Pipe Samples Research Articles

A Novel Investigation on Microstructural Analysis of a Rupture GRE Composite Pipe for Underground Fire Water System

This study investigates how underground fire water systems using Glass Reinforced Epoxy (GRE) pipes are affected by aging. Over time, GRE pipes can degrade, potentially reducing their expected lifespan. The study compared damaged and undamaged areas of pipes to assess how damage impacts their structural integrity. Microscopic and chemical analyses (SEM and EDX) were performed on pipe samples from different locations of the pipe. Mechanical testing (following ASTM standards) was conducted beforehand. Analyses revealed that as damage increased (closer to damaged area), the levels of carbon (C) and oxygen (O) changed significantly with the weight percentage exposed 45.62% difference and 11.62% difference, respectively, as compared with the undamaged area. This suggests that the epoxy resin degrades with age, releasing these elements. Additionally, the presence of foreign objects around the pipes can affect how they bear loads. These findings highlight the importance of understanding how aging and surrounding conditions can influence the performance of GRE pipes in real-world fire water systems.

DEFORMATION MECHANISMS IN CASE OF DESTRUCTION OF THE TUBING NOZZLE MADE OF FERRITE-PEARLITE STEEL

In the work by methods of experimental studies and computer modeling, deformation mechanisms were analyzed during the destruction of the steel suspended branch pipe of the tubing. Tubing rupture occurred during production well operation for 306 days as a result of hydrogen sulfide stress corrosion cracking (SSCC), which was preceded by hydrogen embrittlement of the metal and cyclic action of external forces. Scanning electron microscopy (SEM) shows that the suspended branch pipe is characterized by a ferrite-pearlite structure, and in the area of its fracture, which occurred in the threaded part, there is an increased content of degenerated pearlite grains and traces of hydrogen blisters. Analysis of the crystallographic texture of the original nozzle showed the presence of Br {110} < 112 >, G {110} < 001 >, TG1 {111} < 110 >, TG2 {111} < 011 >, RG {110} < 110 > and RC {001} < 110 > grain texture components. It was found that after operation of the nozzle in well conditions, in the area far from the fracture, the grain orientations related to Cube {001} < 100 >, TG1 {111} < 110 >, TG2 {111} < 011 >, TB3 {331} < 136 > texture components increase. It was found that in the fracture area, in addition to the grain orientations characteristic of the nozzle body, there are also Br {110} < 112 >, G {110} < 001 >, RC {001} < 110 >, RG {110} < 110 >, TC {112} < 110 >, TB1 {111} < 112 > and TB2 {554} < 225 > texture components It is shown that Cube and grain orientation TB3 in the branch pipe after operation accelerate the process of hydrogen embrittlement of metal, and the presence of TB1 orientation indicates the process of return and/or recrystallization in the product. It was found that the process of hydrogen embrittlement led to a decrease in the strength properties and ductility of the steel of the branch pipe. Within the framework of viscoplastic self-consistent (VPCC) model, textures and deformation behavior of samples cut from different sections of the nozzle (before and after operation) were simulated. It was found that at the initial stages of tension the samples of the new branch pipe, the most active is the operation of {110} < 111 > slip systems. In samples of the nozzle after operation, the activity of {110} < 111 > slip systems decreases. At the same time, the activity of {123} < 111 > slip systems increases, and the nature of the operation < 112 > {111} of the slip system does not change. It was found that in all studied states before destruction the activity of {123} < 111 > systems increases ~ 1.4 times. It was concluded that the growth of TG2 {111} < 011 >, {332} < 110 > and {557} < 110 > texture components, as well as the activity of < 123 > {111} slip systems are associated with the effect of shear deformations that generate microcracks in pearlitic grains, and the applied forces contribute to the development of cracks and subsequent destruction of the product. It has been shown that by controlling the crystallographic texture and, accordingly, deformation mechanisms, it is possible to produce new pipeline steels that are more resistant to SSCC.

Design and Calculation of Products from Composite Materials Using Software

This article analyzes six types of composite pipes that are good replacements for corrosive steel and metal pipes for oil, gas, and water. The analysis of the six samples of composite pipes was done using the software program Hoffman Engineering, which is intended for the design and calculation of various types of products made of composite materials. For the analysis of the six composite pipes, the same diameter and the same length were taken, and variable parameters are: the type of material from which the composite pipes are made (carbon/epoxy, carbon-glass/epoxy and glass/epoxy), and the angle of winding of the fibers (10º and 90º degrees). Using the Hoffman Engineering software package, an analysis of the durability of the six differently designed composite pipes at high internal pressure was performed. The same conclusion was obtained from all analyses: the high internal pressure resistance of composite pipes is highly dependent on the fiber winding angle and the type of fibers used. Composite pipes obtained with a fiber winding angle of 90º have twice the internal pressure resistance compared to composite pipes obtained with a fiber winding angle of 10º. Composite pipes based on carbon fibers have the highest resistance to internal pressure, then composite pipes based on hybrid materials (glass and carbon fibers) and finally composite pipes based on glass fibers. Finally, a comparison was made with the obtained laboratory results for the same composite pipes. The same conclusion was obtained from all analyses: the high internal pressure resistance of composite pipes is highly dependent on the fiber winding angle and the type of fibers used. The composite pipes obtained by this process are durable and resistant to very high pressures.

Research on ultrasonic non-destructive evaluation algorithm for ultimate tensile strength of stainless-steel welded pipe welds based on width learning

ABSTRACT The regression prediction between ultrasonic signal and ultimate tensile strength of stainless-steel pipe weld is studied in this paper. First, ultrasonic signals were collected from the weld of AISI304 austenitic stainless steel welded pipe sample, and its ultimate tensile strength was tested. The data sets of ultrasonic signal and ultimate tensile strength of weld were constructed. The random forest algorithm is used to extract the characteristic value set of the ultrasonic signal set of the welding seam and reduce the dimension of the characteristic value set. Then, the set of eigenvalues after dimensionality reduction is input into the Bayesian BLS network for training. The results of the training were compared with those of other regression models. The results show that the model established by Bayes BLS algorithm is feasible and reliable to predict the ultimate tensile strength of stainless-steel pipe weld. The results also show that the model established by the Bayesian BLS algorithm has high accuracy and stability in predicting the ultimate tensile strength of stainless-steel pipe weld. This method can be used to predict the ultimate tensile strength of welds in different types of materials.

Correlation to predict thermal characteristics of pulsating heat pipes with long evaporator section

In terms of employing closed-loop pulsating heat pipes as heat transfer devices in solar water heaters, the evaporator should be extremely long according to the length of the solar collector. However, there is a noticeable shortage of Semi-Empirical Correlations for predicting the thermal performance of extra-long closed-loop pulsating heat pipes utilized for heat absorption within solar collectors. The primary objective of this study was to formulate a Semi-Empirical Correlation specifically designed for predicting the thermal efficiency in extra-long closed-loop pulsating heat pipe configurations. This study extensively examined the thermal efficiency of a comprehensive design of closed-loop pulsating heat pipe samples when implemented in an evacuated-tube solar water heater system strategically designed for individual households. The specified maximum length for the evaporator section of the closed-loop pulsating heat pipes is set at 1.50 m, in contrast to the conventional design, which typically features an evaporator section of approximately 0.15 m. Furthermore, the investigation encompasses a number of sets, varying as one, two, and four. Therefore, a Semi-Empirical Correlation derived from the experimental data concerning seven pertinent non-dimensional parameters is presented, demonstrating a standard deviation percentage of 4.4 %. Among these parameters, the number of sets emerged as the most influential, inducing a maximum percentage change in the heat rate of water of 20.47 %. Moreover, compared with other studies utilizing pulsating heat pipes in solar water heaters, the correlation exhibited a 1.52 % error. These findings suggest that the developed Semi-Empirical Correlation is a valuable tool for predicting the thermal performance of an extra-long closed-loop pulsating heat pipe. It is particularly well suited for estimating the thermal behavior of closed-loop pulsating heat pipes with extended configurations, showcasing its enhanced accuracy and relevance in capturing the distinction of heat transfer in extra-long closed-loop pulsating heat pipe systems.

A mechanistic deterioration point assignment model for water pipe condition assessment

ABSTRACT A pipe condition assessment model is required to implement effective and economical planned maintenance of the water distribution system. The application of such a model requires sufficient accuracy, which, however, is limited by the complexity of the pipe deterioration process and data storage capacity of the water utility. The majority of previous studies have focused on the improvement of assessment algorithms for data mining. In this study, a mechanistic deterioration point assignment (MDPA) model is developed to make advancements in the modes of data input and result output to enhance the model's accuracy and application scope for cast iron and steel pipes. In this MDPA model, (1) indicators/sub-indicators on external corrosion, external load, internal corrosion, and internal load are constructed and can be obtained by data estimation or techniques and (2) assessment results include both pipe overall condition and detailed conditions on corrosion and load, offering evidence for primary maintenance measures. The weights of the indicators/sub-indicators are estimated using the Bayesian statistics theory. The modelling results of pipe samples demonstrate that this MDPA model is an effective tool for pipe condition assessment.

Failure analysis of local effusion corrosion in small diameter gas pipeline: Experiment and numerical

In the later stage of gas well production, water–gas ratio increases, liquid carrying capacity decreases, gas field water accumulates in pipes for a long time, and the corrosion environment of pipelines becomes more and more severe. On the basis of carbon dioxide corrosion, microbial corrosion in gas field water accelerates catalytic pitting and finally leads to serious internal corrosion of pipelines. Therefore, accurate prediction of fluid distribution and flow characteristics in pipes is of great significance for engineering applications. In this work, the location and morphology of the corrosion pit were determined by physicochemical analysis. A computational fluid dynamics (CFD) model was established by using VOF and RNG k-ε models to predict fluid distribution characteristics and fluid accumulation locations in pipelines. The results showed that: 1) Corrosion and perforation occurred in the position of pipeline fluid accumulation. 2) The main elements of the corrosion pit on the inner surface of the pipe sample are O, Fe, C, S and Cl. The main corrosive substances in the pipeline corrosion pit are FeCO3 and Fe2O3. 3) The low-lying areas and uphill sections are prone to corrosion. A decrease in the fluid velocity in the pipe and a corresponding increase in the gas–liquid ratio will result in a greater accumulation of liquid in the pipe. 4) Magnetic flux leakage (MFL) detection method can be used to detect the characteristics and distribution of pipeline corrosion defects and determine the corrosion area. The research results are of great significance to the safety evaluation of small diameter pipelines for gathering and transporting in oil fields.

Applying the modified UV-activated TOP assay to complex matrices impacted by aqueous film-forming foams

Per- and polyfluoroalkyl substances (PFAS) are a large chemical family, and numerous chemical species can co-exist in environmental samples, especially those impacted by aqueous film-forming foams (AFFFs). Given the limited availability of chemical standards, capturing the total amount of PFAS is challenging. Thus, the total oxidizable precursor (TOP) assay has been developed to estimate the total amount of PFAS via the oxidative conversion of precursors into perfluorocarboxylic acids (PFCAs). This study aims to enhance the robustness of the TOP assay by replacing heat activation with UV activation. We evaluated the molar yields of known precursors in water in the presence of varying levels of Suwannee River natural organic matter (SRNOM) and in two soils. The impact of UV activation was also evaluated in two soils spiked with three well-characterized AFFFs, six AFFF-impacted field soils, and nine rinse samples of AFFF-impacted stainless-steel pipe. In the presence of 100 mg/L SNROM, 6:2 fluorotelomer sulfonate (FTS), 8:2 FTS, and N-ethyl perfluorooctane sulfonamidoacetic acid (N-EtFOSAA) in deionized water had good molar recovery as PFCAs (average of 102 ± 9.8 %); at 500 mg/L SNROM, the recovery significantly dropped to an average of 51 ± 19 %. In two soils (with 4 % and 8.8 % organic matter) with individual precursor spikes, the average molar recovery was 101 ± 9.4 %, except N-EtFOSAA, which had a reduced recovery in the soil with 8.8 % organic matter (OM). UV-activated assays outperformed heat-activated ones, especially in AFFF-impacted soils and pipe extract samples, with an average of 1.4–1.5× higher PFCA recovery. In almost all test samples, UV activation resulted in a notable shift towards longer PFCA chain lengths, particularly for samples with high OM content. The study confirmed the advantages of UV activation, including a significantly shortened exposure time (1 h vs. 6 h) and reduced matrix effects from OM due to the dual functions of UV in activating persulfate and photodegrading OM.

Correlating pipe dimensions and success of local heat treatment: Developing nomograms to deduce heat treatment parameters

Local post-weld heat treatment (PWHT) is the only option for heat treating field welded joints. Quite often, the success of local PWHT in alleviating the residual stress and tempering the material within the soak band (SB) is dependent on the ability to achieve the required heat treatment temperature and maintain through-thickness temperature gradient (TTG) within the specified limits at the end of heating cycle, whence soaking begins. Field observations reveal the inadequacy of AWS D 10.10 specified parameters viz. rate of heating (ROH), heat band (HB) and insulation band width in not achieving the required TTG for certain pipe dimensions. Although prior works have attempted to address this issue by widening the HB, the capacity of the heating equipment often pose a limitation. In such cases, reducing ROH is a plausible alternative. With, no such prior studies seen in literature, an exhaustive finite-element analysis simulating the local PWHT on 81, SA106GrC pipe samples (diameter and thickness varied in 9 levels each) was performed, thrice. First as per AWS recommendations, second by halving the code deduced ROH and third by doubling the code deduced HB. The trend of important outcomes (TTG, power source rating and energy consumption) with great significance to the heat treatment industry were also compared and analysed. Two nomograms were developed to serve as a ready reckoner for field heat treater in not only assessing the adequacy of heat treatment parameters but also with possible alternatives in achieving the desired TTG using field-available power source.

Study on the impact of soil environment organic substances on the ageing of urban PE gas pipes in service

PurposeThe service environment of urban polyethylene (PE) pipes has a crucial influence on their long-term safety and performance. Based on the application and structural performance analysis of PE pipe failure cases, this study aims to investigate the impact of organic substances in the soil on the aging behavior of PE pipes by designing organic solutions with different concentrations, which are based on the composition of organic substances in the soil environment, and periodic immersion tests.Design/methodology/approachSoil samples in the vicinity of the failed pipes were analyzed by gas chromatography-mass spectrometry, sensitive organic substances were screened and soaking solutions of different concentrations were designed. After the soaking test, the PE pipe samples were analyzed using differential scanning calorimetry, Fourier-transform infrared spectroscopy and other testing methods.FindingsThe performance difference between the outer surface and the middle of the cross section of PE pipes highlights the influence of the soil service environment on their aging. Different organic solutions can have varying impacts on the aging behavior of PE pipes when immersed. For instance, when exposed to amine organic solutions, PE pipes may have an increased weight and decreased material yield strength, although there is no reduction in their thermal or oxygen stability. On the contrary, when subjected to ether organic solutions, the surface of PE pipe specimens may be affected, leading to a reduction in material fracture elongation and a decrease in their thermal and oxygen stability. Furthermore, immersion in either amine or ether organic solutions may result in the production of hydroxyl and other aging groups on the surface of the material.Originality/valueUnderstanding the potential impact of organic substances in the soil environment on the aging of PE pipe ensures the long-term performance and safety of urban PE pipe. This research approach will provide valuable insights into improving the durability and reliability of urban PE pipes in soil environments.

Polymer Fatigue Evaluation Methodology for Unbonded Flexible Pipes

Polymer layers have been used in the offshore Oil & Gas industry for many years in unbonded flexible pipes for static and dynamic applications. The evaluation of fatigue performance for polymer grades in such applications is complex and no qualification method is well defined nor standardized at the time this article is written.Though historically no reported polymer fatigue field failures the complexity of unbonded flexible pipes, the conservatism of this industry makes the introduction of new polymer grades in risers for dynamic applications challenging. Development of a polymer fatigue methodology will allow the industry to quantitatively evaluate risks of fatigue failure of liners and thereby be important in introducing new material grades.In this paper, a design fatigue methodology is built based on inputs from a specific project and results from small- and full-scale tests. The pipe curvature ranges, extracted from the project location, are used to obtain an accumulated tensile strain which is then converted into an accumulated tensile stress. The fatigue damage is then determined, using a design curve established from bending or tension-tension fatigue testing performed on dumbbells from pipe samples. Parameters are included to reflect geometrical effects from manufacturing process but also service life conditions with several temperature profiles. This method can be applied for pressure sheaths as well as sealed outer sheaths with relevant inputs related to their operating conditions. The obtained fatigue damage can then be used to validate the use of polymer grades for specific unbonded pipe designs under their service conditions.

Machine learning-assisted high precision predictive modelling of convective heat transfer in fluid channels fabricated by laser powder bed fusion

Laser powder bed fusion (LPBF) has proven to be an effective tool in fabricating heat transfer devices with improved efficiency. However, the accurate prediction of convective heat transfer in LPBF-fabricated fluid channels remains a challenge. The classical Gnielinski model is regarded as the most accurate correlation for predicting forced convective heat transfer in traditional pipes. However, whether it is applicable to LPBF-fabricated pipes is yet to be determined. To address this challenge, in this study, pipe samples with diameters of 3 mm, 4 mm, and 5 mm were designed and fabricated using LPBF along the building angles of 0°, 45°, and 90°. The pressure loss and heat transfer characteristics of these samples were experimentally measured. Results showed that there was a maximum prediction error of 72.1 % between the classical Gnielinski model and experimental results. To improve the prediction accuracy, a corrected Colebrook model with improved prediction accuracy of the friction factor was developed, introduced into the classical Gnielinski model, and reduced the maximum prediction error down to 36.8 %. To further improve the prediction accuracy, a gradient descent-based machine learning method was adopted to reconstruct the Gnielinski model, which achieved a high prediction accuracy with prediction errors of below 10 %. With the assistance of machine learning, a high precision predictive model of convective heat transfer in LPBF-fabricated fluid channels was established.

Seasonal occurrence of toxic phytoplankton and phycotoxins at a mussel aquaculture site in Nova Scotia, Canada

A three-year field study at a mussel (Mytilus edulis) aquaculture site in Ship Harbour, Nova Scotia, Canada was carried out between 2004 and 2006 to detect toxic phytoplankton species and dissolved lipophilic phycotoxins and domoic acid. A combination of plankton monitoring and solid phase adsorption toxin tracking (SPATT) techniques were used. Net tow and pipe phytoplankton samples were taken weekly to determine the abundance of potentially toxic species and SPATT samplers were deployed weekly for phycotoxin analysis. Mussels were also collected for toxin analysis in 2005. Liquid chromatography–tandem mass spectrometry (LC–MS/MS) was used to analyse the samples for spirolides (SPXs), pectenotoxins (PTXs), okadaic acid group toxins (OA, DTXs) and domoic acid (DA). Phycotoxins were detected with SPATT samplers beginning from the time of deployment until after the producing organisms were no longer observed in pipe samples. Seasonal changes in toxin composition occurred over the sampling period and were related to changes in cell concentrations of Alexandrium Halim, Dinophysis Ehrenberg and Pseudo-nitzschia (Hasle) Hasle. Spirolides peaked in late spring and early summer, followed by DA in mid-July. Okadaic acid, DTX1 and PTXs occurred throughout the field season but peaked in late summer. Concentrations of some phycotoxins detected in SPATT samplers deployed within the area where mussels were suspended on lines were lower than in those deployed outside the mussel farm. The SPATT samplers provided a useful tool to detect the presence of phycotoxins and to establish trends in their appearance in the Ship Harbour estuary.

Results of Full-Scale Studies of Corrosion and Abrasive Resistance of Ion-Plasma Coating Formed on Samples of Pipe Heating Surfaces of a Biofuel Boiler

Results of Full-Scale Studies of Corrosion and Abrasive Resistance of Ion-Plasma Coating Formed on Samples of Pipe Heating Surfaces of a Biofuel Boiler

Mechanical Properties of Experimental SiC/SiC Pipe Samples for Application in Nuclear Power Engineering Devices

Mechanical Properties of Experimental SiC/SiC Pipe Samples for Application in Nuclear Power Engineering Devices

A comprehensive analysis of the erosion in a carbon steel boiler tube elbow through the use of 3D mapping of the corroded surface and CFD modeling

Erosion corrosion is a common problem that affects boiler tubes, particularly those in power plants and industrial settings where hard water and abrasive particles are present in the flow. These particles can cause physical erosion to the surface of the tubes, which can then lead to further corrosion. This type of corrosion is often accelerated by the high temperatures and pressures present in a boiler system, as well as the presence of oxygen. The combination of physical erosion and chemical corrosion attack can cause significant damage to the tubes, reducing their ability to efficiently transfer heat and potentially leading to system failure. Therefore, it is important to predict rates of erosion to prevent costly and potentially dangerous failures. The focus of this paper is an investigation into the effects of erosion caused by hard water particles on a carbon steel boiler tube elbow (ANSI 16.9). A semi-empirical procedure, which considers properties of the material and flow parameters, is developed for predicting erosion rates. The study revealed that the primary erosion damage occurred on the extrados of the bend. The findings indicated that particles within the flow began to separate from the front wall surface, resulting in significant erosion along the lateral sides. The disappearance of erosion from the front surface of the bend was also consistent with the erosion patterns observed on the eroded pipe sample, which was extracted from the line. Moreover, it was demonstrated the presence of two different erosion patterns in the separation region, which matched qualitatively the erosion pattern observed on the sample wall.

Assessment of chemo-mechanical degradation of concrete sewer pipes through an integrated experimental approach

The chemo-mechanical degradation of unreinforced concrete sewer pipes applied in domestic service locations is assessed through a systematic, integrated experimental approach, considering 18 new and 35 used sewer pipes. The characteristics and environmental conditions of the sewer pipes are reported, and data obtained from surface condition classification, residual alkalinity tests and XRD analyses are combined to identify the type and degree of chemical attack of the used sewer pipes. Concrete material properties are determined by material tests on sewer pipe samples, providing quantitative insight into the age dependency of the Young’s modulus, compressive strength, tensile strength and mode I toughness. All relatively old pipes (installed in the 1920s and 1950s) show substantial chemical attack by biogenic sulphide corrosion (at the inner side of the pipe) and carbonation (at the outer side of the pipe). The time development of the corresponding corrosion depths on average follows a linear trend, whereby the corrosion rate for biogenic sulphide corrosion is about a factor of 1.3 larger than for carbonation. Due to these chemical processes, the mechanical properties of concrete may significantly depend on the age of the sewer pipe. In particular, the average compressive strength and average tensile strength decrease approximately linearly with the age of the pipe, in correspondence with relative reductions of, respectively, a factor of 1.7 and 1.5 over a period of almost 100 years. The values and time-dependent trends found for the concrete properties and corrosion depths of sewer pipes can serve as input for practical analyses and advanced numerical simulations on their bearing capacity and time-dependent degradation. The experimental results also emphasize the importance of regularly assessing the amount of chemical degradation of (especially older) in-situ sewer pipes, by determining the (decrease in) effective wall thickness via core sampling and laser profiling.

Resonant Fatigue Tests on Drill Pipe Connections with Different Geometries and Sizes

In this study, a resonant bending fatigue test rig, designed and implemented by the University of Pisa, is presented, providing a detailed description of the set-up of the machine, the strain gauges calibrations, and the control system used with the main electronic devices. Several geometries of drill pipe connections and pipe samples made of different materials were tested, and all the obtained experimental fatigue results are presented in the paper and compared to previous experimental data. Fractographic images are provided to clearly show that, in two kinds of drill pipe connections, the crack initiation was found at the connection zone, whereas for another connection geometry, it was found at the pipe body. In order to interpret these latter results, a discussion about the section modulus of bending of the various sections of the drill pipes was provided, along with an FE model of a specific zone of one of these connections.

Nondestructive Characterization and Monitoring of Cracking in Pressurized Piping Using Surface Strain Measurements

Primary loop piping integrity is a regulatory and safety concern for the long-term operation (LTO) commercial light water reactor (LWR) nuclear power plants (NPPs). Typically, primary loop piping in existing LWRs was manufactured from cast or wrought austenitic stainless steel alloy material and operates at a pressure of ~2250 psi (16MPa) for a pressurized water reactor (PWR) design type and ~1000 psi (7 MPa) for a boiling water reactor (BWR). The objective of this research was to determine if measurement of surface strains can be used to characterize inner diameter flaws. For this feasibility study, wrought carbon steel Alloy A106 Grade B material was selected in lieu of stainless steel. This research was performed on pre-notched, 10 in. (25 cm) nominal outer diameter (OD) Schedule 120 (0.844 in. [21.4 mm) wall thickness) pipe samples of 24 in. (61 cm) length. The notches were made using electrical discharge machining (EDM) on the inner diameter (ID) of the pipe samples, with notch features two-dimensional (2D) and planar in nature to simulate cracking. The surface strains in the samples were evaluated under increasing hydrostatic pressure, up to a maximum of 2300 psi (16MPa) to determine their response to flaws with variable depth. Reusable end caps were utilized in lieu of welded caps for the pressure testing. This article describes the test procedure for the pressure testing and results of the feasibility study, which is the first phase of research with the end goal of the development of online crack monitoring capability for use at operating NPPs.

INFLUENCE OF GAS MIXTURES OF HYDROGEN WITH METHANE ON THE OPERATIONAL AND THERMOPHYSICAL CHARACTERISTICS OF POLYETHYLENE PIPES OF OPERATING GAS DISTRIBUTION NETWORKS OF UKRAINE

The paper presents the results of complex studies of the influence of mixtures of hydrogen gas with natural gas in the ratios of 10%Н2/90%СН4 and 20%Н2/80%СН4 on the operational and thermophysical characteristics of PE-80 polyethylene pipes and their material Research was conducted on an experimental stand, the diagram of which is attached. The results of comprehensive strength and thermophysical studies of the material of PE-80 polyethylene pipes, which were previously operated in the current gas distribution networks of Ukraine for 15 years, after 6 months of hydrogen exposure, are presented. In order to indicate possible changes in the properties of the material, the same complex of studies was carried out before hydrogen exposure of the samples. The influence of gas mixtures on the thermophysical properties of polyethylene pipes has been established, which is manifested in the reduction of the size of polyethylene crystallites and their orderliness in the volume of pipe walls under the influence of gas mixtures. At the same time, the appearance of crystallites of a new shape was found on the surface of the inner wall of the pipes. It is assumed that this may be caused by the competing action of methane and hydrogen molecules. In the course of conducting hydraulic tests on the resistance of pipes to internal pressure and mechanical studies on uniaxial tension, it was determined that all pipe samples, according to their strength characteristics, meet the requirements of regulatory documents issued for polyethylene pipes used for natural gas transportation. The relationship between the concentration of hydrogen in the mixture and the degree of its influence on the strength characteristics of the samples was established. No changes in the chemical structure of the material of polyethylene pipes were detected. It should be noted that the given results are only the beginning of a more detailed study, during which it is also planned to investigate the effect of hydrogen mixtures on technical polyethylenes after 12 and 24 months of hydrogen exposure. Bibl. 17, Fig. 11, Tab. 2.