Pipeline defects have long been the primary cause of pipeline failure, and the use of internal inspection technologies to detect and identify such defects has become a widely recognized practice both domestically and internationally. To further promote the development of internal inspection technologies and enhance management standards, this study systematically reviews the technical capabilities and evolutionary trajectories of leading domestic and international companies providing internal inspection services for pipelines. It also analyzes the limitations of existing internal inspection techniques in addressing circumferential weld defects, crack defects, pinhole corrosion defects, and the assessment of pipeline stress states. On the basis of an examination of current practices at the levels of government, pipeline operators, and internal inspection service providers, the study identifies key issues in the management of internal inspection technologies and proposes a multidimensional strategy to address these limitations. The findings are intended to serve as a reference for the future development of internal inspection technologies and the enhancement of management practices in the oil and gas pipeline sector.

The use of in-line inspection technologies to detect and characterize various pipeline defects is a widely recognized practice both domestically and internationally. These technologies can effectively keep the failure frequency of oil and gas transmission pipelines within a stable range; for example, in recent years, PetroChina Pipeline Company has maintained the failure frequency of its oil pipelines at 0.4 incidents per 10³ km·year and that of its gas pipelines at 0.1 incidents per 10³ km·year. Currently, the main in-line inspection techniques include magnetic flux leakage testing, ultrasonic thickness measurement, ultrasonic crack detection, geometric inspection, and centerline measurement using an inertial measurement unit (IMU). For weld defects in service pipelines, magnetic flux leakage and ultrasonic testing are the two primary methods currently employed.

Magnetic flux leakage (MFL) internal inspection technology primarily involves locally magnetizing the test component and using magnetic sensors such as Hall-effect devices to detect changes in the leakage magnetic field [1]. Defects can then be identified based on the measured leakage-field signals, making this technique widely used for in-line inspection of oil and gas pipelines [2–3]. For crack defects, ultrasonic crack detectors are predominantly employed internationally; however, their application is currently limited to internal inspection of liquid pipelines [4]. In ultrasonic crack detection, an ultrasonic transducer emits ultrasound waves at a specific angle; when these waves encounter the crack’s opening surface, they are reflected back, and the resulting data are recorded. Because the crack’s opening surface exhibits a certain orientation, if the propagation direction of the ultrasonic wave is parallel to the crack’s opening surface, the reflected signal is typically not received, meaning the crack detector cannot detect the crack defect. Consequently, most ultrasonic crack detectors are designed to target cracks oriented in specific directions, such as those parallel or perpendicular to the pipeline axis [5–6]. There are relatively few reported applications of ultrasonic crack detectors for detecting cracks in circumferential welds, and the detection accuracy and evaluation methods for microcracks in such welds remain unclear.

In 2007, marked by the construction of the Lanzhou–Zhengzhou–Changsha refined-oil pipeline, China’s pipeline engineering entered its fourth phase of rapid development [7]. With the comprehensive on-site application of new pipeline materials—X70 and X80 steel—and advanced technologies, the demand for human and material resources surged, leading to a pronounced mismatch between resource supply and project needs. For instance, numerous small-scale pipe-manufacturing plants began supplying high-grade steel pipes for pipeline construction, resulting in loss of quality control over certain subcontracted works [8–10]. In addition, the shortage of skilled pipeline welders and well-trained inspection and supervision personnel further exacerbated the challenges in ensuring the quality of circumferential welds in X70 and X80 steel pipelines constructed during this period. At the same time, construction firms placed excessive emphasis on construction speed while neglecting quality management, thereby creating hidden risks that could lead to defects in pipeline circumferential welds. Since the “June 10” and “July 2” accidents on the China–Myanmar natural gas pipeline, the need for internal inspection of pipeline circumferential-weld defects—particularly for detecting cracks in circumferential welds of X70 and X80 high-strength steel pipelines—has become increasingly urgent. Moreover, following the completion of projects such as the Weinan refined-oil branch line and the Ningxia refined-oil export pipeline, prolonged periods of inactivity before commissioning have resulted in pinhole-corrosion-type defects inside the pipelines, posing another significant technical challenge for international pipeline internal inspection.

This study systematically reviews the inspection technology capabilities and development trajectories of leading domestic and international pipeline internal inspection service providers, and, in light of China’s oil and gas transmission pipeline inspection needs, conducts an in-depth analysis of the limitations of internal inspection technologies and the challenges in internal inspection management. Based on this analysis, it proposes targeted solutions, thereby providing a reference for advancing internal inspection technologies and enhancing management standards in China’s oil and gas pipeline sector going forward.

1. Current Status of Internal Inspection Technology Applications

1.1 Internal Inspection Technology Service Company

Currently, internal inspection technologies for detecting metal-loss defects such as corrosion and scratches are highly mature [11–13]. With regard to defect detection in spiral-welded pipelines, a joint research effort between China National Petroleum Corporation Pipeline Company and GE PII Inspection has successfully overcome this challenge [14]. Over the past decade, pipeline internal inspection technology has made substantial progress, particularly in sensor technology, magnetization techniques, and signal-algorithm optimization, which have given rise to advanced methods such as three-axis high-definition magnetic-flux leakage inspection, ultra-high-definition magnetic-flux leakage inspection, and electromagnetic ultrasonic inspection. Concurrent with the rapid growth in demand for pipeline internal inspection, the number of domestic and international organizations engaged in research and service provision in this field has also been steadily increasing.

(1) GE PII Pipeline In-Service Inspection Services is the successor to the pipeline inspection division of BG, the largest pipeline company in the United Kingdom. In 1977, the company developed the world’s first high-resolution magnetic flux leakage detector; in 1999, it acquired Pipetronix, a German firm primarily engaged in ultrasonic in-line inspection; and in 2002, it was acquired by General Electric (GE) of the United States. The company is headquartered in Cramlington, UK, with a workforce of more than 1,000 employees, 13 operational bases worldwide, and 8 data-analysis centers staffed by over 130 data-analysis engineers. It maintains two R&D centers—one in the UK and one in Germany—dedicated respectively to magnetic flux leakage technology and ultrasonic testing technology. The company owns more than 350 sets of various types of inspection tools for metal-loss detection, crack detection, deformation assessment, and centerline mapping, covering pipe diameters from 168 mm to 1,422 mm. To date, it has completed pipeline inspections totaling over 1 million kilometers globally, including more than 40,000 kilometers in China.

(2) ROSEN Pipeline Inspection Services, founded in 1981, is a family-owned enterprise named after its founder, ROSEN. Over more than three decades of development, the company is now headquartered in Lingen, Germany, with operational bases and R&D centers established across five continents. It employs over 2,500 permanent staff, including more than 1,200 R&D professionals, and maintains a team of over 100 personnel at its Asia-Pacific hub. ROSEN’s service portfolio encompasses pigging, metal-loss detection, intelligent diameter measurement, deformation inspection, centerline mapping, and crack detection—primarily utilizing its newly developed electromagnetic ultrasonic crack detector—with coverage spanning pipe sizes from 168 to 1,422 mm. As the design and manufacture of all its inspection tools are conducted in-house, with over 85% of component parts—including transducers, pig cups, and electronic components—produced internally, the company can rapidly fabricate customized inspection tools tailored to the specific requirements of each project. ROSEN currently holds a market share of more than 30% in the global inspection market, making it the world’s largest inspection service provider.

(3) Baker Hughes is the world’s third-largest oilfield services provider. In August 2009, it acquired BJ Services in a cash-and-stock deal valued at USD 55 million, aiming to strengthen its natural gas and deepwater oilfield operations. BJ Services’ pipeline inspection business unit—boasting more than 25 years of inspection expertise—was integrated into Baker Hughes’ Pipeline Services segment, providing onshore and subsea pipeline inspection services to pipeline operators. The company’s inspection technologies primarily include geometric deformation inspection, centerline mapping, and magnetic flux leakage testing. For certain pipelines without pigging systems, BJ Services has developed pull‑type inspection tools; moreover, its latest proprietary inspection technology can verify the effectiveness of pipeline cathodic protection, making it the only company currently capable of performing this function through internal inspection. Prior to its acquisition by Baker Hughes, BJ Services mainly conducted pipeline inspections in North America and Europe; following the acquisition, it has gradually expanded into markets such as Asia.

(4) T.D. Williamson (TDW), founded in 1920 and headquartered in Tulsa, Oklahoma, USA, developed the world’s first pipeline pigging tool. The company specializes in the manufacture of pipe opening and plugging equipment, pig launching and receiving systems, inspection tools, and pipeline cleaning products, while also providing related technical services. In the field of in-line pipeline inspection, TDW primarily employs magnetic flux leakage (MFL) technology, but also offers geometric inspection, centerline mapping, and electromagnetic ultrasonic testing. Although its global market share remains relatively small, the company is capable of customizing inspection solutions for pipelines operating under harsh conditions. Its newly developed helical magnetization detector integrates the advantages of both axial and transverse MFL techniques, and TDW has also established a multi-data-set platform, thereby creating more favorable conditions for unlocking the value of in-line inspection data. To date, TDW has completed in-line inspections on a cumulative total of over 800,000 kilometers of pipeline worldwide, with limited operations in China.

(5) NDT Systems & Services (NDT), headquartered in Karlsruhe, Germany, is a company specializing in the R&D and provision of nondestructive testing systems and services. Its core business is supplying NDT equipment and services to the rail, pipeline, and metals industries, as well as offering internal inspection services for long-distance oil and gas pipelines. In its early years, NDT’s internal inspection equipment was primarily based on ultrasonic testing technology, with a focus on high-precision ultrasonic thickness measurement and crack detection, covering pipe diameters from 168 to 1,422 mm. Subsequently, the company acquired Tubescope, which specialized in magnetic flux leakage equipment, and reorganized its internal inspection technologies into two main product lines: the LineExplorer series, centered on ultrasonic testing, and the Linalog series, focused on magnetic flux leakage testing. NDT’s inspection services encompass pigging, diameter gauging, metal-loss detection, crack detection, centerline mapping, and post-inspection integrity assessment, with its primary markets concentrated in Europe, the United States, and select Central Asian countries; the company is now expanding into emerging markets such as China.

(6) DIASCAN is affiliated with the Technical Diagnostics Center of Transneft, the Russian oil transportation company. Its primary business is the inspection of pipelines under Transneft’s jurisdiction—approximately 65,000 km in total—and it has also participated in the inspection of the Heilongjiang River crossing section of the China–Russia crude oil pipeline in China. DIASCAN’s inspection tools cover pipe diameters from 168 to 1,219 mm and are capable of performing geometric deformation detection, metal loss detection, crack detection, and pigging operations. The company mainly conducts inspections of oil (crude oil and refined products) pipelines. Its inspection tool designs predominantly feature multi-function integration, combining multiple modules—such as geometry plus magnetic flux leakage, ultrasonic thickness measurement plus ultrasonic crack detection plus magnetic flux leakage—into a single tool to acquire multiple types of inspection data in a single run. However, this type of tool tends to be relatively long and places stringent requirements on the dimensions of the cylindrical housing.

(7) PipeSurvey International is a Dutch inspection company headquartered in Zwijndrecht, the Netherlands. In 2009, it partnered with Sichuan Yutong Pipeline Technology Co., Ltd. to enter the Chinese market and jointly carry out intelligent pipeline inspection and assessment services. In 2014, Henan Woodpecker Underground Pipeline Inspection Company acquired a 51% stake in PipeSurvey and established Henan Qianbaidu Pipeline Technology Co., Ltd. in China, gradually expanding its presence in the domestic pipeline internal inspection market. PipeSurvey is a rapidly growing, internationally oriented pipeline technical service provider that offers a wide range of inspection services, including visual inspection, geometric measurement, centerline surveying, and magnetic flux leakage testing. The company’s internal inspection operations span Europe, the Middle East, Asia, the United States, and Australia, with inspection tools capable of handling pipe diameters from 168 mm to 1,219 mm; additional sizes or multi-size tools can be custom-designed according to customer requirements. A key feature of its pigging and inspection equipment is its ability to operate in both directions.

(8) Korea Gas Corporation (KAGAS), established by the South Korean government in 1983, is primarily responsible for LNG import operations and has since grown to become the world’s largest LNG importer. The company operates LNG receiving terminals and approximately 4,100 km of associated transmission pipelines. Its R&D Division, which oversees pipeline inspection and maintenance, is equipped with capabilities for geometric inspection, magnetic flux leakage testing, and centerline alignment measurement. KAGAS’s in-house inspection services have historically been focused internally; however, since 2013 the company has expanded its inspection business into neighboring countries, including China.

(9) China Oil Pipeline Inspection Technology Co., Ltd. is affiliated with China National Petroleum Pipeline Bureau Engineering Co., Ltd. Established in 1992, the company is a specialized technical service provider whose core businesses include intelligent internal corrosion inspection of pipelines, pipeline deformation inspection, pipeline pigging, and inspection and evaluation of external anti-corrosion coatings on buried pipelines. It is the largest inspection company in China, with its in-line inspection technologies primarily based on magnetic flux leakage and geometric deformation detection. The company also offers pig production and pipeline pigging services, with inspection tool diameters ranging from 168 to 1,219 mm. Over nearly three decades of development, the company has undertaken inspection projects for a substantial portion of China’s oil and gas transmission pipelines and has established a presence in the pipeline inspection markets of Sudan, Libya, and Syria. It has further expanded into overseas inspection services in Kazakhstan, India, and other countries, accumulating a total of 60,000 km of domestic and international oil and gas pipeline inspections. In recent years, the company has initiated research and development of new technologies such as electromagnetic ultrasonic testing and electromagnetic eddy current testing, steadily increasing its market share and continuously strengthening its technological innovation capabilities.

1.2 New Pipeline Internal Inspection Technologies

(1) Axial strain-based in-line inspection technology. Pipeline systems are subjected to strains induced by a variety of loads along their axial length. Although the design of pipeline systems accounts for strains resulting from known operating-temperature loads as well as those caused by unknown external loads during the design or construction phases [20–22], the axial strain conditions of the pipeline system can still change during operation due to influences from the surrounding environment and construction activities. Consequently, the detection and monitoring of these axial strains have become a critical component of pipeline integrity management programs. In recent years, Baker Hughes has developed an axial-strain in-line inspection tool called Vectra™–AXISS™, which is an integrated instrument incorporating multiple technologies.

The main components of the axial strain internal inspection equipment are the centerline detection module, the axial strain detection module, and the magnetic flux leakage detection module. The magnetic flux leakage detection module is equipped with multiple uniformly spaced magnetic flux leakage sensors around its circumference, with high-strength magnetic elements mounted at both ends of each sensor. These magnetic elements make contact with the pipe wall and magnetize it, driving the wall into a state of uniform magnetic saturation, thereby enabling detection of defects such as metal loss that may be present in the pipeline. At the same time, the magnetic field generated by the high-strength magnetic elements helps to reduce hysteresis induced during pipeline fabrication, creating an optimal environment for the axial strain sensors to accurately measure the stress state of the pipeline. The axial strain detection module, depending on the pipe diameter, evenly distributes a varying number of axial strain sensors along the longitudinal axis; typically, a certain degree of redundancy is provided to enhance data resolution.

(2) Electromagnetic eddy-current in-line inspection technology. In recent years, the electromagnetic eddy-current technique based on a wound magnetometer array, developed by JENTEK Sensor in the United States, has been proven capable of detecting axial cracks in oil and gas pipelines and determining their dimensions [24–25]. Both the U.S. Department of Transportation and the International Pipeline Association have conducted related research on this technology, primarily for the detection of stress-corrosion cracks. The key features of electromagnetic eddy-current in-line inspection are as follows: ① high signal acquisition density, with data acquisition rates ranging from 3,000 to 10,000 samples per second, enabling measurements every 1–3 mm at an operating speed of 10 m/s; ② robust performance under wide-ranging velocity fluctuations, with a detection speed range of 0.5–15 m/s; ③ reliable crack detection, as this technology has been demonstrated to outperform other methods in terms of detection reliability, lift-off correction, and velocity correction when applied to stress-corrosion cracking.

From 2014 to 2017, China National Petroleum Pipeline Company organized a research team to conduct “Research on Electromagnetic Eddy Current Internal Inspection Technology for Circumferential In-Service Surface-Like Crack Defects in Pipelines,” completing extensive experimental testing. The main tests and studies included: (1) selection of single-probe equipment and design of an automated testing system; (2) analysis of factors influencing single-probe testing and establishment of a signal database; (3) interpretation and analysis of electromagnetic eddy current signals from a single probe; and (4) acquisition and analysis of signals from an arrayed electromagnetic eddy current probe. Through these studies, the feasibility of using electromagnetic eddy current internal inspection technology for circumferential in-service surface-like crack defects in oil and gas pipelines was confirmed, thereby laying a theoretical foundation for subsequent industrial application research on the equipment.

            1.3 Issues with Internal Inspection Technology

Due to its high defect detection rate and ease of operation, in-line inspection technology has increasingly become the preferred method for pipeline operators. However, the growing demand in recent years for detecting girth weld defects and pinhole defects in the pipe body of in-service pipelines has posed new challenges to conventional in-line inspection techniques. The width of girth welds on long-distance oil and gas transmission pipelines typically ranges from about 10 to 20 mm; during detector passage, the available inspection time window is very short, and the irregular geometry of the girth weld makes it difficult to distinguish defect signals. Moreover, small, isolated pinhole corrosion results in minimal metal loss and a small projected area, rendering conventional magnetic flux leakage and ultrasonic inspection signals insensitive. For such unconventional defects, even when anomalous signals are detected, effective identification still depends on the reliability of the evaluation criteria. Both girth weld defects and pinhole corrosion defects represent significant technical challenges currently faced by in-line pipeline inspection. With the continuous advancement of in-line inspection technology, research and development on girth weld defect detection has already begun, and ultra-high-resolution magnetic flux leakage inspection technology has also been developed specifically for detecting pinhole corrosion defects.

            1.3.1 Internal Inspection of Girth Weld Defects

Welding defects in pipeline girth welds have long been a critical factor affecting the safe operation of pipelines. Because girth welds are typically completed on-site, inadequate welding expertise or lax site construction management can readily give rise to quality defects. Following commissioning and operation, some pipelines reveal serious girth-weld defects such as lack of fusion, incomplete penetration, insufficient fill, and excessive grinding. In certain pipeline inspections, high-definition magnetic-flux- leakage internal inspection has detected numerous anomalous signals in girth welds; however, due to the absence of analytical models specifically tailored to magnetic-flux-leakage signals associated with girth-weld defects, these anomalies cannot be accurately identified, classified, or quantified. Moreover, substantial errors in the identification and quantification of girth-weld defects, coupled with significant variations in the mechanical properties of the material at defect locations, result in considerable discrepancies between integrity assessment results and actual conditions. Nevertheless, key inspection metrics such as detection rate, identification rate, and accuracy must continue to be validated and refined through prolonged field practice.

1.3.2 Internal Inspection for Crack Defects

Once a crack defect initiates propagation, the consequences can be extremely severe. Currently, leading international internal inspection companies have developed relatively mature ultrasonic crack detectors, such as GE PII’s UltraScan CD and NDT’s LineExplorer UCC, which are suitable for detecting defects like lack of fusion, circumferential cracks, stress-corrosion cracks, and porosity. However, these systems are primarily designed to detect cracks oriented in specific directions, such as those parallel or perpendicular to the pipe axis. Ultrasonic-based crack detection technology is currently applicable only to the internal inspection of liquid pipelines; for gas pipelines, internal inspection using this approach is still in the early stages of research and application. ROSEN and GE PII have conducted research on using electromagnetic ultrasonic techniques to detect body cracks in gas transmission pipelines and have accumulated substantial experience in the initial phases of implementation. As for circumferential crack defects—particularly those at girth welds—there is currently no mature internal inspection technology available for their detection.

            1.3.3 Internal Inspection for Pinhole Corrosion Defects

Pinhole defects have become a major cause of failure in oil and gas pipelines both domestically and internationally. Due to the limitations of magnetic flux leakage (MFL) internal inspection tools, the detection probability, identification accuracy, and dimensional quantification precision for pinhole defects are currently suboptimal across various MFL tools offered by domestic and international inspection service providers, with significant discrepancies between field excavation verification results and internal inspection report findings. Pinhole defects exhibit rapid corrosion rates; once perforation occurs, they can lead to leakage of pipeline transport media and even trigger explosions. Oil pipelines are typically equipped with leak detection systems; however, because pressure fluctuations caused by pinhole leaks are extremely subtle, the probability of triggering an alarm for such leaks is very low. Therefore, there is an urgent need to conduct in-depth research and development on internal inspection technologies and equipment specifically for pinhole corrosion defects. In 2016, the Pipeline Integrity Management Center team at China National Petroleum Corporation’s Pipeline Company initiated a project under the International Pipeline Research Association to study internal inspection technologies for pinhole corrosion defects. The team has completed pull-test validations—conducted by multiple inspection service providers including GE PII, ROSEN, and PipeSurvey—on the detection rates and detection thresholds for pinhole corrosion defects. The next step will be to develop targeted measures to improve internal inspection equipment, based on the characteristics of pinhole corrosion defects and the results of these pull tests.

1.3.4 In-line Inspection of Pipeline Stress Conditions

The ultimate failure of defective pipelines is influenced not only by the geometric dimensions and shape of the defects, but also by internal pressure, various external loads, and additional stresses. In recent years, China has experienced several incidents of weld cracking in pipelines; analyses indicate that the combined effect of external loads on girth-weld defects is the primary cause of pipeline failure. In most cases of girth-weld failure, external forces inducing deformation of the pipeline are the direct trigger for such failures. The presence of defects leads to localized stress concentrations at the girth weld, which can substantially reduce the allowable stress capacity of the pipe and significantly decrease its allowable deformation, thereby making crack initiation at weld defects highly likely. Consequently, stress concentration in pipelines is a major factor contributing to the failure of oil and gas pipelines. Therefore, accurately determining the local stress state of a pipeline and promptly identifying abnormal stress conditions in the pipeline structure—so as to early predict pipeline segments with a propensity for cracking—holds significant practical importance for controlling the risk of catastrophic failure. Previously, both domestic and international in-line inspections of pipelines have focused on macroscopic defects such as wall corrosion and cracks, while systematic assessment of the pipeline’s stress state—namely bending stress and axial stress—has not been conducted. To date, no reliable in-line inspection method exists for performing such assessments.

            2. Issues in Internal Inspection Management

During the implementation of in-line inspection, inconsistencies in inspection quality arise due to government regulatory requirements, varying levels of management oversight by pipeline operators, and differences in the quality of execution by in-line inspection service providers. The impact of government regulation on inspection quality is reflected in the criteria for certifying inspection contractors’ qualifications and the extent to which these standards meet market demands; the influence of pipeline operators is evident in their contractor selection practices, the capabilities of their management teams, and the operating conditions of the pipelines; and the impact of in-line inspection service providers is manifested in issues such as false or missed detection reports and deficiencies in inspection software and hardware.

2.1 Government

Since the promulgation of the Special Equipment Safety Law on January 1, 2014, long-distance oil and gas pipelines have been brought under the regulatory scope of special equipment, with explicit requirements that inspection service providers must possess the requisite qualifications for their inspection reports to be recognized. Currently, the technical threshold for obtaining magnetic flux leakage (MFL) inspection qualifications is relatively low for internal inspection contractors, whereas the requirements for comprehensive periodic inspection qualifications are extremely stringent. As a result, very few inspection contractors hold both types of qualifications, making it impossible to meet the enormous demand in China’s inspection market. Moreover, MFL inspection qualifications impose only minimal performance and capability standards on MFL inspection equipment, while there remains a significant gap in the certification of equipment capabilities and performance for electromagnetic ultrasonic internal inspection, ultrasonic crack detection, ultrasonic wall-thickness measurement, centerline inspection, and other similar technologies—leaving insufficient criteria to effectively select and prioritize inspection contractors.

On November 23, 2016, the former General Administration of Quality Supervision, Inspection and Quarantine and two other ministries jointly issued the “Notice on Standardizing and Promoting Statutory Inspection of Oil and Gas Transmission Pipelines” (Guo Zhi Jian Te Lian [2016] No. 560), which called for strengthening statutory inspection of pipelines. However, the corresponding implementing technical specifications have yet to be promulgated. TSG D7003—2010, “Rules for Periodic Inspection of Pressure Piping—Long-Distance (Oil and Gas) Pipelines,” focuses primarily on the periodic inspection requirements for industrial pipelines and contains provisions that are not entirely appropriate for the periodic inspection of buried oil and gas transmission pipelines, thereby to some extent affecting the standards applied by pipeline operators in carrying out statutory inspections.

Since the promulgation of the Special Equipment Safety Law on January 1, 2014, long-distance oil and gas pipelines have been brought under the regulatory jurisdiction of special equipment, with explicit requirements that inspection service providers must possess the requisite qualifications for their inspection reports to be recognized. At present, the technical threshold for obtaining magnetic flux leakage inspection qualifications is relatively low for internal inspection contractors, whereas the requirements for comprehensive periodic inspection qualifications are extremely stringent; consequently, very few inspection contractors hold both types of qualifications, making it difficult to meet China’s vast inspection market demand. Moreover, the magnetic flux leakage inspection qualification sets only modest performance and capability standards for magnetic flux leakage inspection equipment, while certification of the capabilities and track records of electromagnetic ultrasonic internal inspection equipment, ultrasonic crack detection equipment, ultrasonic wall-thickness measurement equipment, and centerline inspection equipment remains entirely lacking, thus falling short of providing a reliable basis for selecting the most qualified inspection contractors.

On November 23, 2016, the former General Administration of Quality Supervision, Inspection and Quarantine and two other ministries jointly issued the “Notice on Standardizing and Promoting Statutory Inspection of Oil and Gas Transmission Pipelines” (Document No. Guo Zhi Jian Te Lian [2016] No. 560), which mandated the strengthening of statutory pipeline inspections. However, the corresponding implementing technical specifications have yet to be promulgated. TSG D7003—2010, “Rules for Periodic Inspection of Pressure Piping—Long-Distance (Oil and Gas) Pipelines,” focuses primarily on the periodic inspection requirements for industrial pipelines and contains provisions that are not entirely appropriate for the periodic inspection of buried oil and gas transmission pipelines, thereby to some extent affecting the standards applied by pipeline operators in carrying out their statutory inspections.

2.2 Pipeline Enterprises

2.2.1 Internal Inspection Management

A large number of pipeline operators generally lack dedicated personnel for internal inspection quality control, resulting in the inability to implement end-to-end, professional management across the entire process—covering internal inspection service providers, the inspection execution itself, the inspection deliverables, excavation verification of inspection results, and final inspection acceptance. With regard to the management of internal inspection service providers, there is a lack of an admission mechanism and a quality-assessment system, making it impossible to evaluate service providers’ equipment capabilities and service quality; moreover, some companies face the issue of discrepancies between the contracted inspection service provider and the actual provider carrying out the work. In terms of the inspection execution process, pipeline operators often exhibit deficiencies in process control—for example, inadequate preliminary surveys prior to internal inspection, which prevent accurate understanding of critical parameters such as check-valve opening degrees, bend radiuses, dimensions of pig launcher/receiver stations and associated modifications, assessments of historical operating conditions, and evaluations of similar pipeline inspections. During the inspection process, operational conditions frequently fail to meet the requirements for internal inspection, leading to difficulties in coordinating inspection operations, insufficient coordination of throughput, inadequate assurance of operating conditions, challenges in handling contaminated refined oil products, and missed inspection time windows. As for the management of inspection deliverables, quality reviews are not adequately conducted on inspection reports, lists, and signal data submitted by inspection contractors; furthermore, some pipeline data are improperly stored, resulting in issues such as inaccessible data files or data loss. Regarding excavation verification and acceptance, there is inconsistency in inspection acceptance criteria and practices, with no unified, standardized acceptance procedures or requirements. Typically, expert reviews or meeting-based acceptances merely satisfy procedural formalities without actually assessing the quality of the inspection results, and excavation verification outcomes are likewise not effectively utilized to guide the acceptance process.

            2.2.2 Application of Internal Inspection Data

Currently, pipeline operators face insufficient and incomplete utilization of internal inspection data. With respect to IMU-based internal inspection data, the weld joint coordinates obtained are primarily used for defect localization; however, due to factors such as the confidentiality of pipeline centerline coordinates, this data has not yet been leveraged in pipeline route management, nor have field personnel fully integrated IMU coordinate information into their operational workflows. Moreover, the bending strain values derived from IMU inspection data are currently employed only to identify areas with significant bending strain, without being applied to specialized weld joint excavation or stress–strain monitoring and other weld integrity assessment activities. While field-measured coordinates can serve as reference points to further validate IMU-derived pipeline coordinates, extensive on-site pipeline excavations have not been accompanied by coordinate collection, thereby limiting the ability to enhance the accuracy of IMU inspection results. For pipelines in geologically active zones, IMU inspections should be conducted on a regular schedule; comparative analysis can promptly detect newly emerging localized bends; yet, verification and evaluation through excavation of large-span bending deformations remain infrequent. In addition, there is a lack of standardized specifications for IMU inspections and their data analysis, leading to inconsistent practices among pipeline operators and the absence of established technical guidelines for the application and validation of IMU inspection results.

3. Development Recommendations

3.1 Technology Development Strategy

In the field of in-line inspection technology for oil and gas pipelines, it is essential to both acknowledge the current limitations of such technologies and actively explore the integrated analysis of multi-dimensional data, thereby maximizing the value of existing techniques. Efforts should be made to enhance the detection and identification rates of girth weld defects, pinhole corrosion defects, and crack-like defects. Based on advancements in sensor technology, it is recommended to accumulate practical experience in pipeline in-line inspection and related data applications, and to adopt the following strategies for continuous improvement.

(1) Combined detector strategy: By integrating well-established inspection techniques—such as magnetic flux leakage testing, geometric inspection, weak-magnetic-field detection, and centerline detection—various types of inspection signals are acquired, and comprehensive analytical methods are employed to achieve breakthroughs in pipeline defect detection.

(2) Multi-frequency flux leakage detector: By employing a multi-frequency flux leakage detector and conducting comparative analysis of the acquired girth weld signal feature data, efforts are made to reduce background noise caused by geometric irregularities, lift-off, and vibration.

(3) Strategy for Enhancing Signal Analysis Capabilities: By collecting and organizing excavation-and-repair data, integrating the results of data alignment, and feeding the excavation outcomes back to the inspection company, we will enrich the correlation between actual defect characteristics and corresponding signals, thereby elevating signal-processing expertise and striving to achieve breakthroughs in defect-signal interpretation.

(4) R&D Strategy: Strive to achieve breakthroughs in the development of new technologies for pipeline defect detection, such as electromagnetic phased-array technology, electromagnetic eddy-current technology, electromagnetic ultrasonic technology, and ultra-high-definition magnetic-flux- leakage inspection technology.

3.2 Quality Management Improvement Strategies

Due to the limitations in the development of in-pipe inspection technologies and the mismatch between qualification capabilities and statutory inspection requirements, as well as the difficulties in performance verification, quality management of in-pipe inspections should be strengthened and enhanced in the following aspects:

(1) Establish a specialized management team for internal inspection, strengthen oversight of internal inspection contractors, conduct timely quality analyses of internal inspection work, and implement professionalized management across the entire lifecycle—ranging from contractor selection and in-process quality control to assessment of inspection deliverables, excavation verification, and final acceptance—to create more robust conditions for quality control and assurance in internal inspection.

(2) Strengthen excavation verification based on internal inspection results by promptly conducting excavation verification and statistical analysis of such results, thereby addressing potential defects and vulnerabilities in the pipeline body that may arise from the reliability, accuracy, and limitations of internal inspection technologies. Establish a mechanism for feeding back excavation verification results to internal inspection service providers to enhance their capability in identifying and analyzing inspection signals.

(3) Based on relevant internal inspection standards and statutory inspection requirements, refine the pipeline internal inspection management procedures and operational documents, establish a quality assessment system for internal inspection service providers, and incorporate the assessment results into the provider access mechanism and the internal inspection vendor selection process, thereby ensuring that the most suitable internal inspection service provider is selected in accordance with the specific risk profile of each pipeline.

(4) Continuously conduct business training and qualification certification programs to comprehensively enhance the management capabilities and technical performance control of personnel engaged in pipeline internal inspection, and gradually establish an integrity-based management model for pipeline internal inspection service contractors.

(5) Actively coordinate with relevant national regulatory authorities to develop codes and standards tailored for statutory inspections of long-distance oil and gas pipelines. At the same time, draw on best practices accumulated during internal inspection operations to enhance the quality of pipeline internal inspections and strengthen the capability to ensure the safe operation of oil and gas pipelines through internal inspection technologies.

4. Conclusion

In-line inspection is currently the most mature, effective, cost-efficient, and readily scalable inspection technology for in-service pipelines. However, each in-line inspection technique has its own specific scope of application and limitations; therefore, the appropriate in-line inspection technology and equipment should be selected based on the objectives and goals of the inspection, ensuring that the capabilities and performance of the inspection equipment are aligned with those objectives. At the same time, in view of the threats posed by girth weld defects, pinhole corrosion defects, and crack-like defects that long-distance oil and gas pipelines are currently facing, more proactive response strategies are needed. While promoting the enhancement of in-line inspection management, we must take the independent research and development of key core technologies and equipment as a breakthrough point, focusing on the application development, engineering implementation, and industrialization of high-end general scientific instruments and specialized major scientific instruments, thereby effectively elevating the technical level and equipment capabilities of in-line pipeline inspection.

This article was published in Oil & Gas Storage and Transportation, November 2020. Authors: Wu Zhiping1, Xuan Wenbo2, Dai Liangshuang1, Li Yan2, Chang Jinglong1, Wang Fuxiang2 (1. National Pipeline Group; 2. National Pipeline Northern Pipeline).