Tilt detector and system

In the method of operating sub-sea drilling equipment including a tool stack located on the sea floor, a riser pipe extending upwardly from the stack, a universal ball joint interconnecting the riser pipe and stack, azimuthally aligned first and second two-directional component tilt detectors on the stack and riser pipe, respectively, and a drilling vessel at the sea surface and from which the riser pipe extends downwardly, and wherein the riser pipe is tilted relative to the stack at the ball joint, the steps that include

• a. operating the first tilt detector carried by said stack, to produce a first output indicative of the magnitude of tilt with respect to vertical,
• b. operating the second tilt detector carried by the riser pipe near the ball joint, to produce a second output indicative of the magnitude of tilt with respect to vertical,
• c. determining the difference between said outputs, and
• d. maneuvering the vessel to reduce the magnitude of riser tilt relative to the stack.

A system including the combination comprising a sub-surface stack of wellhead equipment on the ocean-floor and a riser pipe projecting upwardly from said stack, the riser pipe proximate the stack tilted from vertical, and relative to the stack, and a tilt accomodating universal joint connecting the riser pipe and stack, and including means maintaining the stack and riser pipe in aligned azimuthal relation, a pair of tilt detectors, one carried by said-surface stack of equipment on the ocean floor and the other carried by said riser pipe projecting upwardly from said stack, said other detector spaced above said stack, and control means on a vessel at the ocean surface operatively connected with each detector for providing a visual display corresponding to the magnitude of tilt of said riser with respect to said stack, each detector comprising:

• a. a container,
• b. liquid in the container having an upper surface tending to remain generally horizontal as the container tilts,
• c. sensors having independently movable members engaging the liquid at spaced locations to sense the relative levels of the liquid surface at said locations and relative to the container during said tilting, the output of said detector corresponding to the magnitude of tilt of said detector with respect to vertical,
• d. the liquid in the container defining pools having restricted intercommunication, the pools respectively engaged by said sensors, said members comprising floats engaging the liquid pools at the surfaces thereof,
• e. said sensors also including plungers carried by the floats, there being differential transformer coils magnetically coupled to cores carried by the plungers, said plungers having generally polygonal cross sections along plunger length dimensioned to be movable endwise within generally circular guide bores surrounded by said coils, thereby to form liquid drainage spaces between the plungers and bores, the guide bores formed in a relatively upper portion of the container.