Abstract
The derivation of the classical equation for flow through an orifice assumes a fixed
orifice area. However, pipe materials exhibit expansion behaviour with increasing
pressure, which alters the size of orifices and results in greater leakage rates. The purpose
of this investigation was to study the behaviour of round holes and cracks in pipes
through theoretical and experimental work.
The results of the study include equations derived for increased flow through round holes
in pressurized cylindrical shells and pipes. The theoretical models explain the increased
flow experienced due to the leak area increasing. The models incorporate material
properties, shell geometry and fluid properties for both uni-axially and bi-axially stressed
pipe sections. Analytical results are compared with previous finite element investigations.
In addition, an experimental study into the effects of pressure on a round hole in a class 6
uPVC pipe was conducted. Conclusions are made relating to the influence of material
expansion to increased flow rate through openings in pressurised cylinders. The results
compared positively with those of the theoretical equations.
Conclusions are made relating to the influence of round hole or crack expansion to an
increased flow rate through openings in pressurised pipes. Results include the effects of
geometrical and material variables on the expansion of round holes. Better explanation
of the increased flow through orifices, documented by practical observations, is
presented. Results indicate that round hole area is linearly related to pressure. However,
testing on longitudinal cracks resulted in a non-linear relationship between crack area and
internal pipe pressure. Results indicate the expansion of round hole area is minimal.
Leakage however is greatly affected over extended time periods by even the smallest
increase in defect area.
Critical pressures before brittle fracture obtained from testing on longitudinal cracks were
compared to theoretical formulation. Results show a close relationship between current
theory and experimentation.
Prof. K. van Zyl