Historical condition and lifetime prediction for Amethyst, Wollaston and Whittle

The purpose of this project was to produce a Historical Condition Review and Lifetime Prediction for fields in the Southern North Sea.

As part of a larger decommissioning study, a client required a Historical condition review and lifetime prediction for Amethyst, Wollaston and Whittle Fields.  A Historical Condition Review is used to identify the seabed conditions throughout the pipeline's life. Features such as the exposures, spans, mattresses, rockdump and the depth of burial were identified using PRISM (a program used for analysing inspection data) and compared with previous years to identify any trends that exist. The data can be used to determine the stability of the seabed and whether there are any areas that could become hazardous to other sea users after decommissioning.

Jee determined the predicted lifetime of the pipelines using DNV-RP-B401 ‘Cathodic Protection Design’. Subsea pipelines are protected against external corrosion using a Cathodic Protection (CP) system comprising of sacrificial anodes. Once the CP system has deteriorated, the pipeline starts to corrode and lose integrity.  Jee determined the effectiveness of the CP system by assessing how long it would take for the anode mass to reach 40% of its design mass. This was based on the pipelines external coatings, the burial status of the pipeline and the dimensions and number of anodes on each pipeline.

A Historical condition review and lifetime prediction is required when creating a decommissioning programme for a group of pipelines. Jee has the experience to interrogate pipeline inspection data and use it to create a document that can be used as evidence when creating a decommissioning programme. The client was able to rely on Jee’s expertise in pipeline engineering to create an accurate review and prediction document and be safe in the knowledge that it will be in accordance with standard industry codes and regulations.