Pipe Stress Research Articles

Enhanced elastic stress solutions for junctions in various pipe bends under internal pressure and combined loading ([formula omitted] pipe bend, U-bend, double-bend pipe)

Piping systems in nuclear power plants normally operate under high pressure and high temperature. To efficiently manage space within these systems, pipe bends are extensively used. However, the welded joints connecting these pipes may be susceptible to flaws due to weld residual stress, transient loads, and operating environments. When flaws are present in such areas, analytical evaluation of flaws is to be carried out based on fracture mechanics parameters such as stress intensity factor. To calculate the stress intensity factor, distributions of the elastic stress are required. Therefore, this paper presents closed-form approximations of elastic stress in the junction between a pipe bend and a straight pipe under internal pressure. Review of the existing elastic stress solutions for estimating the stresses in pipe bends was carried out analyzing their limitations. Based on those limitations elastic stress solutions for thick to thin wall pipe bends were proposed and were validated against finite element (FE) analysis for thick-wall to thin-wall pipe bends under internal pressure and combined loading (i.e. internal pressure, in-plane bending, out-of-plane bending inflicted simultaneously). 90° pipe bend, U-bend and double-bend pipe configurations were considered and showed good agreement with the FE results exhibiting less than 5.8 % discrepancies. The accuracy of the elastic stress solutions for pipe bends provided in the existing code are summarized and validated in the appendix as well.

Numerical modeling and the ultimate bending experiment of the directional drill pipes bending at the dog-leg of the multi-branch well

Directional drill pipes are prone to failure in the fish-bone branch wells. The primary cause of the directional drill pipes failure is excessive bending. This paper established a mathematical analysis model for the bending stress of the directional drill pipes at any point along its trajectory. Tested the mechanical properties of the directional drill pipe. An ultimate bending experiment was conducted on the directional drill pipes based on the pure bending moment theory. Additionally, a non-linear finite element model(FEM) of the directional drill pipes was established to analyze the influence of different bending loads on the stress distribution of the directional drill pipes connection. The FEM results were consistent with the results of the ultimate bending experiment. The FEM results indicate that the Box bending under transverse force is the primary cause of the failure for the Tooth top. The research results enable engineers and operators to easily obtain the stress distribution of the directional drill pipes under borehole curvature.

Stress and deformation response of pipe jacking in upper-soft and lower-hard strata: A case study in Changsha

Constructing underground structures using the pipe jacking technique presents challenges in upper-soft and lower-hard strata. The complicated strata conditions make pipes prone to deflection, leading to problems such as cracking, pipe joints failure and water leakage. To determine the stress and jacking force characteristics of pipe jacking during the entire construction period in upper-soft and lower-hard strata, this paper presents a case study of pipe jacking passing through upper-soft and lower-hard strata in Changsha, China. Pipes stresses at two wings, and the top crest in the longitudinal directions for six different pipe sections were monitored. Then, a jacking force model is proposed to describe the additional thrust after deflection in upper-soft and lower-hard strata. The results show that the jacking force induced by upper-soft and lower-hard strata exhibits a tortuous increase and causes pipe deflection. The stress and deflection patterns in different monitoring pipes are consistent. The maximum pipe stresses during the jacking were 9.26 MPa in the longitudinal direction and 394 % increasing after deflection. Axial stress in test pipes exhibit nonlinearly transfer, with the distribution of friction resistance forms a“W”shape between pipes. An excessive alignment deflection would generate incremental jacking force, which strengthens with larger deflection. By regarding the composite formation area as a fully contact model with the surrounding rock, and uniform formation as a contact with the bottom of the surrounding rock, and the formulas were corrected for deeply buried pipe under uniform formation. Combining the calculation results and field data, the predict model is validated. The calculation method that can effectively predict the jacking force after pipe alignment deflection in upper-soft and lower-hard strata. The results of this study can provide beneficial guidance for the design and construction of pipe jacking.

Prediction model of maximum stress for concrete pipes based on XGBoost-PSO algorithm

Due to varying burial conditions and service environments, concrete pipes exhibit complex mechanical behavior. Existing theoretical, simulation, and test methods for determining the maximum stress of pipes have significant limitations, including excessive assumptions, low efficiency, and restricted applicable conditions. Therefore, there is an urgent need to propose a multi-factor associated method for pipe stress prediction. This paper proposed an innovative approach to finely simulate the mechanics response for concrete pipes under the coupling action of stress-seepage-fluid fields. The accuracy of this numerical simulation method was validated through full-scale test. Sensitivity analysis based on Morris sensitivity analysis theory was conducted on traffic load magnitude and speed, buried depth, groundwater table, fluid height and velocity, bedding strength, backfill strength, and pipe diameter. A dataset of “physical variables - maximum stress” for concrete pipes was established. A multi-factor-correlated prediction model of maximum stress for concrete pipe was proposed using XGBoost machine learning method optimized by Particle Swarm Optimization (PSO) algorithm. The results indicate that pipe diameter is highly sensitive; buried depth and traffic load magnitude are sensitive; groundwater table, bedding strength, and backfill strength are moderately sensitive; while fluid height, traffic speed, and flow velocity are insensitive. The XGBoost-PSO model demonstrates the highest accuracy and lowest error compared to BP, RF, and XGBoost models, with improvements in prediction accuracy of 59.6 %, 23.8 %, and 8.6 %, respectively. The model achieves RMSE of 0.118 and MAE of 0.213, demonstrating the suitability of the XGBoost-PSO model for predicting maximum stress for concrete pipes.

Long-term performance of concrete pipes under fatigue traffic loads

In recent years, there has been a concerning increase in road collapses triggered by failures in urban drainage systems. Concrete pipes, commonly uesd in urban drainage pipelines, endure prolonged cyclic loading from traffic above. However, the mechanisms governing the long-term performance and fatigue damage remain unclear. Through conducting fatigue model box tests on concrete pipes, the effects of different fatigue loading cycles on the circumferential strain of concrete pipes were investigated. A fatigue life prediction equation for concrete pipes was proposed, and the crack propagation under various fatigue loading cycles was observed. Additionally, corresponding 3D FE models of concrete pipe-soil interaction with bell-and-spigot joints and gaskets were constructed. These models were used to explore the vertical displacements, circumferential bending moments, and circumferential stresses of the concrete pipes under different fatigue loading cycles, the damage and failure mechanisms of the concrete pipes under fatigue loading were revealed. The results indicate that the potential failure location of concrete pipes is within the inner crown of the bell under the fatigue traffic loads. The circumferential strains and crack propagation exhibiting a three-stage evolution pattern under fatigue loads. The proposed fatigue life prediction equation accurately predicts the remaining life of concrete pipes. Upon reaching 21.89 million loading cycles, the strain at the inner crown of the bell reaches 575.0 με, resulting in complete failure. Cracks on the inner crown of the bell extend inward and to the right from the middle of the joint, forming a channel for crack propagation. The vertical displacements at the crown and the circumferential bending moments of the bell and spigot exhibit rapid increases, stabilization, and subsequent declines with the increasing loading cycles. When concrete pipes undergo fatigue fracture, the maximum vertical displacement and circumferential bending moment at the bell are measured as 2.26 mm and 17.82 kN·m/m, respectively. Stress concentration at the bell and spigot during fatigue loading leads to crack propagation and convergence, causing redistribution of stress fields characterized by an initial increase followed by a decrease in the inner crown and invert of the bell.

Field monitoring and numerical simulation for force characteristics of pipe jacking in deep buried moderately weathered slate

Understanding the force characteristics of pipe jacking in rock formations is crucial for ensuring the stability of the structure and construction safety during construction. Yet, very little is explored about its characteristics in rock formations of pipe jacking. This paper presents a case study of constructing a deeply buried moderately weathered slate sewage pipeline using pipe jacking method in Changsha, China. To this end, we propose a novel method to combine field monitoring and numerical simulation representation in an efficacious way. Field monitoring was conducted to investigate the spatial distribution characteristics of jacking force, axial stress, and hoop stress in moderately weathered slate. Numerical simulation methods were employed to discuss the influences of several factors on pipe stress: the pipe-rock contact area, contact relationships at pipe joint interfaces, the height of the jacking force position, and the depth of pipe burial. The results show that hand shield is influenced by the excavation technology, and the distribution of jacking force exhibits a stepped or oscillating upward pattern in moderately weathered slate. The maximum axial stress occurs at the mid-span position of the arched roof of pipe at 30 MPa. Hoop stresses are dominated by compressive stresses with the maximum at-8 MPa. As the pipe burial depth increases, so does the axial stress on the pipe. Lower positioning of the jacking force heightens this stress effect. A larger pipe-rock contact area correlates with reduced axial stress levels. The weakening of the contact interface between pipe joints minimally affects axial stress, as stress primarily transmits through non-weakened areas. To ensure the reliability of the data, automatic monitoring and measuring instruments calibrated for on-site monitoring are used. The results of this study can provide beneficial guidance for the design and construction of pipe jacking.

Comprehensive analysis of the effect of structural parameters on erosion wear, structural stress, and deformation of high-pressure double-elbow in shale-gas fracturing

In field hydraulic fracturing operation of shale gas development, the high pressure and large displacement liquid-particle two-phase fracturing fluid can be forced to change direction many times through high-pressure double-elbow, and be transported from the outlet pipeline of the fracturing pump to the main pipeline. The high-pressure double-elbow is prone to be affected by erosion wear and Fluid-Structure Interaction (FSI), resulting in perforation and fracture, posing a potential safety threat to field operation. In this study, we conducted the erosion wear experiments on 35CrMo steel used for high-pressure double-elbow in shale-gas fracturing. The erosion rates under different impact angles and flow velocities were obtained, and proposed a novel model of erosion prediction for high-pressure double-elbow. Then the numerical investigation was employed to conduct a comprehensive analysis of erosion wear, structural stress and deformation by the coupling of Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA). The effects of structural parameters such as connection straight pipe length, pipe inner diameter and fluid turning direction were discussed. The results indicate that with the increase of connection straight pipe length, the flow erosion decreases first then varies little, and the deformation gradually increases. Slight erosion wear but large structural stress and deformation in major inner diameter pipe. And the minimum degree of erosion and flow-induced deformation present with the fluid turning direction of double-elbow as 0°. The study can provide references for the design, installation and detection of high-pressure double-elbow and ensure safety in the process of shale gas fracturing.

Leakage Quantification in Metallic Pipes under Different Corrosion Exposure Times

The combined effects of aqueous corrosion, stress factors, and seeded cracks on leakage in cast iron pipes have not been thoroughly examined due to the complexity and difficulty in predicting their interactions. This study seeks to address this gap by investigating the interdependencies between corrosion, stress, and cracks in cast iron pipes to optimise the material selection and design in corrosive environments. Leakage experiments were conducted under simulated localised corrosive conditions and internal pressure, revealing that leakage increased from 0 to 25 mL with crack sizes of 0.5 mm, 0.8 mm, 1 mm, and 1.2 mm, along with corrosion times of 0, 120, 160, and 200 h, and varying stress levels. An empirical model was developed using a curve-fitting approach to map the relationships among corrosion time, crack propagation, and leakage amount. The results demonstrate that the interaction between corrosion, stress, and crack propagation was complex and nonlinear, and the leakage amount increased from 0.7 to 0.10 mm every 15 min, as evidenced by SEM microstructure images and empirical data.

Improving safety design for gas pipeline installation via horizontal directional drilling: a pipe stress analysis approach

Horizontal Directional Drilling (HDD) has today emerged as a significant and efficient Horizontal Directional Drilling (HDD) has today emerged as a significant and efficient technique for installing pipelines for a variety of purposes, including the production of oil, natural gas, water, sewer, electrical, and telecommunications. Due to the complexity of the technology and the intricate interplay of numerous processes, the safety risks associated with process uncertainty are substantial. However, risk analysis for HDD projects is generally done using qualitative methods. One of the most common factors used for HDD risk assessment is Pipe Stress Analysis (PSA). In this article, a combination of material evaluation and PSA for HDD safety design is suggested to improve the risk analysis. The evaluation will commence with an assessment of the material, followed by an examination of the wall thickness. Subsequently, an analysis of HDD design and pipe stress will be conducted. Using 10-inch API 5L Gr. B pipe, the safety design was successfully tested for a gas pipe project. When using HDD, a natural bend value of no less than 415.3 meters must have a horizontal length of 168 meters. According to the curvature, the length of the entire pipe is 169.03 meters. The combined installation stress was less than 1, while the combined operation stress was 114.87 MPa. These two values met the criteria specified in the standard. Overall, those steps were able to ensure that the HDD installation design is safe for construction.

Optimized design of large-diameter directly buried heating pipe

Abstract The elbow of a large-diameter directly buried hot water heating pipeline is the weak part of the whole pipe system. The foam cushion is often used to reduce the stress on the elbow. However, the foam cushion raises the temperature on the outer protective pipe’s surface, which may trigger thermal stress damage to the pipes. In this paper, the insulating pipe at the elbow section is designed with a variable diameter. The numerical simulation of the thermal stress for the outer protective pipe and the working pipe was conducted. The maximum stress for the outer protective pipe is about 3 MPa, and the average stress for the working pipe is 83 MPa, much smaller than the yield stress. Combined with the simulation results, the design ensures the reliability of the elbow and provides a reference for the design of large-diameter and high-temperature heat transfer pipelines.

Research on the residual stress of stainless steel pipe after overlay repair

The weld overlays are widely used to repair metal butt welds or piping components by depositing weld metal on the outside surface of the welds and piping components. This paper presents the detailed residual stress distribution of girth weld in stainless steel pipe after butt welding and weld overlay repair by using finite element analysis. Two dimensional (2D) cross-section models, axisymmetric assumptions for piping girth welds are used to simulate the welding process in order to predict the residual stress distribution in the weld and base material. A project has been implemented to validate the analytical models used to perform welding residual stress analysis against measured residual stresses data in literature. It is found that the simulation results of butt welding are consistent with the experimental results in literature, which means that the analysis model and its results are accurate and reliable. A series of simulations are conducted to investigate the changing rules of influencing factors of overlay repair for stainless steel pipe. The results show that appropriate interpass temperature and heat input, increasing the thickness of overlay can effectively increase the range of compressive stress in pipe, so as to prevent and limit the generation and propagation of cracks. This research may provide an important support for the formulation of weld overlay repair standards in service.

Analysis of the stability of a novel assembled working shaft support structure during pipe jacking construction: Experiments and numerical simulations

Pipe jacking construction is a commonly employed trenchless technique for laying underground pipes in urban areas. However, the conventional support structure for pipe jacking shafts poses challenges, including difficulty in reserving pipe jacking holes, susceptibility to tilting, low bearing capacity, and the potential for failure during construction. Taking the 5# pipe jacking shaft of the pipe jacking construction for diverting the Yellow River through the river at Niukouyu in Zhengzhou City as the research background, investigates the soil settle deformation around the working shaft and the mechanical response law of the supporting structure during the short-distance, long-distance and second long-distance pipe jacking construction by combining the practical engineering field test and finite element numerical simulation, and carries out a sensitivity analysis on the main design parameters affecting the stability of the supporting structure through orthogonal test. The findings reveal that during the second pipe jacking construction, stress and deformation of the supporting structure are higher than those observed in the first pipe jacking. Notably, support piles and waist beams at the entrance of the pipe jacking experience greater force, and the back and side walls undergo increased force and deformation in the later stages of pipe jacking, and support pile spacing is the main control factor affecting the mechanical performance of the novel support structure. The study concludes that monitoring and protection measures should be reinforced, particularly in areas prone to failure and damage during construction. The insights gained from this research can serve as a reference for designing, optimizing, and safely monitoring novel assembled pipe jacking shaft support structures.

Effect of Process Parameters on Welding Residual Stress of 316L Stainless Steel Pipe.

316L stainless steel pipes are widely used in the storage and transportation of low-temperature media due to their excellent low-temperature mechanical properties and corrosion resistance. However, due to their low thermal conductivity and large coefficient of linear expansion, they often lead to significant welding residual tensile stress and thermal cracks in the weld seam. This also poses many challenges for their secure and reliable applications. In order to effectively control the crack defects caused by stress concentration near the heat-affected zone of the weld, this paper establishes a thermal elastoplastic three-dimensional finite element (FE) model, constructs a welding heat source, and simulates and studies the influence of process parameters on the residual stress around the pipeline circumference and axial direction in the heat-affected zone. Comparison and verification were conducted using simulation and experimental methods, respectively, proving the rationality of the finite element model establishment. The axial and circumferential residual stress distribution obtained by the simulation method did not have an average deviation of more than 30 MPa from the numerical values obtained by the experimental method. This study also considers the effects of welding energy, welding speed, and welding start position on the pipe's circumferential and axial residual stress laws. The results indicate that changes in welding energy and welding speed have almost no effect on the longitudinal residual stress but have a more significant effect on the transverse residual stress. The maximum transverse residual stress is reached at a welding energy of 1007.4~859.3 J/mm and a welding speed of 6.6 mm/s. Various interlayer arc-striking deflection angles can impact the cyclic phase angle of the transverse residual stress distribution in the seam center, but they do not alter its cyclic pattern. They do influence the amplitude and distribution of the longitudinal residual stress along the circumference. The residual stress distribution on the surface of the pipe fitting is homogenized and improved at 120°.

Determination of equivalent stresses of pipes made of 12Kh1МF steel using FEM method, taking into account changes in geometry and scaling during operation

Determination of equivalent stresses of pipes made of 12Kh1МF steel using FEM method, taking into account changes in geometry and scaling during operation

Test blanket modules piping systems calculation method according to RCC-MRx code

The ITER Test Blanket Modules (TBMs) are installed and operated inside the vacuum vessel (VV) at equatorial ports located within port plugs (PP). The Pipe Forest (PF) is a network of pipes connecting the Ancillary Equipment Unit (AEU) to the TBMs. Depending of the TBM, the Pipe Forest includes various piping system such as Water Coolant (350°, 188 bars), Helium Coolant (500°, 100 bars) Lithium Lead and Tritium Extraction System. During operating states, the Pipe Forest main function is to withstand loads in normal, incidental and accidental situations according to RCC-MRx code criteria (including design rules for mechanical components for fusion installations). It includes severe thermomechanical loadings due to the thermal expansion added to seismic and vertical displacements events. In addition, the PF layout must satisfy constructability in constraint environments and maximize the space available for man access, which constitutes a real challenge for design.Since no existing RCC-MRx post-processing tool exists off the shelves, a specific methodology for pipe stress analysis is being developed by ITER, CEA and ASSYSTEM. This methodology starts with a post-processing calculation tool of stresses and reaction forces for looping back into the structural calculation. Moreover, a specific extraction module from 3D model to processing tool allows the conversion of CAD data to calculation entry files. Finally, a feedback loop is also re-integrated into the core CAD model through an import module, enabling the tracking of displacements and evaluate the impact of incorporating pipe movements into the analysis.This paper describes the pipe stress analysis methodology and its application for Pipe Forest system design life cycle. It covers the historical evolution of the routing including introduction of expansion loops. More recently, it incorporates the integrated calculation of the entire port cell, spanning from the back of the TBM sets, up to the connection pipes of the vertical shaft.

Failure Analysis and Ultimate Expansion Mechanical Behavior Analysis of Thin-Walled Solid Expandable Tubular

Summary With the vigorous exploitation of shale gas, the cost of drilling and production of shale gas wells, which can reduce the cost, has also received attention. Equal-diameter solid expandable tubular (SET) technology is one of the best choices at present. For this paper, we carried out a series of expansion experiments for 20G pipe, and the experimental results show that the pipe breaks and fails at 30% expansion ratio. The cracked pipe is analyzed by scanning electron microscopy (SEM), and the method to solve the failure of cracked pipe is proposed. In addition, a 3D dynamic model is established to study the relationship between the inner diameter, wall thickness, expansion ratio, and ultimate expansion ratio of the pipeline. The study results show that (1) SET made of 20G expanded successfully at 25% expansion ratio and failed at 30% expansion ratio, the fracture surface presents 45°, with typical shear failure characteristics; (2) SEM results showed that the pit characteristics were normal, the pipe was cracked under high stress, and the 20G pipe could not meet the expansion ratio of 30%; and (3) the maximum stress of 20G pipe during expansion is proportional to the expansion ratio. It is recommended that the SET expansion rate of 20G material should not exceed 26%. The research results will provide ideas and methods for the design of SET.

A Sustainable Solution with Improved Chemical Resilience Using Repurposed Glass Fibers for Sewage Rehabilitation Pipes

This paper introduces a sustainable sewage rehabilitation solution, utilizing repurposed glass fibers for enhanced chemical resilience and environmental conservation. The approach involves dividing a unitary pipe into segments, assembled during commissioning, aiming to reduce installation and transportation costs, particularly in less accessible areas. Each pipe segment comprises a multi-layered glass fiber composite sandwich, joined by an adhesive reinforced with recycled glass fibers. The glass fiber-reinforced plastic (GFRP) pipe features a core of blended sand impregnated with resin, an outer layer for impact resistance, and an inner layer to prevent corrosion. Chemical resilience is assessed through a 10,000 h strain corrosion study exposing both unitary and two-piece circular GFRP pipes to sulfuric acid in a deflected condition. An apparent hoop tensile test evaluates mechanical integrity before and after exposure. The experimental results reveal that the two-piece pipe with a tongue and groove joint (TGJ) with recycled glass fiber adhesive exhibits superior long-term bending stress and failure strain % compared to unitary pipes. This enhancement is attributed to the TGJ’s improved load-bearing capability and chemical resistance. The failure strain % of the two-piece pipe (1.697%) is higher compared to the unitary pipe (1.2613%). The long-term bending stress of the two-piece pipe obtained is 119.94 MPa whereas the unitary pipe reaches 93.48 MPa at the 50-year mark. The cost analysis supports the adoption of the two-piece pipe over unitary pipes due to a 40% reduction in carbon emissions and transportation cost. The novelty lies in the utilization of multi-piece pipes with enhanced chemical resilience, achieved through the incorporation of milled fiberglass reinforcements in the TGJ. Strain corrosion tests take a long time to perform; hence, an accelerated test is needed to improve the current recommended testing standard.

Influence of the Advance Jacked Pipe on the Jacking Force of the Subsequent Pipe Based on Pipe–Soil Full Contact Model

Abstract In pipe jacking engineering, accurate prediction of jacking force is the key to pipe jacking design. Based on a project of the Beijing Daxing Airport Line, the influence of the advance jacked pipes on the jacking force of the subsequent pipe is carried out in the present work. First, the verified numerical model of practical engineering was established, and the jacking force and radial stress of different pipes were analyzed. Then, the two pipes were taken as research object, and the parameters of spacing, angle, buried depth, and pipe diameter were investigated, respectively. The results show that in the actual project, the advance jacked pipes have amplification and superposition effects on friction resistance of the subsequent pipe, and the maximum growth rate is 37.2%. The friction resistance of the subsequent pipe presents a trend of first increasing and then decreasing with the change of the layout angle of advance jacked pipe from 0° to 180°. With the increase of buried depth and pipe diameter, the absolute value of incremental friction resistance of the subsequent pipe increases gradually, but the growth rate remains constant. Finally, the empirical formulas for predicting the friction resistance growth rate of subsequent pipes under different angles are proposed. The research results can provide some reference for the design of pipe jacking.

Complex Function Solution of Stratum Displacements and Stresses in Shallow Rectangular Pipe Jacking Excavation Considering the Convergence Boundary

The construction of pipe jacking has little impact on the environment and is usually used to build underground passages with shallow buried depths and short lengths. Compared with circular pipe jacking, rectangular pipe jacking has the advantages of shallow buried depth and high space utilization. Therefore, research on the excavation of rectangular pipe jacking is necessary. This paper establishes a cross-section model of shallow buried rectangular pipe jacking excavation. Taking advantage of complex functions for solving problems involving non-circular tunnels, an analytical solution is obtained using an approximate mapping function and potential functions in series forms for the stress and displacement of the stratum with a displacement condition at the excavation boundary and a stress condition at the ground surface boundary. The finite element simulation results and the engineering-measured data are used for comparisons and verifications. With the analytical solution of the complex function, the influence of selecting control points for the mapping function on the accuracy is calculated and analyzed, as well as the influence of the stratum loss rate, span, buried depth, and stratum unit weight on surface subsidence and major principal stress of the excavation boundary. The proposed analytical solution can be applied to the construction of rectangular pipe jacking tunnels.

Parametric modelling of control cable fittings geometric configuration with interpolation of FEA results

Studying the behavior of control cable fittings (actually a pipe-type part) during radial crimping for fixation on the pipeline is a difficult task since it is necessary to control the presence of obvious plastic deformations: on the one hand, insufficient crimping can cause the fitting to break off from the cable conduit (axial loads over 100 kgf), and on other – the excessive crimping can block the operation of the cable (the core will jam). The selection of the optimal ratio of the fitting diameter and its wall thickness at different load values is the topic of a multi-parameter problem, and one of the ways of solving it will be presented in our research. To evaluate the nonlinear behavior of the Structural Steel NL Ansys material will be used Bilinear Isotropic Hardening stress-strain model with further interpolation of the Tangent Angle Coefficient (TAC) which is suggested as a new calculation parameter of pipe stress estimation.