『『Original Article No. 1 by HaiChuan Translation Team』Analysis of the Thermal Effects of Chemicals in Long-Distance Pipelines

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1.jpg English title: Thermal Profiling Of Long Distance Pipelines Carrying Chemicals (Gas And Liquid) Original link: https://www.cheresources.com/inv ... als-gas-and-liquid/ Original author: ankur2061 Translator ID: @Shuangmu_DTQO Proofreader ID: @Jacob(Jingwei)82 Final reviewer ID: @henjuese When conducting studies on pipeline operations, an important task is to analyze the thermal effects of pipelines under various operating conditions and environmental scenarios. However, most of the young engineers tasked with this work have little understanding of the actual work involved in thermal analysis. In fact, many young engineers are not even aware that thermal analysis of pipelines is necessary to understand the potential problems that may arise during the transport of fluid media through them. First, let me list the problems related to thermal effects in the following long-distance pipelines: 1. For gas pipelines, the frictional pressure drop of the gas within the pipeline can cause Joule-Thomson cooling, which is an isenthalpic process. When the length of the pipeline exceeds a certain value, the temperature of the gas flowing within it drops below its hydrate formation temperature, which causes ice crystals to form inside the pipeline. This ultimately leads to a disruption in transportation as part or all of the pipeline becomes blocked. In the worst case, it could cause pipes to burst, resulting in property damage and casualties. High-pressure and low-temperature pipelines, such as those under the sea floor, facilitate the formation of hydrates. Thermal analysis is essential to determine whether this will occur and what mitigation measures are needed. 2. During emergency situations or routine maintenance operations, pressure reduction of gas pipelines is another issue that needs to be considered in thermal analysis studies under reduced-pressure conditions. Adiabatic depressurization results in an extremely low temperature downstream of the pressure reduction source and the pressure reduction device (valve or orifice plate). Plain carbon steel may suffer catastrophic brittle fracture at very low temperatures, posing a threat to pipeline safety. Commercial carbon steel grades commonly used in steel pipe manufacturing, such as ASTM A 106 and ASTM A 53, are not suitable for temperatures below -29°C. During the processing, pipes need to be classified based on the material’s \"minimum design metal temperature,\" abbreviated as MDMT. ASTM A333 Gr.1 and Gr.6 in carbon steel are suitable for low temperatures of -45°C and below, and impact testing at such temperatures is required. Thermal analysis during the depressurization process can provide an estimated minimum temperature for the pipeline, thereby defining the MDMT of the pipe material. For example, if differential scanning calorimetry indicates that the temperature in the pipeline could be below -29°C, material experts are most likely to recommend the use of \"low-temperature carbon steel\", abbreviated as LTCS, and to conduct a \"Charpy notched impact test\" to determine the brittleness of the material at low temperatures. If differential thermal analysis shows that the pipe temperature is below -46°C or above -80°C, further reducing the MDMT of the pipe material, material experts may upgrade the material to duplex stainless steel (DSS). Whether during normal operation or due to freezing temperatures in the pipes that occur during maintenance, austenitic stainless steel should be used in such situations. Similarly, this temperature can be determined through thermal analysis of the system. 3. Pipelines for transporting crude oil, especially those carrying oil with high viscosity and high asphaltenes content, require thermal analysis to determine whether the pipeline temperature will drop below the pour point. Pipeline blockages caused by temperatures below the pour point can lead to production interruptions, costly cleaning efforts, demolition work, and significant financial losses. After determining the minimum temperature of the pipeline using thermal analysis, corrective measures can be taken to prevent the aforementioned situation from occurring. 4. The pipeline transportation of liquefied petroleum gas (propane and mixtures of propane and butane) is another area that requires special attention in pipeline thermodynamics research. LPG pipelines laid above ground in environments with high temperatures, or those partially laid above ground, require detailed thermal studies to ensure that the LPG does not vaporize within the pipelines at operating pressure; vaporization could otherwise lead to gas blockages and two-phase flow inside the pipelines. At the destination end of the pipeline, if there are flow or pressure control valves, as the temperature of the LPG rises along the pipeline, partial vaporization of the LPG at the inlet of the control valve results in a two-phase flow. From the perspective of the valve’s integrity, such a two-phase flow is very harmful to the proper operation of the control valve. In short, two-phase flow is not allowed in LPG pipelines, and thermal analysis can be used to determine at the source whether such a phenomenon will occur. However, when performing thermal analysis on pipes laid above ground and exposed to the atmospheric environment, the actual environmental conditions must be entered as input. To handle this properly, a good designer will take into account the average high and low values of ambient temperature, as well as the average high or low wind speeds over a certain period (such as those in summer/winter or the annual average), rather than relying on extreme temperatures that occur once in a century or wind speeds that are unlikely to occur again. Roughly speaking, environmental temperatures and wind speeds under extreme weather conditions should not be used for the thermal analysis of pipes exposed to the atmosphere. Adopting such extreme environmental conditions incurs huge economic costs and is unreasonable for the normal operation of pipelines. In fact, when environmental conditions are abnormal, an order is given to stop or reduce the operation of the pipeline. 5. There are many pipeline and process simulation software tools available for thermal analysis of pipelines. Software specialized for pipeline simulation, such as PIPESIM, PIPEPHASE, PIPELINE STUDIO, AFT, OLGA, etc., are the best choices for conducting thermal studies of pipelines. However, general process simulation software such as Aspen HYSYS, UniSim, and Aspen Plus can also perform pipe heat analysis, although these software tools have certain limitations. Aspen HYSYS has a very good \"depression\" tool module that can provide the thermal profile of any device or pipe under depression. The key to using such simulation software is for the user to have a thorough understanding of what is required for thermal analysis and to enter the correct values, including checking the accuracy of the default values set by the software for a particular study and, if necessary, modifying these defaults to suit the specific case under consideration. In short, such software should be used from the perspective of a process or chemical engineer, rather than just as a data entry clerk.