High Density Polyethylene Pipe Material Research Articles

Ultrasonic defect detection of high-density polyethylene pipe materials using FIR filtering and block-wise singular value decomposition

Condition monitoring of high-density polyethylene (HDPE) pipes used for fluid and gas transfer is important for the safety of energy conservation and the environment. Ultrasonic phased array imaging methods provide a solution to detect and assess defects in HDPE pipes. However, ultrasonic bulk waves propagating in these viscoelastic media are strongly attenuated, resulting in reduced signal amplitude. In this study, a linear-phase Finite Impulse Response (FIR) filter is used to remove unwanted frequency components from the measured ultrasonic signals to improve the signal-to-noise ratio before applying the imaging algorithm of the total focusing method (TFM). Building upon this, a block-wise singular value decomposition (SVD) technique, which can adaptively determine the singular value cutoff threshold based on each block in the whole TFM image, is used to enhance the obtained TFM image quality. The performance of the combination of FIR filtering and block-wise SVD technique is validated by experimental data of HDPE pipe materials. Results demonstrate that the proposed approach generates good images to provide the detection and characterization of side-drilled holes in HDPE pipe materials.

Detection of defects in highly attenuating materials using ultrasonic least-squares reverse time migration with preconditioned stochastic gradient descent

Accurate detection and characterization of defects in high-density polyethylene (HDPE) pipe materials are very important in assessing the structural integrity of critical structures in the nuclear industry. One specific challenge here is the presence of the viscoelastic attenuation of this material, which can lead to resolution degradation and loss of detail in ultrasound imaging. In this work, an effective ultrasonic imaging technique using the least-squares reverse time migration with preconditioned stochastic gradient descent (LSRTM-PSGD) is developed to improve image quality. Compared with standard ultrasonic imaging methods which only consider the direct ray path of ultrasound, least-squares reverse time migration (LSRTM) is a powerful wave-equation-based approach and it has the ability to account for rapid spatial velocity variations and to utilize all wavefield information. The LSRTM is an inversion method, which iteratively updates the reflectivity model by minimizing the modeled data and measured data. The proposed LSRTM-PSGD combines the advantages of stochastic gradient descent (SGD) and adaptive learning rate. The SGD updates the parameter on each transmitter and the fluctuation of SGD can enable it to reach a better minimum, thus improving the imaging quality. Compared with the conventional LSRTM algorithm using a fixed step size, the proposed LSRTM-PSGD algorithm can use the adaptive moment estimation to calculate the adaptive learning rate for the parameter, thereby updating the parameter appropriately. The performance of the LSRTM-PSGD algorithm is tested with experimental data. The results show high-quality reconstructed images with good resolution for defect identification in HDPE pipe materials, especially for deep defects.

Ultrasonic array imaging of highly attenuative materials with spatio-temporal singular value decomposition

With the increasing use of high density polyethylene (HDPE) pipes in nuclear industry which puts safety at the forefront, ultrasonic array imaging methods play a vital role in the structural integrity of HDPE pipe materials. However, the viscoelastic attenuation of HDPE pipe materials significantly decreases the level of signals, leading to a low signal-to-noise ratio caused by electronic noise. In this work, a domain-adapted spatio-temporal singular value decomposition (STSVD) processing algorithm combined with the total focusing method is proposed to improve the ultrasonic array image quality. First, the real-valued radio frequency (RF) data or A-scan signals are demodulated into the complex analytic signals containing in-phase and quadrature (I/Q) components. Then, the STSVD processing algorithm is used to filter the I/Q data, and the filtered I/Q data is converted into RF signals. Finally, the total focusing method is applied to the processed RF signals to produce the image of the region under detection as a stage of post-processing. Experiments are carried out with an ultrasonic linear phased array in contact with the HDPE pipe materials containing multiple side-drilled holes and through-wall notches. Results show that the proposed method can produce images with high quality to provide good inspection and characterization of defects in highly attenuative materials, especially the deeper defects.

Integrity and cost evaluation of natural fibers/HDPE composite tailored for piping applications

This paper focused on the establishment of performance level and cost of plantain fibers reinforced High Density Polyethylene (HDPE) matrixes as gas pipeline material using pressure containment of the new materials as performance criterion. The cost of modified plantain fibers, the cost of plantain fibers reinforced HDPE (PFRHDPE) and the cost of PFRHDPE master batch (HDPE resin + plantain fiber particles + stabilizer, plasticizer) for pipes extrusion production and pipelines fittings injection productions were established. The burst pressure evaluated for available standard outside diameter ratio (SDR) using the ultimate tensile strength of PFRHDE is very much greater than the standard SDR design pressures even when the temperature derating factors were applied. The Maximum Allowable Operating Pressure (MAOP) of PFRHDPE and induced stresses of pressurized pipes established indicated that the new material is suitable for pipeline design for natural gas and liquid petroleum (LPG) lines. The PFRHDPE developed has better specific properties than the conventional steel and HDPE pipe material in terms of yield strength, elastic modulus and density of the new material. But in terms of cost, steel and HDPE has approximate desirability for selection with PFRHDPE. The energy required to manufacture and process steel products is about 480 MJ/m2, while that of plastics is about 320 MJ/m2. The study further established that PFRHDPE can be applied in the design of oil and gas gathering, transportation and distribution lines.

Random propagation times for ultrasonics through polyethyilene

Low power ultrasonics are used for testing high density polyethylene pipe material. Attenuation and velocity give valuable information on the material in situ and without damages. In this paper we revisit recent data in the frequency band (4,10) megahertz. We prove that propagation is equivalent to random delays following stable probability laws. Moreover, the emergence of a companion noise non-detectable by devices is compliant with the law of conservation of energy.

Scale Deposition Inhibiting Composites by HDPE/Silicified Acrylate Polymer/Nano-Silica for Landfill Leachate Piping.

Scaling commonly occurs at pipe wall during landfill leachate collection and transportation, which may give rise to pipe rupture, thus posing harm to public health and environment. To prevent scaling, this study prepared a low surface energy nanocomposite by incorporating silicone-acrylate polymer and hydrophobically modified nano-SiO2 into the high-density polyethylene (HDPE) substrate. Through the characterization of contact angle, scanning electron microscopy and thermogravimetry, the results showed that the prepared composite has low wettability and surface free energy, excellent thermal stability and acid-base resistance. In addition, the prepared composite was compared with the commercial HDPE pipe material regarding their performance on anti-scaling by using an immersion test that places their samples into a simulated landfill leachate. It was apparent that the prepared composite shows better scaling resistance. The study further expects to provide insight into pipe materials design and manufacture, thus to improve landfill leachate collection and transportation.

Simplified Equations and Ansys Simulation of Head Loss on Nonlinear (Sliced) Bend for Piping Network

The head loss in the nonlinear bend caused by the friction of the wall along the bend and the direction change of the flow due to suddenly angle change. The essential elements include velocity (U) number of slices (n), length of the average slices wall (Li), angle change (α), friction coefficient (f), acceleration of gravity (g), and slope of the pipe base (S). Based on equation 12, with fixed discharge, the bigger diameter, and more number of slices in used, then the smaller head loss. Conversely, if the diameter used is getting smaller and less the number of slices, then the head loss bigger. This analysis is expected to provide optimal benefits for activities related design to piping networks, especially main networks that use large diameter pipes. Especially piping networks with the use of steel pipe or High-Density Polyethylene pipe materials. Such as oil pipes, gas pipes, and freshwater distribution pipes. The head loss that occurs will more measurable, fast, easy, and economical in implementation.

Ultrasonic attenuation and phase velocity of high-density polyethylene pipe material.

Knowledge of acoustic properties is crucial for ultrasonic or sonic imaging and signal detection in nondestructive evaluation (NDE), medical imaging, and seismology. Accurately and reliably obtaining these is particularly challenging for the NDE of high-density polyethylene (HDPE), such as is used in many water or gas pipes, because the properties vary greatly with frequency, temperature, direction and spatial location. Therefore the work reported here was undertaken in order to establish a basis for such a multiparameter description. The approach is general but the study specifically addresses HDPE and includes measured data values. Applicable to any such multiparameter acoustic properties dataset is a devised regression method that uses a neural network algorithm. This algorithm includes constraints to respect the Kramers-Kronig causality relationship between speed and attenuation of waves in a viscoelastic medium. These constrained acoustic properties are fully described in a multidimensional parameter space to vary with frequency, depth, temperature, and direction. The resulting uncertainties in acoustic properties dependence on the above variables are better than 4% and 2%, respectively, for attenuation and phase velocity and therefore can prevent major defect imaging errors.

Effects of Addition of Ultra-High Molecular Weight Polyethylene on Tie-Molecule and Crystallization Behavior of Unimodal PE-100 Pipe Materials

ABSTRACTWith the fast-growing global market demand for high-grade plastic pipe materials, high-density polyethylene (HDPE) products, such as PE-100, are playing a more and more important role. On the other hand, lack of basic understanding about these materials hinders the further development of this field. To investigate the effects of addition of an ultra-high molecular weight polyethylene (UHMWPE) on tie-molecules, crystallization kinetics and long-term properties of a unimodal HDPE pipe material (UMPE-100) made from a Cr-based catalyst, the blends of UMPE-100/UHMWPE were prepared through a twin-screw extruder. The probability of tie-molecules was calculated by a statistical approach, which has been proposed by Huang and Brown (Huang, Y.L.; Brown, N.J. Polym. Sci. B. 1991, 29, 129–137). It showed that as UHMWPE was added, the probability of tie-molecules increased due to increased molecular weight. The crystallization kinetics of the blends was investigated by an isothermal crystallization method using differential scanning calorimetry. Addition of small amount of UHMWPE improved the crystallization rate greatly. The natural draw ratio of blends decreased with improvement of tie-molecule probability and crystallization rate, indicating improvement in long-term properties.

Effect of Specimen Geometry on the Predicted Mechanical Behavior of Polyethylene Pipe Material1

The primary objective of the present paper is to depict the mechanical behavior of high density polyethylene (HDPE) pipes under different loading conditions with different specimen geometries to provide the designer with reliable design data relevant to practical applications. Therefore, it is necessary to study the effect of strain rate, ring configuration, and grip or fixture type on the mechanical behavior of dumb-bell-shaped (DBS), and ring specimens made from HDPE pipe material. DBS and ring specimens are cut from the pipe in longitudinal and circumferential (transverse) directions, respectively. On the other hand, the ring specimen configuration is classified into two types; full ring (FR), and notched ring (NR) (equal double notch from two sides of NR specimen) specimens according to ASTM D 2290-12 standard. Tensile tests are conducted on specimens cut out from the pipe with thickness of 10 mm at different crosshead speeds (10–1000 mm/min), and ambient temperature, Ta = 20 °C to investigate the mechanical properties of DBS and ring specimens. In the case of test specimens taken from the longitudinal direction from the pipe, a necking phenomenon before failure appears at different locations along the gauge section. On the other hand, the fracture of NR specimens occurs at one notched side. The results demonstrated that the NR specimen has higher yield stress than DBS and FR specimens at all crosshead speeds. The present experimental work reveals that the crosshead speed has a significant effect on the mechanical behavior of both DBS and ring specimens. The fixture type plays an important role in the mechanical behavior for both FR and NR specimens at all crosshead speeds.

A novel viscoplastic model of high-density polyethylene pipe material

ABSTRACT: A nonlinear three-component elastic viscoplastic strain-rate-dependent model was developed for a high-density polyethylene pipe material. In this model, the stress at any point is assumed to be a unique function of the instantaneous irreversible strain, its rate and acceleration, irrespective of any intermediate stress and strain history. However, a reference strain rate was assumed and below this the response was independent of the strain rate. Parameters of the model were determined using published data on strain-rate-dependent material responses. The model was developed within the elasto-viscoplastic framework so that it could be used in solving boundary value problems. The return mapping algorithm of strain-rate-dependent elasto-plastic material is described with the detailed derivation of the consistent tangent operator for quadratic convergence. The model was successfully implemented in an existing finite-element code. Finite-element analyses using this model were capable of simulating the strain-rate-dependent stress–strain relation, the response to a jump in the strain rate and an unloading–reloading response for a high-density polyethylene pipe material published in the literature.

Fracture characterization of high-density polyethylene pipe materials using the $$J$$ J -integral and the essential work of fracture

In this paper, fracture mechanics concepts are reviewed and their relevance to examine the toughness of highly deformable materials such as high-density polyethylene (HDPE) pipe materials is discussed. Using two different specimen configurations (single edge notched bending and compact tension), it was found that the \(J-R\) approach is unable to give pertinent indications on fracture toughness of HDPE. Alternatively, applying the essential work of fracture approach to double edge notched tension specimen, seems a more appropriate way to measure the fracture strength of HDPE and therefore to analyze the fracture process of such materials. Nevertheless, the severe necking occurring at the crack tip and in the plastic zone makes difficult the crack growth measurement, which clearly depends on the strain state and on the stress triaxiality level.

Short Chain Branches Distribution Characterization of Ethylene/1‐Hexene Copolymers by Using TREF + 13C‐NMR and TREF + SC Methods

AbstractSummary: Short chain branches distribution (SCBD) is the key factor for high density polyethylene (HDPE) pipe materials to achieve their excellent performance for long term (50 years) applications. However, the precise SCBD characterization of these HDPE materials with relatively low content of comonomer incorporation still remained as a challenge in this field. In this work, two characterization methods, namely temperature rising elution fractionation (TREF) cross step crystallization (SC) (TREF + SC) and TREF cross 13C‐NMR (TREF + 13C‐NMR), have been respectively used to qualitatively and quantitatively investigate the SCBD for two HDPE pipe materials (PE‐1 and PE‐2 with different long term performances) with small amount of 1‐hexene incorporation prepared from SiO2‐supported silyl chromate catalyst system (S‐2 catalyst) during UNIPOL gas phase polymerization. The comparison of SCBD between the two samples showed that: although short chain branches of PE‐2 with good performance were less than those of PE‐1 with bad performance, PE‐2 showed less comonomer incorporation on the low crystallinity and low molecular weight (MW) fractions keeping even higher comonomer incorporation on the high crystallinity and high MW parts compared with PE‐1. This difference on the SCBD for PE‐1 and PE‐2 was thought to be the key factor which is responsible for their great difference on environment slow crack resistance (ESCR). Moreover, TREF + SC method further reflected the intra‐ and inter‐molecular heterogeneities of each fraction from the two HDPE samples through the lamella thickness distribution compared with TREF + 13C‐NMR.

Fracture Surface Analysis in HDPE Pipe Material Fatigued at Different Temperatures and Loading Frequencies

Effect of temperature and loading frequency on the fatigue fracture process in high-density polyethylene (HDPE) pipe material has been investigated in this study via optical and scanning electron microscopy. Fatigue tests were performed using rectangular coupons obtained by slitting and flattening 50-mm-wide ring sections from 4-inch schedule 80 HDPE pipes. The flattening was carried out in a specially designed compression fixture at a temperature of 105 °C. Fatigue tests were conducted at temperatures of 0, 23, and 40 °C and loading frequencies of 0.1, 1, and 50 Hz. Fracture surface examinations reveal that the fatigue crack-growth process at all the test temperatures and loading frequencies involved mechanisms of shear yielding and crazing. Crack growth via crazing was found to be the dominant mechanism at higher temperature of 40 °C, while at 0 °C, a small amount of initial shear yielding precede the crazing process. Filler material particles contained in the HDPE pipe material play an important role of stress concentrators and help in micro-void nucleation, which promotes crack growth via crazing. The fatigue resistance of HDPE may thus be improved by addressing the stress concentration effect of filler particles.

Improvement of Mechanical Properties and Ultraviolet Resistance of Polyethylene Pipe Materials Using High Density Polyethylene Matrix Grafted Carbon Black

In recent years, high grade high density polyethylene (HDPE) pipe materials are being more and more widely used for water and gas supply. Carbon black (CB) is usually used as an anti-UV-light reagent for pipe materials. However, homogeneous dispersion of CB in the HDPE matrix and modification of the interface has always been a great challenge. In this work, HDPE matrix grafted CB (HDPE-g-CB) was successfully prepared through HDPE radicals formation by a thermo-mechanical method and subsequent radical capture by the CB surface. The weight percentage of grafted HDPE approached 10 wt% and the modification sharply reduced the surface free energy of the CB. The SEM (scanning electron micrographs) and TEM (transmission electron microscopy) results showed that HDPE-g-CB was uniformly dispersed in the HDPE pipe materials and the domain size of the dispersed phase was remarkably decreased from that in HDPE/CB. Therefore, compared with the HDPE/CB, the mechanical properties and ultraviolet (UV) resistance of HDPE/HDPE-g-CB were significantly improved, positively influencing the expected life span of pipelines.

Pennsylvania Thermoplastic Pipe Deep Burial Project: 20th Year Investigations

In June of 2007, the Ohio University research team visited the 610-mm (24-in.) diameter corrugated high density polyethylene (HDPE) pipeline structure located under 30.5-m (100.0-ft) high embankment of Interstate Highway 279, near Pittsburgh. This visit marked the 20th year of the field research project. The team conducted visual inspections of the pipeline along with in-situ pipe drilling experiments. The in-situ pipe wall drilling experiments conducted at the site induced strains in the pipe wall. However, the strains dissipated completely within 5 s. This demonstrated the nature of the viscoelastic material and a lack of significant stress levels existing in the pipe wall. These in-situ pipe wall drilling experiments are an innovative procedure for showing the stress relaxation capability of HDPE. Localized cracking of the pipe end was observed at joints positioned under more than 21.3 m (70.0 ft) soil fill and where two sections of Type C pipe were connected. The cracking observed in 2007 appeared to show insignificant changes from those observed during the 2002 inspections. No signs of structural distress were detected inside pipe sections that were under less than 21.3 m (70.0 ft) of soil fill. The pipe deflections, which were measured under 30.5 m (100.0 ft) of fill, have been stable for a number of years. The horizontal deflection changed by only 0.3% over the past 17 years. The vertical deflection has hardly changed over the past 18 years. The pipe circumferential shortening has increased by less than 0.2% over the last 18 years. Finally, the results of the laboratory tests showed that no noticeable changes took place in the basic engineering properties of the HDPE pipe material over the past 20 years.

Study on Fracture Behaviors of High-Density Polyethylene Pipe Material Based on Local Approach

Study on Fracture Behaviors of High-Density Polyethylene Pipe Material Based on Local Approach

Experimental approach to mechanical property variability through a high‐density polyethylene gas pipe wall

AbstractAn experimental investigation was designed to establish the distribution of mechanical properties throughout a high‐density polyethylene (HDPE) gas pipe wall. The proposed approach used a continuous and uniform filament that was automatically machined from the pipe on a precision lathe at a very low cutting speed and an optimal depth of cut to minimize heating and structural disturbances. Typical engineering stress–strain curves, in every layer, were obtained on a testing machine especially designed for polymers, and they were statistically analyzed. The stress–strain behavior of HDPE pipe material could basically be divided into three distinctive zones, the second of which remained important. The average stress level illustrating cold drawing for a given layer was almost constant throughout the pipe wall. The measured stresses and moduli correlated very well with the pipe thickness, and they increased from the outer layers toward the inner layers. This was explained by the crystallinity evolution because the pipe production process was based on a convective water‐cooling system with a temperature gradient, which generated residual stresses. Computed statistical stress–strain correlations at yielding, the onset of cold drawing, and fracture points revealed acceptable linear relations for an error level of p ≤ 0.05. On the other hand, an increasing linear correlation characterized the relationship of the yield stress and elastic modulus. This result was confirmed by literature for standard specimens, prepared by compression molding, that did not represent an actual pipe structure with respect to an extrusion thermomechanical history. Such an approach to mechanical property variability within an HDPE pipe wall highlighted the complexity of the hierarchical structure behavior in terms of stress–strain and long‐term brittle failure. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 272–281, 2005

Study on Fracture Properties of High-Density Polyethylene (HDPE) Pipe

Butt-fusion welding is the main technology to join high-density polyethylene (HDPE) plastic pipes, which are widely used in transport the water, gas and corrosive liquid. Investigation shows that one of the failure modes of HDPE pipe is the crack slowly grows across the thick direction and leads to failure at last, so that it is very important to study the resistance to crack initiation of HDPE pipe and its butt-fusion welded joint. In this study, the elastic-plastic fracture mechanics parameter, crack opening displacement (COD) is used to describe the fracture initiation behaviors for the HDPE materials and its butt-fusion welded joints. The resistance to initiation fracture of HDPE pipe materials and butt-fusion welded joints were investigated at different temperature by using multiple specimen resistance curve method and silicon-rubber replica method. The results show that saturation initial crack COD- δis of HDPE pipe materials and butt-fusion welded joints decreases with the decreasing temperature. The δis of butt-fusion welded joints is lower than that of HDPE pipe materials. Investigation also proved that the silicon-rubber replica method is more suitable for HDPE engineering material than the multiple specimen method. At the same time the statistic distribution of the δis of HDPE butt-fusion welded joint was conducted. The results show that the value of the δis has the statistic variance inherently. The optimum fitting distribution of COD is Weibull distribution with three parameters.