Lifetime Extension at Minimized Risk

During the lifting of the pipe, significant strain would be placed on the pipeline, this could further damage features possibly located in the line. Furthermore, this strain could potentially cause the formation of new features in the pipeline, thus reducing the overall integrity. In order to ensure that the modification could be carried out safely, more knowledge concerning the current status of the line was essential. As is often the case, this project did not end with just one challenge: The team was faced with accessibility, negotiability, and propulsion issues, specifically:

• Single access to the line from the tank farm area
• Propulsion of the tool in both directions
• The tool had to stop five meters before the wye pi

Specific requirements also stated that an onsite report was essential to identify features greater than or equal to 50% wall loss and any metal loss >10% wall loss for the last 500 meters before the PLEM, which had to be completed within three working days at the most. This information would assist in best determining the cut-in point when replacing the PLEM, so that the pipe that was in poor condition could also be removed and/or replaced during the modification exercise. In addition, any detected defects that could worsen during the lifting operation could be repaired prior to any movement of the pipe.

In order to increase efficiency and to determine an ideal ‘reverse’ point, a subsea monitoring system was deployed consisting of:

• Electronic Tool Detector III (EPD III) read-out consoles
• EPD subsea antennas placed on the pipeline for permanent and undisrupted communication

A transmitter unit was installed onboard the inspection tool, which could be adjusted to emit both a continuous and pulsed radio frequency. For this inspection, the transmitter was set to emit a continuous frequency. Though this can increase the battery consumption of the transmitter unit, the signal tends to be easier to detect with the specialized subsea antennas. This signal, once detected, triggers an indication on the read-out console connected to the antennas, indicating the passage of the inspection tool.

As the radio frequency emitted by the transmitter unit was not strong enough to be detected above the water line, EPD antennas were positioned in predetermined intervals of 50m, 20m, and 10m along the subsea line before the wye piece. To ensure the antennas would remain stationary, they were secured with sand bags onto the topside of the subsea pipe. The connection cables for the antennas were routed along the pipeline up to the PLEM and then ran up to the center table of the Single Point Mooring buoy (SPM) alongside its securing chains. There they were connected to the individual EPD III detector consoles that monitored the inspection tool’s passage in either direction. On its way towards the wye piece, the inspection tool signaled its passing at the 50m antenna. The pumps were slowed down to reduce the velocity to 0.2m/s. Once it passed the 20m antenna, the pumps were slowed further to 0.1m/s. Finally, once the passage of the tool was detected at the antenna located 10m from the wye, the pumps were shut down, stopping the inspection tool within 5m of the wye piece. As soon as the barge crew was ready, the flow was then reversed and the inspection tool pushed back to the launcher/receiver station. The three detectors confirmed the tool’s passage again to ensure that the tool was traveling at an ideal velocity.

In order to guarantee the success of the in-line inspection and to ensure the highest data quality, a cleaning program was implemented by the client that was monitored by ROSEN technicians. To ensure proper cleaning, a bi-directional cleaning tool equipped with gauge plates was deployed prior to the MFL inspection. As standard cleaning tools are designed to push debris in one direction, a specialized tool was required to ensure that any debris was not pushed into the PLEM, but rather brought back to the onshore launcher/receiver station. To accomplish this, the tool design allowed for it to pass over debris in one direction, however when pushed in the opposite direction, the cleaning was optimized and pushed the debris along. This is achieved by ensuing the cleaning discs are softer and more pliable on the outward (to the PLEM) direction and more ridged on the inward direction (back onshore).

Often, these types of assets are inspected with self-propelled UT measurement technologies with reduced measuring specifications. As both data quality and measuring specifications were so critical to ensuring all the defects were repaired prior to and during the replacement operation, MFL technology was chosen over other less validated techniques. This technology provides ideal measuring performance for small pit-like defects and general corrosion. Furthermore, MFL technology is less susceptible to debris in the pipeline, which would influence the measuring performance of other measurement technologies such as UT.

The in-line inspection tool itself was a bi-directional MFL-A solution containing the following elements:

• Bi-directional low-friction 40” MFL unit
• High-resolution MFL technology
• 1.5D back-to-back bend-passage capabilities

The low-friction magnetizer ensures that an ideal tool velocity can be achieved while also reducing the pumping equipment required for the inspection operation. Though this specialized magnetizer was designed for lower friction and bi-directional operation, there is no reduction in the tool’s measurement performance when compared to traditional inspection tools.

In spite of unforeseen environmental influences, such as multiple typhoons, the project was completed as scheduled. The ILI run was completed within the required velocity range of 0.1 m/s – 3.0 m/s, and the specified magnetization levels of 10 kA/m– 30 kA/m. The collected data ensured a detailed integrity assessment of the entire pipeline. In fact, multiple girth weld anomalies with greater than or equal to 10% wall loss were observed for the last 500 meters before the PLEM. These indications were likely caused by typical weld anomalies such as lack of penetration, lack of fusion, or minor misalignments. As these features fell within the critical 500-meter zone identified earlier, additional assessments were performed on these defects by ROSEN’s integrity engineers to provide depth sizing details. With this detailed information, the client was able to make informed decisions to avoid any incidents.

Your benefit

Minimized Risk Exposure
Risk is always a focal point when it comes to dealing with the integrity of any oil or gas asset. If this asset is located in a subsea environment, the concern around risk increases tenfold. Therefore, the prevention of integrity flaws is a primary concern. This solution, offering 100% coverage in one pass, not only saves operational cost, but also offers the highest probability of anomaly detection.

Increased Uptime
Loading lines are not only deemed critical because of the dramatic effects of integrity flaws but also because of their vital need in feeding entire distribution networks. Their essential role in the systems means downtime has a prominent effect on the entire supply or receipt of product. Because of this, inspecting these assets must occur in a timely and efficient manner. The solution applied in this case offers a quick turnaround time as well as a robust and proven technology to ensure downtime is minimized.

Lifetime Extension
The current market situation calls for an even sharper focus on the care of existing assets in the oil and gas industry. This includes extending the useful life of aging assets. In the case of this particular loading line, the main reason for conducting this inspection was to provide required information to ensure the safe rehabilitation of a vital component.