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Vessel Tie-in Units

Pipe-in-pipe alignment for vessel tie-ins


A pipelay contractor in the USA was looking to upgrade their spoolbase with a new system to ensure single pipe alignment during vessel tie-ins. The existing systems were only used for pipe-in-pipe (PiP) carrier pipe closure.

MDL Approach

MDL focused on providing the client with a future-proof solution: Vessel Tie-in Units (VTUs), designed together with the client to ensure that they met all operational and budget objectives. These included ensuring the VTUs are easily removable with equipment readily available in the spoolbase; ensuring that there is a mechanism for rolling the bevel machine easily in/out of the work location; and ensuring that the HPUs could be housed outside the spoolbase in a separate shed to ensure a quieter working environment - improving HSEQ performance. The systems would be delivered to Mobile, Alabama and integrated into the client's spoolbase.

MDL Solution

The MDL VTU is a pull-through-type unit that houses two heads to position the end of pipe stalks for them to be joined. One head is fixed while the other is a travelling head that pulls the pipe stalk horizontally along its axis and also manipulates the end of the pipe. Based on MDL's market-leading flex-lay technology, the VTUs feature a proven failsafe system, preventing unwanted product release in the event of power loss or critical failure, controlled by PLC. The units are road-transportable and mounted so that they can be easily removed in severe weather. The system can be designed to be hydraulically or electrically driven.

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