Felix-Wankel-Str. 18 D Oldenburg Germany Telefon: / Fax: /

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1 2009 Felix-Wankel-Str. 18 D Oldenburg Germany Telefon: / Fax: / germany@tracerco.com Pipeline Assurance using radioisotope Applications to go from installation over inspection to overhauling Dipl.-Ing. (FH) Stephan von Olearius stephan.vonolearius@tracerco.com Abstract The increasing demand of fossil fuels brings with it a rising number of sub-sea pipelines for oil and gas. This paper will describe different applications using radioisotope technology to assist during a number of critical stages related to deepwater pipeline operations. They support accurate assistance starting with monitoring the Pipeline during construction and the final Inspection after installation. The technology offers several types of inspection services for investigation of deposits in a pipeline while in operation. The collected data will determine whether local deposits in a pipeline, have caused blockages and if they are present in limited locations or if they are distributed evenly through the line. The total volume of deposits and percentage bore restriction within the pipeline can also be identified. Also measurements can be accomplished to determine whether the annulus of a Pipe-in-Pipe system is dry or flooded with seawater. In combination with Pig Tracking applications radioisotopes are indispensable for pipe cleaning or for detection of a leakage. The employment of these applications will considerable increase the productivity, lower the operational costs and allows optimising downtimes. The paper will give a survey about the use of radioisotope technology in the field of Pipeline assurance, recent examples of all of the above, discuss the scope and limitations of the technology, and conclude with the benefits the technology brings to pipeline operators and cleaning contractors. Alfa Aesar GmbH & Co KG Persönlich haftende Gesellschafterin Johnson Matthey Verwaltungsgesellschaft mbh, Sitz Emmerich, AG Kleve B 3448 Geschäftsführer Ian Huddart Hauptsitz Emmerich AG Kleve A 1232

2 Full paper Pipeline Assurance using radioisotope Applications to go from installation over inspection to overhauling 1 Introduction The increasing demand of fossil fuels leads to a rising number of sub-sea pipelines for crude oil and gas. The flow lines involved in longer tiebacks will become more prone to blockage from deposits, such as hydrates or waxes. As assets mature and pipelines require inspection to generate effective maintenance programs, non-intrusive point measurements are essential as a tool to reduce unnecessary downtime. Different applications are available using radioisotope technology to assist during a number of critical stages related to deepwater pipeline operations. They support monitoring of the Pipeline during construction and the final Inspections after installation. In order not to exceed the critical weight limitations during pipe laying operations the water levels inside deepwater pipes can be monitored or tracking the location of a sealing or a de-watering pig. The technology offers several types of inspection services for investigation of deposits in a pipeline while in operation. The collected data will determine whether local deposits in a pipeline have caused blockages and if they are present in limited locations or if they are distributed evenly through the line. In addition to this the total volume of deposits and the percentage of bore restriction within the pipeline can also be identified. Measurements can be taken to determine whether the annulus of a Pipe-in-Pipe system is dry or flooded with seawater. In conjunction with Pig Tracking Applications radioisotopes are indispensable for pipe cleaning or for detection of a leak. The employment of these applications will considerably increase the productivity, lower the operational costs and allows optimizing downtimes. This paper aims to give a survey about the use of radioisotope technology in the field of Pipeline Assurance, recent examples of all of the above, discuss the scope and limitations of the technology and conclude with the benefits of the technology delivered to pipeline operators and cleaning contractors. 2 Radioisotope Technology 2.1 Radiation and Radioisotope technologies Radioisotopes send out different types of radiation. There are alpha particles, beta particles, gamma rays and neutrons. The type of radiation and the energy of each depend on the isotope. Alpha and beta particles can only penetrate short distances and are therefore not suitable for the use in industrial applications. Neutrons are used for industrial applications such as investigation of moisture under insulation. This is based on different concentrations of hydrogenous material per volume. There are two basic types of applications using the presence of gamma rays: sealed source applications and unsealed source applications Sealed source applications use radioactive sources that are small pellets of a radioisotope in an encapsulated stainless steel capsule, which will not allow the alpha and beta particles to get out. Only the gamma rays are present outside the capsule. Page 2 of 9

3 The use of sealed radioactive sources will not create any contamination nor is the radiation fissile (strong enough to activate any of the material investigated). After completion of the test it will not be possible to prove radiation was used at that spot. Unsealed source applications use short half-live radioisotopes in chemical compounds with properties that mimic the process conditions. These radioactive compounds are injected into the process flow and the emitted radiation will be detected from the outside of the vessel or the pipe as it passes by. There is a minor risk of creating a contamination around the injection point but in many cases it is possible to inject the radioisotope directly into the centre of the main flow. As only short half live isotopes are used the possible contamination will not stay for a long period of time. The activity used in both sealed and unsealed source applications is rather small, thus minor damage to living tissue would be possible but chemicals and oil products being present in process pipelines will not have any defect in their chemical structure after applying these technologies. Both applications require the presence of a license for the use of those radioisotopes. In many countries around the world Tracerco holds these or has partners who can provide them. In some countries the operator of pipelines or other process units might need additional licenses. 2.2 Gamma-ray transmission scanning The non-intrusive gamma-scanning technology uses sealed radioactive sources only. Most common for this type of industrial application are Cobalt-60 and Caesium-137. Cobalt-60 has a rather big gamma-energy and it is used for vessels with thick walls or big diameters. Caesium-137 is usually used for vessels with small to normal wall thickness and in most cases when performing investigation of pipelines. Gamma-rays of selected isotopes with reasonable energies are used for industrial applications. These gamma rays will be absorbed by the surrounding material. This absorption is a function of density and distance. It is described with Beer-Lamberts-Law: The radiation intensity I o of the source is constant, µ is a constant and if the distance is fixed (being the diameter of pipe), measuring the intensity I at the detector will allow bulk density between the two points to be measured. Gamma-scanning has been successfully applied to determine changes in density of pipeline contents, and can be used for surface applications as well as sub-sea. Some typical project examples include: scale or sludge thickness in well flow lines and associated manifolds deposit in sub-sea lines hydrate blockage in sub-sea gas lines air/liquid interface measurement in pipe lines stuck pig detection slugging regime within a sub-sea multiphase flow line Page 3 of 9

4 determination of whether the annulus in a pipe-in-pipe system is dry or flooded 2.3 Radioisotope tracer injection technology The need to measure flow of all types of material in industrial processes arises frequently. Radiotracer techniques have been found useful among the available methods, often offering advantage over the more conventional ones. Common applications for this technique include: checking or calibration of installed flowmeters measurement of flow in systems where no flowmeters are installed flow distribution studies in multiflow systems. The pulse velocity method is the predominant method used as it is recognised internationally as the most accurate. This involves the injection of a sharp pulse of suitable radiotracer into the process stream and its passage downstream observed by pairs of radiation detectors positioned externally on the pipe. It is required to allow the first detector to be sufficiently far from the injection point to ensure lateral mixing of tracer. By measuring the time interval between detector pairs responses and knowing the distance between the detector the mean linear velocity can be calculated. If full bore turbulent flow can be assumed then the velocity can be converted to volumetric flow knowing the pipe internal diameter. Accuracy will depend on the precise circumstances but over long line lengths the mean velocity can usually be measured to better than ± 0.1%. This method is usually employed in basic flow measurement but it has been successfully used in the area of Flow Assurance as well, where it is used to measure the location and extent of solids within a pipeline. In this application the flow rate through the system must be known and kept constant. Detectors are positioned at known distances apart along the pipeline. A pulse of tracer is added to the pipeline and its velocity is calculated from the signal at each detector position measured. Using the velocity and flow rate the average bore size, and hence total amount of deposit build-up can be calculated between detector locations. This measurement can give critical information before any proposed pigging and cleaning operations are performed. 2.4 Neutron Backscatter Scan A probe consisting of a source of high energy, or fast neutrons and a detector, which is sensitive to low energy, thermal or slow neutrons is held against the side of the vessel or pipe under inspection and moved up and down over the surface. Fast neutrons from the source penetrate the wall of the vessel or pipe and interact with the medium inside. If the medium is hydrogenous, neutrons are moderated to thermal energies by collision with hydrogen nuclei. Slow neutrons diffusing back out from the vessel are detected. The detector response is a function of the hydrogen concentration per volume of the material adjacent to the probe. A large change in signal is observed when the probe moves across a liquid vapour interface. Fewer changes in signal occur at interfaces between liquids of different hydrogen Page 4 of 9

5 concentrations. In general, the greater the magnitude of the slow neutron signal the greater the concentration of hydrogen nuclei per volume and this is to an extent correlated with bulk density for similar media. However, geometrical effects at the macroscopic and microscopic level mean that the technique is not strictly quantitative for measuring the density of liquids in vessels. This technique has some advantages over the Gamma-Ray Transmission Technique of interface detection because access to only one side of the vessel is required. The useful range of the technique is limited, however, to a depth of 75 to 150 mm because of the difficulty of obtaining a useful flux of slow neutrons at the detector. 3 Pipeline Assurance techniques 3.1 Service for Pipeline Installation Monitoring The continuing drive to tap into even deeper oil field developments leads to oil and gas transfer through deepwater pipelines. New technologies are available to assist during a number of critical activities related to deepwater pipeline operations. For example to monitor the water level inside deepwater piping during pipe laying operation, in order that the critical weight limitations are not exceeded. It can be used for monitoring the location of seals or dewatering pigs. After installation the effectiveness of de-watering activities can be measured. When Oil and Gas production commences the technologies can detect the presence, size and velocity of water and gas slugs either sub-sea or topsides. It can measure the location of any sub-sea blockages such as hydrate or wax plugs or assist during critical pig track activities. The range of TRACERCO Diagnostics Pipeline Assurance technologies are all none intrusive, offer the best reliability within the industry and can very easily be integrated with other sub-sea equipment for easy deployment such as a pipe laying stinger, work class ROV or de-watering pigs. Case Study: The Use of the TRACERCO Diagnostics Pipeline Assurance techniques during pipeline installation within the Gulf of Mexico Tracerco have recently been involved with a large-scale pipe laying project for a major operator in the Gulf of Mexico, providing Pipeline Installation Monitoring services. During the laying of the pipeline, which was taking place in deepwater, the pipeline had exceeded its critical weight and had been dropped from the barge, consequently the pipeline had filled with seawater. The recovery stage involved using de-watering pigs to decrease the lift weight, these pigs were tracked using acoustic pinger technology. Unfortunately for the pipe installation contractor the de-watering pigs became stuck and the pingers failed, meaning that the location of the pig was unknown and could not be found. Tracerco were requested to use TRACERCO Diagnostics Pipeline Assurance technologies to confirm the location of the stuck pig, so the Pig Tracking technology was used and pinpointed the stuck pig to within +/- 5cm. This technology was used again by Tracerco Page 5 of 9

6 Services during the next stage of de-watering, so that the location of the pig was known at all times. Finally, Tracerco were requested to use the TRACERCO Diagnostics Pipeline Assurance technology again after the dry pipe had been lifted. Using the Pipeline Installation Monitoring technique, the water level in the pipeline was continuously monitored to ensure that the water level didn t rise too far, which would have caused the critical weight to have been exceeded again. 3.2 Service for Pipeline Inspection Pipeline Assurance - Flow Assurance Using a TRACERCO Diagnostics Pipeline Assurance Service for Flow Assurance you have a reliable system to detect the presence of solid build up (wax, scale or hydrate) or blockage within an operational gas, water or oil flowing pipeline. It provides the information regarding the nature of three phase flow through transfer pipelines. This technology is applicable to both surface or sub-sea systems. Case Study: TRACERCO Diagnostics TM Flow Assurance Tracerco had been requested by a North Sea major to determine the total amount of deposit within a 22km long, 16 diameter sub sea pipeline running between two platforms, by the use of the TRACERCO Diagnostics TM Flow Assurance Study. Measurement of the accurate velocity of a pulse of tracer between the platforms would be compared to the flow rate through the line and used to determine the effective average internal diameter of the pipe and therefore highlight the extent of deposit within the line. The 16 oil line had not been pigged for a number of years, therefore the amount of deposit in the line needed to be measured to enable a cleaning program to be devised, and confirm the amount of expected deposits that would have to be disposed. A sharp pulse of suitable radiotracer was injected into the pipeline at the sending platform, and a Tracerco data logger mounted externally on the pipe work measured the exact time that it passed the known position on the riser. A second Tracerco data logger measured the exact timing of the eventual arrival of the pulse of tracer on the receiving platform, and a simple measurement of flow velocity obtained by dividing the time of flight of the pulse by the total distance traveled. The accuracy of the transit time was +/- 0.05%, derived from the error produced in the measuring of the centroid of the tracer pulse at the receiving platform. The fiscally metered flow rate during the tracer test was then compared to the measured velocity, allowing the effective average internal diameter of the pipe to be calculated. Any reduction from the internal diameter schedule of the pipe will be due to deposit within the pipe, as long as the flow is full bore and turbulent during the measurement period. An average deposit throughout the full 22km of 10mm was detected within the line, which equated to a total measured deposit volume of approximately 140 cubic metres. The accuracy of this measurement depends on the accuracy of the fiscal flow meter. Detector responses on each platform: Page 6 of 9

7 Unfortunately, it was not possible to arrange for the deployment of subsea detectors, which would have provided further intermediate velocity measurements, which would give further information on the location of the deposit within the line Pipeline Assurance - Pipe-in-Pipe Using a pipe detector system to measure the integrity of the pipeline you can determine whether the annulus in your pipe-in-pipe system is dry and not full of seawater or inner pipeline contents. The Non-intrusive measurement can be operated by a ROV or diver and is usable for any pipeline diameter or wall thickness up to 3000 meters water depth. The pipeline can be filled with Gas or liquid. Case Study: Confirmation of Annulus Integrity in a 1000 metre subsea line A major oil and gas operator was concerned that one of their installed pipe-in-pipe lines had been breached at specific locations and seawater had ingressed into the annulus. A TRACERCO Diagnostics Pipe-in-pipe Annulus Integrity Measurement service was provided to determine whether this was the case, and confirm whether the annulus was dry or flooded. Two separate non-intrusive radioisotope scanning techniques were used, gamma-ray transmission and neutron backscatter, both operated by ROV to give quick and immediate measurements of annulus contents. Neutron Backscatter Gamma-Ray Transmission Page 7 of 9

8 Calibration measurements were taken to obtain readings for the two different conditions, and subsequent readings on each of the suspected problem sections of line were consistent with annulus empty conditions, conclusively proving that the annulus in each case had not been compromised and there was no liquid ingress Pipeline Assurance - Pig Tracking During pipeline operations it is required to have a 100% reliable monitoring system for locating a pig. It must be applicable to monitor a range of different types of pigging tools from foam to intelligent pigs, independent of the size of the pig. The monitoring System must be sensitive to detect pig movements in gas or dual walled systems and to monitor an interface between two immiscible materials within a pipeline. It can be used to continuously assess sealing pigs for movement during pipeline coupling or repair over an extended period of time. The system must be capable for the use to sub-sea depth of 10,000 feet. The System allows to confirm the pig passage past a critical pipeline positions and the time the pig past the specific position. If a number of pigs have been used, the number of pigs past a specific location can be counted. The monitoring system is able to locate a stationary pig to +/- 5cms or the monitoring of an isolation tool. Case Study: TRACERCO Diagnostics TM Pipeline Assurance - Pig Tracking Tracerco were requested by a large Oil company in South East Asia to provide TRACERCO Diagnostics TM Pig Tracking services during the repair of a 24 inch offshore Pipeline. The 24 pipeline had a damaged area on a pipe joint, which had been temporarily clamped. The aim of this job was to position and set one isolation Plug on each side of the damaged joint to allow repair without emptying / depressurising the pipeline. In order to minimize discharge to the environment, and allow the efficient repair, accurate and precise positioning of the isolation plugs was required. For this reason, small radioactive sources were attached to the plugs prior to launching, enabling them to be tracked and positioned to within 5cm accuracy using the TRACERCO Diagnostics TM Pig Tracker technique. Page 8 of 9

9 Two BiDi pigs either side of the isolation plugs also had radioactive sources attached as shown above. The BiDi pigs were being utilised to provide additional sealing protection. The position of each isolation plug and pig was known at all times. After the launch, each pig was tracked through topside pipe work, ensuring transition through valves and departure from the platform. Tracerco Subsea Pig Tracking equipment deployed by ROV from the vessel confirmed movement and separation of each pig and plug. Tracking was continued from the vessel until the repair area about 10km from the receiving platform was reached and each pig and plug was stopped at the required position. The isolation plugs were then activated, and tracking equipment and personnel were on standby during the repair work. After the repair was complete and the plugs deactivated, the Subsea Pig Tracking equipment was used to confirm movement of the Plugs towards the receiving platform. At the platform, the arrival of the BiDi s and Plugs was confirmed by a Tracerco pig tracker on the riser and movement of the BiDi s and Plugs were observed through isolation valves to the receiver. The radioactive sources were subsequently recovered and returned to the Tracerco Office. KEYWORDS Gamma ray transmission scan, pipe scan, Pig Tracking, radioisotope, sealed source, unsealed tracer, flow assurance, deposit survey, pipeline cleaning, hydrate, scale, wax Page 9 of 9