Cross-linked Polyethylene Pipes Research Articles

Deep Learning Analysis of the Propagation of Stabilizing Additive Hydrolysis in a Cross-Linked Polyethylene Pipe

Deep Learning Analysis of the Propagation of Stabilizing Additive Hydrolysis in a Cross-Linked Polyethylene Pipe

Quantification and stability assessment of 7,9-di‑tert‑butyl‑1-oxaspiro(4,5)deca-6,9-diene-2,8‑dione leaching from cross-linked polyethylene pipes using gas and liquid chromatography.

This study assesses the formation and stability of the water contaminant 7,9-di‑tert‑butyl‑1-oxaspiro(4,5)deca-6,9-diene-2,8‑dione ([1]) which repeatedly occurs in the migration waters of cross-linked polyethylene (PE-X) pipes. In aqueous solution [1] is partially transformed to 3-(3,5-di‑tert‑butyl‑1‑hydroxy-4-oxo-2,5-cyclohexadien-1-yl)propionic acid ([2]). For a better understanding of the formation of [1] and its transformation into [2] an analytical method was established to allow the analysis of both species separately. Because of thermal instability [2] cannot be detected with GC-MS. Therefore, two methods were validated for a reliable and reproducible quantification: GC-MS for [1] and HPLC-MS/MS for both [1] and [2]. Comparative measurements of migration waters from PE-X pipes using GC-MS and HPLC-MS/MS methods showed that the concentrations of [1] detected with GC-MS corresponds to the sum of [1] and [2] measured with HPLC-MS/MS. In the migration waters [1] was detected in higher concentrations than [2]. The highest concentrations of [1], detected with GC-MS, were > 300µg/L. The longer the materials are stored without contact with water, the more [1] is measured in the migration waters. Most of the previous values reported in the literature for [1] were based on semi-quantification. Hence, we compared results of the semi-quantitative determination according to EN 15768 with those of a quantitative method with a standard. The results gained with the semi-quantitative method represent less than 50% of the quantified values for the amount leaching from the pipes, which means that the semi-quantification method according to EN 15768 leads to a significant underestimation of [1]. Finally, stability assessment showed that [1] developed an equilibrium with [2] under acidic conditions, whereas it will completely be transferred to [2] at pH 10. At pH 7, it takes more than 50 days for [1] to reach an equilibrium with [2]. However, at increasing the temperature to 60°C, [1] will be rapidly transformed into [2]. Besides [1] and [2], other currently unknown degradation products are formed. As there is no comprehensive toxicological assessment for both substances available today, our findings underline the need for regulatory consequences.

Deep Generative Modeling of Infrared Images Provides Signature of Cracking in Cross-Linked Polyethylene Pipe

Hyperspectral infrared (IR) images contain a large amount of highly spatially resolved information about the chemical composition of a sample. However, the analysis of hyperspectral IR imaging data for complex heterogeneous systems can be challenging because of the spectroscopic and spatial complexity of the data. We implement a deep generative modeling approach using a β-variational autoencoder to learn disentangled representations of the generative factors of variance in a data set of cross-linked polyethylene (PEX-a) pipe. We identify three distinct physicochemical factors of aging and degradation learned by the model and apply the trained model to high-resolution hyperspectral IR images of cross-sectional slices of unused virgin, used in-service, and cracked PEX-a pipe. By mapping the learned representations of aging and degradation to the IR images, we extract detailed information on the physicochemical changes that occur during aging, degradation, and cracking in PEX-a pipe. This study shows how representation learning by deep generative modeling can significantly enhance the analysis of high-resolution IR images of complex heterogeneous samples.

Quantifying stabilizing additive hydrolysis and kinetics through principal component analysis of infrared spectra of cross-linked polyethylene pipe

Peroxide crosslinked high-density polyethylene (PEX-a) is increasingly being used to replace traditional metal and concrete pipes in applications such as water, gas, and sewage transport. Stabilizing additives play important roles in enhancing the long-term stability of PEX-a pipes and understanding changes to these additives under in-service conditions is critical to further improvements in pipe lifetimes. We used infrared (IR) microscopy to measure spectra within the central portion of the walls of PEX-a pipe subjected to two different types of ageing: exposure to high temperature (85∘C) air and exposure to high temperature (85∘C) water. To analyze these data, we used principal component analysis (PCA) to implement an unsupervised multivariate analytical approach. This allowed us to identify distinct ageing pathways for the two types of ageing in the two-dimensional space defined by the first two principal components PC1 and PC2, which together account for 88% of the variance in the data. This representation of the data allowed us to associate each PC with different ageing processes in the pipes: changes in PC1 were due primarily to hydrolysis of stabilizing additive ester linkages, whereas changes in PC2 were due primarily to elevated temperature. The PCA showed that ageing in high temperature water produced spectral changes consistent with those measured for an in-service pipe and that water is the key component driving the changes. The results provide important information for PEX-a pipe ageing and stabilizing additive formulation design.

Formation and sorption of trihalomethanes from cross-linked polyethylene pipes following chlorinated water exposure

Formation and sorption of trihalomethanes (THMs) occurs in chlorinated waters exposed to cross-linked polyethylene (PEX) pipes, impacting water quality in building plumbing.

Impacts of Organic Matter Migrating from Pipe Materials on Microbial Regrowth in Drinking Water

Polymeric materials are widely used in premise plumbing. To assess the potential of pipe materials to promote microbial regrowth in drinking water, we incubated drinking water in a new cross-linked polyethylene pipe (N-PEX), a new steel pipe lined with powdered polyethylene (N-SPE), and an old steel pipe lined with powdered polyethylene (O-SPE). As a reference, we also incubated drinking water in a carbon-free glass bottle (REF). Free chlorine rapidly depleted to below the quantification limit in the pipe incubations. While the original drinking water contained 0.4 mg C/L of dissolved organic carbon (DOC), the DOC concentration in N-PEX, N-SPE and O-SPE increased to 5.2, 3.1 and 1.7 mg C/L, respectively, after 8 days of incubation. The total cell count (TCC) in N-PEX, N-SPE, and O-SPE increased from <103 cells/mL to 6.0 × 105, 2.8 × 105, and 3.6 × 106 cells/mL after 8 days of incubation, respectively. On the other hand, the TCC in REF increased to 1.4 × 105 cells/mL after 14 days of incubation. Dominant bacterial groups were different under the different incubation conditions. These results indicated that organic matter migrating from pipe materials promote microbial regrowth and affect the microbial community composition in drinking water.

Study on simplified calculating method for hot water temperature and condensation in presumed steady condition of cross-linked polyethylene pipe

Study on simplified calculating method for hot water temperature and condensation in presumed steady condition of cross-linked polyethylene pipe

Classifying formulations of crosslinked polyethylene pipe by applying machine‐learning concepts to infrared spectra

ABSTRACTCrosslinked polyethylene (PEX‐a) pipes are emerging as promising replacements for traditional metal or concrete pipes used for water, gas, and sewage transport. Understanding the relationship between pipe formulation and performance is critical to their proper design and implementation. We have developed a methodology using principal component analysis (PCA) and the machine learning techniques of k‐means clustering and support vector machines (SVM) to compare and classify different PEX‐a pipe formulations based on characteristic infrared (IR) spectroscopy absorbance peaks. The application of PCA revealed that a large percentage (89%) of the total variance could be explained by the first three principal components (PC1‐PC3), with distinct clustering of the data for each formulation. By examining the contribution of the individual IR bands to the PCs, we determined that PC1 could be attributed to different peroxide crosslinkers, whereas PC2 and PC3 could be attributed to differences in the additives. Using the PCA results as input to k‐means clustering and SVM resulted in very high accuracy of classifying the different pipe formulations. Our approach highlights the advantages of using PCA and machine learning techniques to characterize different formulations of PEX‐a pipes, which is important to achieve a detailed understanding of the pipe formulation and manufacturing process. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1255–1262

Transfer of phthalates from c-polyvinyl chloride and cross-linked polyethylene pipe (PEX-b) into drinking water

Several different materials have been used for production of domestic water pipes throughout history. In recent years, the use of cross-linked polyethylene (PEX) pipe has increased dramatically, yet the potential for leaching of phthalates, which are endocrine disrupting compounds associated with adverse reproductive effects in humans, has not been examined. In this study, the potential of chlorinated polyvinyl chloride (cPVC) and red, blue, and heat PEX piping to leach phthalates into static hot and cold water after 2, 8, and 48 hours was evaluated. Concentrations of six phthalates, dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), benzyl-butyl phthalate (BBP), di(2-ethylhexyl) phthalate (DEHP), and di(n-octyl) phthalate (DNOP), were determined by gas chromatography-mass spectrometry. Pipe type (F3,71 = 15.6, P = 0.001) contributed significantly to phthalate concentrations in water, while temperature (F4,71 = 1.74, P = 0.106) and time (F4,71 = 1.02, P = 0.427) were not significant factors. Significantly higher concentrations of DEP, DBP, and BBP were observed in cPVC pipe (&amp;lt;method detection limits (MDL) to 466 ng L−1, 252–4,219 ng L−1, 473–18,400 ng L−1, respectively) compared to blue PEX (T2 = 12.2, P &amp;lt; 0.001; &amp;lt;MDL, &amp;lt;MDL − 140 ng L−1, &amp;lt;MDL − 459 ng L−1, respectively), red PEX (T2 = 19.3, P &amp;lt; 0.001; &amp;lt;MDL, &amp;lt;MDL − 188 ng L−1, &amp;lt;MDL − 881 ng L−1, respectively), and heat PEX (T2 = 19.9, P &amp;lt; 0.001; &amp;lt;MDL, &amp;lt;MDL − 162 ng L−1, &amp;lt;MDL − 169 ng L−1, respectively). Phthalate exposure from drinking water via cPVC or PEX is low when compared to other dietary sources. Nonetheless, a shift from cPVC to PEX pipes in households would decrease potential exposure to phthalates.

Evaluation of cross-linked Polyethylene pipes for fuel cell

Evaluation of cross-linked Polyethylene pipes for fuel cell

Carbon nanotube-reinforced crosslinked polyethylene pipes for geothermal applications: From synthesis to decomposition using analytical pyrolysis–GC/MS and thermogravimetric analysis

Abstract Carbon nanotube reinforced crosslinked high density polyethylene (PEX) nanocomposites were synthesized for geothermal applications requiring higher polymer thermal conductivity and a comprehensive thermal decomposition study was performed. The prepared nanocomposites were investigated by laser flash analysis and temperature modulated differential scanning calorimetry revealing a great enhancement on the specific heat capacity along with a further enhancement on the thermal diffusivity, resulting in some cases in an overall thermal conductivity increase of more than 200%. For the thermal decomposition or recycling process of the produced nanocomposites, a thorough examination of the decomposition process and its kinetics was performed by using thermogravimetry and analytical pyrolysis–gas chromatography–mass spectroscopy. From this systematic study, two possible decomposition mechanisms for PEX were proposed for the first time in literature and the decomposition kinetics results, which were conducted using isoconversional and model-fitting methods, were in agreement with the proposed mechanisms. From the complementary use of analytical pyrolysis and thermal analysis techniques study it was revealed that the presence of carbon nanotubes hinders the diffusion of the primary scission products of PEX and enhances its thermal stability.

Study on the Structure of Peroxide Cross-Linked Polyethylene Pipes with Several Stabilizers

Cross-linked polyethylene (PEX) pipes used in hot water supply are required for high mechanical strength and high creep resistance at high temperature. Especially PEX-a pipes which are made by peroxide cross-linking have better performance, such as creep resistance and thermal shock resistance than the pipes made by the other cross-linking method. Because the PEX-a pipes indicate the higher cross-link degree as compared with the other PEX pipes. In this study, the PEX-a pipes which were mixed with several stabilizers were tested to evaluate the effects on cross-link degree and the oxygen induction time. And also they are evaluated with the chlorine aqueous solution by the performance of the long-term hydrostatic pressure test and the long-term hydro dynamic pressure test. As a result, it was found that the combination of antioxidants for PEX-a pipes plays an important role to prolong the oxygen induction time without inhibiting the cross-linking. From the results of the 1H pulsed NMR measurement over the melting point of polyethylene, it was found that each peroxide PEX pipe with different antioxidant combinations indicated the different proportion and crosslink density of cross-linked region, in addition, that these pipes had the effective structure of cross-linking for the hydrostatic and hydrodynamic pressure test with the chlorine aqueous solution. Therefore, it was considered to be useful results for studies of the stricture of cross-linking of polyethylene.

Evaluation of Durability for Peroxide Cross-linked Polyethylene Pipes by Stabilizer Influence

Evaluation of Durability for Peroxide Cross-linked Polyethylene Pipes by Stabilizer Influence

407 架橋ポリエチレン管の電気式融着継手における界面層の評価(締結・接合部の力学・プロセスと信頼性評価)

407 架橋ポリエチレン管の電気式融着継手における界面層の評価(締結・接合部の力学・プロセスと信頼性評価)

Durability of cross-linked polyethylene pipes under pressure

This article summarizes about 20 years of experimental studies on the durability of cross-linked polyethylene (XPE) extruded pipes for hot water transport. The time to failure was determined against hoop stress and temperature (in the 20–120°C range). The XPE samples (16 distinct materials) were compared to classical PE ones (6 distinct materials). It appears clearly that cross-linking suppresses the ductile-brittle transition (average coordinates: t C = t C0 exp(Q/RT) with In t C0 = −24.2 and Q = 84.6 kJ mol−1 but does not modify significantly the behavior in ductile regions. It can be assumed that, for XPE, the ceiling conditions are determined by the oxidation embrittlement of which the (tentative) coordinates could be given by t E = t E0 exp(H E/RT) with In t E = −24.45 and H E = 116 kJ. Thus, XPE performs better than PE in the (t C − t E) interval. On this side of t E, the lifetime t of XPE is linked to the hoop stress σ and the temperature by an equation of which a simplified form could be: σ = α(T M − T)(β − log t) where α = 4 × 10−3 and β = 30 for T ≤ 80°C and α = 6 × 10−3 and β = 20 for T ≥ 80°C, σ being in MPa, t in hours and T M being the melting point (137°C).

Welding of Crosslinked Polyethylene Pipes

The butt-welding of pipes made of crosslinked polyethylene, the most efficient joining method for the material PE-X, which up to now has been regarded an ‘non-weldable’, will enable it to be used for industrial and underground pipes and hence will make a major contribution to state-of-the-art and future-orientated pipeline applications. In the future, it should also be possible to weld PE-X pipes with diameters of less than 90 mm and work is also being performed to develop welded joints with the same temperature resistance as the pipes. This will permit the use of welded PE-X pipes for hot-water systems and heating technology.

Oriented crosslinked polyethylene pipes by a novel extrusion method

AbstractCrosslinking and stretching (2.5 times along the circumferential direction) of the molten polymer during extrusion produced pipes with dominantly circumferential orientation and a lower degree of axial chain orientation. Differential scanning calorimetry (crystallinity and crystal thickness), density measurements (crystallinity), X‐ray diffraction (c‐axis orientation), infrared dichroism measurements (crystalline and amorphous chain orientation) and contraction measurements (molecular draw ratio) assessed the microstructure of the pipe material. The mechanical properties of the oriented material were assessed by uniaxial tensile tests. The orientation was biaxial with the main orientation in the circumferential direction and a lesser orientation in the axial direction. The maximum degree of circumferential orientation was obtained at the inner wall of the pipe. The lower degree of crosslinking of the core material allowed slippage of chains during the stretching of the molten polymer and it is suggested that this is the cause of the lower degree of orientation of the core material. The oriented pipe material exhibited a 5‐10% higher degree of crystallinity and higher crystal thickness than conventionally crosslinked material. The tensile modulus and the tensile strength of the oriented, cross‐linked material was greater along the axial direction than along the circumferential direction. The circumferential and axial moduli for the oriented, crosslinked pipe were greater than the corresponding moduli of the non‐oriented cross‐linked pipe material. Another pipe based on crosslinked PE that were first circumferentially stretched 2.5 times and later axially stretched 10 times (in the molten state) showed, despite the fact that it exhibited pronounced axial orientation almost a balanced tensile modulus (4.3±0.2 GPa) in the axial‐circumferential plane. Atomistic modelling showed that the orientational dependence of the density of the amorphous phase is small.