Pipe Axis Research Articles

A Two-dimensional Numerical Model of Heat Exchange in the Soil Massif During the Operation of a Shallow Horizontal Soil Heat Exchanger

The current article uses a two-dimensional numerical model to represent the results of theoretical studies of the heat exchange in the soil massif during the operation of a shallow horizontal soil heat exchanger. The analysis of literature sources showed that one of the important conditions for the effective operation of a shallow-soil heat exchange is its rational design parameters, such as the total length of the pipeline, the diameter of the pipe, the distance between the axis of the adjacent pipes, the depth of the heat exchanger placement, etc. A two-dimensional heat exchange model in the soil mass was developed, which made it possible to investigate the operation of a shallow horizontal soil heat exchanger. It was found that the step between the axis of the adjacent pipes of the multi-loop heat exchanger, which is 0.95 m, is optimal when creating a shallow horizontal soil heat exchanger in the soil conditions of Kyiv.

Local Scanned Point-Cloud Registration of Aeroengine Pipeline System Based on Axial Constraints

The final assembled state is one of the crucial factors in the quality of an aeroengine pipeline system. It directly affects the safety, reliability, and thrust-to-weight ratio. Because of the limitations of aeroengine assembly and inspection technologies, ensuring the consistent assembly of pipeline systems in aeroengine production has become a challenging and key issue. We inspect the assembly of an aeroengine pipeline system with high precision and reliability using a single-frame point cloud that is acquired with a structured-light 3D scanner. To achieve this, we propose a novel registration framework that considers the structural constraints of the aeroengine pipeline system to achieve an accurate point-cloud alignment between the single-frame point-cloud data and the standard model. First, pipe axes are extracted from the single-frame point-cloud and standard models as the constraints for the coarse registration. Subsequently, a new point-cloud descriptor for curved segment features is designed to implement the rapid retrieval of structural features from both the single-frame data and relative models automatically. Finally, we use a voting mechanism to determine the best result when there are multiple matches. This allows us to achieve accurate and efficient registration with a non-uniform assembly structure. Experiments on both actual and synthetic datasets illustrate that the proposed registration method achieves higher accuracy and efficiency. Compared with the state-of-the-art algorithm, our method reduces the RMSE value by approximately 9 times during the quasi-real-time single-view raw point cloud assembly process of the aeroengine pipeline system.

Thermal mixing characteristics of T-junction incident along central axis based on Large-Eddy simulations

A large eddy simulation model was used to explore the temperature mixing characteristics of a T-junction in which a branch pipe extends into the main and the branch fluid is injected along the central axis of the main pipe. The influence of the incident velocity of the branch tube on the temperature fluctuation of the fluid mixing is considered. In the main mixing region, the dimensionless time-averaged temperature（T∗¯）is positively related to the dimensionless root mean square（Trms∗）, while the connecting pipe region shows the opposite trend. With the increase of the velocity ratio, the influence of the branch pipe structure on the main flow field gradually decreases. The rebound vortex accelerates the rupture of the vortex ring, and the higher injection speed of the branch pipe leads to an increase in the vortex strength and the range of mixing area, which enhances the mixing of the fluid and makes the temperature distribution of the flow field more uniform. Finally, through the power spectral density analysis of temperature fluctuations, it is not only found that the high-energy vortex ring falls off to the near-wall region, dominating the temperature fluctuation in this region, but also this type of T-junction greatly reduces the risk of thermal fatigue failure.

Investigation of the inlet layout effect on the solid waste removal in an octagonal aquaculture tank

The optimization of the inlet layout in aquaculture systems is essential to ensure minimal solid waste discharge into the environment and improve fish production efficiency. In the present study, laboratory experiments were carried out to investigate the effects of the jetting position d/a (where d is the distance from the pipe axis to the tank side and a is the side length of the tank wall) and the jetting angle θ (the acute angle between the jetting direction and the nearest tank wall) on the solid waste removal efficiency in single-inlet and dual-inlet octagonal Recirculating Aquaculture System (RAS) tanks. To this end, three jetting positions (d/a) of 1/50, 1/8, and 1/4 and ten jetting angles (θ) of 0° to 80° were considered in the experiments. The Particle Image Velocimetry (PIV) technique was applied to measure the flow characteristics in the tank and analyze the solid waste removal under different working conditions. Residual mass of the solid waste, time of complete removal of solid waste, average velocity (vavg), and uniformity coefficient of velocity distribution (DU50) were analyzed to evaluate the solid waste removal efficiency. The obtained results indicate that adjustments of the inlet layout significantly affect the solid waste removal efficiency. It was found that a single-inlet tank with a d/a of 1/8 and θ in the range 10° to 40° has a good solid wastes removal performance, and the optimal efficiency occurs at a jetting angle of 30°. Moreover, the optimal solid waste removal efficiency in a dual-inlet tank can be achieved with a d/a ratio of 1/8 and a θ of 20°. The performed analyses reveal that from the aspect of solid waste removal efficiency, a tank with a d/a ratio of 1/8 outperforms a tank with a d/a ratio of 1/4 or 1/50. The results of this article offer novel insights in the layout of octagonal RAS tanks and provide a guideline to improve self-cleaning features of aquaculture tanks.

High speed stereoscopic PIV investigation of the statistical characteristics of the axially restricted turbulent swirl flow behind the axial fan in pipe

Investigation of the turbulent swirl flow in the piping system is one of the most complex investigations in the field of energetics and turbulence. Axial fans in a pipe, without guide vanes, are widely used in practice and the problem of their duty point and energy efficiency is still extensively discussed. Analysis of the interaction between axial fans energy and construction parameters is one of the main topics in defining the fans energy efficiency potential. On one side, there is a three-dimensional velocity field in the wall-bounded flow with regions of great turbulence intensity. On the other side, there is a complex blade geometry, which generates the turbulent swirl flow. This paper presents research on the turbulent swirl flow, Rankine type, in an axially restricted system, using high-speed stereo particle image velocimetry (HSS PIV). Axial fan impeller, with outer diameter 0.399 m and nine twisted blades is the flow generator. The Reynolds number Re = 176,529 is achieved in the pipe. Reynolds stresses, statistical moments of higher order, and invariant maps are calculated based on the three component velocity fields. Here, intensive changes of all statistical parameters occur in radial and axial direction. In the flow region, four flow regions can be identified. Interaction of all these four flow regions produces extremely complex turbulent swirl flow, which is generated behind the axial fans. Determined invariant maps reveal turbulence structure. It is shown that the state of turbulence on the pipe axis is three-component isotropic, which is contrary to the case of axially unrestricted turbulent swirl flows. In the rest of the space, in the region up to r/ R = 0.52, the states of turbulence occur in the area in between the boundaries which designate axis-symmetric turbulence (contraction) and axis-symmetric turbulence (expansion), in the vicinity of the state of three-component isotropic turbulence.

Design for snake robot motion via partial grasping on pipes

This paper proposes a method for the movement of a snake robot on crowded pipes or one with large branches. The robot moves along a pipe by grasping it with its entire body instead of wrapping around it, and it adjusts its body shape to the target curve. The proposed robot contains a part that does not contact the pipe, allowing it to move in two directions: along or around the pipe axis. It avoids obstacles by combining these movements while making contact with itself to reduce joint torque and preserve body shape. Experiments demonstrated the efficacy of the proposed robotic snake motion by circumnavigating an obstacle on a pipe in several situations.

Characterization of flow field of swirling flow conveying in bulk grain pipeline based on gas‐solid multiphase coupling

AbstractAn experiment was carried out to study the characteristics of swirling pneumatic conveying of grain particles in horizontal pipeline, which can provide a reference for the design and optimization of swirling pneumatic conveying system of bulk grain pipeline. The numerical simulation of swirling pneumatic conveying under the guidance of vane swirling generator was performed via CFD‐DEM coupling method. The axial velocity of grain particles was symmetrical along the radial direction, and the tangential velocity was symmetrical along the pipe axis. When the blade number of the swirling device was 6–9, the static pressure drop and standard deviation of the flow field were large, the instantaneous energy consumption of the system and the dispersion of particles were high, and the conveying effect was good. When the blade number was six, the spiral distance of the flow field in the pipe was longer with better quality of swirl flow. In accordance with the simulation results, the best effect of swirling conveying is achieved when the equivalent diameter of the grain particles is 4 mm, the multiphase flow conveying speed is 20 m/s, and the spiral blade number of the swirling flow generator with flow deflector is six.Practical applicationIn the practical application, the swirling flow generated by the swirling device can suppress the settlement of particles and the blockage of the pipeline in the straight pipe conveying, and avoid the high speed collision between particles and the pipe wall in the curved pipe conveying, slow down the impact, reduce the particle breakage and the wear of the pipe wall. The generation and maintenance of swirling flow play a key role in the long‐distance conveying of various chemical raw materials, grain, fertilizer and other granular materials. Swirling flow pneumatic conveying has the advantages of simple equipment structure, small occupation space, flexible pipeline layout, easy to automatic control, high production efficiency, recycling, environmental protection, and so on. It has become an important conveying mode in bulk material conveying.

Numerical study of microwave impact on gas hydrate plugs in a pipeline

Purpose. Development of a technique for the numerical study on the decomposition of gas hydrate plugs in deep-water pipelines under microwave radiation using a coaxial source. Theoretical efficiency evaluation of using such an impact to unblock the pipelines. Methodology. Mathematical modeling and computational experiment. Findings. An original mathematical model is proposed to describe heat transfer processes during the decomposition of gas hydrates in a pipeline under the action of heat sources distributed over the volume. The non-stationary problem of heat transfer was considered in a one-dimensional formulation. An algorithm for numerical computation is proposed. A mathematical expression is obtained for distributed heat sources generated by the microwave radiation from a coaxially located SHF antenna. Parametric numerical studies on temperature fields and decomposition dynamics of a gas hydrate plug are performed for specified parameters of pipe and microwave radiation power. The boundaries of the decomposition area and the dynamics of change in this area are determined. The decomposition time of a gas hydrate plug with a diameter of 0.3 m was determined using a 300 W microwave source. The complete decomposition took approximately 40 hours. Originality. The task of thermal decomposition of a cylindrical gas hydrate plug in a pipeline due to microwave heating using a coaxial microwave power source has been considered for the first time. The process is viewed as a sequence of several stages: heating, heating and decomposition, decomposition after complete heating of the gas hydrate layer. To model the volumetric dissociation of gas hydrate, it was proposed to use special functions that characterize the amount of decomposed gas hydrate. The introduction of such functions makes it possible to construct an efficient computational algorithm taking into account the action of volumetric sources in the decomposition area. The known models mainly consider only surface thermal effect or microwave impact on gas hydrate in porous mediums. The presented model allows describing the decomposition during volumetric heating of a solid hydrate adequately. Practical value. Blocking plugs may occur due to hydrate formation when transporting gas through deep-water pipelines or through pipelines in cold environments. The elimination of such complications is a complex technical task. In particular, a special source of microwave radiation, which was proposed by the authors in previous works, can be used to unblock the pipeline. The device that makes the microwave radiation is located along the pipe axis. The results of this work allow us to evaluate the effectiveness of the microwave method for eliminating the gas hydrate plug. The mathematical model and computational method can be used in the development of appropriate technologies using a coaxial microwave heating source.

Design and Proof-of-Concept of a Matrix Transducer Array for Clamp-On Ultrasonic Flow Measurements.

Common clamp-on ultrasonic flow meters consist of two single-element transducers placed on the pipe wall. Flow speed is measured noninvasively, i.e., without interrupting the flow and without perforating the pipe wall, which also minimizes safety risks and avoids pressure drops inside the pipe. However, before metering, the transducers have to be carefully positioned along the pipe axis to correctly align the acoustic beams and obtain a well-calibrated flowmeter. This process is done manually, is dependent on the properties of the pipe and the liquid, does not account for pipe imperfections, and becomes troublesome on pipelines with an intricate shape. Matrix transducer arrays are suitable to dynamically steer acoustic beams and realize self-alignment upon reception, without user input. In this work, the design of a broadband 37×17 matrix array (center frequency of 1 MHz) to perform clamp-on ultrasonic flow measurements over a wide range of liquids ( c=1000-2000 m/s, α ≤ 1 dB/MHz · cm) and pipe sizes is presented. Three critical aspects were assessed: efficiency, electronic beam steering, and wave mode conversion in the pipe wall. A prototype of a proof-of-concept flowmeter consisting of two 36-element linear arrays (center frequency of 1.1 MHz) was fabricated and placed on a 1-mm-thick, 40-mm inner diameter stainless steel pipe in a custom-made flow loop filled with water. At resonance, simulated and measured efficiencies in water of the linear arrays compared well: 0.88 and 0.81 kPa/V, respectively. Mean flow measurements were achieved by electronic beam steering of the acoustic beams and using both compressional and shear waves generated in the pipe wall. Correlation coefficients of between measured and reference flow speeds were obtained, thus showing the operational concept of an array-based clamp-on ultrasonic flowmeter.

A Finite Element Model for Monitoring the Displacement of Pipelines in Landslide Regions by Discrete FBG Strain Sensors

This study investigates a system for monitoring displacements of underground pipelines in landslide-prone regions. This information is an important alarm indicator, not only to prevent the failure of the line itself but also to mitigate the direct consequences of landslides on buildings and infrastructures in the affected area. Specifically, a numerical processing tool coupled with a data acquisition system is proposed. The starting point is the measurement of axial strain at three points of discrete sections of the pipeline by Fiber Bragg grating sensors, used to approximate the trend of mean axial strain and bending curvatures along the pipe axis. A finite element analysis based on a 3D geometrically exact beam model is developed for computing the deformed configuration corresponding to the input strain field. After assigning the boundary conditions, a mixed iterative scheme is used for a quick solution to the nonlinear problem. Firstly, the tool is validated theoretically with benchmarks on beam-like structures undergoing large deflections. Then, experimental results are produced on a monitored pipe buried in a wedge of land subject to an artificial slide. The overall sensor-modeling system, with zero displacements far from the landslide as a boundary condition, provides a satisfactory displacement trend with a mean error of about 18% with just three effective monitored sections in the affected pipe stretch of 18 m. The acquisition and processing tool is implemented in a web application as a real-time alarm system.

Electrically Conducting Fluid Flow and Electric Potential in a Square Cavity Subjected to a Point Magnetic Source

ABSTRACT Magnetohydrodynamics (MHD) flow in cavities subjected to both the magnetisation and the Lorentz forces due to a point magnetic source is studied. The governing PDEs are derived and iteratively solved by the dual reciprocity boundary elements method (DRBEM) with linear elements. It is shown that the magnetic field decelerates the axial flow around the point magnetic source, and a further increase in Ha causes a reverse flow in the pipe axis direction. An increase in Re, Ha, or Mn reduces the electric potential in magnitude. The planar velocity values decrease at the same rate as the Re increment. The influence of the magnetisation force lessens in high Re cases without alternating the axial velocity and the electric potential within the pipe. This study is the first to give the effects of both the magnetisation and the Lorentz forces on the fluid behaviour in terms of velocity, pressure, and electric potential.

Research on fracture toughness and strength of thin-walled Ti–B25 pipes using small notched beams

One of the most essential processing procedures for thin-walled titanium pipe is hot extrusion. The non-uniform distribution of microstructure along the wall thickness and pipe axis of thin-walled pipes produced with this technology, on the other hand, would affect the non-uniformity of mechanical characteristics. Although it is generally difficult to process specimens that meet the linear elastic fracture mechanics (LEFM) conditions for this thin-walled titanium alloy Ti–B25 pipe, a simple method for non-linear elastic fracture of material was used to test the yield strength σY and fracture toughness KIC of this thin-walled titanium alloy Ti–B25 pipe in this paper. Three-point bending (3-p-b) was used to test the single edge notched beam (SENB) specimens. The fracture surface of each specimen was examined using a scanning electron microscope (SEM). The discrepancy of yield strength values measured by 3-p-b test and tensile test is 0.6% when the fictitious crack zone △afic equals 2.5 mm, and the fracture toughness KIC of the Ti–B25 pipe is determined to be 83.28 MPa m0.5. This method is a simple and practical way to evaluate the fracture toughness of thin-walled pipe, and it can be used to ensure the safe design and application of titanium alloy pipe.

Effect of fiber reinforcement on extrudability and buildability of mineral additive modified Portland cement mortars: A rheometer based simulation analysis

This study aims to analyze the role of fiber reinforcement on the extrudability/buildability of mortars with an alternative rheometer-based simulation method. Mortars reinforced with an innovative high tenacity polymeric fiber and w/o fiber are prepared. The subjected shear rate history of mortars throughout the extrusion pipe is simulated with aid of a rheometer equipped by a dragging ball. Shear rate dependent variation of shear stress and viscosity values as a function of time have been measured. These parameters are associated with the expected shear rates at longitudinal axis of extrusion pipe. Critical points where cross section changes at longitudinal direction are determined and effect of shear rate variation on rheological parameters is discussed. Extrudability and buildability coefficients are proposed based on shear stress and viscosity values at these critical points throughout the extrusion pipe. Test results revealed that fiber reinforcement has a paramount effect on rheological parameters of mortars where proposed simulation method is capable of precisely detect the buildability of fiber-reinforced mortars.

Controlling the thickness dependence of torsional wave mode in pipe-like structures with the gradient-index phononic crystal lens

The fundamental torsional wave mode, T(0,1), is typically preferred in monitoring defects in long-range pipe-like structures due to non-dispersive and low attenuation characteristics such that the wave packet is not distorted with distance. However, the sensitivity of T(0,1) wave mode depends on the defect type and orientation. While it is highly sensitive to cracks along the axis of pipes, the sensitivity to detect thickness change is low as T(0,1) wave mode generates tangential displacement motion around the pipe circumference. In this study, a gradient-index phononic crystal (GRIN-PC) lens is integrated into a steel pipe to manipulate its dispersion characteristics such that the phase velocity of T(0,1) wave mode is affected by the overall change in pipe thickness. The modified behavior of T(0,1) wave mode within the GRIN-PC lens region increases the damage detection capability of T(0,1) wave mode. Numerical models involving a parametric unit cell study indicate that the phase velocity of T(0,1) wave mode decreases as the thickness of the pipe with the GRIN-PC lens decreases, in contrast with the conventional pipe. The signal difference coefficient (SDC) is applied to the acquired signal from the focal point of GRIN-PC lens to quantify the uniform thickness change. Full-scale wave propagation simulations involving solid mechanics coupled with the piezoelectric actuation demonstrate that the SDC increases as the thickness decreases. The numerical results are validated with experiments using three steel pipes with different wall thicknesses.

Impact of the pipe row spacing on the capacity of ice bank formed in a volume-limited water bath

In this study, a design of an ice bank heat exchanger with pipes arranged in a column inside a volume-limited water bath, was investigated by a numerical simulation. The aim of the research is to determine the design of heat exchanger which would result in the highest quantity of ice formed in a given time period. Prior to the consideration, the accuracy of the numerical model was validated by comparison with experimental measurements. The boundary conditions are chosen to simulate the real process during the regeneration of the ice bank in the draft beverage cooler. The study is carried out for the condition of natural convection in a water bath and constant temperatures of a secondary coolant flowing through the pipes. The base design of the water bath and the heat exchanger used in the experimental measurements was further considered by CFD simulations through the variation of number of pipes in a column i.e. pipe row spacing. The optimal distance between the axes of the adjacent pipes and consequently the optimal distance gap between the pipes (x) are found as a function of the pipe diameter (d) as x/d ∼ 1.5. This finding is further confirmed by CFD simulations which are performed for cases of different pipe diameters, with different water bath height as well as by heat flow analysis for individual pipes in the bundle.

The elastic spiral phase pipe

We design a device for the passive mode conversion of guided, axisymmetric, ultrasonic waves in hollow elastic pipes into arbitrary non-axisymmetric flexural waves that have a constant angular profile along the pipe axis. To achieve this we create an elastic analogue to optical spiral phase plates—the elastic spiral phase pipe. Three possible configurations of the elastic spiral phase pipe are presented which allow the efficient generation of non-axisymmetric flexural waves from an axisymmetric, longitudinal forcing. The theory leverages the dispersive nature of the guided elastic waves that are supported in pipes through a defined relative refractive index. As such we include a spectral collocation method used to aid the design of the elastic spiral phase pipe that is corroborated with numerical simulations and then experimentally verified.

Точное решение основного уравнения акустики для развивающейся по двум направлениям волны давления

The authors proceed from the hyperbolic equation for acoustic pressure. Using the integral Fourier transform along the axial coordinate, an equation in partial derivatives for the kernel of this transformation is found. This equation contains only one spatial coordinate and time. Applying the integral Laplace transform in time to the last equation, we obtain an ordinary differential equation with respect to the radial coordinate for the corresponding image. It turns out that the solution of the last equation is the well-known Macdonald function. For this function, it was possible to find the original image according to Laplace. All this made it possible to write an integral formula for the pressure in a sound wave. If the function of the initial pressure distribution along the pipe axis is taken in the form of a Gaussian impulse, then the integrals included in the representation of the desired solution are taken explicitly. As a result, we obtain an explicit compact formula for the acoustic pressure distribution in the axisymmetric case. It is convenient to use this formula to analyze the distribution of sound disturbances both along the pipe axis and in the radial direction. Therefore, the results are presented as isobars in the (z, r) plane corresponding to different times.

Measurement of Pipe and Fluid Properties With a Matrix Array-Based Ultrasonic Clamp-On Flow Meter.

Current ultrasonic clamp-on flow meters consist of a pair of single-element transducers that are carefully positioned before use. This positioning process consists of manually finding the distance between the transducer elements, along the pipe axis, for which maximum signal-to-noise ratio (SNR) is achieved. This distance depends on the sound speed, thickness, and diameter of the pipe and on the sound speed of the liquid. However, these parameters are either known with low accuracy or completely unknown during positioning, making it a manual and troublesome process. Furthermore, even when sensor positioning is done properly, uncertainty about the mentioned parameters, and therefore on the path of the acoustic beams, limits the final accuracy of flow measurements. In this research, we address these issues using an ultrasonic clamp-on flow meter consisting of two matrix arrays, which enables the measurement of pipe and liquid parameters by the flow meter itself. Automatic parameter extraction, combined with the beam-steering capabilities of transducer arrays, yields a sensor capable of compensating for pipe imperfections. Three parameter extraction procedures are presented. In contrast to similar literature, the procedures proposed here do not require that the medium be submerged nor do they require a priori information about it. First, axial Lamb waves are excited along the pipe wall and recorded with one of the arrays. A dispersion curve-fitting algorithm is used to extract bulk sound speeds and wall thickness of the pipe from the measured dispersion curves. Second, circumferential Lamb waves are excited, measured, and corrected for dispersion to extract the pipe diameter. Third, pulse-echo measurements provide the sound speed of the liquid. The effectiveness of the first two procedures has been evaluated using simulated and measured data of stainless steel and aluminum pipes, and the feasibility of the third procedure has been evaluated using simulated data.

Measurement of large gas turbine cooling air flowrate for power generation using the heater method.

In large gas turbines, the cooling air flow rate is an important parameter for analyzing the temperature and efficiency of the stators and the blades, so measurement is desired. However, ultrasonic flowmeters are difficult to use because the temperature of the measuring section usually exceeds 300°C, while insertion-type flowmeters are difficult to apply because they require modifications to the piping for installation and cause a pressure drop. In this study, an attempt was made to apply the heater method to the measurement of cooling flow rates. In this method, an annular heater is attached to the outside of the pipe and the temperature distribution along the pipe axis is measured using thermocouples. The temperature distribution is affected by the flow velocity of the fluid in the pipe. The flow velocity can therefore be analyzed from the temperature distribution in the pipe. Measurements were conducted for two kinds of cooling air pipe at an advanced combined cycle power plant. In one, cooling air is extracted from the 13th stage of a compressor and supplied to the 2nd stators of the gas turbine; in the other, cooling air is extracted from the 9th stage of the compressor and supplied to the 3rd stators of the gas turbine. As a result, it was clarified that the cooling air flowrate had a positive dependence on atmospheric temperature at the plant. The dependence was also compared to that of a tit 1,600 degrees centigrade-class combined cycle power plant, with a power output of 700 MW.

Susceptibility of carbon pipeline steels operated in natural gas distribution network to hydrogen-induced cracking

The existing network of both transit and distribution gas pipelines has recently been proposed to be used for the transportation of hydrogen as an energy fuel in the multifaceted structure of the development of renewable energy sources. From this point of view, the paper considers the sensitivity of a long-term operated steel of distribution gas pipeline to hydrogen assisted cracking as a result of preliminary electrolytic hydrogenation of flat tensile specimens, followed by determination of strength and plasticity characteristics. The research methodology has two features: (i) the specimens are cut out from the pipe in the transverse direction to the pipe axis; in this case the fracture plane is parallel to the rolling direction of metal sheet from which the pipes were made; (ii) specimen thickness is 1.2 mm maximally providing through hydrogenation. The study additionally includes determination of hydrogen concentration in the steel, and fractographic analysis. It is shown that the low-carbon steel of the 52-year-old gas pipeline with high residual hydrogen content especially sensitive to hydrogen assisted cracking, indicated by signs of low-energy fracture at the micro scale.