Underwater pipe laying method and apparatus

Apparatus useable with a pipe laying vessel for installing a pipe section having a bulky device larger than the diameter of such pipe section in the upper end of a pipeline, such apparatus comprising:

• a tower on the vessel;
• a welding station at the lower portion of the tower;
• a pipe clamping mechanism at the lower portion of the tower to selectively engage and releasable hold the upper end of the pipeline;
• hoisting means on the vessel selectively engageable with the upper end of said pipe to support said pipe section on the tower as the lower end of the pipe section is attached to the upper end of said pipeline at the welding station;
• whereafter the pipeline is disengaged from the pipe clamping mechanism and the hoisting means moves the pipe section and attached pipeline to a position spaced away from the point of attachment of said pipe section to the upper end of the pipeline, lowers the pipe section and attached pipeline into the sea wherein the bulky item is positioned at a predetermined depth below the tower;
• and
• then returns the upper end of the pipe section to the pipe clamping mechanism.

A method for installing a pipe section having a bulky device larger than the diameter of such pipe section, said method including the steps of:

• providing a pipe laying vessel equipped with a tower and with hoisting means;
• providing a pipe clamping mechanism at the lower portion of the tower to engage and releasably hold the upper end of the pipeline at a first position;
• attaching the lower end of said pipe section held in the pipe clamping mechanism to the upper end of said pipeline;
• releasably securing the hoisting means to the upper end of said pipe section;
• disengaging the upper end of the pipeline from the pipe clamping mechanism;
• using the hoisting means to first move the pipe section and attached pipeline to a second position spaced away from the point of attachment of said pipe section to the upper end of the pipeline, next using the hoisting means to lower the pipe section and attached pipeline into the sea wherein the bulky item is positioned at a predetermined location and depth below the tower;
• then using the hoisting means to return the upper end of the pipeline to the pipe clamping mechanism;
• and
• engaging the pipe clamping mechanism with the upper end of said pipe section and attached pipeline.

Apparatus usable with a pipe laying vessel for installing a pipe section containing a bulky device having a diameter larger than the diameter of the pipe section in a pipeline, said apparatus including:

• a tower carried by the vessel in a near vertical position, said tower including two columns defining a tower opening therebetween;
• a pipe supply on the vessel;
• a strongback adjacent the tower and having its rear end slidably connected to one of the columns for movement between a generally horizontal pipe section pick-up position and a near vertical pipe section hand-off position adjacent said one of the columns;
• grippers on the strongback that pick-up said pipe section from the pipe supply at the pick-up position and swing said pipe section into the tower opening at the hand-off position;
• tower rollers in the upper portion of the tower adjacent the hand-off position movable between an open position and a closed position, said rollers receiving the upper end of said pipe section from the grippers while disposed in an open position whereafter the tower rollers are moved into their closed position;
• a hang-off clamp in the lower portion of the tower selectively operable between a closed first position wherein it supports the pipeline-attached pipe section forming the top portion of the pipeline and a second open position wherein the pipeline-attached section and pipeline can be lowered relative to the tower;
• a line-up clamp in the lower portion of the tower above the hang-off clamp, said line-up clamp receiving the lower portion of said pipe section from the grippers as said pipe section is moved into the hand-off position, said line-up clamp then engaging said pipe section to lower said pipe section onto the upper end of the pipeline-attached pipe section for attachment of the latter to said pipe section, with the strongback then immediately returning to its pick-up position for the grippers to engage a new pipe section at the pipe supply to be added to the upper end of said pipe section while said pipe section is being attached to the upper end of the pipeline;
• and
• hoisting means releasably securable to the upper end of said pipe section to lower said pipe section and pipeline after the lower end of said pipe section has attached to the pipeline, with the hang-off clamp then being disposed in its open position.