Pipe Wall Thickness Research Articles

Stress triaxiality as a postponer of the collapse pressure of thick-walled submarine pipes

One of the main concerns of pipeline design engineers for ultra-deepwater applications is to predict the pipes’ collapse capacity due to buckling caused by the hydrostatic pressure. DNV-ST-F101 is one of the most used guides for such systems, and presents the equations for the computation of the collapse pressure of submarine pipelines considering a limited diameter-to-thickness (D/t) range, not taking into account thick-walled structures. This work aims to investigate the accuracy of DNV-ST-F101 equations for submarine pipes with low D/t ratios. We show that, for these specific configurations, the analytical equations provided tend to underestimate the collapse capacity, which might result in the design of unnecessarily thick structures. Using finite element analyses we conclude that thick-walled pipes show a high level of stress triaxiality inside its wall at the moment of collapse, making it necessary a different analytical approach than that of DNV-ST-F101. Finite element simulations of four different metallic materials and five pipe configurations (D/t ratios) are performed to develop an alternative approach for the computation of the plastic collapse of pipes under hidrostatic pressure that takes into account the stress triaxiality at the moment of the pipes’ collapse. Our results improve the accuracy of the original DNV design equation for pipe diameter-to-thickness ratio within the range commonly found in the pre-salt offshore exploration.

Reliability Analysis of Pipe Wall Thinning based on Quantification of Ultrasonic Testing

Piping in nuclear power plants is subject to corrosion and erosion caused by the interaction with fluids it carries. In order to prevent accidents such as pipe rupture, it is necessary to non-destructively inspect the thickness of the pipe wall and predict the remaining pipe life. In contrast, signals obtained by non-destructive inspection are affected by various uncontrollable and unknown factors, which will result in uncertainty in evaluating pipe wall thickness. Ignoring the uncertainty would lead to a large error in the pipe reliability assessment. Therefore, it is important to develop a reasonable pipe wall thinning management that can takes the uncertainty of non-destructive testing into consideration. Based on this background, this study aimed to develop a piping wall thinning prediction model that accounts for the uncertainty in evaluating pipe wall thickness and to evaluate its applicability to ultrasonic testing. At first, ultrasonic tests were performed to measure the thickness of specimens simulating flow accelerated corrosion. The results of the measurements were statistically analysed to obtain a mathematical model correlating the evaluated and true thickness. A numerical model to predict the reduction of wall thinning with its uncertainty is developed. Compared to the conventional method, the proposed method is able to predict wall thickness with high accuracy.

Detection and Measurement of Pitting Corrosion using Short Range Guided Wave Scanning

Short range guided wave scanning is an inspection method enabling an indirect, quantitative measurement of remaining pipe wall thickness. It has seen widespread industrial use as an inspection solution for corrosion under pipe support (e.g. [1]). Pitting corrosion represents a significant challenge in industrial pipelines and its presence complicates short range guided wave scanning analysis as the wavelength used for inspection is larger than the diameter of small pitting-type defects. This work investigates the reflected signal from pitting corrosion, both in isolation and in the presence of larger corrosion patches, to improve the understanding of the complex signals received. This work provides the foundation and guidance for analysis techniques used in guided wave scanning. To achieve this a series of representative pitting defects with varying diameter and depth have been investigated using explicit finite element modelling. It is shown that using currently established analysis techniques, the pit depth can be quantified for pitting with a diameter larger than approximately 13 mm. Smaller diameter pitting may only be qualitatively detected at this time due to mode conversion occurring at the defect, which obscure features that are used to provide quantitative analysis of the defect depth. Quantitative sizing of defects where pitting is present will require further investigation.

Ultrasonic guided wave imaging of pipelines based on physics embedded inversion neural network

Pipeline corrosion quantification plays a vital role in guaranteeing the safety of critical industrial structures and thus significant work has been carried out to address such an issue. Although quantitative imaging is crucial for non-destructive testing, research in guided wave pipeline testing has primarily centered on qualitative approaches. Here, we propose a deep neural network built upon physical model to reconstruct pipe wall thickness from ultrasonic guided wave (UGW) signals. The workflow of reconstruction contains three layers, where each layer consists of a fixed forward network and a residual inversion network. The forward model is represented by an agent convolutional neural network which would be embedded into the entire inversion network. The residuals between data from the forward model and real signals are then mapped into velocity profile differences through sub-inversion network. Numerical experiments were conducted to verify the inversion performance of the deep neural network using thickness maps obtained from guided wave frequency domain information. Results show that inversion images are capable to reveal the positions, shapes, and depths of corrosion with high resolution and precision, yielding an average inversion of 87.37% in the test set. In addition, by utilizing the periodicity of the pipeline, the inversion accuracy of eight pairs of transducers were improved from 67.7% to 89.43% with high-order helical guided wave. Compared with traditional high-precision inversion methods such as full waveform inversion, the proposed method achieved approximately 300 times faster inversion speed at the cost of some accuracy. The research demonstrates that real-time quantitative imaging of defects on pipes can be achieved accurately by physics embedded network. Furthermore, an experimental verification of the method was carried out through UGW pipeline testing, demonstrating its feasibility. The mean squared error of wall thickness reconstruction was 0.0070, achieving a high level of precision.

Effect of Supercritical Bending on the Mechanical & Tribological Properties of Inconel 625 Welded Using the Cold Metal Transfer Method on a 16Mo3 Steel Pipe.

The presented work deals with the investigation of mechanical tribological properties on Inconel 625 superalloy, which is welded on a 16Mo3 steel pipe. The wall thickness of the basic steel pipe was 7 mm, while the average thickness of the welded layer was 3.5 mm. The coating was made by the cold metal transfer (CMT) method. A supercritical bending of 180° was performed on the material welded in this way while cold. The mechanical properties evaluated were hardness, wear resistance, coefficient of friction (COF) and change in surface roughness for both materials. The UMT Tribolab laboratory equipment was used to measure COF and wear resistance by the Ball-on-flat method, which used a G40 steel pressure ball. The entire process took place at an elevated temperature of 500 °C. The measured results show that the materials after bending are reinforced by plastic deformation, which leads to an increase in hardness and also resistance to wear. Superalloy Inconel 625 shows approximately seven times higher rate of wear compared to steel 16Mo3 due to the creation of local oxidation areas that support the formation of abrasive wear and do not create a solid lubricant, as in the case of steel 16Mo3. Strain hardening leads to a reduction of possible wear on Inconel 625 superalloy as well as on 16Mo3 steel. In the case of the friction process, the places of supercritical bending of the structure showed the greatest resistance to wear compared to the non-deformed structure.

Exact solution of burst pressure for thick-walled pipes using the flow theory of plasticity

This paper develops an exact solution of burst pressure for defect-free, thick-walled pipes using the flow theory of plasticity in terms of the average shear stress yield criterion (or Zhu-Leis yield criterion). The pipe steel is assumed to obey the power-law strain hardening rule, and large plastic deformation is described by the finite strain theory. On this basis, internal pressure is obtained as a power series function of the effective strains on the inside and outside surfaces of the thick-walled pipe with use of the second Bernoulli numbers. At burst failure, the Zhu-Leis flow solution of burst pressure is determined as a power series solution, and the burst effective strains, the burst effective stresses, and the burst pressure are functions of the diameter ratio (Do / Di), strain hardening exponent (n), and ultimate tensile strength (UTS). Similarly, the Tresca and von Mises flow solutions of burst pressure are also determined as a power series solution in terms of the Tresca and von Mises yield criteria. A general closed-from exact solution of burst pressure is then proposed for the three yield criteria, and the results showed that the proposed exact solution matches well with the power series solution for each yield criterion. Moreover, the von Mises flow solution is an upper bound prediction, the Tresca flow solution is a lower bound prediction, and the Zhu-Leis flow solution is an intermediate prediction that agrees well with the finite element analysis results of burst pressure for thick-walled pipes. Two datasets of full-scale burst tests are then utilized to evaluate and validate the proposed flow solutions of burst pressure for both thin and thick-walled pipes.

Residual stresses in austenitic thin-walled pipe girth welds: Manufacture and measurements

Determining residual stresses in thin-walled pipes is challenging. They are potentially difficult targets for simulation, because they may not behave as simple axisymmetric structures during welding. Thin-walled pipes are more sensitive to changes in the welding heat input than thick-walled pipes. They are also under-represented in the existing population of residual stress measurements used to generate upper bound residual stress profiles for structural integrity assessments. In this paper, residual stress characterisation of two thin-walled austenitic girth welded pipes is presented. The overall geometries of the two mock-up designs were the same; they differed in the linear heat input per pass and the total number of weld passes. The residual stress characterisation was carried out using two independent measurement techniques; the contour method and neutron diffraction. The multiple-cut contour strategy was implemented to measure the cross-sectional maps of hoop and axial stresses on axial-radial and hoop-radial planes respectively. The contour method results are compared with stresses measured using neutron diffraction and specific residual stress distribution signatures observed are discussed.

Testing the Dynamics of Flight for the Products of Explosion for a Warhead with a Weight of 250 kg

This study presents the results of the testing of the explosion process of a warhead with a weight of 250 kg, filled with 87 kg of TNT with 20% of aluminium dust, in two configurations: with horizontal and vertical alignment of the warheads longitudinal axis, and with the centre of length of the warhead body located at a height of approx. 1 m above the ground. Four warheads were detonated in each configuration. The horizontal configuration allowed the collection of some amount of the fragments from the ground, with sizes and spatial distribution of the fragments corresponding to the location on the body from which they came, with the largest fragments from the central part of the shell measuring approximately 9 30 280 mm. For the vertical configuration, the warheads nose was pointed downwards, with an up-down excitation. In both configurations, the explosion process was recorded from a distance of 300 m using a PHANTOM fast camera with a time resolution (frame interval) of 55 s to 133 s: for the horizontal configuration along the bodys longitudinal axis, for the vertical configuration perpendicular to this axis. In the vertical configuration, the bodys expansion process was recorded using short-circuit sensors spaced every 5 mm along the flight radius. The sensors sent short-circuit signals to the time meter, whereas the first sensor was installed at a distance of approx. 1 mm from the body surface and was used to initiate the processes of time counting and recording the overpressure diagrams over time at the front of the explosion/shock (FU) wave. The recorded expansion velocity was approx. 1300 m/s, with the shell radius increasing by 20 mm. Overpressure at the front of the FU was measured by PCB pencil-tip piezoelectric sensors (CzP). Every sensor had two active surfaces arranged in tandem at a distance of 100 mm, which made it possible to determine the local FU velocity. Signals from CzP were recorded every 200 ns using a DEWETRON recorder with software allowing their initial and further processing. Three sensors were spaced 8 m from each other, whereas the first was located 8 m to 10 m from the warheads longitudinal axis. Under a row of the sensors a thick-wall steel pipe was placed to protect the sensors from destruction by the fragments. The determined local FU velocities varied from approx. (590 m/s to 740 m/s) at a distance of approx. 8 m from the epicentre up to approx. 370 m/s at a distance of approx. 26 m from the epicentre; the overpressure measured values varied from approx. (230 kPa to 550 kPa) at a distance of approx. 8 m to approx. 22 kPa at a distance of approx. 26 m from the epicentre; satisfying conformance of the velocity and pressure values under the flat FU model was found. The FU trajectory was also taken from the video recording the velocities measured varied from approx. 2,650 m/s at a distance of 0.3 m to approx. 670 m/s at a distance of 6 m from the epicentre, which corresponds to the CzP data. The fragments flying next to the CzP, generally with the highest mass to effective transverse surface ratio, left traces of their conical FU on the CzP overpressure records, which allowed the determination of average velocities for some of them across the access path to the CzP, whereas these velocities ranged from approx. 1700 m/s at a distance of approx. 8 m and (1500 m/s to 1600 m/s) at a distance of 16 m to approx. 1300 to 1400 m/s at a distance of 26 m from the epicentre. Average access velocities of the selected fragments to the field marks were determined on the basis of the video recording ranged from approx. 1800 m/s at a distance of 5 m to approx. 1500 m/s at a distance of 20 m from the explosion epicentre.

Study on bearing failure characteristics and parameters of pipe roof support in super shallow buried tunnel in soft surrounding rock

Through theoretical analysis, laboratory test and numerical simulation, this paper studies the bearing failure characteristics and support parameters of pipe roof support in super shallow buried double track railway tunnel crossing soft surrounding rock. Based on the analysis of the load and load range of the pipe roof in the super shallow double track railway tunnel, Pasternak double parameter model is selected as the mechanical analysis model of the pipe roof. Based on this, 11 groups of laboratory tests of pipe roof grouting steel pipes are proposed and designed, and the influence of pipe diameter, wall thickness, grouting fullness and reinforcement cage measures of pipe roof grouting steel pipes on the change law of bearing capacity of pipe roof grouting steel pipes is analyzed. The bearing capacity of pipe roof grouting steel pipes under different parameters was obtained and compared with the numerical simulation results of ABAQUS for verification. Based on the analysis and summary of the bearing failure characteristics of pipe roof support and the test results, it is concluded that the grouting steel pipe with full grouting, wall thickness of 4 mm and pipe diameter of 108 mm without reinforcement cage can meet the support capacity requirements of most super shallow buried double track railway tunnels crossing soft surrounding rock. At the same time, in the actual engineering, the grouting fullness of the pipe roof should be focused on to prevent the pipe roof steel pipe from separating from the internal grouting body, and the wall thickness of the steel pipe can be reduced and no reinforcement cage can be set up if unnecessary.

Pipe Wall Thickness Comparison of Seamless, ERW, and SAW Type for Steam Piping System

Pipe Wall Thickness Comparison of Seamless, ERW, and SAW Type for Steam Piping System

Effect of Design Parameters and Support Conditions on Natural Frequency of Pipe Excited by a Turbulent Internal Flow

In this study, the effect of design parameters such as pipe diameter, pipe wall thickness, pipe material and the effect of fluid velocity on the natural frequency of fluid-structure interaction in straight pipe conveying fully developed turbulent flow were investigate numerically,analytically and experimentally. Also the effect of support conditions, simply-simply and clamped-clamped was investigated. Experimentally, pipe vibrations were characterized by accelerometer mounted on the pipe wall. The natural frequencies of vibration were analyzed by using Fast Fourier Transformer (FFT). Five test sections of two different pipe diameters of 76.2 mm and 50.8 mm with two pipe thicknesses of 3.7 mm and 2.4 mm and two pipe materials,stainless steel and polyvinyl chloride PVC in the range of Reynolds numbers from 4*104 to 5*105 were studied. Mathematically, the governing continuity and momentum equations were solved numerically by using the finite volume method to compute the characteristics of two dimensional turbulent flow. The dynamics of a pipe conveying fluid was described by the Transfer Matrix Method (TMM) which is provides a numerical technique for solving the equations of pipe vibrations for simply-simply and clamped supports. The results showed that,the natural frequencies increase with pipe diameter increase and the natural frequencies slightly increases with pipe wall thickness increase. Also, the natural frequencies in clamped-clamped supported pipe are higher than those in simply-simply supported pipe.

Magnetic Permeability Perturbation Testing for Internal Axial Cracks in Small-Diameter Thick-Walled Steel Pipes

Special geometric features and complex working environments render the internal defects of small-diameter thick-walled steel pipes “easy to expand, difficult to detect”. In this paper, a magnetic permeability perturbation testing (MPPT) method is proposed to assess the internal axial cracks of small-diameter thick-walled steel pipes. The mechanism of the MPPT method and its corresponding probe and magnetizer are introduced, and its feasibility is verified through a series of simulations and experiments. Experiments conducted using different sizes of small-diameter thick-walled pipes show that this method offers good performance with respect to the detection of internal axial cracks. Additionally, both diameter and wall thickness significantly affect the MPPT signal. To a certain extent, a greater wall thickness or a smaller diameter brings about a weaker signal. This method does not benefit from the lift-off effect, nor is it limited by the skin effect, which has great practical value as a supplement to the evaluation of thick-walled steel pipes.

Mathematical Modeling of Digital Twins and Industry 4.0 Technologies for Measuring Pipe Wall Thickness at Angra 1 Nuclear Power Plant

Mathematical Modeling of Digital Twins and Industry 4.0 Technologies for Measuring Pipe Wall Thickness at Angra 1 Nuclear Power Plant

An Analytical Calculation Method and Mechanical Response Laws of Buried Pipelines Subjected to the Impact of Transverse Landslides

When the buried gathering and transportation pipelines cross the landslide area transversally, the migration of the landslide mass can cause the pipelines to be subjected to lateral thrust, which can seriously affect the safe operation of the buried pipelines. In order to study the mechanical response laws of the buried pipelines under the impact of transverse landslides, based on the elastic-plastic foundation beam theory, the mechanical models of buried pipelines are established for three situations, and the analytical solution of pipeline displacement is obtained by genetic algorithm. The influences of landslide thrust, landslide width, soil resistance coefficient, the pipe outer diameter and wall thickness on pipeline peak displacement and peak stress are also investigated. The results show that under the impact of the transverse landslide, with the increase of landslide thrust, the maximum displacement and maximum tensile stress of pipeline increase exponentially, and the failure risk of pipe increases. Secondly, with the increase of landslide width, the maximum displacement of pipeline increases in the beginning and then decreases to be constant, and the maximum tensile stress decreases sharply to be constant. Thirdly, with the increase of soil resistance coefficient, the maximum displacement and maximum tensile stress of pipeline decrease in a negative power trend, and the pipeline is safer. Fourthly, when the pipe outer diameter increases to a certain value, the maximum displacement and maximum tensile stress of the pipeline change very little, hence, pipe outer diameter can be optimized when designing pipe structure. Fifthly, the smaller the pipe wall thickness is, the greater the maximum tensile stress of the pipe is, therefore, pipe corrosion protection should be paid attention to. Sixthly, when the landslide thrust is large, the landslide width is small, or the pipeline outer diameter is small, the maximum tensile stress of the pipeline is located at the centre of the landslide, otherwise, it is located at 0.56L ~ 0.7L away from the landslide centre. In order to ensure the safe operation of the pipeline, the stress state of these two positions should be focused on. It is concluded that the study can provide the basis for the evaluation of pipeline safety status and has practical significance for ensuring the safe operation of buried pipelines.

Optimal design of iron-cored coil sensor in magnetic flux leakage detection of thick-walled steel pipe

Thick-walled steel pipes, which bear high internal pressure, are widely applied in nuclear power and pressure pipelines. If there are defects in the inner wall, they are easy to expand and cause accidents. Therefore, the thick-walled steel pipe must be subject to non-destructive testing after production. For the magnetic flux leakage (MFL) testing method, the detection sensitivity gradually decreases with the increase of wall thickness. To solve this problem, a new structure of MFL probe is proposed in this paper. The influence of the iron core permeability on the MFL signal is analyzed theoretically, and the effect of the core length and diameter on the MFL signal is analyzed by simulation. The variation of the MFL signal with the change of the iron core and coil lift-off is studied respectively. The simulation results are verified by experiments. It is found that the lift-off of the iron-cored coil is determined by the iron core position. Based on this phenomenon, an MFL array probe is designed, which can be used for online detection of thick-walled steel pipes to improve the detection sensitivity of inner wall defects.

Fracture behavior analysis of X80 pipelines welded joints with unequal wall thickness

Pipeline transportation is one of the main methods for transporting oil and natural gas worldwide. The structural safety of welded joints of large diameter pipes with cracks and unequal wall thickness has become a research focus due to discontinuous geometrical structure and cracks in weld seams. In this paper, the tensile experiment and analysis of specimens with unequal wall thickness across welding seam based on the digital image correlation technology are carried out. Moreover, the influence of transition length and transition form on fracture behavior of welded joints of unequal wall thickness pipeline is obtained. In addition, a three-dimensional finite element model of welded joint of unequal wall thickness pipe with oblique line transition form and circular arc transition form is established. and the accuracy of the full-scale pipeline finite element model modeling method is verified by small-scale experiment data. On this basis, the influence of geometrical parameters of the transition section and wall thickness ratio, pipe diameter, and weld strength matching coefficient on the crack driving force of welded joints with unequal wall thickness is obtained. From the perspective of strain-based design, a method for obtaining the minimum transition length section and avoiding girth weld fracture is proposed. The research results guide the design and safety evaluation of welded joints with unequal wall thickness.

Response of UPVC pipes buried in sand under lateral ground movement

As a key part of global lifeline infrastructure, buried pipelines play a vital role in transporting products for the daily life of human beings. However, the ultimate soil resistance and yield displacement are only derived for rigid pipes in current design guidelines, which are difficult to guide the analysis of flexible pipes. This investigation presents large-scale laboratory tests on flexible UPVC pipes subjected to lateral ground movements. The soil failure mechanism and pipe deformation were tracked. The reaction developing on UPVC pipe was measured as a function of pipe lateral displacement, embedment depth, sand bed density and pipe wall thickness. Analysis results reveal that the failure mode of soil changed from the general shear failure to the local shear failure, in which the soil arching effect occurred in both the active and passive loading areas, as the embedment ratio increased. Current design approaches could overestimate or underestimate the ultimate soil resistance of UPVC pipe heavily under various conditions, while the measured yield displacement was 2 to 3 times the prediction from the design guidelines. Finally, a simplified design method was proposed based on the pipe yield displacement for predicting the maximum longitudinal strain of UPVC pipes under lateral loading.

Failure analysis of slurry TBM discharge pipe in complex strata combined with wear and vibration characteristics

The slurry TBM circulation system plays a crucial role in supplying the slurry to the excavation face and conveying the cut rock particles to the ground. Rock particles in excavated materials will cause damage and failure of slurry discharge pipelines, which seriously restricts the efficiency of slurry TBM tunneling. In this paper, the two major behaviors of wear and vibration that induce slurry discharge pipelines failure are systematically investigated based on a water delivery tunnel located in Beijing. The wear morphology of typical pipes is studied combining the measured wear data and CFD-DEM coupling simulation. The time–frequency characteristics of slurry discharge pipe in different strata are measured and analyzed. Furthermore, the variation of time–frequency characteristics with the decrease of pipe wall thickness is investigated, a multi-parameters early warning methods based on vibration characteristics is proposed for detecting pipe wear. The results show that The CFD-DEM coupling method and Archard wear model can accurately determine the location of the maximum wear point of various pipes conducive to local thickening of pipes. The elbow pipe joints are prone to fatigue damage and have a high risk of slurry leakage during transport of large-sized particles. When the pipeline is severely worn, the interaction between the rock particles and the worn wall causes local elastic deformation, resulting in a high frequency response of 50–150 Hz and a rapid increase in the kurtosis K.

Quantitative study on the propagation characteristics of MFL signals of outer surface defects in long-distance oil and gas pipelines

The magnetic flux leakage (MFL) internal detection is one of the most effective methods for assessment of long-distance oil and gas pipelines. To quantify the outer surface defect through MFL signals, which are affected by pipe wall and its shielding effect, propagation compensation factor (PCF) was proposed to apply to a classical magnetic charge model. Using the established model for outer surface defects in long-distance oil and gas pipelines, characteristics of MFL signals with different wall thicknesses and defect sizes along with their propagation patterns were analyzed. To verify the analytical model, X70 pipes with different wall thicknesses were used for systematic experiments. The results showed that the pipe wall thickness had a significant attenuation effect on the MFL signals of external defects. As the wall thickness increased from 7 to 17 mm, the MFL signals exhibited a first-order exponential decay, with a maximum error of 25.8% and a minimum error of 2.5%. When the defect depth increased from 0.6 to 7.2 mm, the MFL signals showed a first-order exponential upward trend, with a maximum error of 18.8% and a minimum error of 2.0%. This study effectively described the propagation characteristics of MFL signals of outer surface defects, and facilitated identification and quantitative evaluation of outer surface defects.

Numerical optimization of billet diameter in the wide-spread and split extrusion process

The research object was the wide-spread shunt extrusion production of large-diameter thick-walled AZ31 magnesium alloy pipe with 360mm outer diameter and 10mm wall thickness. Based on the DEFORM-3D finite element software platform, the simulation study on the influence of billet diameter on extrusion pressure was carried out to provide theoretical support for the reasonable selection of equipment tonnage. The results show that the peak extrusion pressure increases with the increase of billet diameter, and the increasing speed is accelerated. By reducing the billet diameter, the peak extrusion pressure can be gradually reduced from 4800 tons to 2200 tons, and the maximum extrusion cargo can be saved by more than 50%. If 3600 tons extruder is used, the billet diameter should be less than 325mm; If 2500 tons extruder is used, the billet diameter should be less than 285mm.