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Maret 14, 2022
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EVALUATION OF MECHANICAL PROPERTIES AND LONG- TERM DURABILITY OF AGED POLYETHYLENE PIPES FOR GAS DISTRIBUTION

Shuhei Nishida, Shintaro Iwasaki, Hidefumi Yamanaka, Takahiro Kasatani

# 2021 Amsterdam

Polyethylene pipelines have been used for natural gas service applications for over 40 years in Japan. It is thought that they will continue to be used widely for many years. Therefore, it is important to confirm the conditions of the existing pipelines being used for the long term. In this study, polyethylene pipes comprising two types of resin and installed for a long term (more than 30 years) in Japan were investigated. Certain physical properties of these polyethylene pipes (such as the Charpy impact strength and melt mass flow rate (MFR)) changed in comparison with the properties of unused pipes of the same age. In contrast, the results regarding the full notch creep test (FNCT) of these pipes were approximately equal to those of the unused pipes. These results suggest that although the physical properties of polyethylene pipes buried for a long period of up to 30 years changed, the creep characteristics, which are more important for the life of the pipes, hardly changed. Therefore, these polyethylene pipes can be used for years to come.

articles source :  https://www.pe100plus.com/PPCA/EVALUATION-OF-MECHANICAL-PROPERTIES-AND-LONG-TERM-DURABILITY-OF-AGED-POLYETHYLENE-PIPES-FOR-GAS-DISTRIBUTION-p1764.html

Maret 7, 2022
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MECHANICAL INTERGRITY OF HDPE BUTT FUSION JOINTS – EFFECT OF CARBON BLACK DISTRIBUTION

Suleyman Deveci, Nisha Preschilla, Sulistiyanto Nugroho, Birkan Eryigit

# 2021 Amsterdam

Carbon black (CB) has been used as a perfect and the cheapest solution to prevent photo degradation of polyethylene against UV light exposure. The effect of carbon black on the mechanical properties of polyethylene pipes was studied extensively, but only on well dispersed and distributed carbon black polyethylene composites. As a continuation of the previous work presented at PPXIX Las Vegas in 2018 [1], the effect of carbon black distribution on the mechanical properties of butt- fusion joints was investigated in this current work. Polyethylene pipes with similar carbon black concentrations but different distributions were produced with industrial scale compounding and extrusion equipment. Waisted tensile test specimens were milled out directly from the butt-fused pipe samples and elongated to fracture at fusion zone. Carbon black distributions at the butt fusion interphase, both in axial and radial directions, were investigated. A significant decrease in joint integrity, measured as work of fracture, was observed for the welds made with polyethylene pipes with inhomogeneous carbon black distributions. It was found that the width of areas that do not contain carbon black (windows) can significantly enlarge at the butt fusion interphase due to shearing, resulting in brittle failures at the butt fusion interphase with a magnitude related to the level of inhomogeneity. This work focuses on the evaluation of fracture surfaces of weld interphases and their relationship with the level of carbon black inhomogeneity in the polyethylene matrix.

article source : https://www.pe100plus.com/PPCA/MECHANICAL-INTERGRITY-OF-HDPE-BUTT-FUSION-JOINTS-EFFECT-OF-CARBON-BLACK-DISTRIBUTION-p1756.html

Maret 1, 2022
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EFFECT OF INSUFFICIENT HOMOGENIZATION DURING THE EXTRUSION OF POLYETHYLENE PIPES ON BUTT FUSION JOINT INTEGRITY

Mike Troughton, Amir Khamsehnezhad, Changyi Yu

# 2021 Amsterdam

When butt fusion welding polyethylene (PE) pipes in the field, it is often specified that the pipes must undergo fusibility testing in all combinations of suppliers, diameters and thicknesses before being fused in production. This is a very onerous and expensive task, but must be carried out to ensure that the PE pipes are of sufficient quality to produce acceptable butt fusion joints. One of the reasons why PE pipes might not be of sufficient quality is insufficient homogenization of the resin, which during the extrusion of black pigmented PE pipes, may result in features called “windows”. These are local areas where there is a lack of carbon black pigmentation and normally occur in thicker- walled pipes, towards the mid-wall thickness. They can be seen, for example, in the shavings from the end of the pipes produced during the trimming stage of the butt fusion process. Two potential reasons why insufficient homogenization of pigmented PE resin might cause a reduction in the performance of butt fusion joints are: 1) if there are areas in thepipe where the carbon black content is zero, there are likely to be areas where the carbon black concentration is significantly higher than the average. These areas may act as either stress concentrations or cause lack of fusion in the butt fusion joints; 2) after the PE melt passes through the mandrel support plate in the pipe extruder, which contains hundreds of holes, the molten strands need to fuse back together to form a homogeneous melt stream. However, if there are areas in the melt that contain higher viscosity material, these melt strands may not fuse together perfectly and may subsequently result in areas of reduced fusion in the butt fusion joint. This paper describes an investigation into the effect of insufficient homogenization of pigmented resin in PE pipes on the integrity of the subsequent butt fusion joints and the development of a test to quantify the amount of windows in the pipe. It will describe the analysis carried out on a number of PE pipes, made using both pre-compounded and in- line compounded resin on the same pipe extruder but using different extrusion conditions in order to obtain different degrees of homogenization. The results of mechanical tests carried out on the butt fusion joints from these pipes were used to determine a critical value of windows below which the joint integrity is not affected.

search article : https://www.pe100plus.com/PPCA/EFFECT-OF-INSUFFICIENT-HOMOGENIZATION-DURING-THE-EXTRUSION-OF-POLYETHYLENE-PIPES-ON-BUTT-FUSION-JOINT-INTEGRITY-p1738.html

Februari 21, 2022
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ALLOWABLE SCRATCH DEPTH HISTORY & RECOMMENDATIONS FOR PE PRESSURE PIPE

Chris Ampfer, Gene Palermo, Ernest & Oren Lever

# 2021 Amsterdam

This paper looks at the origin of the 10% allowable scratch depth rule for polyethylene (PE) pressure pipe developed in 1971 and research that has been performed over the years since its inception to determine the validity of this rule. The 10% rule has been used by natural gas pipeline operators since the 1970’s to determine if scratched pressure pipe is acceptable for service or should be removed from service. This rule has crept over into other pressure applications like water distribution. Polyethylene pipe can be scratched or gouged in many ways before, during, or after it is installed. The 10% scratch depth rule was developed on first generation PE pipe and was left unquestioned until after a test to predict slow crack growth resistance (SCGR) was developed in the late 1990’s. Since that time, research has shown that allowable scratch depth is dependent on the pipe’s slow crack growth resistance, operating temperature, and operating pressure. As the SCGR of pressure pipe resins have increased since the 1970’s, it has become the greatest factor in determining allowable scratch depth.

This paper concludes with recommended maximum scratch depths for polyethylene pipe of 35% for gas distribution and 10% for water distribution and non-regulated gas gathering dependent on average operating temperature over the pipe’s estimated life. Data from historic research was reviewed and re-analyzed to formulate a simplified equation for estimating allowable scratch depth based on failure time, PENT value, operating temperature, and hydrostatic design stress. Allowable scratch depth limits along with a depth measurement tool can be used by pipeline operators to determine if scratched pipe can remain in service or if it must be removed.

https://www.pe100plus.com/PPCA/ALLOWABLE-SCRATCH-DEPTH-HISTORY-RECOMMENDATIONS-FOR-PE-PRESSURE-PIPE-p1812.html

Februari 14, 2022
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PRESSURE PIPELINE MADE OF HDPE – DETERMINATION OF REMAINING LIFETIME AFTER 47 YEARS OF OPERATION IN LAKE OSSIACH (CARINTHIA, AUSTRIA)

Ulrich Schulte, Dr. -Ing. Joachim Hessel

# 2021 Amsterdam

In order to protect the Austrian lakes effectively against the discharge of effluent, a 13 km long pressure pipeline made of high density polyethylene was laid on the bottom of Lake Ossiach back in 1971. The DN355 to DN200 pipes were produced from a first generation HDPE-compound. The classification would have been close to “PE63”. [1]. This pipeline serves to collect waste water and to pump an average volume of about 1.1 Mill. m3/year with a maximum pressure of 4 bar to a nearby sewage treatment plant. The maximum temperature of the lake water is 15°C.

In the design phase in 1970 the planned lifetime for such a pipeline was set to 50 years. While this pipeline is still in operation to the satisfaction of all stakeholders, it now reaches the end of the planned operating time. As part of a general risk assessment of pressure pipelines in the Austrian lakes, studies were carried out to determine the residual life of a sample that had been installed in 1971 to allow the operator to decide whether a rehabilitation of the pipeline needs to be considered or whether a longer operation time can be justified. The studies are based on the empirical relationships for temperature dependent reactions, discovered by the Swedish physicist Arrhenius in the 19th century. The Arrhenius law allows for accelerated testing at elevated temperatures and extrapolation to expected lifetimes at ambient temperatures.

A sample of a DN 355 SDR 17 pipe had been taken from the pipeline and analysed with respect to slow crack growth resistance, as well as thermal ageing properties. With the Arrhenius approach, it could be concluded that with respect to both stress crac k resistance as well as thermal aging, the pipe made out of Ziegler HDPE could be operated for at least another 50 years, doubling the lifetime of the original plan [2]. The outcome of these investigations confirms like former investigations on other pipes

Article source : https://www.pe100plus.com/PPCA/PRESSURE-PIPELINE-MADE-OF-HDPE-DETERMINATION-OF-REMAINING-LIFETIME-AFTER-47-YEARS-OF-OPERATION-IN-LAKE-OSSIACH-CARINTHIA-AUSTRIA-p1729.html
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