In a Nutshell:

Salt caverns are artificially created cavities in salt formations below the ground surface. Often, they are converted oil wells that are drilled until they reach the salt formation. Water is then injected to dissolve the rock salt, thereby creating a cave that may measure several hundred thousand cubic meters or more. Because of the favorable mechanical properties of the salt, those caves often serve as storage facilities for products such as compressed air, hydrogen, LPG, natural gas and crude oil. While the storage cavern itself poses relatively few challenges in terms of integrity maintenance, the situation is different for the associated piping. In this case, a German customer approached ROSEN experts in our EU region to apply our proven ILI technology utilizing high-resolution technology to well casing pipes.

Pipe corrosion is a common threat in the harsh environment of oil and gas systems. Casing pipes, which are vertical pipelines connecting the ground surface with underground caverns, are not exempt from this threat. Similar to other assets in the oil and gas industry, casing pipes are also aging, and thus even failing at times.

Managing the integrity and ensuring the performance of these assets is critical. Verification or repair of defects is often difficult and, in some cases, even impossible. Therefore, these operators are even more dependent on the accuracy and quality of the data collected during an internal inspection.

Figure 1 – Typical salt cavern

Figure 1 – Typical salt cavern


That is why, after successful cooperation on conventional pipeline in-line inspections utilizing high-resolution technology, an operator in Germany approached ROSEN to develop an additional inspection solution – this time to apply the proven ILI technology to well casing pipes.

In addition to the known unstable environmental conditions, which included a sinking cavern ceiling, the operator had general concerns about the integrity of the casing pipes. However, using only the downhole inspection solutions available on the market, these concerns had yet to be explored with the necessary precision.

The pipelines in question have a diameter of 13 3/8 inches and vary in length from 800 to 1,500 meters. The pipe sections are connected via threaded couplings, which also vary in both diameter and length. The task was to detect and size corrosion and metal loss features on the pipe wall and measure the opening width of the threaded couplings.

Figure 2 – Riser tower for testing vertical inspections

Figure 2 – Riser tower for testing vertical inspections


Metal loss, threaded couplings and their corresponding defects are characterized by wall thickness. Therefore, high-resolution Magnetic Flux Leakage (MFL) technology was preferred for this inspection, as it is sensitive to wall thickness changes. High-resolution data collection is possible due to a concept that was developed to combine strong magnetization with a unique low-friction magnetizer and sensor suspension system. Through this, the powerful magnetic tool can be deployed safely into the pipe casings.

The ultra-compact and lightweight tool design is capable of bidirectional movement and supported by a gravity-based wireline operation. Thanks to this wireline connection, clear monitoring during the inspection process was possible, including monitoring the tool’s progress and identifying any potential obstacles, helping to ensure the best possible data collection and provide high-resolution results.

Figure 3 – The ultra-compact and lightweight tool design is capable of bidirectional movement and supported by a gravity-based wireline operation

Figure 3 – The ultra-compact and lightweight tool design is capable of bidirectional movement and supported by a gravity-based wireline operation

After extensive testing to validate the new approach, the solution was successfully applied to the operator’s downhole casing pipelines, collecting valuable high-resolution data and enabling future integrity management.


Even though salt storage caverns are relatively unsusceptible to breaches, incidents do occur. When they do, moreover, their carbon footprint may be even larger than that of some of the oil and gas industry’s most infamous incidents. This is mainly due to the fact that it may take several years until they are even discovered — oftentimes by mere chance because a farmer stepped out one day to find their crops covered in oil. It is exactly this aspect of hidden danger that causes public concern and needs to be addressed progressively with appropriate integrity measures.

If a breach occurs in the steel casing of a well pipe, it is in most cases due to corrosion, poor condition of the seam welds or threaded connections, or excessive deformation of the rock formation. In many cases, traditional well inspection methods are not able to deliver results that are precise and comprehensive enough to make an accurate statement on the asset’s current condition, let alone assess risk and remaining life. The application of proven ILI technology and expert integrity consultancy based on high-quality inspection data may assist operators in complying with the public’s demand for safety measures while keeping mitigation costs to a minimum.

The solution can be applied during a scheduled operational shutdown window, and adjustments can be made to suit last-minute changes to accommodate operational demands, which, in turn, minimizes the need for extended downtime, expensive auxiliary equipment and on-site personnel.