Chapter 13: Applications of Radiotracers and Sealed Sources in Industries PDF

# Chapter 13: Applications of Radiotracers and Sealed Sources in Industries for Troubleshooting and Process Optimization ## Introduction The widespread utilization of radioisotopes in modern society is a phenomenal success story. A myriad of vital applications of radioisotopes in industry is well...

# Chapter 13: Applications of Radiotracers and Sealed Sources in Industries for Troubleshooting and Process Optimization ## Introduction The widespread utilization of radioisotopes in modern society is a phenomenal success story. A myriad of vital applications of radioisotopes in industry is well established throughout the world. These applications, which began over a half-century ago, have been increasing rapidly over the past several decades. Radioisotope techniques: * can perform many tasks better, easier, quicker, relatively simply, and cost effectively than most alternative methods. * have no substitutes in many applications. * are used extensively in all areas of industry, science, medicine, agriculture, and research. The use of radioisotope materials in virtually all industries is of immense importance for process development and improvement, measurement and automation, operations research, quality control and testing, cost reduction and other purposes. ## Radiotracers & Sealed Source Applications: The applications of radioisotope in industry can be broadly divided into two categories: * **Radiotracer Applications:** * Leak detection and location in buried pipelines and industrial system * Mean residence time and residence time distribution measurement * Flow rate measurement * Sediment transport & effluent dispersion * Mixing/blending time measurement * Wear and corrosion rate monitoring * Effective management of oil field * **Sealed Source Applications:** * Industrial radiography * Gamma scanning of process columns * Computed tomography * Nucleonic control systems * Radiation processing of materials ## Advantages of radiotracers: * High detection senisitivity * On-line detection * Physico-chemical compatibility * Availability of wide range of compatible radiotracers * Quick analysis ## Table 1: Commonly used tracer in industry | Isotope | Half life | Radiation energy (Intensity) (Mev) | Chemical form | Tracing of phase | |---|---|---|---|---| | Tritium-3 | 12.6 y | β 0.018 (100%) | Tritiated water | Aqueous | | Sodium-24 | 15 h | γ: 1.37(100%) 2.75(100%) | Sodium carbonate | Aqueous | | Lanthanum-140 | 40 h | γ: 1.16(95%) 0.92 (10%) | Lanthanum Chloride | Solid (absorbed) | | Bromine-82 | 36 h | γ: 0.55 (70%) 1.32 (27) | Amonium bromide p-dibromobenzene dibromobiphenyl | Aqueous Organic Organic | | Gold-198 | 2.7 d | γ 0.41(100%) | Chloroauric acid | Solid (absorbed). | | Scandium-46 | 84 d | γ 0.89(100%) 1.84(100%) | Scandium oxide | Solid (Particle) | | Krypton-79 | 35 h | γ 0.51 (15%) | Krypton gas | Gas | | Argon-41 | 110 min | y 1.29 (99%) | Argon gas | Gas | | Modybdenum-99 | 67 h | γ 0.18 (4.5%) β 0.74 (10%) | Sodium molybdate | Aqueous | | Technitium-99m | 6 h | γ 0.14 (90%) | Sodium technetate | Aqueous | ## While analyzing industrial systems the knowledge of following parameters is essential: * Process parameters (Temp., Pressure, Volume, Expected Mean Residence Time) * Properties of process material (Phase, Density, Viscocity) * Expected or designed flow type (Plug type, Mixed type) * Expected degree of mixing * Choice of suitable radiotracer ## 13.1. Leak detection studies using radiotracers The occurrence of blockage and leakage in underground pipelines and process systems is one of the common encountered problems in industry. These problems affect production efficiency, product quality, material inventory, safety and environment. Radiotracer techniques are routinely used for detection and location of leaks resulting in high economic benefits. ### 13.1.1. Leak detection & location in Heat exchangers & pipes The inherent sensitivity of radiotracer technique make them extremely valuable in leakage detection in heat exchanger and buried pipelines. Measurements are carried out with the unit on-line and without interference to the process. The method also allows the estimation of leak size, and leaks as small as 0.1 litres per minute can be measured. More than 50 leakage detection tests have been successfully carried out in different systems. This is probably the most wide spread use of radiotracers in industrial trouble shooting with highest benefit to cost ratio. Any undesirable interconnection between isolated parts of any system or between two systems is a leak. A leak is suspected if there is any abnormal behavior of a system such as loss of pressure contamination of product or loss of process efficiency. Detection of leak if any is unambiguously achieved by injecting the radioactive tracer into the part suspected to be leaking and monitoring for the tracer in the contaminated part. Care should be taken to inject adequate quantity of tracer so that a lowest suspected leak rate will result in tracer detection. Otherwise the interpretation of non-detection of the tracer would no more be unambiguous. ### 13.1.2 New Development: PIG for leak detection in buried pipe-line A radioisotope based pipeline inspection gauge(PIG) for detection & location was developed by isotope and radiation applications division to detect leaks in the underground pipelines. The system consists of a scintillation detector, high voltage power supply, Pulse processing, data acquisition system, readout unit and software to transfer data to computer and further processing. The prototype microcontroller based version of the pig is very useful in a field radiotracer investigation for leak detection in underground pipeline from 6 inch diameter and above. The leakage in the pipeline can be precisely located. The battery operated pig system developed indigenously is suitable for field radiotracer applications as it is rugged and portable with data storage capacity up to 20 hours. The system was tested under simulated leak conditions and field trials are being planned. **Figure 13.1: Pipe inspection gauge developed by BARC** ### 13.1.3. Leak detection in a high pressure heat exchangers BARC have developed technique for leak detection in high pressure heat exchangers. BARC Scientists were part of IAEA team for developing protocols for leak detection in heat exchangers. The technique developed was successfully applied to test about 100 exchangers online in various Indian refineries, leading to thousand crores of rupees saving to the industry. ## Economical Benefits of leak detection studies A number of industries, particularly chemical industry, have been considerably benefited from various radiotracer applications. Some of the main factors considered for estimating the cost to benefit ratios are as follows: * Direct cost comparison with alternative conventional techniques * Savings due to increased production efficiency * Savings due to improved product quality * Savings due to reduction in down time of the plant savings due to avoiding expenditure. ## 13.2. Process Investigation: Residence Time Distribution (RTD) Studies A major application of tracers is for residence time investigations to determine parameters for plant optimizations and modeling. Once optimum performance of the plant has been achieved, tracer experiments can be conducted to indicate deviations from optimum conditions. The reasons for malfunctions such as unwanted by-pass streams or obstruction of vessels and pipes can be determined and remedied. The necessity for a plant shutdown can be assessed and vital information for required repairs obtained prior to shutdown. **Figure 13.2: Tracer principle.** In radiotracer technique, tracer is injected into the system and its flow is measured with the installed detectors at the inlet, outlet and other important locations. ## Selection of a radiotracer: For selecting proper radiotracer for study following properties are required: * Physical/chemical form and properties of tracer with respect to the system under investigation should be same * Half-life of tracer should be sufficiently long * Specific activity of tracer should be large * Type and energy of radiation emitted(gamma emitting) * Easy Availability and low cost of tracer * Method of measurement should be in-situ * Easy Handling of radioactive materials, radiological protection/regulations. ## Radiotracer injection: The instantaneous injection (Dirac pulse) of tracer is normally applied in practice because is simple. An injection is considered as instantaneous when its duration is less than 3% of the whole mean residence time. ## Post injection measurements: Residence Time Distribution (RTD) is an important characteristic of continuous flow systems and provides vital information such as mean residence time (MRT) of process fluid, degree of axial mixing and flow behaviour. The concept of RTD can be applied to various industrial processes to indirectly obtain hydrodynamic data for subsequent improvement in design and optimization of the processes. The measured RTD data obtained from an industrial system needs to be analyzed using suitable mathematical models in order to draw physically meaningful conclusions. A few case studies are described 10-11, Flow type in chemical reactors is classified in 2 classes: * Axial dispersed plug * Perfect mixers in series or tanks in series' or 'perfect mixing cells in series' flow ## Mean residence time (MRT) Mean residence time from the radiotracer experiment mean time spent by reactants in the process system can be find out using following formula: **Figure 13.3: Industrial Process reactors; Plug Flow, CSTR.** ## 13.3. Flow rate measurements Flow rates of product streams (liquid, solids and slurry) flows are measured to an accuracy of 1-2 % in situations where flow-meters are either not installed or are unreliable due to deposits or corrosion. Tracer techniques are recognized as ISO 4053 standards. Flow-rate can be measured through any pipe, reactor or open channel without interrupting the process. ### Transit Time Method: The flow rate measurement in pipeline is described below: **Figure 13.5: Principle of pulse velocity method.** ### Constant Rate Injection Method: In constant-rate injection method, a tracer solution of concentration q, is injected continuously, at a volumetric rate q, for a period such that an equilibrium concentration C2 is established for a finite time at a sampling station downstream. **Figure 13.6: Principle of constant rate injection method.** ## 13.4. Sediment transport investigations at ports Bedload transport studies in ports and harbors are of economic significance for optimizing dredging activities. Radioactive isotopes as tracer are widely used to study the dynamic behavior of sediment at Ports and navigation channels in harbours. At ports there is movement of big ships, the maintenance of the optimum depth for smooth sailing of vessels demands continuous dredging in channels throughout the year. Disposal sites for dredged material are selected based on physical models., Subsequently the proposed dumping site is validated by injecting suitable radiotracer, to monitor the movement of dredged material. Which helps in reducing the dredging cost. Since the study is long term, usually flow pattern of injected radiotracer is monitored up to 3 months, Sc-46 labelled glass was found suitable as having long half life, gamma emitter and can be matched with particle size of sand physico-chemically in 50-100 micron range. During last one decade 8 such investigations were carried out at various ports. The studies help in selecting suitability of site for disposing off dredged sediment and port gained significantly from such investigations. ## 13.5. Mixing time measurement Mixing is a crucial step in many processes, consuming time and energy and making use of expensive equipment. Radiotracer applications play an important role in optimizationof mixing processes. For example, insertion of radionuclide in melting furnaces makes it possible to check the influence of mixing and of turbulence on the speed with which homogeneity is achieved. In order to estimate the extent of mixing, isotopes are introduced into molten metal and simultaneous readings are taken at frequent intervals at all the furnace openings. The metal is then poured into identical molds to form samples, and the degree of homogeneity can be ascertained. ## 13.6. Wear and corrosion rate monitoring The oldest industrial application of radioisotopes predates World War-2, when a patent was issued covering the use of radioactive isotopes for measuring friction wear. Loss of material from surfaces i.e. wears and corrosion of metallic, polymeric components is a common problem in industry and various technological areas. The loss of material is primarily due to mechanical, chemical and electrical phenomena. Measurement and quantification of wear and corrosion is often desired for quality control and assessment of reliability and durability of various mechanical parts and tools. The conventional techniques such as gravimetery, micrometery, profilography, replica method etc. are used for wear and corrosion measurements in industry but these techniques have poor accuracy, low sensitivity, cumbersome to use as the component need to be dismantled or removed for each measurement and cannot be applied in all situations due to non-accessibility. During seventies a radiotracer technique called Thin Layer Activation (TLA) technique was developed which overcomes the drawbacks of conventional techniques. The TLA technique is highly sensitive (0.1 ± 0.01 mm thickness wear or corrosion and 1 µg to 1 ng mass loss), can be used for online monitoring, accurate, easy to use, does not require elaborate safety measures, can be applied in case of commonly used materials (iron, cadmium, zinc, iridium, platinum, silver, tin, palladium, lead, tantalum), adaptable in various situations and can be used for localized measurements. The techniques is widely used in many countries to measure wear, corrosion in various industries such as automobile industry, power plants, process industry, oil and petroleum refineries and in many high technology areas. ## 13.7. Tracers in oil field Tracers have been applied to obtain information on interwell communication for residual oil estimation and enhancement of oil recovery. For the secondary recovery of oil, water is injected through the water injection well in to the reservoir at high pressure (~70 - 150 kg/cm²) to displace the residual oil. Radiotracers help in locating the direction of movement of the injected water and mean residence time from the injection well to the production well. The enhancement of oil production from the radiotracer investigation of the secondary processes is more than 15% of the residual oil. Economic benefit amounts to several million US dollars per year. Several injections were carried out in ONGC oil wells during last three decade. ## 13.8 Sealed source applications In sealed sources applications, the radioisotope remains permanently sealed in the source capsule and makes no contact with the plant or process material. Radiation from the source is directed at the item of interest and by analyzing the modified radiation pattern, either transmitted or in scattered beam, it is possible to draw conclusion about the internals of the process vessel. Due to their greater penetrating power, gamma and neutron sources are most useful. These applications can be broadly divided in 4 categories: * Industrial Radiography Testing * Gamma Scanning of Industrial Process Columns * Nucleonic Control Systems * Computed Tomography * Radiation processing of materials ### 13.8.1 Industrial Radiography Testing Radiography testing is an important member of Non Destructive Testing (NDT) family and is now well established in India. Present happy status of industrial radiography in India is largely due to the efforts of BARC and BRIT. A Radiography essentially is a shadow pattern when certain radiation penetrates an object and differentially absorbed on variation of thickness and density of material. The shadow graphs indicate the extent of inhomogenity, inherent flaws and created defects during working on the component being radiographed. Thus technique involve exposing the object with gamma or X rays and recording the intensity of transmitted radiation on a recording media such as film, phosphor image plate or-a flat panel detector. The image pattern in terms of optical density provides information about flaws / defects, voids and internal structure of the object. As per AERB data (June 2021) there are 3176.Radiography testing equipment registered with AERB, present about 647 licensees industries for radiography cameras, 740 industrial X-ray device, 676 entities carrying out commercial activity in the country and 1354 RSO are registered with AERB. Radiography testing forms the single largest application for the inspection of hardware such as pressure vessels and chemical reactors. Quality of welds on these systems is needed to be certified by radiography tests as a mandatory requirement. Vital information such as corrosion, plugging, cracking and other plant parameter can also be conveniently obtained with radiographic examination. ### 13.8.2 Training program on radiography testing The reliability and success of NDT applications greatly depends upon the technical skill and ability of their practitioners, as the data generated during these tests has to be analyzed and interpreted to arrive at a correlation with the soundness of the material under test. Realizing this, the industrially advanced countries have developed training and certification schemes for their NDT practitioners about 40 years back. In India, BARC has been playing a pivotal role. Certification courses on radiography testing are held regularly at different places in the country in collaboration with various centers for various levels for radiography personnel such as operators, site-in-charge /RSO (RT-2) and managers (RT-3). ### 13.8.3 Gamma scanning of industrial process columns In chemical petroleum and chemical industries, columns such as distillation, fractionation, stripping, and extraction play a vital role in chemical processing. Optimum working of these columns is very important, as it governs the production efficiency of the plant. Malfunctioning of columns causes huge production and financial losses, in addition it may lead to fire hazard and atmospheric pollution. Gamma scanning technique is very effective for troubleshooting and predictive maintenance of process columns. Scanning results in conjuction with simulation studies can be used to diagnose most of the column problems and improve design of the column. So far Isotope Applications Division of BARC and BRIT have carried out gamma scanning of 300 columns for troubleshooting and signature scan in different petroleum refineries in India. Gamma scanning can provide following information about the column. * Presence or absence of trays and other internals. * Identification and location of extent of flooding * Liquid level on trays and liquid distribution in packed bed columns * Location and severity of entertainment. * Presence of weeping and foaming * Integrity of mist eliminators. * Extent of vapor/liquid maldistribution in packed beds * Presence of liquid in reflux drums..... ### Other applications * Measurement of gas/ liquid holdup in process column. * Thickness measurement. * Detection and measurement of corrosion. * Density measurement. ### 13.8.4 Nucleonic control systems During plant operation, occasions frequently arise in which the operator requires information about the level of material inside a plant vessel. Determination of fluid level in container is frequently required in petroleum industry. Sealed source radioisotopes are used in a variety of equipment for different applications. A range of level gauges, alarms and density gauges are used worldwide in oil refineries, chemical plants, oil platforms and terminals, in mining and mineral extraction industries. Indian industry has been using nucleonic gauges for over three decades. There are about 5,000 nucleonic control systems are in operation in India today. ### Nucleonic control systems used in industries * **(1) Nucleonic level gauge:** These are widely used to indicate whether a bin is over or under filled in places where adverse conditions of high temperature, high pressure and handling of highly corrosive substances are encountered. They include cement, steel, coal, thermal power and chemical industries. ECIL* has supplied over 1600 gauges to various industries in India. * **(2) Radiometric density gauge:** These are generally used to measure the densities of slurries flowing in pipes employing the gamma ray transmission technique. They are widely used in various mineral, metal, chemical and sugar industries. ECIL has supplied 60 such gauges in India. * **(3) Radiometric belt weigher:** This is a non-contact weigh scale which continuously measures the rate of conveyor loading and total weight of the material transported. Nucleonic scales find application where materials of corrosive abrasive or toxic nature are weighed in fertilizer, steel, cement and coal sectors. * **(4) Thickness gauge:** It is used for non-contact, on line measurement of thickness of sheets and strips in steel, plastic, paper and textile rolling mills. They normally employ nuclear radiation absorption technique for measurement of thickness and basis weight. It consists of a measuring head in the form of a 'C' or '0' frame, an electronic processing unit, and a suitable front end drive mechanism, normally apneumatic one. The measuring chamber is normally fixed in the upper arm and the source holder is mounted in the lower arm. The C frame or o frame can be taken to either on line or offline by suitable drive mechanism as and when required. There is a cooling jacket and a blower which prevents collection of dust. Normally Am-241 or Cs-137 are used for steel applications and Sr-90, Kr-85 or Pm-147 for plastic, paper and textile applications. ECIL has supplied around 40 gauges to steel mills and plastic industries. * **(5) Nucleonic moisture gauge:** Moisture gauges are used for measurement of moisture in bulk materials like coke, iron ore in steel industry, sinter mix and paper industry. The principle of moderation of fast neutrons by elastic collision with hydrogen atoms in the moisture of the medium is utilized in the measurements, when the energy of the neutron is reduced to a point when they are in thermal equilibrium with the medium, they are called thermal neutrons. BF3 proportional counters is used for their detection. The detector output is proportional to the moisture content in the medium. Source used is Am-241-Be. * **(6) On-line coal ash monitor:** The operating principle is based on the concept that when low energy gamma radiation passes through coal, the absorption depends on the average atomic no. (Z). The higher the atomic no. of the sample the greater is the absorption. The variation of absorption with the atomic no. can be directly to the ash determination since the ash forming elements (Al, Si, Cu & Fe) are of higher atomic no. than those of coal (C, H) elements. The source and detector are in a 'C' frame. These systems have been supplied to Bharat Coking Coal Ltd. * **(7) Gamma ray interlock system for coke oven batteries:** They are used for affecting an interlock in the coke discharge equipment between the coke guide car & coke pusher car. The source is mounted on the coke guide car while the radiation detector is on the pusher car. Only when the source and detector are in line the positional relationship between the coke guide car and the pusher is established and safe operation of pushing the coke is activated. ### 13.8.5. Computed tomography Computed tomography (CT) is a process of collection of transmission data through an object and subsequent mathematical reconstruction of an image. BARC have demonstrated computed tomography system (CITIS) using 7 Ci of cs137 source in 1990. This unit was capable of scanning specimens of small diameters (up to 100 mm) and of varying densities. It has wider applications in the field of nuclear, space and allied fields. A modified industrial CT system with array of detectors was developed subsequently. BARC, Mumbai have also developed x ray based Computerized tomography system. The system consist of x ray 40-450 keV (focal spot 0.4 mm x 1mm) with flat panel detector and a multi-axes precision manipulator for accurately positioning source, detector and specimen. It is capable of scanning specimen upto 400 mm in various orientations. ### 23.8.6. Radiation processing of materials Radiation processing is intentional exposure of materials by high energy ionizing radiation emanating from Co-60, Cs-137 and Electron beam (2 to 5 MeV). Some of the commonly carried out applications are cross-linking and degradation of polymers for quality upgradation, other applications are also listed below: ## Table: Cross-linking and degrading of polymers | Cross-linking type | Degrading type | |---|---| | Not soluble only swells | Remains soluble or solubility kinetics increases | | Cross-linked polymer is single monolith | Molecular weight decreases | | Tensile strength & wear resistance increases | Tensile strength & wear resistance decreases | | Gas permeability decreases | Gas permeability is either unaltered or increases | | No significant change in crystallinity | In some cases (e.g Teflon) crystallinity increases | ### 13.8.7. Food irradiation Irradiation of food has the same benefits as when it is heated, refrigerated, frozen or treated with chemicals (Ethylene oxide/Ethylene dibromide), but without changing the temperature or leaving residues. Thus has proven to be most effective of the alternatives available for food preservation. It has been established that food irradiation does not induce any toxicity neither effects the nutritional value or flavor of food items. Food irradiation using ionizing radiation: * Reduces number of pathogens, parasites & insects (phytosanitary treatment) * Extends shelf life * Delays maturation & sprouting ### Coloration in diamond These applications are in great demand & there are 24 gamma irradiators and 18 EB machine are in operation for various radiation processing application on commercial basis. These numbers are expected to increase in future. ## 13.9 Conclusions From the forgoing it is evident that radiotracer and sealed source techniques are well established and widely used techniques for troubleshooting and process optimization in industry. In most the situations they do not have any equivalent and competing alternatives. High economic benefits are achieved from the application of these techniques and Indian industries got benefitted. ## References 1. J.S. Charlton,, J.A. Heslop and, P. Johnson., "Radioisotope techniquesfor the investigation of process problems in the chemical industry ", Industrial Applications of Radioisotopes and Radiation Technology (proc. Int. Coni, Grenoble, France) IAEA, Vienna, Austria, pp. 217 (1982). 2. V.K. Sharma, H.J. Pant, H.B. Jagadesh, B.K. Girish and Gursharan Singh, Radiotracer investigation for bed load movement at New Mangalore Port, Mangalore, India, Indian Journal of marine Science Vol. 39(1), March 2010, 3. H.J. Pant, V.K. Sharma, Sunil Goswami, J.S. Samanthray and Gursharan Singh "Development and application of radiotracer technique for online detection in high pressure heat exchangers", BARC Newsletter, Issue no.330(Jan-Feb 2013) pp 8-15. 4. H.J. Pant, V.K. Sharma, M. Vidya Kamudu, S.G. Prakash, S. Krishanamoorthy, G. Anandam, P. Seshubabu Rao, N.V.S. Ramani, Gursharan Singh and R.R. Sonde, Investigation of flow behavior of coal particles in a pilot-scale fluidizeded gasifier (FBG) using radiotracer technique, Applied Radiation and Isotopes 67(2009)1609-1615, 5. H.J.Pant, V.K. Sharma, Gursharan Singh, Rohit Kulkarni, A.B. Pandit, M. Kumar, Ph.Berne, Radiotracer study in a bubble column reactor (Vis breaker), Conference on tracer and tracing methods held on June 22-24, 2004 at Ciechocinek, Poland.