The piping tightness tests used today in Israel are performed according to an outdated API standard intended for underground piping only. Also, as opposed to the latest guidelines from the US Environmental Protection Agency – EPA, the standard defines that the pressure at the end of the test should not be lower than a certain threshold and does not define absolute permissible leak rate values.
In order to assess the detection capacity of a static pressure test according to a standard and analyze ways to improve it, a quantitative model was developed. The model takes into account various variables, including: test pressure, gas-liquid proportion in the pipe and the temperature difference uncertainty between the begging and the end of the test.
During the analysis it was found that in case of static pressure test, the proportion of the gases in the pipe has a significant effect on the detection capacity. Therefore, a test procedure was proposed that provides an estimate of the gas proportions in the pipe before the test is performed. A short static pressure employed was found to provide a relatively high detection capacity in the case of underground piping at low test pressures only. It turned out that, in order to meet the detection capacity recommended by the EPA, the pressure drop threshold must be lowered at the end of the test.
The possibility of increasing test duration 24 hours was also examined, it was found that the detection capacity can be significantly improved, however there is a maximum pressure limit in the pipe due to fluctuations in temperature during the test. Therefore, a 24 hour static pressure test is suitable for pipes that are mostly underground, so the average temperature in them varies very little.
In order to provide an excess pressure increase solution, the possibility of maintaining a constant pressure during the test was examined by addition and draining the test liquid from the pipe to a balanced reservoir. It was found that 24 hour test at constant pressure provides a very high detection capacity, without the need to estimate the proportion of gases in the pipe. Moreover, the test is suitable for a wide range of pressures and above all is suitable for piping with varying degree of exposure to environment. Finally, a conceptual design of a relatively simple test system for performance of constant and controlled pressure test, was presented.