The testing operations on subsea flowlines in the North Sea were to be conducted in standard industry fashion using a vessel-based downline spread.

This meant the vessel would need to stay connected to the flowlines via the downline throughout the test period, adding to the client's cost.

EnerMech process, pipelines and umbilicals director Les Graves said the company suggested using its subsea test manifold combined with a data logger as an interface between the downline and flowlines for the proposed tests.

"We have previously used this system successfully on hydro test jobs - and in conjunction with a subsea hydro test pump," he said.

"This allows the vessel to disconnect and leave the flowline on test without the downline being in use."

The manifold is capable of continuous data logging.

EnerMech also proposed the use of an optical modem application it recently developed with a specialist vendor.

The modem would be installed as an integral part of the subsea test manifold.

The optical link system provides real-time data as well as historical data uploaded "remotely" to a remotely operated vehicle, which can access the data without having to make a "hard" connection.

The link saves on vessel time as there is no need to retrieve the manifold during operations.

Depressurisations can also be carried out subsea, saving vessel time.

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.