Oil Storage facilities (terminals) are usually designed with a pressure rating lower than the rating of the pipeline transporting the fluids. During abnormal operations, terminal piping can be subject to unexpected transient pressure surges that can exceed the allowed values. Mitigations are required a common one is installing a relief system. When a relief valve is installed, it is connected to a tank and the location of this relief tank is critical for the proper operation of the relief system and the overall mitigation of pressure surges. Relief design needs to take into account the length and layout of the piping. Facilities in the northern hemisphere contain pipes installed above ground and prone to experiencing cold temperatures during winter months. If the fluid is stagnant in these pipes, the cold weather increases the viscosity of the fluid. If the relief valve activates, the fluid that has been stagnant in the pipe needs to be pushed out of the pipe and into the tank. This requires a high pressure from the system and is directly affected by the distance of the pipe and the properties of the stagnant fluid. This paper will show how transient pressures change for length of pipe and for varied viscosities of the stagnant fluid. With these findings, engineers can improve their understanding of the effects of temperature and length on surge pressures and they can design safer systems for liquid transportation and storage.

Oil Storage facilities (terminals) that receive fluids from pipelines or inject fluid into them, are usually designed with a lower pressure rating than the actual pipeline between these facilities. This is mostly due to the fact that the pressure expected in the terminal is much lower than the pressure required to transport the oil. However, these terminals are still subject to pressure surges caused by abnormal transient events during normal operations. In cases where the surge pressures exceed the allowed operating pressure of the equipment, a relief system can be installed to mitigate these surges to acceptable levels. When constructing a new terminal or altering an existing one, the hydraulic calculations of these terminals are generally based on design values of the project, such as maximum and minimum flow rates. The hydraulic studies and simulations that are normally done by companies are based on steady state conditions, however, to design intrinsically safe facilities, the system’s entire operating envelope should be considered at the design stage of the project. Once transient analysis results show the need to install a pressure relief device, the proper location of this equipment is critical for the effectiveness of the surge relief system to mitigate overpressures properly. The effect of flow rate, piping configuration, and initial pressure profiles were simulated and compared to determine their impact on pressure surges and on the critical devices along the flow path. Secondly, simulations were done with the relief system installed in different locations along the terminal pipe and the resulting changes in maximum pressure surges. The objective of this paper is to show the importance of a detailed transient analysis based not only on design parameters but also on operational scenarios to mitigate surge overpressures in a more cohesive manner. The secondary objective of the paper is to discuss key parameters that need to be considered for selecting the location of the surge relief valve to ensure critical devices are safe during the upset conditions. The analysis presented in this paper is applicable across a broad configuration of oil facilities.

Pipelines transporting different grades of crude oil or products usually operate with fixed setpoints for pressure limit switches and relief valves. These setpoints are calculated for a worst case condition as maximum flow rate combined with a sequence of batches of high viscosity ratio, etc. Under standard operating conditions, this worst case condition never occurs, so the setpoints restrict operating flexibility. With a transient simulation model it is possible to calculate these setpoints for actual hydraulic conditions on-line. Special attention has been paid to fail-safe operation of this on-line model and setpoint calculation. Our approach avoids all the problems linked to software in fail-safe applications and may be used for other applications of on-line simulation too. This concept has been successfully applied to a pipeline system in Austria, the AWP-Pipeline. With the new technology, substantial savings in energy costs (1–2 pump stations out of 11) as well as increased maximum throughput are possible now.

When using nitrogen loaded surge relief valves it is believed that the relief valve is in control of the upper pressure limit of the pipeline. In reality, it is the nitrogen system together with the valve in a master and slave relationship that sets the upper threshold. The negative effects of changing temperature on the stability of a nitrogen loaded relief valve’s set point is well known but poorly understood. There have been many attempts to minimize this effect. Burying the plenum and using the soil as an insulator has proven to be ineffective. Manual adjustments are not cost effective. Regulators offer inconsistent performance and are often misapplied. Evolving technology now allows for this process to be automated. Set points can be held with remarkable accuracy and plenums no longer need to be buried.

Terminals are an integral part of a pipeline system. Typically, petroleum products are transported from an initiating terminal to various delivery terminals along the pipeline. Operation safety is paramount in transporting petroleum products in the pipeline industry. Safety can affect the performance and economics of a pipeline system. While effective operation safety requires well-trained operators, operational procedures, and compliance with regulatory requirements, the best way to ensure operation safety is to implement safety systems during the design stage of the pipeline system. A pressure relief system is an important component of an engineered safety system. This system is intended to prevent catastrophic failure of the transport system due to overpressure conditions that can occur under abnormal operating conditions. This paper discusses pressure surge relief as it applies to the design of pipeline terminals. Different pressure surge relief devices such as pressure relief valves and pressure surge vessels are considered and their advantages and disadvantages are discussed. The effects of transport rates, piping configurations, and other equipment operation, such as pumps and valves, on pressure surge relief system, are evaluated. One of the primary objectives of this paper is to discuss pressure surge events, device simulations, and key parameters to consider when selecting a pressure surge relief system for a terminal design to ensure that the piping system and hydraulic components remain safe during abnormal operating conditions. Although the analyses presented in this paper are applicable across a broad range of operating conditions and equipment and devices in terminal system designs, it is not possible to cover all situations. As such, sound engineering principles and engineering judgment should always be applied in an engineering design.

The majority of oil and refined-product pipelines in Brazil have their protection system designs based on spring-type pressure relief valves. Thus, the proper design and operation of these valves is essential to ensure the safety of transport pipelines and loading/unloading terminals during any abnormal operation conditions that generate a surge pressure. In simple terms, these valves have a disk which is pressed by a spring against the inlet nozzle of the valve. When the pressure rises, the force generated on the surface of the disc increases and, depending on the pressure relief valve set point, the force due to pressure overcomes the force exerted by the spring, causing the disk to rise and discharge the fluid through the outlet nozzle to the relief line, reducing the pressure level within the pipeline. Despite its importance, most commercial applications do not present a specific model to simulate the transient behavior of pressure relief valves. This paper presents an experimental study aimed at determining the dynamic behavior of a commercial spring-type relief valve. The valve was installed in a pipe loop instrumented with pressure and flow transducers. The transient motion of the valve disc was measured with a fast-response displacement transducer. The transient in the flow loop was generated by the controlled closing of a block valve positioned downstream of the relief valve. The recorded transient data for disc position, upstream and downstream pressures, and discharge flow rates were used to compute the discharge coefficient as a function of opening fraction and the opening fraction as a function of time. Simulation models based on a spring-mass damped system were developed and implemented in a PID-actuator-control valve system. The systems were implemented in a commercial pipeline simulation program modeling the experimental loop employed in the tests. The numerical and experimental data of the block valve closure transient were compared displaying good agreement. Simulations results employing a generic relief valve model frequently used in simulations were also obtained revealing problems associated with this approach.

The demand of natural gas in the Brazilian energy market is increasing very fast over the few years and it was necessary to enhance the operational performance and safety of the gas distribution. The perfect operation of the natural gas citygate stations is essential to guarantee the delivery of natural gas for the end users like local distribution companies, thermoelectric power plants and large industrial customers within the contracted marketing conditions. These stations receive natural gas directly from high pressure pipelines and reduce the pressure using regulation valves that provoke a temperature reduction due the Joule-Thompson (JT) behavior, typical of natural gases. This temperature loss is compensated by forcing part of the gas flow through water/glycol bath heaters that use natural gas as fuel in the heating process. Usually the downstream gas temperature condition is controlled above a minimal set point while modifying the three-way valve position that regulates hot and cold streams flows. A numerical tool has been developed to simulate the dynamic process inside the natural gas citygate station, and proved to be a reliable tool to analyze the transient performance of the main equipments (filter, three way valve, heater, JT valve, relief valves) when submitted to abnormal conditions or changes in capacity. The methodology developed is able to handle a variety of citygate design.

Surge will be induced in oil transfer pipeline, due to the changes of transportation materials, operating parameters or pump station equipments. However, the surge induced by Shut-off fast closing valve could be more destructive, for the duration of valve closure time is short, and then the maximum pressure of the surge is much higher, so it’s necessary to control the surge. Based on the characteristic method, this paper establishes a numerical calculation of the accidental Shut-off the terminal fast closing valve at an product pipeline, and simulates the corresponding transient process of pipeline pressure. Upon the upper result, a further research, which combines the boundary condition of surge relief system, is carried out, in order to get the optimal surge control measures through the relief system.