Introduction
In a large industrial plant located in the southern Netherlands, a complex pipeline network traverses multiple sections separated by two major highways. This network, known as the water network, incorporates both steel pipes and glass-reinforced epoxy (GRE) pipes. Over time, sections of the steel piping have been progressively replaced with GRE pipes. This ongoing replacement process aims to enhance the network’s performance and durability.
One notable component of this network is a DN500 GRE pipe that crosses under one of the highways via a tunnel. This pipe replaces an older steel pipe and is supported above ground within the tunnel. The water network serves several clients and connects various hydrants, some of which deliver water at rates up to 500 m³/hr. Routine tests are conducted to assess the network’s firefighting capabilities, during which a fire truck may be connected to a hydrant. Rapid closure of the valve on the truck—within one second—can create significant pressure waves within the system, generating unbalanced loads on the pipes.
From an integrity standpoint, it is crucial that the entire water network, particularly the new DN500 GRE pipe under the A76 highway, can withstand these pressure peaks and unbalanced loads resulting from such rapid closures.
Analysis
To assess the impact of pressure amplitude and axial load on the GRE section within the tunnel, a surge analysis was performed. This analysis involved creating a comprehensive model capable of capturing the effects of pressure waves traveling through the system and their reflections. The model included pumps and hydrants to ensure accurate simulations.
The surge analysis began with simulating the system’s steady-state conditions based on reported flow rates at various points. Various scenarios were then analyzed, specifically focusing on the opening and closing of individual hydrants. This approach reflects the expected operational conditions during firefighting tests.
The primary objective was to determine if the new GRE pipe could withstand the pressure peaks associated with rapid hydrant closures.
Results
The surge analysis revealed that the highest pressure peaks occur when pressure waves traveling in different directions along a ring converge at a single point. With a conservative closure time history applied in the simulation, the maximum pressure in the system was found to be three times the steady-state pressure.
The maximum axial load on the DN500 GRE pipe was calculated, incorporating a Dynamic Load Factor to account for dynamic effects. This calculation was communicated to the client to ensure proper sizing of the axial stop. Given the relatively low pressure compared to the pipe’s strength, both the steel and GRE pipes within the system are well-equipped to handle the pressure peaks effectively.
The surge analysis confirms that the new DN500 GRE pipe, along with the existing steel pipes, can withstand the pressure peaks and unbalanced loads generated by rapid hydrant closures. This ensures the integrity and reliability of the water network under high-stress conditions, maintaining its effectiveness in supplying water for various needs, including firefighting.
