How ROSEN is safeguarding India’s energy supply

India's industrialization as well as urbanization creates huge demands of its energy sector, even though energy use (per capita) is still under half the global average. There are widespread differences in energy use and the quality of service across states and between rural and urban areas. The affordability and reliability of energy supply is a key concern for India.

Over 80% of the energy needs are met by three fuels: coal, oil and biomass. Coal supports the expansion of electricity generation and remains the largest single fuel in this mix. Oil consumption has grown rapidly as well due to rising vehicle ownership and road transport. Biomass, primarily fuelwood, is still widely used as cooking fuel. 

Now, with limited own oil or gas reserves, India heavily relies on import of oil and gas for its energy needs.

Another interesting aspect is that India is a major exporter of refined products due to the presence of in total 23 refineries, which makes them the fourth largest in the world after the United States, China and Russia.

Figure 1: A map of India’s pipeline network

Loading line challenge

In order to import crude oil India relies on crude tankers. These tankers move large quantities of unrefined crude oil from its point of extraction to refineries.

Oil tankers are often classified by their size as well as their occupation. The size classes range from inland or coastal tankers of a few thousand metric tons of deadweight (DWT) to the mammoth ultra large crude carriers (ULCCs) of 550,000 DWT. Tankers move approximately 2.0 billion metric tons (2.2 billion short tons) of oil every year. Second only to pipelines in terms of efficiency, the average cost of transport of crude oil by tanker amounts to only US $5 to $8 per cubic meter.

It is the size that makes these tankers efficient, but often harbors are not large or deep enough to handle them. Instead, the industry often relies on tanker loading and offloading lines.

Figure 2: Typical loading line configuration

These pipelines connect a shore-based installation, such as a refinery or tank farm, to a subsea pipeline end manifold (PLEM). The PLEM usually lies in water around 25m to 60m deep and is connected to a buoy by a flexible hose or hoses. Floating flexible hoses complete the connection to the tanker. 

Due to their position in a pipeline system or network, they are usually one of the most critical assets in the operators' network since there is no alternative means to import or export the product. 

In addition, repairs or replacement is difficult and costly, especially on the sub marine section. For the operator it is therefore of utmost importance to understand the condition and integrity of such pipelines. A solid knowledge will enable suitable preventive actions and ensure the pipeline can be safely operated to avoid any unnecessary downtime that would interfere with regular operations or in a worst-case scenario could result in pipeline failure.

Due to the mechanical configuration the only feasible access point is often within the tank farm of the terminal only, while the line terminates in a subsea PLEM (Pipe Line End Manifold) underneath the mono or calm buoy.  In most cases this necessitates bi-directional inspection.

Threat assessment

Typical threats for offloading lines include internal corrosion due to presence of impurities in the crude (e.g. sulfur, organic acids, additives etc.). The corrosion risk increases due to intermittent operation, use of brackish or sea water to flush the lines and incomplete draining. This allows for water build-up, bacterial accumulation and consequently MI (mycobacteria induced corrosion). A common source for MIC is cross-contamination from the oil ships tankers.

The stagnant conditions in between tanker offloading operation may further allow for sedimentation of solids (debris) present in the product, typically at low points.

In this context, it should be noted that periodical maintenance pigging is typically not done since lines are difficult to pig, and inhibiter is often not used because proper distribution is difficult without pigs.

The below examples show 2 different 48-inch SPM pipelines, each showing the same corrosion characteristics i.e. BOLC (Bottom Of Line Corrosion) and increasing corrosion density and depth approaching the PLEM.

Figure 3: Corrosion characteristics for repeat ILI of 48 inch SPM pipelines with 2 year interval

Inspection methodology

Although conventional pigging in combination with a subsea trap is generally thinkable, the associated cost complexity and risk of such an operation is excessive.

Two ILI methodologies are generally available for these systems:

1. A bi-directional, tethered, self-propelled UT inspection The main benefit of this approach is that no flow is required.

However, the options to clean are limited and the inspection velocity is rather low compared to free swimming ILI.

2. A free-swimming bi-directional MFL and/ or UT inspection This solution is not restricted in distance or bends and allows for effective pre-inspection cleaning. A bi-directional flow is however required.

For India's offloading lines (typically 48" and just under 20 km in length) the free-swimming approach is selected, becauseit is necessary to clean and the available time in between tanker offloading operation is limited and a tethered inspection would take too long.

Setting up a bi-directional flow is easier said than done. Not only very large pumps are needed to establish the flow, also the volume of the line inventory needs to be stored. This means that often the only feasible way to put up a bi-directional flow is to use a tanker. 

The tools are launched onshore close to the terminal/ refinery. They are pushed towards the PLEM using terminal pumps. Upon arrival at the PLEM the tanker is pumping the tool back to the launcher from where it is received.

Due to the location (subsea) and construction of the pipelines (concrete coating) and location of features (6 o'clock) subsea verifications or repairs are very difficult.

Figure 4: Very Large Crude Carrier (VLCC) moored at SPM (Single Point Mooring) buoy

Think about it:
We need a diver to locate a defect in a subsea, potentially buried pipeline, at 6 o'clock. The first challenge is to find the right joint. DGPS does not work subsea and there are typically no external reference points. Next, the diver will need to remove the concrete under the pipe and then try to perform an external NDT measurement but not knowing if he is at the correct location – quite a challenge. If we know this upfront, we can do subsea referencing together with XYZ, or simply install heavy duty reference makers at locations where defects are expected.

But there is a better way: We do UT from the inside. Instead of a few external measurements, this tool with 483 transducers does 483.000 measurements (!) per meter. Not only do we improve the sizing, but we also improve POD and POI. 

In order to obtain high quality inspection data, pre-ILI cleaning is performed. Because of the bi-directional operation, asymmetric cleaning pigs are used. This “soft in-hard out” approach minimizes debris being pushed to the PLEM, but brings the debris back to the entry point.

Figure 5: Bi-directional 40-48" UT tool in 48" configuration

Figure 6: Reverse cleaning pig upon receipt

Geometrical obstacles

During a recent inspection of a 48” x 15.5 km pipeline a geometry tool sustained damage during the passage of the 16% dent at 9.5 km. The MFL inspection was only partially completed, for safety concerns the MFL tool was not propelled through the dent. The client approached ROSEN to provide a MFL solution that was able to not just pass the dent, but also record data in the dent area and keep the high resolution performance specifications and not restricting them to pass the obstacle.

The technical team evaluated the available data provided by the client, and added a more conservative safety barrier by considering a deeper dent penetration (20%) and long distance ovality portion. To achieve this, ROSEN proposed a multi – sectional tool to ensure we would safely pass the bend considering sealing, collapsibility and full measurement performance.

Proposed configuration ensured full sealing and guidance for the forward and backward run, while the available space at the measuring segment was used to ensure free movement for the measuring system to ensure full measurement specification performance.

Figure 7: The three module design for safe dent passage

Our job is to keep pipelines safe, not to damage them. The dent needs to be passed. Safely. With ‘safe’ we do not only mean that there shall be no damage to the tool or risk of a stuck pig. Safe also means that passage of the tool shall not further damage the dent itself.

The team reached out to our integrity experts for advice. Would a passing MFL tool change the dents’ geometry and instigate a failure mechanism? The answer was no. But the flow rate was reduced when the tool passed the dent to minimize impact on dent.

Assessing geometry data prior to MFL ILI confirmed that dent was rather long and sealing of a single body tool would have been compromised. The team assessed all information and concluded that it was safe to load and launch the MFL Inspection tool.

The field work was completed fully in accordance to the plan, and without any accidents or incidents.

Summary

Managing integrity of complex assets is not just about a tool. It is about offering the right technology, competence, knowledge and people together to satisfy the demanding needs of our clients. This is what we do best - Solutions. Because we can.