L51561 Proof Testing of the Pre-Hot-Tap Branch Connection

Proof testing of a hot tap prior to completing the actual tap has, in the past, been an individual company procedure. These proof testing procedures have varied from a low pressure leak test to a high pressure test that has reportedly, in a few cases, caused a rupture through the enclosed circular segment of the main line pipe. The objective of this research was to determine a safe and reasonable test pressure level to apply to the attached branch line before completion of the tap. It is aimed at optimizing the safety of hot tap installations while minimizing the chances of damage to the carrier pipe. An analytical model was developed to predict the elastic response of a critical location of the hot tap joint under proof test conditions. Two experiments instrumented with strain gages were conducted. The strain gages were placed in critical locations to determine which area is most highly strained and to help determine the maximum pressure level to be applied in the test. It was not desired to cause a rupture in these experiments, but the pressure level was taken higher than the “safe and reasonable test pressure” to obtain information that would bracket this test pressure level. Full-scale instrumented pressure tests were then conducted on 30-inch X60 run pipe with three tap sizes. The tests showed the analysis to be accurate for ratios of branch pipe diameter to run pipe diameter greater than 0.3.