# Analyzing the Key Factors Affecting Transient Pressures Occurring During Pipe Filling Using a Numerical Approach

Document Type : Research Article

Authors

1 1- M.Sc. Student, Babol Noshirvani University of Technology

2 Faculty of Civil Engineering, Babol Noshirvani University of Technology, Babol, Iran

3 Hydraulic Specialist &amp;amp; President, Innovative Hydraulic Group Inc.

Abstract

Introduction:
It is common in practice to partially drain the pipelines for inspection and repair. If not properly controlled, refilling of the pipeline may expose them to significant transient pressures which can compromise the integrity of the pipeline and associated joints. Implementing a safe filling protocol requires that the location and size of hydro-mechanical equipment are calculated. Such information can be obtained through analysis of different filling scenarios, but unfortunately, such a detailed analysis is usually ignored in the design stage, not surprising why pipe incidents usually happen during operation.
With the aid of numerical explorations, this paper aims to shed some light on the key factors affecting the filling hydraulics. To this end, a numerical model is proposed to calculate the filling hydraulics. The model uses the method of characteristics to solve the water hammer equations and employs the Discrete Gas Cavity Model (DGCM) to treat column separation. The model is validated with the experiments. Extensive numerical explorations reveal that lack of a safe filling protocol as well as lack or inadequate sizing of the required hydro-mechanical equipment can result in water hammer pressures. The results also show that without a properly sized bypass and air valve, it is impossible to control transient pressures during filling.
Methodology:
Extensive numerical explorations are conducted with a hypothetical water pipeline to analyze the key factors affecting the transient pressures which occur during filling. The pipeline has an undulating profile with the diameter, length, and acoustic wave speed of 0.9 m, 15900 m, and 1000 m/s respectively. The pipeline is supplied by a reservoir with a constant water depth of 5 m which is located at the upstream end of the pipeline. It is assumed that the last 1600 m of the pipelined is drained and an air valve at the end of the pipeline allows air management during the filling. A bypass line located at the upstream end of the empty zone is also equipped with a flow control valve to control the filling flow rates. Several numerical solutions are conducted with the different sizes of the air valve, bypass line and different opening times of the flow control valve, and the maximum and minimum pressure heads induced during filling are recorded.
Results and Discussion:
Analyzing the results obtained from the numerical explorations show that when the flow control valve opens, the empty pipeline starts being filled with a filing flow rate which depends on the size of the bypass and the rate of opening of the flow rate. A large bypass line and rapid opening of the flow control valve result in the rapid filling of the empty pipeline and a significant down surge on the upstream side of the bypass line. The progressing water column in the empty pipe serves as a piston and pushes the air out of the system through the air valve. If the outlet orifice of the air valve is large enough, the air pressure in the empty pipeline does not increase significantly otherwise higher air pressures are built up which can slow down the filling water column. When the last air is eventually released from the system, the water column comes to rest and significant water hammer pressures result. The magnitude of the resulting water hammer pressure depends on the velocity at which the water column hits the pipe’s end as well as the acoustic wave speed of the pipe. Numerical exploration shows that the maximum and minimum pressures induced during filling depend on the diameters of both the outlet orifice of the air valve and the bypass line as well as the opening time of the flow control valve. For this particular case study, it is found that the bypass line diameter = 0.2 m, the outlet orifice diameter = 1.5 cm, and the flow control valve opening time = 40 s can control maximum and minimum pressure head within the acceptable range without unreasonably prolonging the filling time.
Conclusion:
• The proposed model can be successfully assisted in analyzing the hydraulics of filling and in designing a safe filling protocol
• Without a proper filling protocol, the resulting transited pressures can be strong enough to rupture the pipeline
• Without a proposedly sized bypass, it is impossible to control negative pressures in the pipeline
• The rate of opening of the flow control valve might play an important role in controlling the induced maximum and minimum pressures during filling
• Reducing the diameter of the outlet orifice of the air valve significantly reduces the resulting transient pressures but at the same time prolongs the filling.
• An optimum filling protocol can be obtained through an iterative procedure in which the bypass and air valve diameters, as well as the opening time of the flow control valve, are determined in such a way that the induced maximum and minimum transient pressures remain within the acceptable level and the filling is performed as fast as possible

Keywords

#### References

Abreu, J., Cabrera, E., Izquierdo, J. and García-Serra, J. (1999). Flow Modeling in Pressurized Systems Revisited. Journal of Hydraulic Engineering. 125(11), 1154–1169.
Cabrera, E., Abreu, J., Pérez, R. and Vela, A. (1992). Influence of Liquid Length Variation in Hydraulic Transients. Journal of Hydraulic Engineering. 118(12), 1639–1650.
Chaudhry, M.H. (1979). Applied hydraulic transients. Springer, 583p.
Coronado-Hernández, Ó.E., Besharat, M., Fuertes-Miquel, V.S. and Ramos, H.M. (2019). Effect of a Commercial Air Valve on the Rapid Filling of a Single Pipeline: A Numerical and Experimental Analysis, Water. 11(9), 1814.
Daneshfaraz, R., Dastgiri, S., Ali Nejad, B. and Besharat, M. (2020). Investigation of the Behavior 2D of Trapped Air in the Water Conveyance Systems During Rapid Filling or Emptying Process, J. of Water and Wastewater. 31(4), 156–171. (In Persian)
Duan, H.-F., Ghidaoui, M.S., Lee, P.J. and Tung, Y.K. (2012). Relevance of Unsteady Friction to Pipe Size and Length in Pipe Fluid Transients. Journal of Hydraulic Engineering. 138(2), 154–166.
Falvey, H.T. (1980). Air-Water Flow in Hydraulic Structures. Engineering Monograph No. 41, United States Department of the Interior, Water and Power Resources Service, 143p.
Fuertes-Miquel, V.S., Coronado-Hernández, O.E., Mora-Meliá, D. and Iglesias-Rey, P.L. (2019). Hydraulic modeling during filling and emptying processes in pressurized pipelines: a literature review. Urban Water Journal. 16(4), 299–311.
Jönsson, L. (1985). Maximum transient pressures in a conduit with check valve and air entrainment. Proc. Int. Conf. on the Hydraulics of pumping stations, 55–76.
Lee, N.H. (2005). Effect of Pressurization and Expulsion of Entrapped Air in Pipelines, PhD Thesis, University of Georgia, 149p.
Lescovich, J.E. (1972). Locating and Sizing Air-Release Valves. Journal of the American Water Works Association. 64(7), 457–461.
Liou, C.P. and Hunt, W.A. (1996). Filling of pipelines with undulating elevation profiles, Journal of Hydraulic Engineering, ASCE. 122(10), 534–539.
Maddahian, R., Shaygan, F. and Bucur, D.M. (2021). Developing a 1D-3D model to investigate the effect of entrapped air on pressure surge during the rapid filling of a pipe. IOP Conference Series: Earth and Environmental Science, Earth Environ. Sci. 774, 012069.
Malekpour, A. and Karney, B. (2014). Understanding of the Risks of High Pressures Following Rapid Pressurization in Pipelines Containing Entrapped Air Pockets: A Novel Energy Auditing Approach. Volume 4: Production Pipelines and Flowlines; Project Management; Facilities Integrity Management; Operations and Maintenance; Pipelining in Northern and Offshore Environments; Strain-Based Design; Standards and Regulations, American Society of Mechanical Engineers, 1–10, https://doi.org/10.1115/IPC2014 -33616.
Malekpour, A. and Karney, B.W. (2011). Rapid Filling Analysis of Pipelines with Undulating Profiles by the Method of Characteristics. ISRN Applied Mathematics, 2011, 1–16.
Malekpour, A. and Karney, B.W. (2019). Complex interactions of water, air and its controlled removal during pipeline filling operations. Fluid Mechanics research International Journal. 3(1), 4–15.
Martin, C.S. (1976). Entrapped air in pipelines, Proceedings of the 2nd International Conference on Pressure Surges, London.
Martins, N.M.C., Delgado, J.N., Ramos, H.M. and Covas, D.I.C. (2017). Maximum transient pressures in a rapidly filling pipeline with entrapped air using a CFD model. Journal of Hydraulic Research. 55(4), 506–519.
Lee, N.H. (2005). Effect of pressurization and expulsion of entrapped air in pipelines. PhD Thesis, Georgia Institute of Technology.
Ramezani, L., Karney, B. and Malekpour, A. (2015). The Challenge of Air Valves: A Selective Critical Literature Review. Journal of Water Resources Planning and Management. 141(10), 04015017.
Simpson, A.R. and Bergant, A. (1994). Numerical Comparison of Pipe‐Column‐Separation Models. Journal of Hydraulic Engineering. 120(3), 361–377.
Staff, A. (2001). Air Release, Air/Vacuum Valves and Combination Air Valves (M51). American Water Works Association.
Vasconcelos, J.G. and Leite, G.M. (2012). Pressure Surges Following Sudden Air Pocket Entrapment in Storm-Water Tunnels. Journal of Hydraulic Engineering. 138(12), 1081–1089.
Vasconcelos, J.G. and Wright, S.J. (2008). Rapid Flow Startup in Filled Horizontal Pipelines. Journal of Hydraulic Engineering. 134(7), 984–992.
Wang, L., Wang, F., Karney, B. and Malekpour, A. (2017). Numerical investigation of rapid filling in bypass pipelines. Journal of Hydraulic Research. 55(5), 647–656.
Wylei, E.B. and Streeter, V.L. (1978). Fluid Tranients in Systems, McGraw-Hill International Book Co., 401 p.
Zhou, F., Hicks, F.E., and Steffler, P.M. (2002). Transient Flow in a Rapidly Filling Horizontal Pipe Containing Trapped Air. Journal of Hydraulic Engineering. 128(6), 625–634.
Zhou, L., Cao, Y., Karney, B., Vasconcelos, J.G., Liu, D. and Wang, P. (2021). Unsteady friction in transient vertical-pipe flow with trapped air. Journal of Hydraulic Research. 59(5), 820–834.
Zhou, L., Liu, D., and Karney, B. (2013). Investigation of Hydraulic Transients of Two Entrapped Air Pockets in a Water Pipeline. Journal of Hydraulic Engineering. 139(9), 949–959.
Zhou, L., Liu, D., Karney, B. and Zhang, Q. (2011a). Influence of Entrapped Air Pockets on Hydraulic Transients in Water Pipelines. Journal of Hydraulic Engineering. 137(12), 1686–1692.
Zhou, L., Liu, D. and Ou, C. (2011b). Simulation of Flow Transients in a Water Filling Pipe Containing Entrapped Air Pocket with VOF Model. Engineering Applications of Computational Fluid Mechanics. 5(1), 127–140.
Zhou, L., Wang, H., Karney, B., Liu, D., Wang, P. and Guo, S. (2018). Dynamic Behavior of Entrapped Air Pocket in a Water Filling Pipeline. Journal of Hydraulic Engineering, ASCE. 144(8), 04018045.

### History

• Receive Date: 08 December 2021
• Revise Date: 02 February 2022
• Accept Date: 16 March 2022