Impact of orifice-to-pipe diameter ratio on leakage flow: an experimental study

Abstract

The traditional orifice discharge formula used to estimate the flow rate through a leak opening at a pipe wall often produces inaccurate results. This paper reports an original experimental study in which the influence of orifice-to-pipe diameter ratio on leakage flow rate was investigated for several internal/external flow conditions and orifice holes with different shapes. The results revealed that orifice-to-pipe diameter ratio (or pipe wall curvature) indeed influenced the leakage flow, with the discharge coefficient (Cd) presenting a wide variation (0.60–0.85). As the orifice-to-pipe diameter ratio decreased, the values of Cd systematically decreased from about 12% to 3%. Overall, the values of Cd also decreased with β (ratio of pressure head differential at the orifice to wall thickness), as observed in previous studies. On the other hand, orifice shape, main pipe flow velocity, and external medium (water or air) all had a secondary effect on Cd. The results obtained in the present study not only demonstrated that orifice-to-pipe diameter ratio affects the outflow, but also that real scale pipes may exhibit a relevant deviation of Cd from the classical range (0.61–0.67) reported in the literature.