Gazovaya promyshlennost’ Спецвыпуск № 3 2021

Gas pipeline construction and repair processes imply much girth butt welding. Arc welded joints are prone to defects: cracks, incomplete fusion with groove, pores, non-metallic inclusions, undercuts, incomplete penetration, imperfect shape, and more. At present, butt welded joints are subject to visual, measuring, radiographic, and ultrasonic non-destructive testing (NDT) as per PJSC Gazprom regulatory documents. These methods are used in both manual and automated modes. Data analysis and weld quality assurance based on the test results are carried out for each test method separately, given their advantages and disadvantages. Importantly, modern non-destructive testing means allow the accumulation of various data digitally to further analyze, process, and structure them. To date, there are many different analysis algorithms and models whose selection is based on the data amount and format and other specific features. The study considers the existing approaches to weld quality assurance in gas pipelines that imply an integrated analysis of non-destructive test data. The technique will significantly increase the likelihood of detecting weld defects and reduce the false indication rejection.

The article presents a technology for a digital antenna array focusing on ultrasonic testing. It considers methods for obtaining various types of defect images using various acoustic schemes. We proposed a new zonal discrimination method based on the multi-view digital antenna array focusing technology. This method surpasses the conventional zonal discrimination methods used in the existing automated ultrasonic testing systems. We also considered some options of digital focusing method application in antenna array scanning both lengthwise and crosswise a welded joint. Any scanning type can use two- and three-dimensional coherent methods that broaden the antenna array aperture and significantly improve image quality. The study shows the advantages of the multi-view digital antenna array focusing technology in testing dissimilar material joints with an austenite inner surfacing. All the considered methods are implemented in the AVGUR-TF automated ultrasonic testing system (SPC ECHOPLUS, Ltd., Russia) created based on the AVGUR-ART multi-channel flaw detector.

Enhancing the reliability and safety of gas transportation systems requires improving non-destructive testing technologies for welded joints, including new domestic equipment development for import substitution. To achieve this, the experts from the base university of PJSC Gazprom, Tomsk Polytechnic University, have developed an import-substitution self-propelled flaw detection system for radiographic examination of girth welded joints in pipelines to execute the order of A.B. Miller, the Chairman of PJSC Gazprom Management Committee, within the research and development contract with Gazprom transgaz Tomsk LLC. The system comprises a newly created panoramic x-ray generator and pipeline crawler, both with wireless control. The article describes the main specifications of the developed system and the results of its field testing by Gazprom transgaz Tomsk LLC. The test confirmed the system’s required functional characteristics and convenience for radiographic examination of girth welded joints in the main pipeline. Thus, LLC Attestation and Certification Center “Engineering and Technological Service of Welding Production” has successfully certified the self-propelled flaw detection system in the INTERGAZCERT Voluntary Certification System, which allows its application in the facilities.

According to the International Energy Agency, the world’s 70 % and 50 % remaining oil and gas reserves, respectively, have high sulfur and CO2 contents [1]. These high contents have resulted in corrosion of the inner pipeline surfaces, causing an intense depreciation of line pipeline sections. One of the prospective lines of work to resolve the issue is using clad pipes in pipeline construction. The article considers the current issues of welding clad pipelines and girth weld quality assurance in them. It presents the main lines of research on dissimilar metal fusion zones and structural changes at given thermal cycles and evaluates their effect on the physical properties of welded joints in clad pipes. In addition, the paper considers the specific features of welding different steel families and basic requirements for welded joints to ensure hot and cold crack resistance, high mechanical properties and corrosion resistance, including intercrystalline corrosion resistance when girth welding clad pipeline elements. It also considers a set of activities based on the research and test results. These activities are needed to establish norms for evaluation, scope definition, and non-destructive test (NDT) methods for clad pipe welded joints. The requirements are set for the scope and methods for mechanical testing of clad pipe welded joints. Besides, the article provides the core content of the research to develop welding and weld quality assurance technologies for pipelines made of clad pipes to implement the PJSC Gazprom Welding Fabrication Development Program for 2021–2023.

Over the past few years, the main gas pipeline pigging practice increasingly reveals a new defect type, cracks across the circular welds, primarily over 50 % of pipe wall thickness not expanding to the base metal. We took part in pipeline pigging carried out by LLC NPC VTD. It revealed that the studied defects are primarily found in circular welded joints of submerged-arc-weld gas pipelines with a diameter nominal of 1400 mm (DN 1400). The existing PJSC Gazprom regulatory requirements for welded joint quality prohibit any cracks. However, the pipeline operation practice and the advanced research results show that circular welded joints with these defects have some life capabilities. The studies revealed several scenarios of this defect type formation. The most likely one is associated to upset submerged-arc welding conditions during gas pipeline construction. This is evidenced by the metallurgical study (coarse-grain acicular structure forming in the inner layers of weld) and increased hardness compared to the allowable value for the weld metal.

The article analyzes the mechanical properties of girth welded joint metal and base metal determined by instrumented indentation relative to standardized mechanical testing of K52–K60 strength grade pipes with outside diameters of 530–1420 mm and wall thicknesses of 10–23.2 mm. The study employed AIS–3000HD (Frontics Inc., Korea) recognized for being compact, vibration-resistant, and operable at down to –30 °С. The examination temperatures ranged from –20 to 20 °С. The properties were correlated by a simple linear relationship. For various specimen types, strength properties of pipe base metal showed high reliability of linear approximation: R2 = 0.80–0.99. The final mechanical properties of welded joint metal and base metal used as input data for the calculation can be derived from the indentation results using a set of correction factors. This allows considering the differences in hardness and other properties on the surface and in a ≈ 0.5 mm thick near-surface metal layer compared with the major part of pipe wall section or welded joints. These differences are related to the specific features of rolled steel production for pipes and multiple-pass welding technology for welded joints. The results show the general possibility of using the instrumented indentation technique instead of mechanical testing and applying mechanical properties obtained (including strength, fracturing resistance, impact energy) to evaluate the operability of welded joints in operation in wide ranges of pipe strengths, pipe sizes, and test temperatures.

Cut line marking for spool fitting is a crucial and tedious stage in repair operations on main gas pipelines. Its precision defines the quality and time spent on installation and welding. To date, the quality of marking methods used in PJSC Gazprom is often insufficient. This is because the cut sections of pipes deviate from the ideal geometry. Using specialized geodetic devices, robotic laser tacheometers would enhance the accuracy and reduce the time needed for marking. The application software allows modeling the connected pipeline components and assembling them virtually, ensuring optimal parameters. The article reveals the causes of errors and limitations of conventional cut line marking methods used for pipeline component fitting. A description is given for a cut line marking method that uses a high-precision robotic laser tacheometer: reference point setting, surface scanning and mathematical modeling of the connected components, transferring virtual marking lines onto the connected parts. The full-scale test results are provided for the Leica MS60 laser tacheometer with specialized SpatialAnalyzer software under basic conditions of Gazprom transgaz Makhachkala LLC and other organizations’ production capacities. The tests confirmed the application potential of robotic laser tacheometer in cut line marking for pipe and pipeline component fitting within main gas pipeline repair operations. The paper also describes the demonstrated practical advantages of the method, which has never been used at PJSC Gazprom facilities for those purposes.