Pipe Wall Thickness Research Articles

Buckling resistance of an X80 steel pipeline at corrosion defect under bending moment

This work investigated the resistance of a corroded X80 steel pipe to local buckling at a corrosion defect under bending moment. A nonlinear finite element model was developed to study buckling behavior of the pipe and determine critical bending moment. Parametric effects, including geometry of the corrosion defect (shape, depth, length and width), pipe geometry (pipe outer diameter and wall thickness) and operating pressure, were determined. Results show that pipeline buckling at the corrosion defect depends on the defect geometry. A rectangular corrosion feature results in a lower buckling resistance than a semispherical corrosion pit or a cylindrical grooved corrosion. The depth and width of the corrosion defect are primarily factors affecting the buckling resistance, while the effect of defect length is negligible. The critical bending moment to cause buckling of the pipe, i.e., the critical buckling moment, decreases as the defect depth and width increase. The buckling resistance of the corroded pipe can be improved by increasing the pipe outer diameter and wall thickness. The role of internal pressure in buckling resistance depends on whether a constraint condition is applied at both ends of the pipe. For buried pipelines without sealing ends, the critical buckling moment decreases as the internal pressure increases.

Effect of pipe flattening on pressure drop in vapor core and thermal characteristic of miniature round and flat-shape heat pipe with sintered fiber wick

The effect of pipe flattening on pressure drop in vapor core and also heat transfer characteristic of the sintered fiber heat pipes has been investigated. The original diameter of heat pipes were 2 mm and 3 mm, respectively, with the effective length of 100 mm. Thermal performance of the flat-shaped heat pipe with the sintered fiber bundle wick was experimentally investigated under a horizontal orientation in this study. The proper fiber bundle wicks were fabricated at porosity of 0.54, and firmly filled within internal heat pipe wall by the sintering process. The heat pipes were pressed into two final thickness by the flattened process which results in vapor core minimizing. The numerical method was established in modified forms to represent the related wick-heat pipe design parameters, for example, wick thickness, wick porosity, wall thickness, flattened width and height, corresponding to thermal performance of fiber wick heat pipes. The numerical analysis for pressure drop was only focused on vapor core region. The vapor flow was assumed to be laminar and incompressible. It is found that when the heat pipe was flattened, the pressure drop increased. The flattening of heat pipe caused the smaller space of vapor core, therefore the working fluid in vapor phase could not easily transfer heat. In this case, the critical final thickness of 0.45 mm (for original diameter of 2 mm) which the vapor core area nearly approaches to zero, has an effect on the high value of thermal resistance considered in vapor core (z5). In addition, the overall thermal resistance estimated from ESDU79012 agrees well with that obtained from the experiment with the standard deviation (STD) of ±15 %, and it shows that the thermal resistance model can provides a reasonable prediction for the thermal resistance of flat-shaped heat pipes with sintered fiber wicks. Moreover, the new normalized parameter h′v/hv is proposed to represent the appearance of vapor core after pipe flattening which can be used to suggest a desirable normal region of flattened heat pipe with the sintered fiber wick. The critical remaining vapor core height after pipe flattening has been further analyzed to be 0.06 (about 74% from original diameter).

Numerical and experimental investigations on the temperature field in local post weld heat treatment of 9 % Cr heat resistant steel welded pipes

Local post weld heat treatment (PWHT) is usually employed in the field fabrication of large-sized 9% Cr heat resistant steel welded components, such as power plant boilers. Temperature field in local PWHT plays critical roles in both achieving PWHT purposes and avoiding detrimental effects of local heating. The objective of this research is to quantify the effects of local PWHT parameters and pipe dimensions on the temperature field in local PWHT of 9% Cr heat resistant steel pipes and finding the optimal process window to engineer desired weld properties. Finite element (FE) models were developed to simulate the temperature field of local PWHT and carefully verified by eight experiments using four 9% Cr heat resistant steel pipes with typical dimensions employed in ultra-supercritical (USC) boilers. The results show that the through-thickness temperature gradient is severely aggravated with the increase of pipe diameter and wall thickness, which will lead to inadequate tempering in the weld metal close to the inside surface of the pipe. To enlarge heated band (HB) width is an efficient way to mitigate the through-thickness temperature gradient, and the axial temperature gradient can be effectively relieved by augmenting gradient control band (GCB) width. The through-thickness temperature gradient is the major factor in implementing successful local PWHT for 9% Cr heat resistant steel pipes. A much smaller process window is found in 9% Cr heat resistant steel pipes due to their higher PWHT temperatures and narrower range of permissible PWHT temperatures.

Probabilistic evaluation of EMAR signals to evaluate pipe wall thickness and its application to pipe wall thinning management

In this study an approach is proposed to probabilistically evaluate wall thickness and the probability of pipe failure when subjected to wall thinning based on the results of periodic non-destructive evaluations. Electromagnetic acoustic resonance (EMAR) has been adopted as a specific non-destructive method to evaluate pipe wall thickness. A probabilistic model correlating the true and evaluated thicknesses was proposed on the basis of the results of laboratory experiments to measure 38 artificially corroded carbon steel plates. A Bayesian approach was proposed to estimate the probability of true thickness and the probability of failure from results of multiple non-destructive evaluations at certain time intervals. The approach was applied to the analyses of several virtual periodic EMAR evaluations of pipe wall thickness that gradually became thinner, whose results demonstrate that the proposed approach is effective regardless of the variability of corrosion rates.

Reconstruction of 3D MHD liquid metal velocity from measurements of electric potential on the external surface of a thick-walled pipe

Liquid metal magnetohydrodynamic pipe flow experiments have been performed in a non-uniform strong magnetic field in order to get further insight into the physics of this type of three-dimensional MHD flow and to enlarge the database for validation of numerical tools. In these experiments, in addition to measurements of the axial pressure distribution, the electric potential has been recorded at a large number of axial and circumferential positions by probes distributed around the periphery of the pipe. Since the wall of the pipe is relatively thick, the electric potential varies across the wall thickness, and surface potentials differ from those at the fluid-wall interface. However, the dense population of potential sensors on the pipe surface allows for a reconstruction of data on the fluid-wall interface, from which we can determine components of potential gradient in the fluid in a plane perpendicular to the magnetic field. The latter ones are closely related to the velocity field, because the electric potential may serve as approximate streamfunction of the flow.

A Preliminary Study of Internal Corrosion in Condensate Pipelines at Geothermal Power Plants

In this study, we presented observations and analyze related to internal corrosion in condensate pipes in geothermal power plants. A damaged pipe of condensate pipeline taken from a power plant was investigated to determine the root cause of failure. The observation and failure analysis was carried out by visual and dimensional examination, chemical composition testing, macroscopic, and microscopic examination, Scanning Electron Microscope (SEM) examination with Energy Dispersed Spectrometer (EDS). The deposit in the pipe was analyzed by X-Ray Diffraction (XRD). The quality of the condensate fluid and their tendencies were determined by Langelier Saturation Index (LSI). Also, the corrosion rate of the pipe was simulated by condensate fluid by using a corrosion measurement system (Tafel polarization). The internal corrosion was found in the condensate line is strongly suspected to occur due to erosion-corrosion. Erosion corrosion is caused by insoluble and hard particles in the condensate fluid. The results of XRD found the presence of calcium-silicate compounds in the sediment that is suspected to be the cause of erosion particles. The reduction of the thickness of the bottom pipe wall and occurs in longitudinal directions the alleged damage to the pipe due to sediment corrosion. The presence of hard compounds and differential oxygen can accelerate the process of corrosion so that the corrosion rate in condensate pipelines was a category in the severe category based on NACE SP0775 standards.

Analysis of regulatory requirements for the assessment of carbon dioxide corrosion at gas production facilities

Aim.In many fields, the produced gas contains corrosive CO2, which, in combination with moisture and other factors, stimulates the intensive development of corrosion processes, including local ones, which requires careful attention to the assessment of the corrosiveness of operating fluids in order to select effective anti-corrosion protection. Ensuring reliable and safe operation of equipment and pipelines prevents not only man-made risks, but also no less important environmental risks, which are especially dangerous for marine underwater facilities for Arctic coastal facilities.Methods.The analysis of normative and technical documentation in the field of assessment of corrosion risks, aggressive factors of internal corrosion and operating conditions of gas and gas condensate fields has been carried out.Results.One of the criteria for assessing the corrosion hazard is the corrosion rate of steel under operating conditions. However, the normative documents predominantly regulate the general corrosion rate, which evaluates the uniform thinning of the metal. But the rate of local corrosion is in no way taken into account, which is most relevant precisely for the conditions of carbon dioxide corrosion of steel. Another tool for identifying risks can be a corrosion allowance to the pipe wall thickness, which should be selected at the design stage and which is provided to compensate for corrosion losses during the operation of gas pipelines. It is shown that the minimum corrosion allowance (3 mm) specified in the main regulatory documents is insufficient, especially for offshore facilities.Conclusion.The experience of operating gas production facilities confirms that the rate of local corrosion can reach several mm/year. To limit this, effective anti-corrosion measures should be chosen, for example, the use of corrosion inhibitors, and a reasonable level of corrosion allowance should be provided that would take into account the corresponding level of corrosion risks at the gas production facility.

To the forecast of martensitic transformation development during sink drawing of austenitic steel pipes

The work aim is the mathematical modeling of the austenitic steel pipes sink drawing process to establish the effect of the pipe wall thickness on the material stress-strain state and to predict the martensitic transformation development. The drawing process was simulated for thin-walled and thick-walled pipes by the finite element method using the DEFORM-2D software package. There are determined the shape change and deformations distribution, the deformations intensity and the average normal stress for seven variants of pipes with different wall thickness ratios and diameter are determined. Distribution patterns for two extreme variants are shown. The difference is shown in the stress state at the drawing process of thin-walled and thick-walled pipes. The change in the average normal stress in time t of a particle passage through the deformation zone for the outer and the inner surfaces for a thin-walled and extra thick-walled pipe is given. In either case, the compression stresses up to –400 MPa for the inner surface and tensile stresses for the outer surface up to +200 MPa are prevail at the entrance to the deformation zone. Inside the deformation zone, a thin-walled pipe is characterized by the presence of approximately equal compressive stresses both on the outer surface and on the inner one. However, the stresses are close to zero outside and reach –600 MPa inside for a thick-walled pipe. The deformation zone numerical simulation in the sink drawing made of austenitic steel showed that there are differences in the stress-strain state in the case of processing thin-walled and thick-walled pipes. The performed calculations and comparison with the literature data on the stress state influence on the cold martensitic transformation process made it possible to predict the development of this transformation in the drawing process. It was revealed that during thin-walled pipes drawing process are created more favorable conditions for the phase transition development.This work was performed with partial financial support of Resolution No. 211 of the Government of the Russian Federation, contract No. 02.A03.21.

Numerical analysis of the effect of solid rod on the flow field and separation performance of thick-walled overflow pipe hydrocyclone

Hydrocyclone is one of the common equipment for solid-liquid separation. Although the hydrocyclone has a simple structure, it has many shortcomings. Among them, short-circuit flow and air core are two important factors that affect the separation performance. Many researchers have tried to weaken the short-circuit flow by changing the structure of the overflow pipe and the trajectory of the particles. This is certainly a feasible method to reduce the short-circuit flow. Is it possible to reduce the short-circuit flow by increasing the movement distance of the short-circuit flow and re-entering the short-circuit flow into the separation area without changing the structure of the overflow pipe? The answer is yes. In this paper, a thick-walled overflow pipe structure was proposed to increase the distance of the short-circuit flow into the bottom end of the overflow pipe.In the proposed structure, the particles in the short-circuit flow can be brought back into the separation area through the circulating flow at the bottom of the overflow pipe. During the working process, the hydrocyclone produces a unique phenomenon-air core. Although the air core does not participate in particle separation, it consumes energy and compresses the separation area. In order to further improve the separation performance of the thick-walled overflow pipe hydrocyclone, a central solid rod was traversed throughout the hydrocyclone to weaken the air core. In addition, FLUENT was used to numerically analyze the thick-walled overflow pipe hydrocyclone with an inserted solid rod in the center. Moreover, we investigated the effect of the solid rod with different diameters on the separation performance of the hydrocyclone. The numerical simulation was verified by comparing the simulation data with the classic data. The results showed that the pressure distribution of the thick-walled overflow pipe hydrocyclonewas more reasonable. The inserted solid rod significantly improved, the pressure distribution. Compared with the conventional hydrocyclone, the short-circuit flow rate of the thick-walled overflow pipe hydrocyclone was reduced by 8.09%. The cutting size of the particles can be adjusted by changing the diameter of the solid rod. When the diameter of the solid rod was 5–6 mm, the cutting size was in the range of 11.6–12.2 μm. When the diameter of the solid rod exceeded 6 mm, the cutting size gradually increased. The appropriate diameter of the solid rod can improve the separation accuracy of thick-walled overflow pipe hydrocyclone, resulting in thinner and higher quality products.

Bending Steel Billet on Presses of Tube Electrical Welding Aggregation

At the production of the steel thick-walled large-diameter pipes according to UOE-technology at the tube electrical welding aggregation 1020 (TEWA 1020), the steel sheet is in series bent on the flanging press, the pre-forming press and the final-forming press. When the steel sheet is deformed on the final-forming press, the excessively curved sections of the sheet are partially unbent in the opposite direction. The calculation of sheet’s curvature at the alternating bending causes the significant difficulties because of Bauschinger’s effect at bending, in which the mechanical characteristics of the steel change significantly. In this paper, the analytical method for calculating the final curvature of steel pipe billet at the alternating bend at UOE-technology is proposed. The results of the paper can be applied in metallurgy.

Multiple Crack Detection in Thick-walled Pipes Using Artificial Bee Colony Algorithm

An analytical method for diagnosis of cracks in thick-walled pipes with a circular hollow section is investigated in this study. In the proposed method, the defect is assumed to be a non-leaking crack, which is modeled by a massless linear spring with infinitesimal length at the crack location. In order to find the cracks in the pipe, the vibration-based method related to the modal properties of the pipe is utilized. In the modal analysis, the mass and stiffness matrices influence the dynamic properties of the pipe. It is assumed that the mass matrix remains unchanged after the crack initiation, while the corresponding stiffness matrix changes. The stiffness matrix of a cracked element can be formulated by the finite element method with two unknown parameters: location and depth of the crack. Using the eigensolution for an undamped dynamic system to formulate the objective function yields to a complicated optimization problem, which can be solved by an iterative numerical optimization method. Among the optimization approaches, the Artificial Bee Colony (ABC) algorithm is a simple and flexible technique for minimizing the objective function. In this paper, the analytical model is utilized to find the size and position of cracks in a pipe using the ABC algorithm and subsequently some numerical examples are examined in order to assess the accuracy of the method. The results show that the proposed method is able to acceptably estimate the location and depth of multiple cracks in the straight pipes as well as curved ones.

Geometric imperfections of large diameter and thick-walled pipe fabricated by push bending with induction heating

Push bending with local induction heating is a kind of advanced method fabricating large diameter and thick-walled pipe. However, geometric imperfections of the bent pipe (section flattening, excessive wall thinning at the extrados, and wall thinning even wrinkling at the intrados) have done severe damage to the safe operation of the pipeline system. In this article, a finite element model of the push bending for large diameter and thick-walled pipe with local induction heating is built and validated via experimental results first, and then the characteristics of temperature distribution and the geometric imperfections mentioned above are investigated based on the finite element model built. It is found that (1) the wall thickness fluctuates a little bit along the bending direction, and the section flattening is severest if the section position angle is between 50 and 60°; (2) the section flattening become more serious with smaller relative bending radius or narrower induction coil or lower heating temperature or faster push velocity because greater bending moment acts on the pipe under these situations; (3) relative bending radius affects the extrados wall thinning and intrados wall thickening much more than other three parameters; and (4) the intrados is probably to wrinkle if the heat temperature is too low or the induction coil is too wide or the push velocity is too fast.

Total Potential Optimization Using Metaheuristic Algorithms for Solving Nonlinear Plane Strain Systems

Total Potential Optimization using Metaheuristic Algorithms (TPO/MA) is an alternative tool for the analysis of structures. It is shown that this emerging method is advantageous in solving nonlinear problems like trusses, tensegrity structures, cable networks, and plane stress systems. In the present study, TPO/MA, which does not need any specific implementation for nonlinearity, is demonstrated to be successfully applied to the analysis of plane strain structures. A numerical investigation is performed using nine different metaheuristic algorithms and an adaptive harmony search in linear analysis of a structural mechanics problem having 8 free nodes defined as design variables in the minimization problem of total potential energy. For nonlinear stress-strain relation cases, two structural mechanics problems, one being a thick-walled pipe and the other being a cantilever retaining wall, are analyzed by employing adaptive harmony search, which was found to be the best one in linear analyses. The nonlinear stress-strain relations considered in these analyses are hypothetical ones due to the lack of any such relationship in the literature. The results have shown that TPO/MA can solve nonlinear plane strain problems that can be encountered as engineering problems in structural mechanics.

Carbon fibre buckle arrestors for offshore pipelines

Feasibility and efficiency of using carbon fibre reinforced polymer (CFRP) buckle arrestors in steel offshore pipelines with D/t of 28 and 40 are investigated using hyperbaric chamber tests. CFRP arrestors are manufactured using Prepreg (PP), Wet-Layup (WL) and Vacuum Bagging (VB) curing methods, with coarse and fine sand surface preparations. A parametric study is performed that outlines the performance of CFRP arrestors in various geometric configurations. Efficiency of CFRP arrestors using different manufacturing methods and various geometric configurations are calculated and compared with those of conventional steel buckle arrestors. It is shown that the efficiencies of CFRP arrestors vary between 0.74 and 1.0 for different manufacturing methods. Optimum efficiencies are obtained in the WL technique, using fine sanding, with CFRP arrestor of thickness twice the steel pipe-wall thickness, and fibres oriented in the hoop direction. Results show that at similar efficiencies, the CFRP arrestors can be much thinner than conventional slip-on or integral arrestors.

RFEC Based Oil Downhole Metal Pipe Thickness Measurement

Oil downhole metal pipe wall thickness measurement is of great importance for pipe evaluation and maintenance. Regular pipe inspection can be used to prevent pipe failure, which could otherwise lead to major failure and financial loss. In this paper, a low-frequency remote field eddy current (RFEC) based internal testing approach is presented, and the analytical solutions of the RFEC electromagnetic equation are obtained based on Dodd and Cheng’s method. Meanwhile, induced voltage under different low frequencies is analyzed, and proper frequencies are chosen for follow-up calculations. For reducing the inspection time of pipe thickness measurement, quasi-Newton’s method (QNM) is implemented based on the deduced solutions. Experimental results indicate that the RFEC and QNM based method is feasible for metal pipe thickness measurement. Pipe thickness is obtained accurately, and the lift-off effect, which has a considerable influence on eddy current testing results, is effectively overcome. The proposed method achieves pipe thickness measurement with proper accuracy and reduction in inspection time.

COMPREHENSIVE STUDY OF THE DYNAMICS OF THE RETAINING MECHANISM OF THE AUTOMATIC MILL

The results of the study of the dynamics of the mechanism for holding the mandrel of an automatic TPA mill are presented. The value of the axial force acting on the mandrel and the rod system of the mechanism of its holding is determined. Developed models of the mandrel retention mechanism have been developed, which made it possible to establish the nature of the development of dynamic processes on the output side of the automatic mill, taking into account the force parameters of the longitudinal rolling process of the sleeve and the parameters of the output side of the automatic mill. Mathematical models of the mandrel retention mechanism have been developed, taking into account the parameters of the technological process and the inertness of the rolled sleeve. The solution of the system of differential equations with variable coefficients is implemented numerically using the Runge-Kutta method for the corresponding dynamic models of the mandrel retention mechanism on the example of calculating the automatic mill TPA 350. The picture of the formation of dynamic processes in the mandrel retention mechanism during the implementation of the entire technological process of pipe production on an automatic mill has been clarified. taking into account the variable impact from the deformation zone and the change in the mass of the rolled sleeve. For various dynamic models, numerical solutions of problems were implemented, which made it possible to select the necessary technological and dynamic parameters of the mechanical system, to assign stable modes of rolling the sleeves on the automatic mill TPA 350. It is shown that the refined solution of the problem for three developed dynamic models of the mechanical system differs significantly from the previously known mathematical models. It has been established that the dynamics of the mechanism for holding the mandrel of the automatic TPA 350 mill is equivalent to the formation of the mechanism for the formation of different wall thickness of pipes. A mechanism for stabilizing the dynamics of the mandrel holding mechanism by separating the sections of the output side of the mill is proposed.

PROCEDURE FOR DETERMINING THE MAIN GEOMETRIC INDICATORS OF THE PIPELINE BY THE MULTI-CRITERIAL OPTIMIZATION METHOD

Background The wall thickness of the main pipeline is mainly determined by calculating the internal pressure. The need to clarify the existing calculation methodology is associated with the presence of some natural and anthropogenic hazards of mechanical damage to the pipeline due to various types of mechanical influences. The existing methods for determining pipe wall thickness in Russian and American regulations determine the dependence of hoop stresses on internal pressure using the Barlow formula. It is assumed that the distribution of hoop stresses over the pipe wall thickness is uniform, and radial stresses are not taken into account. Meanwhile, in relation to areas of increased danger in the presence of external mechanical influences (earthquakes, landslides, mudflows and other destructive phenomena), the design of pipeline lines requires optimal consideration of these effects. Aims and Objectives The aim of the work is to study the issue of developing a methodology for determining the main geometric parameters of the pipeline using the method of multicriteria optimization. Results A method of shock-mechanical action for calculating the optimal thickness of the pipeline wall has been developed. It is assumed that the impact is exerted by the bucket teeth of an earth-moving excavator. The proposed optimization criterion is a scalar convolution of two particular criteria, the first of which determines the resistance of the pipe to puncture, and the second, the resistance to the propagation of the emerging crack. It is shown that the optimal value of the pipe wall thickness is directly proportional to the pipe diameter and hoop stress and inversely proportional to the minimum value of the yield stress, the length and width of the tooth acting on the pipeline.

CALCULATION FOR THE STRENGTH AND ENSURING THE OPERATION SAFETY OF PIPELINES WITH EXTERNAL CORROSION

Background The main oil and gas pipelines are mainly laid underground. Under the influence of the environment surrounding the underground pipeline, over time, there is a decrease in the protective properties of the outer insulation coating of the pipeline. In addition, for various reasons, mechanical destruction of the coating occurs in certain sections of the pipeline. These processes lead to external corrosion of the pipe wall in sections of underground pipelines. Corrosion is associated with a decrease in pipe wall thickness and an increase in the level of hoop stresses in them. As a result, the problem arises of assessing the strength of pipes and ensuring the safe operation of pipelines with external corrosion. At present, the installation of a metal sleeve on a pipeline in places with external corrosion has received a fairly widespread use. The coupling takes a part of the load from the operating pressure and thereby reduces the load and hoop stresses on the corroded section of the pipeline. At the same time, the coupling creates a local deformation stiffness under the operating pressure with a significant change in the stressstrain state of the pipeline. The stress-strain state of a pipe-wire with external corrosion and a sleeve installed on it depends on the geometric characteristics of the pipe and sleeve, as well as the residual pipe wall thickness after corrosion. Aims and Objectives Ensuring the strength of a pipeline with external corrosion repaired with the use of a coupling and the safe operation of oil and gas trunk pipelines based on a reasonable calculation of the geometric characteristics of the repair couplings. Results Calculation formulas were obtained and, on their basis, an assessment of the magnitude of stresses from the action of the working pressure in the walls of the pipeline and the coupling in the corroded section, as well as in the sections of the pipeline along the edges of the repair coupling outside of it, was carried out. Technical solutions are proposed to ensure the safe operation of a pipeline section with external corrosion, repaired using repair couplings.

New material-saving technologies of pipe rolling on pilgrim units

In this work, based on the analysis of the process of hot pilger rolling of pipes of a wide range of sizes and grades from a round continuous cast billet, new and improved existing metal-saving technologies have been developed to reduce metal losses in the pilger head.Using scientific and patent sources of information in the field of pilger rolling and its mathematical modeling with the calculation of tables for rolling pipes of a wide range of sizes from a round continuous-cast billet with a diameter of 385-470 mm, metal losses into technological scrap on a pilgerstan are determined: a seed and a pilger head.On the basis of the results of the theoretical determination of metal losses in the process scrap on the pilgerstan: the seed and the pilger head, a forecast was made to reduce the weight of the pilger head, which was used to develop new material-saving technologies for pilger rolling of pipes, both thick-walled with D / S = 6 - 12.5, and thin-walled with D / S = 12.5 - 40. Metal losses in the pilger head are the main factor of increased metal consumption coefficients on pilger units, which reduces their competitiveness in comparison with other units when using round continuously cast billets as a starting material.The forecast for the reduction of metal losses in the pilger head made for the first time makes it possible to estimate the reserves for reducing the mass of the pilger head both by eliminating the underflow of the liner and trimming of the pipe end adjacent to the pilger head, and by means of individual parts of its profile part and predicting its decrease to the minimum possible size, ensuring the removal of the pipe from the mandrel using a gate device.To reduce the weight of the pilger head when rolling thick-walled pipes, it is recom-?ended to use improved technologies for butt-end rolling and rolling of the pilger head on the free section of the mandrel.The results of the studies and the proposed new material-saving technologies can be used on pilgrim units when rolling thick-walled (D / S = 6 - 12.5) and thin-walled (D / S = 12.5 - 40) pipes of a wide range of brands (carbon, alloyed, highly alloyed and special) from both continuous casting machine and forged and centrifugally cast billets, as well as ingots.

Influence of depth thresholds and interaction rules on the burst capacity evaluation of naturally corroded pipelines

Based on 14 naturally corroded full-scale pipe specimens, the present study investigates to what extent a corrosion depth threshold influences the burst capacity of naturally corroded pipelines predicted using the finite element analysis (FEA) and well-known RSTRENG model. The study also employs FEA and RSTRENG to investigate the accuracy and effectiveness of five representative interaction rules, namely the B31G, B31.4, CSA, DNV and CW rules, for combining individual naturally-occurring corrosion anomalies into clusters. The analysis results indicate that applying a corrosion depth threshold of 10% of the pipe wall thickness (t) (i.e. any corrosion depths < 10%t are ignored) has a negligible impact on the predicted burst capacity. Furthermore, the CSA interaction rule is considered the most effective among the five interaction rules investigated in that it captures the most critical region of a corroded area without resulting in very large corrosion clusters that are time-consuming to identify and analyze.