Not all assets are created equal. And while some may be more difficult to inspect than others, that does not minimize the need for inspection. In fact, it may be the opposite. In the case of loading lines from tank farms to loading vessels, these are often considered critical to ensuring stable and reliable security of supply. They also often present challenges for inspection, such as bidirectional pigging operation, low flow and complex on-site operations. Frequently, tailored solutions or new developments are needed.

The Dalmeny tank farm has eight 500,000-barrel aboveground tanks used for storing stabilized crude prior to loading vessels at Hound Point for sale to the open market. Under normal operations, flow is delivered via a 48”, 4.2-km pipeline and 40”, 4.5-km pipelines from Dalmeny tank farm to Hound Point, and ultimately to load tankers. The terminal loads 200 tankers annually, and any unscheduled interruptions could drastically affect security of supply. Therefore, not only do the 2 loading lines qualify as critical, their integrity management and necessary inspections require perfect planning.

In addition to careful planning, a few other conditions make the in-line inspection of these lines challenging, to say the least. In previous inspections by ROSEN (in 2002) and other vendors, a unidirectional approach proved possible but difficult during the pipelines’ regulatory inspection timeframes. A substantial effort by the operator was required, which included removing very large pipe spools and installing launchers and receivers both on- and offshore. This meant a crane barge was required for the installation of temporary pipework and pig traps, which meant an extremely tight work area between marine berth and berthed tanker for launching in-line inspection tools. For this reason, an alternative, possibly bidirectional, approach needed to be considered.


Moving forward, technical solutions specialists at ROSEN conducted a feasibility study for a bidirectional inspection approach, which included an on-site visit to the tank farm. The system’s design made it feasible to proceed with a bidirectional approach with only minor modifications required. A feasibility document was submitted to the operator with 3 options for stop/return points, each considering a barred production tee at Hound Point. The options with stop/return points closest to the tee would clearly provide the most meters of data collection in the pipework but would come with additional effort, system operations and a risk to the inspection. The proposal also considered the system providing flow based on the tank’s gravity feed to propel tools in the direction of marine berth. The maximum pressure this would provide was 1.2 bar, which is significantly less than the standard in-line inspection operating pressure. This, in turn, called for careful design of the inspection tools to reduce friction for launching and running both dynamic and static frictional force. At the same time, however, it also removed the need for pumps, creating a cost-saving measure for the operator. A tanker would be used for bunkering the crude and as the driving force to pump tools back to the tank farm.

Conduction feasibility study

Figure 1: On-site visits were required to properly complete the feasibility study.


Following the acceptance of the feasibility study and the approach, it was time to select the appropriate tools and technologies for the inspection. The primary goal was to collect high-resolution geometry data to cover previously reported dents (some reported as large as 12%). For the 40” line, this would require the production of a new bidirectional geometry tool equipped with a bore measurement device. Design, construction and testing had to take place prior to the designated inspection window in just over 8 months. One element of the tool design was a standalone body, meaning a single module as opposed to the standard dual-bodied tools.

Once constructed, testing at the ROSEN Research and Technology Center in Lingen (Ems), Germany, ensured confidence in the tool’s ability to travel through and effectively collect data at the low flow rate to be provided by the system. In addition, the flip pressure was tested as a contingency. Should the tool fail to stop at the desired location during operation, there would be a 4” inlet to facilitate pumping from the dead leg located directly after the barred production tee at Hound Point.

Having solved the inspection needs of the 40” line with a new development, additional tool design complications were presented when the operator reported a suspected 50” section in the 48” pipeline. Reported by another in-line inspection vendor, this insight fortunately was shared well in advance. The subsequent workaround to ensure tool navigation of the 50” spool was to install 51” sealing discs to boost confidence in the inspection success.

tailor-made inspection tool

Figure 2: A new high-resolution geometry inspection tool was designed and built for this project.

tool testing

Figure 3: To ensure confidence in the new tool extensive testing was conducted.


Inspection route map

Figure 4: Mapping out the inspection route.

In order to ensure all inspection goals were meet, a series of in-line inspection runs took place in each line, starting with an easy-in, hard-out cleaning run equipped with a pipeline data logger (PDL), followed by the high-resolution geometry inspection and ending with a high-resolution MFL metal loss inspection.

Operationally, to reduce the time and cost of the required tankers on the marine berth during inspection, a 24-hour on-site operation was utilized, requiring additional personnel and dedicated tools for each pipeline. To avoid tool modifications between runs, additional on-site personnel from ROSEN Newcastle and Oldenzaal was brought to the site. Monitoring of the accumulated product volume used was recalculated at each known tracking location to confirm accuracy and dependability regarding the placed fluid to the tool location. This step provided accuracy to allow the tool to be stopped at the predetermined stop/return point, removing the need for the contingency plan of pumping the tool from the dead leg. There were only 5 linear meters of pipework for margin of error, and implementing this contingency plan would add 12 hours to the operation – with the berthed tanker being charged by the hour. Therefore, accuracy was key, and very slow operational control valves and appropriate recording times were required during this critical phase of the operation.

At the end of the campaign, all 6 inspection runs were successful, no contingency plans had to be put in place (although they were available, of course) and high-resolution data was collected to facilitate the continuation of the pipeline integrity management journey.