As part of a recent North Sea pipeline project, EnerMech were contracted to flood and hydro test offshore subsea flowlines.
The testing operations were to be conducted in standard industry fashion by using a vessel-based downline spread. This meant the vessel would need to remain connected to the flowlines via the downline throughout the test period, adding to client cost.
EnerMech Process, Pipelines & Umbilicals director, Les Graves, said: “We suggested an alternative to the client, using our innovative Subsea Test Manifold (STM) combined with a data-logger as an interface between the downline and flowlines for the proposed testing operations.
“We have previously used this system successfully on hydro test jobs (and in conjunction with a subsea hydro test pump). This allows the vessel to disconnect and leave the flowline on test without the downline being in use.”
Aberdeen-based mechanical services group EnerMech also proposed the innovative use of a recently (jointly with a specialist vendor) developed optical modem application, installed as an integral part of the STM.
The optical link system means there is no need for the vessel to be connected to retrieve test data real-time, or retrieve the manifold during operations if the vessel has to disconnect due to bad weather or other duties. The optical link system provides real-time data as well as historical data uploaded “remotely” to an ROV which can access this data without hard connection.
This proposal was accepted and the operation was a success, saving significant vessel time and cost and reducing vessel standby risk due to bad weather.
The client intends to use this system in future whenever the benefits can be realised.
Potential Benefits of Subsea Test Manifold
- Allows vessel to have a pipeline on test while it completes other operations in the field, no need to have the downline attached.
- The manifold is capable of continuous logging.
- Downline can be disconnected at any time (i.e. bad weather, unplanned urgent tasks) without depressurising the pipeline.
- Optical link provides real-time data and historical data upload to a nearby ROV without hard connection.
- Optical link saves on vessel time as there no need to retrieve the manifold during operations.
- Depressurisation can be carried out subsea, saving vessel time.