Case Study:

Pipeline & Process

North Sea Dewatering Campaign For 60 km Gas Export Pipeline

United Kingdom
Methanol pumping equipment, Diesel pumps Nitrogen convertors, Subsea sample analysis


As part of a large North Sea field redevelopment project, our client required support to provide a safe and efficient methanol dewatering spread to carry out dewatering of a new 60km 16” gas export pipeline. Given that water can potentially lead to the formation of hydrates, this task is a critical part of a pre-commissioning project.



The Altus team worked closely together with the client to develop procedures and prepare a DNV approved methanol and liquid nitrogen spread.  The equipment spread was mobilised together with a highly skilled Altus crew.
Once the line was successfully leak tested, the five pig train was launched, containing methanol and gaseous nitrogen slugs, propelled by nitrogen. Packing of the pipeline to FLAGS pressure, allowed the line to be fully dewatered with FLAGS gas. 

On completion, a subsea sampling and analysis unit was used to prove the effectiveness of the dewatering.  A large volume of methanol (60 m3) was mobilised to a remote location (Lerwick). 



Extensive engineering, planning and coordination resulted in the safe delivery of this project and the offshore team successfully prepared the 16” gas export pipeline for introduction of system hydrocarbons.