ROSEN was contracted by a South American company to provide a solution to inspect two offshore loading pipelines, one 24” pipeline with a length of 16.7 km and the other 36” pipeline of 10.1 km. These systems connect onshore storage facilities to two subsea pipeline end manifold’s (PLEM’s), which are connected to a buoy by a flexible hose for the critical task of loading tankers. Due to its position in the pipeline system, this asset was deemed critical since there was no alternative means to import or export the product. The loading line in this case, by design, could not be inspected with a conventional inspection approach due to the following challenges:
- Single access
- No traps - subsea line ends at PLEM
- Unknown cleanliness
- Single flow direction
Additionally, the customer’s comprehensive integrity system does not allow for reduced quality in their inspection datasets. As such, it was requested that ROSEN provide a high-resolution solution with optimal defect detection and identification for both internal and external corrosion features. The data analysis scope also required a post-inspection Corrosion Growth Analysis to be provided by ROSEN’s Integrity Services. The customer also requested subsea georeferencing of their loading line system.
Conventional inspection methods would not obtain the high-quality data requested by the customer. Therefore, a free-swimming, bidirectional MFL-equipped solution, with a reversed cleaning approach, was devised. The benefits of this approach are:
- MFL technology is robust and known to be least sensitive to debris.
- Reversed cleaning allows for debris to be collected onshore, thus minimizing expensive subsea operations.
In order to provide a suitable solution for georeferencing the pipelines, ROSEN performed an in-depth market assessment on available technologies. The approach identified to be the most suitable for this application was a combination of technologies, including:
- A Differential Global Positioning System (DGPS) base station within the terminal and a mobile DGPS station on the vessel.
- An Ultra-Short Baseline (USBL) system on the vessel, from which the underwater positioning measurements are conducted.
In addition, at all pre-determined subsea reference points, the salinity, conductivity, temperature and pressure depth profile of the water was obtained to establish the speed of sound value.
Despite the challenging offshore conditions, a very demanding scope, and the fact that this was the first utilization of the georeferencing technology, ROSEN was able to complete all onsite activities within the requested time frame. Furthermore, seven inline inspection surveys were completed onsite without any accidents or incidents and to the full satisfaction of the customer. The operator obtained valuable information on the integrity status of the asset, including the identification and localization of subsea defects and accurate strain analysis as a result of pipeline movement. This has allowed the customer to continue safe operation of the loading line system.