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Types of Corrosion in the Offshore Environment
Published in Karan Sotoodeh, Coating Application for Piping, Valves and Actuators in Offshore Oil and Gas Industry, 2023
In the seawater or immersion zone, which is always underwater, the corrosion rate is close to that of the atmospheric zone and lower than that of the splash zone. The corrosion rate is typically 100–200 μm (4–8 mils) or (0.1–0.2 mm) per year. Seawater is highly corrosive to mild steel, as it contains salt (e.g., 3.4%) and chloride. The reason why the corrosion rate is lower in seawater compared to the splash zone could be due to the former’s lower concentration of oxygen. The corrosivity of seawater depends on different parameters, such as chloride or salinity level, oxygen concentration, temperature, the presence of biological organism, etc. In fact, increasing the oxygen, chloride level and temperature increases the seawater corrosion rate. Coating protection in the seawater or immersion zone can be combined with cathodic protection. The other important factor that should be taken into account in seawater is fouling. Fouling refers to the growth or formation of deposits or microorganisms such as bacteria on the surface of subsea structures and components. Fouling can be categorized into four types: (1) crystallization fouling due to the deposition of calcium carbonate or other types of salts, (2) corrosion fouling related to the oxidation or corrosion product, (3) biological fouling due to bacteria or even macroorganisms such as mussels and (4) particulate fouling due to different types of silt, mud and sand in the seawater.
Conducting Polymers
Published in Ram K. Gupta, Conducting Polymers, 2022
N. Raghavendra Naveen, Girirajasekhar Dornadula, Pamayyagari Kalpana, Lakshmi Narasimha Gunturu
Fouling is an intricate and undesirable process where reversible/irreversible adhesion of the unwanted stuff on surfaces occurs. This phenomenon alters dynamically with time. It is precipitated by the deposition of various organic, inorganic, biological, and particulate matters. The foulant may differ extensively in composition, deposition type, and physicochemical properties. Based on the nature of the foulants and their occurrence in various sectors, literature shows various definitions of fouling. Industrially, regarding heat exchangers and membranes, fouling may be defined as the accumulation of unwanted material like scale, suspended solids, insoluble salts, and even algae on the internal surfaces. In marine systems, fouling is regarded as the attachment of micro biofilms or macro bio-species to the hull, engine, or submerged parts of the ship. Whereas in the medical sector, fouling is described as the formation of biofilms by microorganisms (bacteria, yeast) on the living tissues and medical devices. Fouling may also rely on the surface characteristics such as morphology, micro texture, wettability, and surface energy. This phenomenon is ubiquitous and imposes significant problems relating to commercial, environmental, and health issues [1, 2].
Nanofluids: Current Applications and Future Challenges
Published in Rakesh K. Sindhu, Mansi Chitkara, Inderjeet Singh Sandhu, Nanotechnology, 2021
Balwinder Kaur, Subhash Chand, Balraj Saini
Along with merits, there are still some demerits of nanofluids: For the synthesis of nanofluids, highly purified chemicals and sophisticated laboratories are required. As a result, this requirement increases the overall cost of nanofluids.Stability of nanofluids is one of the challenges during their synthesis. Despite various methods for increasing stability, such as addition of surfactants and surface modifications, the stability of nanofluids is still not long lasting due to their high reactive surface. After some time, they start to coagulate and settle down under the influence the gravity.Nanoparticles deposit on the heat transfer surfaces of various devices in which the nanofluids are used. This deposition of nanofluids is called fouling effect. Fouling reduces the mechanical and thermal efficiency of heat exchangers, hinder fluid flow, and increase pressure drop and corrosion.The high viscosity and density of nanofluids lead to enhancement in pressure drop. Many studies have shown that nanofluids show significant pressure drop as compared to the base fluid.
Experimental Study of Antifouling Effect of Ultrasonic/Magnetic Compound Treatment in Heat Transfer
Published in Heat Transfer Engineering, 2023
Genyuan Liu, Yongchang Chen, Tengfei Hou, Chongfang Ma
Fouling usually exists in heat exchangers of industrial processes, which can lead to both the degradation in heat transfer performance and the increase of flow resistance, thus resulting in increasing of energy consumption in the process. The economic loss related to the fouling accounts for about 0.25% of the GNP of industrialized countries [1]. Previously the chemical method commonly used in industry for water treatment displayed disadvantages of vast consumption of chemical agents and of second pollution again to the environment [2]. Compared with the chemical methods, the physical method of water treatment, for example, surface modification, thermal shock, ultrasonic, and magnetic techniques [3–7] presented remarkable advantages in energy saving and environmental protection by effectively constraining the scaling on heat transfer surface.
Multi-Objective Optimization Tool of Shell-and-Tube Heat Exchangers Using a Modified Teaching-Learning-Based Optimization Algorithm and a Compact Bell-Delaware Method
Published in Heat Transfer Engineering, 2022
Thomas McCaughtry, Sung in Kim
Fouling is the accumulation of undesirable substances on a surface which increases the thermal resistance of the heat transfer surface, thus reducing the heat transfer rate between the fluids in the heat exchanger [8, 9]. Fouling of heat transfer surfaces in heat exchangers is very costly due to the additional energy required to complete the same amount of heat transfer in a fouled heat exchanger [10]. STHE at risk of fouling due to the working fluids must be designed with additional surface area, ensuring that sufficient heat transfer can still take place when fouling occurs, or its heat transfer surfaces either shell-side or tube-side must be cleaned through chemical or mechanical means. However, there are significant disadvantages with both solutions to fouling, such as; surface area overdesign and operation must stop for a period of time, respectively. Fouling factor models can be static values or dynamic models. Static fouling factors are readily available for various fluids and commonly used in heat exchanger design, but will not provide any indication of the growth rate and the effect of operating conditions. Dynamic fouling models could substantially improve the accuracy under a variety of operating conditions. However, the requirements of various additional case-dependent information and iterative procedures make them challenging to implement [9].
The kinetics and mechanisms of fouling in crude oil heat transfer
Published in Heat Transfer Engineering, 2020
Elisabeth Rammerstorfer, Thomas Karner, Matthäus Siebenhofer
Atmospheric crude oil distillation is the first step in oil refining. The whole energy input for the distillation process is provided by the crude oil, which is heated in the crude preheat train and a downstream furnace. The crude preheat train usually consists of a set of heat exchangers which transfer energy from product side streams and pumparounds of the crude oil distillation column to the feed. Heat exchangers in the crude preheat train tend to become fouled. Fouling is the unwanted buildup of material on the heat exchange surface, which reduces thermal efficiency. Fouling is found in the whole preheat train but is typically severest for heat exchangers where temperatures are high, and velocities are low. The crude oil is usually heated up to about 200 °C in the crude oil heat exchangers. Crude oil fouling also affects furnaces, where temperatures up to 480 °C are reached, and atmospheric distillation columns. Shell-and-tube type heat exchangers are commonly used in the preheat train, with the crude oil usually being processed on the tube side. Fouling can affect the tube side and the shell side. Coletti and Hewitt [1] describe fouling on the shell side in low velocity zones in the vicinity of baffles as well as on the outsides of the tubes.