Pipelines constitute the backbone of oil and gas transportation systems, ensuring the continuous and safe transfer of hydrocarbons from production fields to processing plants and export terminals. Due to their extensive length, aging infrastructure, and exposure to aggressive operating and environmental conditions, pipelines are particularly vulnerable to degradation mechanisms, among which corrosion remains the most critical and prevalent threat [1–3]. If left undetected or inadequately managed, corrosion can lead to wall thickness loss, leakage, environmental pollution, significant economic losses, and, in extreme cases, catastrophic failures endangering human lives [4, 5].

Corrosion in oil and gas pipelines is a complex, multi-factor phenomenon influenced by transported fluids, operating pressure and temperature, material properties, and external environmental conditions such as soil composition, moisture, and microbial activity [6–8]. Various corrosion forms may occur simultaneously, including uniform corrosion, localized pitting corrosion, galvanic corrosion, and stress corrosion cracking, each presenting different inspection and mitigation challenges [9, 10]. In onshore and offshore environments alike, corrosion remains one of the leading causes of pipeline failure worldwide, accounting for a substantial percentage of reported incidents in integrity management databases [11].

Traditional corrosion inspection and monitoring methods, such as visual inspection, spot ultrasonic thickness measurements, radiography, and magnetic flux leakage, generally require direct access to the pipeline surface [12]. These approaches often involve excavation, insulation removal, or shutdown of operations, resulting in high inspection costs, extended downtime, and increased safety risks for inspection personnel [13]. Consequently, there is a growing demand within the oil and gas industry for advanced non-destructive testing (NDT) techniques capable of providing reliable, large-scale assessments while minimizing operational disruptions [14].

Long-Range Ultrasonic Testing (LRUT), also known as guided wave ultrasonic testing, has emerged as a powerful solution to address these limitations. Unlike conventional ultrasonic testing, LRUT employs low-frequency guided ultrasonic waves that propagate over long distances along the pipeline wall, enabling the detection of both internal and external defects from a single inspection location [15–17]. This capability makes LRUT particularly suitable for inspecting buried pipelines, road or river crossings, insulated sections, and areas with restricted access, where conventional inspection techniques are impractical or prohibitively expensive [18].

Over the past two decades, LRUT has gained increasing acceptance as a screening tool for pipeline integrity assessment. Numerous studies have demonstrated its effectiveness in identifying corrosion-related metal loss, weld defects, and geometric anomalies, as well as in prioritizing locations for follow-up inspections using localized techniques [19–21]. When integrated into a comprehensive integrity management program, LRUT contributes significantly to proactive maintenance strategies, risk-based inspection planning, and life extension of aging pipeline assets [22].

In this context, the present study focuses on the application of Long-Range Ultrasonic Testing for corrosion monitoring of hydrocarbon transport pipelines in an operational oil field. A practical case study conducted in the Hassi Berkine (HBNS) petroleum area is presented, highlighting the capability of LRUT to detect, classify, and locate corrosion defects over long distances. The results obtained from field inspections are analyzed and validated through on-site verification, demonstrating the reliability and effectiveness of LRUT as a non-destructive technique for enhancing pipeline safety and integrity in the oil and gas industry.

The case study on corrosion detection in hydrocarbon pipelines using Long-Range Ultrasonic Testing technology (LRUT) was conducted through a practical inspection at the HBNS oil field. This field is located approximately 1100 km from Algiers, 300 km southeast of Hassi Messaoud, 114 km from the Tunisian border, and 160 km from the Libyan border. The HBNS field is operated by the Berkine Group, a joint venture between SONATRACH and the American Anadarko Petroleum Corporation, through its subsidiary ANADARKO Algeria Company LLC.

The Teletest MK4 is a specialized monitoring device based on LRUT technology, used for pipeline and structural inspection. It is designed to emit ultrasonic waves along the structure being inspected, detecting defects such as corrosion, cracks, or thickness loss. [6] The Teletest MK4 is equipped with multiple ultrasonic transducers arranged in a circular formation around the structure, forming a collar or sensor ring. These transducers emit ultrasonic waves that travel along the pipeline and capture the echoes reflected by defects or irregularities. By analyzing these echoes, the Teletest MK4 allows for the detection and evaluation of defects over long distances without requiring direct access to the entire structure, making it a valuable tool for preventive maintenance and pipeline

Teletest Wavescan 2.5 is an advanced software tool used in industry for non-destructive inspection of various materials and components. With its ability to detect small defects and provide detailed analyses, this device plays a crucial role in ensuring product quality and preventing potential failures. [1]

The inspection was conducted on the pipeline named "10 INCH Old FGSS-01" with the following characteristics:

The purpose of the inspection was to assess the integrity of the pipeline in service by monitoring the general condition of the line to detect any metal loss due to corrosion or erosion.

Subsequently, the pipeline inspection data was input into the software, and the guided wave scanning operation was initiated over a length of 52 meters in both directions.

The results obtained using guided wave technology are presented in the graph in Figure.6.

After scanning 52 meters, we obtained the graph shown in Fig. 6, which appears on the LRUT instrument screen as a signal composed of three different colors (black, blue, and red). These signals represent the reflection of energy by obstacles on the pipeline surface.

The LRUT indications were primarily classified into categories 1, 2, and 3, corresponding to "Minor," "Moderate," and "Severe" levels of amplitude, respectively. The Distance Amplitude Correction (DAC) curve was used to assess the category. This curve allows the plotting of amplitude variations of circumferential reflectors (typically welds) at different distances from the guided wave collar [1].

The DAC curves were superimposed on the LRUT indications for category evaluation:

From the LRUT graph in Fig. 6, equidistant peaks composed of three colors are observed, indicating circumferential obstacles with distances equal to the length of a pipe section. These peaks can be interpreted as weld joint indications. This observation aligns with the actual physical conditions verified on-site.

Additionally, two other peaks are noted at positions − 20.41 meters in the negative direction and − 7.64 meters in the negative direction. These two peaks are classified as Category 1 reflections, as their amplitude is below the green reference line on the DAC curve.

Furthermore, two more peaks are identified at positions 16.53 meters and 18.57 meters in the positive direction. These two peaks are classified as Category 3 reflections, as their amplitude exceeds the red reference line on the DAC curve.

The following table summarizes the interpretation of the LRUT graph for the "10 INCH Old FGSS-01" line:

The following table summarizes the interpretation of the LRUT graph for the "10 INCH Old FGSS-01" line:

The on-site verification of the results obtained through LRUT technology for inspecting corrosion on the "10 INCH Old FGSS-01" pipeline demonstrated complete alignment with the actual physical conditions observed in the field. This includes the identification of weld joints and the detection of corrosion at the same locations and severity levels indicated by the LRUT data. These findings underscore the reliability of the results provided by this technology, which proves to be a powerful tool for long-distance defect detection. It enables a comprehensive assessment of pipeline conditions without requiring direct access to each segment, offering significant advantages for monitoring the integrity of hydrocarbon pipelines.

Long-Range Ultrasonic Testing (LRUT) technology offers a highly effective and reliable solution for monitoring pipeline corrosion in oil fields. This paper has emphasized the significance of LRUT through a case study conducted at the HBNS oil field, operated by the Berkine Group. The use of LRUT allowed for precise detection of anomalies, such as weld joints and corrosion, over long pipeline distances without the need for direct access to every segment.

The analysis of the results revealed a complete correlation between the actual site conditions and the data collected via LRUT, further validating the technology’s reliability and effectiveness. The use of the DAC curve enabled accurate classification of detected anomalies, facilitating a detailed evaluation of defect severity.

In conclusion, LRUT technology is a vital tool for proactive maintenance and pipeline safety in the oil and gas industry. By providing comprehensive insights into pipeline integrity over long distances, it significantly reduces the risk of failures and supports the safe and efficient operation of oil infrastructure..