A buckle detector assembly will be positioned at a minimum of 4 joints past the furthest touchdown point. This assembly will provide a mean of identifying any deformity occurring in the pipe string after the string has left the lay barge.
The buckle detector system set-up will consist of the following components:
- One buckle detector system completes with 6mm thk. aluminium gauging plate.
- 7/8” OD x 4000 ft lgth (inclusive 100% back up) wire cable
- 1” ID x 0.049” WT x 10 ft lgth copper tubbing (20 nos. inclusive 100% back up)
- X-ray stop trolley
- Internal line-up clamp
- 5 MT air tugger
- 5 MT Load cell with gauge readout
The X-ray stop trolley will be attached to the 7/8” dia. cable between Station 7 & 8. A 7/8” dia. cable connected to the end of the line-up clamp reach rod and terminating at an air tugger located on the bow completes the assembly.
Refer to Fig. 4.3.8-1 & 4.3.8-2 for the proposed assembly of a 26” Æ buckle detector. Gauging plate will be fixed at 593.9 mm diameter which is based on the DnV 1981 rule:
Ø = (D – 2t) – 0.01D – 0.4t – 5P
Where D = Nominal OD of pipe (660 mm)
t = Wall thickness of pipe (17.5 mm)
P = 0.2t or 5 mm whichever is smaller
The insertion of buckle detector inside the pipes will be easier when more joints are on the seabed such that the back pressure inside the pipeline being laid is minimized. When the pipe joint No. 93 or more at the beadstall, buckle detector shall be deployed by blowing down. The deployment will be carried by means of a pneumatic system (blow down cap) incorporated in the assembly. An air hose will be pre-attached to the blowdown cap to supply pressurised air so that the buckle detector can be blown down along the pipeline profile and moves toward touchdown. With each pull of the pipeline, the wire cable will pay out one joint length of cable. Once all cable is paid out, the buckle detector assembly will be pulled forward using air tugger at the bow of the barge. Refer to Fig. 4.3.9-1 for blow down cap assembly.
The buckle detector assembly will operate typically as follows:
- When welding has been completed at all stations along the mainline, the cable from the air tugger to the reach rod will be disconnected and the barge move ahead 12.2m.
- The next joint will be transferred from the ready rack to the line-up station. The air tugger line will then be pulled through the new joint and connected to the line-up clamp reach rod.
- The air tugger will commence to haul in the cable, the line-up clamp and buckle detector assembly, which will travel up along the pipe string towards the beadstall (Station No.1).
- The load on the buckle detector assembly, indicated by a gauge mounted on the air tugger will be recorded for each corresponding joint number during each pull.
- Any excessive deviations from the average pull force being recorded will initiate the alarm on the load cell. An immediate investigation will be carried out to ascertain the cause
- The line-up clamp will be activated and welding commenced.
Fig. 4.3.8-1 to 4.3.8-6 shows the details of internal pipeline equipments, arrangement, cable make-up and installation process.
The buckle detector assembly will be removed prior to pipe laydown. The buckle detector will be monitored from the tension gauge for every each pipe pull.
DNV 1981 – RULES FOR SUBMARINE PIPELINE SYSTEM – BUCKLE DETECTOR