against a determined correlation between the referenced PEC signal and corresponding (known) wall thickness at the place of measuring the referenced signal. The PEC wall thickness algorithm compares each acquired signal with that of the measurement entered as a reference. PEC inspection results are expressed as a percentage of this reference. Hence, a single point calibration will usually be sufficient to convert the relative PEC readings (%) to the absolute wall thickness values (mm). - Excavation below the pipe: The probes mounted on the Subsea PEC, move to reach all the positions where read the WT, i.e. that the machine needs approximately cm of free span all around the pipe surface, avoiding eventual collision with close structures or on the seabed. - Trimming of the excessive marine growth on the inspection section.

7 SPE PP 7 Statement of Theory and Definitions The Subsea PEC is based on two fundamental technological issues: the method for wall thickness reading and the design of the underwater system aimed at the automatic handling. PEC Theory The PEC sensor generally contains two electric coils, one as transmitter, one as receiver. The probe is positioned close to the metal to be inspected. The representation below shows the principle of the PEC system. Transmitter coil Receiver coil Figure 4-Principle of PEC system operation The application of a voltage pulse to the transmitter coil generates a primary magnetic field. The voltage (then the current through the coil) is switched off and the steel demagnetizes. The rapid expiring of the magnetic field produces electrical eddy currents within the steel, according to the electromagnetism Maxwell-Faraday equation [4]: in which: denotes curl and denotes the partial time derivative holding r fixed. The electrical effect produce a secondary magnetic field in the steel and it s picked up by the receiver coil, transformed in induced voltage by the Lenz law[5]: Which indicates that the induced electromagnetic field and the change in flux ( have opposite signs. This field is picked up by the receiver coil as an induced voltage, The signal is amplified and the result as a function of time is referred to as the PEC signal. The behavior of the eddy currents in the material is fairly complex, being a combination of various modes, each with its own spatial distribution within the substrate. The strongest modes are concentrated near the surface, but they decay quickly with the depth into the material, according to the law below [7]:

8 SPE PP 8 in which: = Standard depth of penetration (mm) = 3.14 = Test Frequency (Hz) = Magnetic permeability (H/mm) = Electrical Conductivity (S/m) Figure 5-Eddy Current Field Depth of Penetration & Density for a specific test frequency The modes that are scattered throughout the thickness of the steel take longer time to decay [1]. The software evaluates the integral of the signal over time, until the signal reach zero: the given result is the indication of the steel wall thickness. The PEC measurement sequence provides for the sampling of readings from the receiver coil (with more than 3,000 readings per second), the analog-to-digital conversion and processing of the digitized samples via the dedicated algorithms. For the result optimization a detailed data post processing is possible after the collection of the readings [3]. Motion Technology Any single measurement made by PEC probe is not to be considered as an end in itself, but has to be evaluated in a wider context including the analyses of close areas. According to this methodology, the machine movements has been designed so to guarantee the maximum flexibility for the various applications. The area covered by measurements (footprint) by PEC sensor has approximately 100mm diameter; the step between each shift has been determined being 50mm in both directions for the following reasons: The readings overlap, so ensuring the full coverage of the inspected area The overlapping of the readings allows to obtain abundant data, allowing to recognize possible wrong measurements and to check again immediately the interested area. Figure 6-Footprint on the pipe, bidirectional steps and complete covering by multiple bidirectional steps

9 SPE PP 9 Reconstruction of single movements allows to obtain a complete mapping of the pipe in the interested area. For the longitudinal movements the number of steps is always the same, while around the pipe they are obviously variable depending on the pipe diameter; for instance, for a 16 pipe the circumference is 1200mm; with 50mm step 24 positions are obtained (rotation intervals of 15 degree each). For a 8 pipe about n.12 positions of 50mm each, corresponding to 30 angle. Figure 7-Principle of mapping construction of the readings An arc structure (Figure 8) is moved to allow a shifting of 1 meter along the pipe length and on the circumference. Sensors are mounted one opposite to the other, so that all the positions are covered. All the shifting is made by oleo-dynamic actuators, controlled by highly reliable industrial electronic systems. Movements are managed by a system through several sensors mounted onboard. A PID (proportional integral derivative) control allows to optimize the speed and the accuracy Figure 8 & Figure 9 show the block diagram of a single shifting; given a specific arrival Setpoint, this is compared with the current position obtained by reading Feedback of the specific sensor; their difference is managed through PID control [2]. Figure 8-Rotating system with the relevant free movement Figure 9-Block diagram of feedback control of the machine movements

10 SPE PP 10 PID control Theory PID control uses the error to calculate three components of the output that correspond to the proportional, integral and derivative feedback, components that give the control scheme its name. The equation for PID control often takes the following form in the time domain. Figure 10-PID time domain equation and relevant block diagram The first component behaves like a spring, generating a control output that acts to force the system to the set point. The second component integrates the error from the starting time to the current time and supplies control effort to drive steady state error to zero. The final component generates control output proportional to change in the error, essentially behaving like an artificial damper. The key is to adjust the three gains (K p, K i and K d ) to weight the three components and to achieve the desired performance characteristics while avoiding system instability.

11 SPE PP 11 Description and Application of Equipment and Processes Description The whole structure is made of various kind of materials, keeping in due consideration the limitations given by the underwater application and by possible interferences that may compromise the proper reading of the probes. Nearby the sensors only the stainless steel and plastic material is used, while, far from the sensible area, the anodized aluminum and stainless steel is used in order to have lightness and strength for the shifting operations. The machine has a fixed structure and a mobile one. Fixed structure Such structure is designed for several aims: - to house most of the electronic and electromechanical systems; Figure 11-Subsea PEC system for the automatic scan on the pipe - to control the movements and to manage the PEC reading sensors, connecting the surface through umbilical cable; - to guarantee an adequate approach onto pipe to be inspected (saddles are mounted at stern and bow of the machine, securing correct positioning on pipeline, and two clamps blocking the structure keeping it integral with the line. Clamps can be activated manually locally (by divers) or remotely by a remote control placed on surface; saddles are adjusted in height to guarantee the proper centering of the rotating system; - to house buoyancy modules in order to lighten the machine when underwater; ensuring maneuverability. Mobile structure In order to have a complete pipe inspection according to procedure, the following two activities are necessary: Translation: electro-hydraulic actuators move a carriage, clamped to the fixed structure through guides so to allow the movement along the pipeline. Rotation: the arc containing the probes is mounted on the carriage; the longitudinal advancement is ensured by a hydraulic engine and checked by multi-turn encoder. All the operations are managed from surface through a laptop and a compact control box. Software for machine management is multilingual, user friendly and intuitive. Figure 12 shows a screenshot of the system manager. Figure 12-Main page of the Control Panel Interface

12 SPE PP 12 Application Subsea PEC is designed to obtain maximum flexibility: there are four configurations allowing to measure all the typical pipelines diameters: in a couple of hours it is possible to pass from the 8 pipelines setup to the 36 one, by simply substituting the specific kit for the selected diameter. The system envisages the installation on pipelines by divers or by ROV; once on the seabed, it is correctly positioned on pipelines according to procedure. Once clamped on the pipe, the reading phase may start. A specific version of Subsea PEC, called Subsea ROV PEC, is equipped with Thrusters, Profilers, Auto Heading allowing autonomous flying, detection of the point to be inspected and landing on pipeline. The PEC system is calibrated before starting the measurement procedure, i.e. it is determined the referenced signal value which corresponds to the known WT (100% signal value). When the machine is installed on the pipeline the automatic average wall thickness measurements commence. Figure 13 shows the typical screenshot for interpretation of signals coming from sensors. Figure 13-Example of PEC software screenshot Scan time for the full reconstruction of the envisaged matrix is variable depending on the pipe diameter, from a minimum of 30 for 8 pipeline up to a maximum of 4 hours for larger diameters. Once reading phase is finished, the machine is released from the pipe and positioned on a new area to be inspected or recovered to surface.

13 SPE PP 13 Presentation of Data and Result At each inspected point, data are immediately available for a first rough evaluation; a second phase is then represented by accurate post-processing for data optimization and deep analyses. The final results are displayed in color 2D and 3D, allowing intuitive and immediate evaluation of the corrosion status of the inspected area. COLOR LEGEND Remaining WT > 110 % 90 To 110 % 85 To 90 % 80 To 85 % 75 To 80 % 70 To 75 % 65 To 70 % 60 To 65 % 55 To 60 % 0 To 55 % Figure 14-Example of 2D and 3D color plot results with color legend and perceptual values The inspection activities performed by Subsea PEC system within great variety of environmental conditions offer important evaluation and confirmation on the efficiency of the inspection method. Some of the interventions carried out are outlined here below. The more detailed results presentation (only for the first 3 projects) is available in the Appendix. REF.1 Location North Sea Inspected structure Gas Flow line Diameter 10 Nominal WT 20 mm Coating Thickness 30 mm concrete Water Depth 75 m Conclusion Refer in appendix Job description The PEC scope of work comprises the 360 degree inspection of 1x 2m section of the 10 production flow-line. Note that due to the line being piggybacked, the 12 O Clock inspection track was not possible. REF.2 Location Gulf of Suez Inspected structure Oil, Gas (and Water) Pipelines, risers Diameter 8, 10, 12, 18, 24, 36 Nominal WT From 9 to 12.7 mm Coating Thickness From 20 mm to 115 mm concrete Water Depth From onshore to 40 underwater meters Conclusion Refer in appendix Job description More than 90 areas inspected, every 500 meters for each pipeline. Risers and onshore locations

14 SPE PP 14 have been inspected with the manual system REF.3 Location Philippines Inspected structure Gas Condensate Export Pipeline, PLEM structure Diameter 24 Nominal WT 17.1 mm Coating Thickness 40 mm concrete Water Depth 95 m Conclusion Refer in appendix Job description The pipeline was inspected circumferentially at 3 locations of 1m length coinciding with the deepest section of the pipeline at the PLEM where water if present, would likely gravitate and potentially initiate corrosion. The 3 inspections were taken over 2 Field joints using the Subsea Automatic PEC machine in preference to manual diver measurements to provide a stable platform from which to reliably measure. The seabed was pre-excavated by divers to enable full rotation of the tool and minimal cleaning of the concrete coated pipeline was required due to its good overall condition. Calibration of the PEC tool was performed subsea on a section of pipeline away from the inspection location. The PLEM has been inspected with the manual handled system, at several locations using PEC and subsequently verified using UT. REF.4 Location Egypt (Delta Nile) Inspected structure Gas Pipeline Diameter 24 Nominal WT 14.2 mm, 15.9mm, 19.1 mm Coating Thickness 10 mm epoxy Water Depth Onshore Job description Inspection of 30 meters of onshore pipeline using the manual PEC, covering all the accessible locations. More than 7,000 reading have been collected. REF.5 Location Gulf of Suez Inspected structure Gas, Oil Sea-line Diameter 6, 10 Nominal WT 9.52 mm, mm Coating Thickness 50 mm concrete Water Depth 30 m and onshore Job description Sea-line inspection on the specific locations, defined by a risk assessment plan. REF.6 Location North Sea Inspected structure Platform Leg Diameter 48 Nominal WT mm, mm Coating Thickness No coating Water Depth 15m and above water Job description Wall thickness inspection, 16 meters deep into the Leg.

15 SPE PP 15 Conclusions The latest technological improvements of the Pulsed Eddy Current hardware and associated software interface have launched the PEC implementation techniques to the level of the inevitable and standardized tools to be employed for subsea pipelines corrosion inspection. The importance of regular and reliable corrosion monitoring services cannot be overemphasized especially in the times when oil and gas subsea facilities reach mature phase in the life cycle of the exploitation. The Subsea PEC characteristics will definitely position this system as advanced and economically viable solution for general metal loss assessment through regular monitoring if the actual pipeline corrosion exceeds predicted corrosion allowance. As a wall thickness reading technique derived from the volumetric metal measurement, the Subsea PEC shows insensitivity to blisters and laminations within the pipe wall and thereby more appropriately identifies general corrosion status on the wall. At the first instance it will allow inspectors to better understand general morphology of the real degradation caused by pipeline corrosion. Its integrated feature to reliably repeat wall thickness measurement brings added value of mapping the estimated corrosion rates through consistent implementation of this system. The Subsea PEC development project has introduced this new ability to relatively easy, reliable and without interrupting the pipeline regular function, determine the key corrosion status parameters what will certainly draw a full attention of the professionals responsible for evaluating the remaining life of the production facilities. The Subsea PEC concept in no way tends to eliminate future need for standard ultrasonic inspection techniques. PEC may function as preferred inspection choice where pipeline shutdown is a critical factor, but it remains at discretion of the integrity control teams at each facility to define and fine tune the exact employment mix between PEC and ultrasonic techniques according to the particular goals of each inspection. The initial, higher prospective investigations of the general corrosion status typically inspected by the Subsea PEC will guide further screening of the identified wall defect locations by ultrasonic based techniques when and where possible and appropriate. UT inspection will be further focused on the assessment of wall local thin areas, pit corrosion and other small size imperfections. However, the great opportunity is offered through this new PEC implementation tool to further optimize the overall economy of the oil and gas facilities corrosion monitoring and associated maintenance or replacement costs. The most important impact of the Subsea PEC may be felt in the near future through an endemic risk reduction; the risk of subsea pipeline integrity failures, unfortunately having often fatal consequences across environmental, safety and hydrocarbon production costs areas.

16 SPE PP 16 Definitions and Nomenclature Auto Heading = automatic system used to maintain an existing Heading, or turn the ROV to a specified Heading Electrical coil = a spiral of two or more turns of insulated wire, used to introduce electromagnetic effect. Footprint = the area of the steel affected by the magnetic field. Frame = the structure composed of parts fitted and joined together. KP = Kilometer Point NDT = Nondestructive Test: a type of testing which does not damage or destroy the original object PEC = Pulsed Eddy Current; typically used also for the relevant probe using the PEC method PID = a proportional integral derivative controller is a generic control loop feedback mechanism widely used in industrial control systems Pig = Pipeline Inspection Gauge: is a tool that is sent down a pipeline for the internal inspection. Probe = the device which permit to transmit and receive the magnetic field to/from the steel Profiler = acoustic instrument employed to explore the strata beneath the sea floor ROV = Remotely Operated Vehicle Saddle = Support and centering system on the pipe UT = Ultrasonic Testing WROV = Work-Class Remotely Operated Vehicle WT = Wall Thickness References 1. Classen T.A.C.M., Mecklenbrauker W.F.G., "The Wigner Distribution A Tool for Time-Frequency Signal Analysis", Philips J. Res., 35, 1980, PP , , Jain A.K. Dulin R.P.W. and Jianchang M., Statistical Pattern Recognition: AReview, IEEE Transaction on Pattern Analysis and Machine Intelligence, Vol. 22, No. 1, January van der Steen H., Dillaway G., Impact magazine, Shell Global Solutions, Automatic Benefit, Issue 2, Nave, Carl R.. "Faraday's Law". HyperPhysics. Georgia State University. Retrieved 29 August Schmitt, Ron. Electromagnetics explained, 2002, Retrieved 16 July Ndt-ed.org/EducationResources/CommunityCollege/EddyCurrents/Physics/depthcurrentdensity 7. An introduction to Eddy Current Testingtheory and technology, Joseph M. Buckley, formerly of HOCKING NDT

17 SPE PP 17 Appendix REF.1 North Sea The exhaustive data analysis and processing is showing the integrity of the pipe, with a general wall loss at the top of the pipe, between 10 o clock and 2 o clock positions. The corrosion value is between 10 to 15% of the original wall thickness, with an increasing corrosion with the upper clock positions. Is present a corroded well from 0 to 1000mm of the scanned section at 4 and 5 o clock positions but not greater than 12% of wall loss. Longitudinal Position Clock Position [hr] [mm] D PLOT COLOR LEGEND Remaining WT > 110 % 90 To 110 % 85 To 90 % 80 To 85 % 75 To 80 % 70 To 75 % 65 To 70 % 60 To 65 % 55 To 60 % 0 To 55 % NOT DEFINED Table 1-2D color plot of the inspected area and the relevant color legend

18 SPE PP 18 REF.2 Gulf of Suez More than 15,000 readings have been collected in this project, so only a sample cam be explained. The picture below show some 2D and 3D color plot result of 8 pipeline inspection. Location 3500 Longitudinal Position SEALINE INSPECTION MEASURE KP 3,500 Position around the pipe [hr] [mm] D PLOT COLOR LEGEND Remaining W T > 14.0 mm 11.4 To 14.0 mm 10.8 To 11.4 mm 10.2 To 10.8 mm 9.5 To 10.2 mm 8.9 To 9.5 mm 8.3 To 8.9 mm 7.6 To 8.3 mm 7.0 To 7.6 mm 0.0 To 7.0 mm NOT DEFINED Table 2-2D color plot result of location KP3500 with legend (right) and the absolute value of remaining Wall Thickness Figure 15-3D color plot results of location KP3500 (with color legend from Table 2)

19 SPE PP 19 Location 8000 Longitudinal Position SEALINE INSPECTION MEASURE KP 8,000 Position around the pipe [hr] [mm] D PLOT COLOR LEGEND Remaining W T > 14.0 mm 11.4 To 14.0 mm 10.8 To 11.4 mm 10.2 To 10.8 mm 9.5 To 10.2 mm 8.9 To 9.5 mm 8.3 To 8.9 mm 7.6 To 8.3 mm 7.0 To 7.6 mm 0.0 To 7.0 mm NOT DEFINED Table 3-2D color plot result of location KP8000 with legend (right) and the absolute value of remaining Wall Thickness Figure 16-3D color plot results of location KP8000 (with color legend from Table 3)

20 SPE PP 20 REF.3 Philippines Condensate Export Pipeline result: At the 1 st location the bottom of the pipeline (6 o clock) has a higher % wall thickness (5%) compared to the top of the pipeline (12 o clock) however this is within the reporting wall thickness criteria % and is therefore not categorized as an anomaly but this trend may be indicative of slight wall loss at the top of the pipe (equates to 0.85mm on 17.1mm wall thickness). At the 2 nd area similar to the above but with a wall thickness difference of approximately 3%. At the 3 rd location there were no indications of wall thickness loss as the measurements were uniform along the 1m axial direction and circumference of the pipeline. PLEM Piping result: Generally the pipe work within the PLEM appears to be in good condition at the areas sampled 1 exception appears to be on the outer bend of the Upper Hose near to the clamp (see Section 7.2.2) where the wall thickness falls into the 85 90% category and a recorded lowest wall thickness of 89%, just within the anomalous reporting criteria. UT measurements were also taken at several of the PEC measurement locations with reasonable agreement varying from 0.1 to 0.3 mm. The figures below show the higher elbow result and the cross check with the UT probe (red squares). Figure 17-PEC results on the PLEM higher elbow, with the cross check by UT measurements

21 SPE PP 21 Tables Table 1-2D color plot of the inspected area and the relevant color legend Table 2-2D color plot result of location KP3500 with legend (right) and the absolute value of remaining Wall Thickness Table 3-2D color plot result of location KP8000 with legend (right) and the absolute value of remaining Wall Thickness Figures Figure 1-Subsea PEC during Wall Thickness reading through the coating Figure 2-Pipe section view with PEC concept description Figure 3-Subsea PEC on pipeline during the measuring through the coating Figure 4-Principle of PEC system operation Figure 5-Eddy Current Field Depth of Penetration & Density for a specific test frequency Figure 6-Footprint on the pipe, bidirectional steps and complete covering by multiple bidirectional steps Figure 7-Principle of mapping construction of the readings Figure 8-Rotating system with the relevant free movement Figure 9-Block diagram of feedback control of the machine movements Figure 10-PID time domain equation and relevant block diagram Figure 11-Subsea PEC system for the automatic scan on the pipe Figure 12-Main page of the Control Panel Interface Figure 13-Example of PEC software screenshot Figure 14-Example of 2D and 3D color plot results with color legend and perceptual values Figure 15-3D color plot results of location KP3500 (with color legend from Table 2) Figure 16-3D color plot results of location KP8000 (with color legend from Table 3) Figure 17-PEC results on the PLEM higher elbow, with the cross check by UT measurements