Pipelines

Pipeline removal is a complex operation and must be considered on a case-by-case basis. REL staff have over 23 years experience in engineering, planning and costing the removal of pipelines and ancllary items.

Pipeline Preparation Phase

A possible scenario follows: Pipeline removal may commence with abandonment of the pipelines operated by others and removal of the intrafield pipeline spoolpieces. The marine operations are case specific and operations will be undertaken from a suitable vessel (i.e. DSV/MSC) following cleaning and filling the pipeline with seawater by the operator. In the event that any dosing of the pipeline fill water is undertaken, the dosing chemicals shall be suitable for discharging without any special procedures having to be adopted. Furthermore, if applicable, it is assumed that the cleaning of the pipelines has been sufficient to remove any LSA Scale / NORM within the pipelines to a level that does not require further cleaning or special handling procedures.

Intrafield Pipeline Removal

A pre-removal ROV survey of the pipeline route would be undertaken prior to the removal operations commencing. The pipeline de-burial machine would then be deployed and tracked along the pipeline route to expose the pipelines.

With the pipelines exposed the ROV would be used to progressively pass along the pipeline cutting the banding straps holding the 2” pipeline saddles on the 12” pipeline and the anode continuity straps. This will enable the pipelines to be recovered independently.

A DSV will be utilised to de-water the pipelines prior to the reel-vessel arriving in the field. With the DSV being used for the compressors at one end of the pipeline, a second vessel with a minimal diving support role is assumed be required to open and close valves and act as a guard vessel as required. Both DSV would be de-mobilised on completion of the pipeline de-watering operation.

The reel-vessel will mobilise to the field and install clump weight to act as a holdback anchor at the recovery termination end. The holdback anchor will be connected to the pipelines by a suitable wire rope through the recovery head. The reel-vessel will then transit to the recovery initiation location and connect the recovery wire to the recovery head on the 2” pipeline. The wire would then be recovered using the A&R winch and the operation continued until the pipeline has passed through the tensioner. The tensioner would then be operated to provide the pipeline tension for recovery.

The pipeline would then be recovered onto the recovery reel. Personnel would be deployed on the working platform beneath the lower tensioner to remove the EPDM piggy-back saddles and anode continuity wires. As the pipeline recovery is completed the tower angle will be adjusted until the end of the pipeline is clear of the seabed. The holdback wire will then be released from the recovery head.

It is assumed that the reel vessel would be capable of recovering both the 2” and 12” pipelines in a single trip. Based on this assumption the reel-vessel would then transit to the recovery initiation location and repeat the operation for the 12” pipeline. During the recovery of the 12” pipeline, the personnel on the working platform below the tensioners would be removing the anodes.

On completion of the pipeline recovery operations, the holdback anchor would be recovered and a ROV survey of the pipeline route would be undertaken. The reel-vessel would then de-mobilise from the field.

On de-mobilisation from the field, the reel-vessel will transit to either its own spoolbase or to a temporary facility. Here the pipelines will be reeled out and sectioned into 200-400m long strings, subject to the site capabilities, and the other recovered materials offloaded. The reel vessel would then be de-mobilised.

Onshore Disposal

Onshore cutting crews would then section the pipe-strings into pipe joint lengths for final disposal.

Some of our clients