In Line Isolation and Weld Test Plug revolustionizes isolation and testing of pipe connections. The Plug allows an operator to posively isolate and monitor potentially explosive vapors during "Hot Work", then effectively hydrotest the new weld connection with easy to use tool. The alumunium / steel construction makes the tool highly portable and easy to position. The volume of water required for a test is so small that testing can be accomplished using a hand pump. This Greatly facilities testing in remote areas of the facilitiy.