During the installation and contruction of an offshore underwater pipeline, pneumatic pressure may be applied internally to the pipeline to prevent it from collapsing or buckling from external pressure. Especially in deep water offshore pipeline construction internal pressure is applied to prevent any radial collapse of the line due to the extremely high pressure exerted against it by the surrounding water. In order to limit the weight of the normally unsupported pipeline between the laybarge and the ocean floor, the pressure generally will be applied pneumatically. Sealing devices such as pigs are required internally of the pipeline and usually near the barge in order to maintain the various sections of the assembled pipeline under an internal pressure. In the event that a sealing device malfunctions and does not hold in place the pig normally would be expelled out of the pipeline onto the laybarge like a cannonball because of the potential energy of the pressurized pipeline. This possibility presents a very serious and dangerous situation which the present invention precludes from happening.
The specific prior art references considered with respect to the present invention include the following U.S. Pat. Nos.: 2,607,370 3,197,195 2,615,413 3,381,714 2,672,161 3,495,626 2,747,690 3,503,424 2,807,937 3,525,226 2,823,634 3,561,320 2,974,685 3,561,490 3,593,749
The foregoing prior art relate to conventional pipeline pigs and plugs and generally disclose the known expedient of providing actuatable means for gripping engagement with the interior wall of the pipe upon occurrence of a predetermined condition. None of the prior art, however, discloses the construction and arrangement of the subject invention per se or in combination with the movable pig which actuates the safety stop apparatus, or the functional interrelationship between the safety stop apparatus which is operable when the sealing pig comes in contact therewith.