Abstract: A locator for determining the depth of a pipeline which carries AC signals. The signals may be those induced by power lines, cathodic protection systems, or pumping equipment or other machinery connected to the pipeline. Also, specifically applied AC signals from a transmitter may be employed in the absence of the other signal sources.The depth determining locator employs three directional detector coils in an elongated housing. Two coils are oriented transversely to the axis of the housing and are located as far apart as a preselected depth of the pipeline. The third coil is beside a forward one of the other two and is oriented at an angle, e.g. 45.degree. to the transverse. There is electronic circuit means for timing the passage of the locator over the pipe between the two coils, and to measure the ratio of a constant (which represents the spacing of the two coils) times the time from the forward of the two coils to alignment with the third coil, divided by the time between the two coils.

Abstract: Methods for releasably plugging off a section of a pipe line and apparatuses for practicing or carrying out the methods are disclosed. An apparatus comprises one or more pigs, each pig having an inflatable ring therearound, inert gas therein for inflating the ring, and a remote thermal command signal receiver for initiation of expansion of the pigs responsive to a remote thermal command signal of one temperature generated by a generator at the ends of the pipe section to be sealed off for sealing the pigs in the pipe as they reach their respective pipe section termini. The remote command signals comprises thermal energy of precise temperatures.