The transmission of natural resources such as water, natural gas, and petroleum is impossible without a network of interconnected pipes. In nearly every country, fluid transportation is done and manage through pipelines. Heavy-duty pipes are used to transport fluids such as water and petrol, while plumbing pipes are used to carry sewage and wastewater.
Pipeline transport is a name given to long-distance transport of liquid or gas through a network of pipes from the plant to the consumption area. The United States has nearly 65% of the world’s pipeline transport service, and there are further pipelines that are either under construction or planned to be installed. The liquids and gases are stable substances and can easily be transported through the pipeline network, but certain calculations and considerations are to be examined to prevent any losses or inconvenient situations.
Pipelines are built and connected to deliver crude and refined fluids such as oil, natural gas, and biofuel over long distances and water, steam, and sewage over short distances. Fluid dynamics is one of the core aspects of the design and framework of the pipelines, and it describes the flow of the fluids or gas to be transmitted. Fluid dynamics involve the study and calculation of various properties of the fluids, which include pressure, temperature, density, and flow velocity. One of the key categories of fluid dynamics is pipe network analysis, which is the examination of the fluid or gas flowing across a hydraulic network. The main emphasis of the pipe network analysis is to know about the flow rates and pressure drops that can impact the flow of fluids through the pipelines.
In a pipeline system, another cause of concern is surge analysis, also known as hydraulic surge, water hammer, and fluid hammer. Surge analysis is the study of pressure changes in transporting a fluid that is caused by sudden changes in flow velocity. The change can be caused due to various reasons such as
- Sudden opening or closing of the valve
- The sudden or abrupt start and stop of the pump either due to power failure or load shedding
- Closure of the check valves
- Sudden opening or closing of a single or multiple pumps
- Air pockets in the pipe system usually at the pump start
- Pipeline filling
- The sudden release of air
Surge analysis is also called pressure surges and can occur in both partly filled pipes and open channels. Surge analysis of pipelines is a vital aspect of ensuring the proper transmission of liquid or gas across the pipeline network. The significant high pressure and velocity changes can lead to
- Bursting of pipes
- Damage to the pipeline components and fittings
- Breakdown of the pumping system
- Defects in the valves and other components of the pipes
The surge analysis is done to prevent the negative flow of the fluid or gas that can make a high-pressure gradient and damage both the valve and the pipe. The maximum pressure surge occurs when all the pumps in operation at the station abruptly stop due to power failure. The resulting change of velocity and pressure is not limited to the point of error and will continue upstream and downstream at pressure wave propagation velocity. The five basic elements of surge analysis are
- Pressure surge: A sudden pressure wave caused due to considerable change in flow velocity
- Acoustic velocity: The speed at which the pressure wave travels through the fluid
- Pipeline period: The time it takes for the pressure wave to travel the length of the pipeline and come back
- Joukowsky equation: It is used to calculate the maximum surge pressure due to sudden valve closure
- Pressure head: The height of the liquid column that reciprocates to particular pressure exerted on the liquid column.
Traditionally the pipeline analysis was done and calculated by hand, but now due to technological advancements, there are sophisticated and fast software that can efficiently determine the pressure surges. The pressure surges are mostly of two types that are transient surge waves, and rising pressure. Both types are not good for pipeline transport and can easily cause damage to the pipeline equipment, bursting issues, and even personal injury. Many times the surging goes unnoticed, but the pipes and fittings take all the stress, and eventually, the cumulative stress can cause pipeline failure.
The surges are always caused by the sudden velocity and pressure changes within the network of the pipes. The pumps and different valves and often the cause of the pressure surge, and the equipment and fittings can be modified to prevent or minimize the damage. The constant high and low-pressure changes result in significant operational issues, and the engineers have to identify and resolve the problem. Many times the design of the pipeline system is outdated, and the recent alterations have not improved the flow and efficiency of fluid transmission. To avoid pressure surges, there are various methods and equipment that are used. The prevention of pressure surges can be done through changes in system design, active and passive protection.
- System Design Changes
- Use of pipes that have a higher pressure rating
- Redirecting of pipelines to avoid high and low points
- Changing the piping material to alternate the speed of the fluid
- Increasing the diameter of the pipe to minimize the velocity changes
- Fitting bypass lines
- Adding a flywheel to increase the pump inertia
- Active Protection
The active protection stage reduces surge impact by introducing devices and equipment that includes variable speed pumps, soft opening and closing valves, and soft starters.
- Passive Protection
The passive protection is also done by certain equipment that is easily available in the market and does not need additional power. The equipment includes
- Surge vessels, and shafts
- Air valves
- Pressure relief valves
- Intermediate check valves
- Surge anticipation valves
- Vacuum breakers
The surge protection equipment must be checked and maintained regularly to ensure proper functionality. Regular maintenance not only reduces the pressure surges but also increases the life expectancy of the pipeline network and systems.