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  • 1.
    Banushi, Gersena
    et al.
    HafenCity University, Germany.
    Vega, Alberto
    RISE Research Institutes of Sweden, Built Environment, Infrastructure and concrete technology.
    Weidlich, Ingo
    HafenCity University, Germany.
    Yarahmadi, Nazdaneh
    RISE Research Institutes of Sweden, Built Environment, Infrastructure and concrete technology.
    Kim, Jooyong
    Korea District Heating Corporation, Korea.
    Jakubowicz, Ignacy
    RISE Research Institutes of Sweden, Built Environment, Infrastructure and concrete technology.
    Sällström, Jan Henrik
    RISE Research Institutes of Sweden, Built Environment, Infrastructure and concrete technology.
    Durability of District Heating Pipelines Exposed to Thermal Aging and Cyclic Operational Loads2021In: Journal of Pipeline Systems Engineering and Practice, ISSN 1949-1190, Vol. 12, no 1, article id 04020067Article in journal (Refereed)
    Abstract [en]

    Fourth generation district heating networks (4GDH) must be designed for future energy systems, integrating renewable volatile energy sources, with lower operation temperatures, and consequent reduction of heat losses and increased energy efficiency. The lower levels of operating temperature and the greater amount of cyclic loading, influence aging, and the service life of 4GDH pipelines, differently from traditional district heating (DH) networks, and thus require proper investigation of the system response at the cross-sectional level. To evaluate the material durability of 4GDH pipelines, we have analyzed the behavior of the service steel pipe, the insulation foam, and their adhesive interaction, using an innovative analytical and experimental procedure. This paper describes the influence of traditional and future operational loading conditions on the performance of preinsulated bonded single-pipe systems, representing the majority of currently operating DH pipelines. The performed fatigue analysis of the steel service pipe showed that the lifetime of 4GDH pipelines is expected to increase because of the lower operating temperature, and the low impact of thermal loading volatility in the network, compared to conventional DH. The accelerated aging tests of DN 50/160 pipes demonstrated that the combined effect of cyclic mechanical loading and thermal aging accelerates the rate of chemical degradation of the PUR foam, leading to a faster deterioration of the mechanical adhesion strength. The shear strength tests of naturally aged DH pipes revealed that, besides the initial pipe system characteristics and aging period, the residual shear strength of the polyurethane (PUR) foam depends on the temperature history, decreasing with the level of operating temperature and amount of fluctuation. The obtained results give a better understanding of the performance of traditional and 4GDH pipelines in operation that need to be appropriately considered in the engineering design standards of DH networks toward a more sustainable and energy-efficient infrastructure. 

  • 2.
    Forsgren, Lilian
    et al.
    Chalmers University of Technology, Sweden.
    Noyan, Ezgi
    Chalmers University of Technology, Sweden.
    Vega, Alberto
    RISE Research Institutes of Sweden, Built Environment, Infrastructure and concrete technology. Chalmers University of Technology, Sweden.
    Yarahmadi, Nazdaneh
    RISE Research Institutes of Sweden, Built Environment, Infrastructure and concrete technology.
    Boldizar, Antal
    Chalmers University of Technology, Sweden.
    The thermo-oxidative durability of polyethylene reinforced with wood-based fibres2020In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 181, article id 109374Article in journal (Refereed)
    Abstract [en]

    Aiming at better understanding the ageing behaviour of cellulose composites, the accelerated thermo-oxidative ageing of polyethylene reinforced with two types of wood-based cellulose fibres was studied. Materials were prepared by extrusion mixing of either un-stabilized or stabilized polyethylene reinforced with 5 and 20 vol % cellulose content. The materials were extruded into strips and then aged at 90°C in circulating air. The effect of accelerated ageing up to 31 days was assessed by oxidation induction time and mechanical properties in tension. The results indicated that the added cellulose fibres did not increase the degradation of the composites during this ageing. Reinforcement with 20 % cellulose fibre having a 28 % lignin content together with 0.005 % Irganox 1010 antioxidant resulted in a remarkable improvement in the resistance against accelerated thermo-oxidation, compared to the pure polyethylene with added antioxidant. The findings of increased lifetime of LDPE by addition of wood-based reinforcement is of great interest, since the durability aspect is crucial to understand and predict before usage in commercial applications and especially as structural composites.

  • 3.
    Vega, Alberto
    et al.
    RISE Research Institutes of Sweden, Built Environment, Infrastructure and concrete technology.
    Yarahmadi, Nazdaneh
    RISE Research Institutes of Sweden, Built Environment, Infrastructure and concrete technology.
    Jakubowicz, Ignacy
    RISE Research Institutes of Sweden, Built Environment, Infrastructure and concrete technology.
    Cyclic axial loads and thermal ageing of district heating pipes2021In: Energy Reports, E-ISSN 2352-4847, Vol. 7, p. 105-109Article in journal (Refereed)
    Abstract [en]

    Thermal ageing at elevated temperatures is the standard method to determine the service life of pre-insulated district heating pipes nowadays. However, DH pipes are also subjected to axial movements which can affect the adhesion strength between the polyurethane foam and the service pipe. This contact surface is usually exposed to the highest temperatures. In this project, DH pipes were aged at elevated temperatures and at the same time cyclic axial loads were applied. Two DH pipes were only exposed to thermal ageing at 130 and 140 °C, while two other similar pipes were also exposed to cyclic axial loads. The adhesion strength was evaluated as the function of ageing time using the RISE plug method. Any changes in the chemical structure of the PUR samples were also observed using Fourier transform infrared spectroscopy. Comparing the results in this investigation, we found that the degradation of the mechanically loaded pipes was significantly faster than the degradation observed in non-loaded pipes at the same ageing temperatures. The FTIR study revealed that cyclic mechanical loads accelerated the chemical degradation of the PUR foam during thermal ageing. This study shows how important it is to consider all influencing factors in accelerated ageing. The methods presented here should be considered as an alternative to thermal ageing at high temperatures because the combination of mechanical and thermal loads reproduces better the real operating conditions. It is even of bigger interest when energy from different sources will be connected to the fourth generation of DH networks, which can cause more temperature fluctuations.

  • 4.
    Vega, Alberto
    et al.
    RISE Research Institutes of Sweden, Built Environment, Infrastructure and concrete technology.
    Yarahmadi, Nazdaneh
    RISE Research Institutes of Sweden, Built Environment, Infrastructure and concrete technology.
    Jakubowicz, Ignacy
    RISE Research Institutes of Sweden, Built Environment, Infrastructure and concrete technology.
    Determining the useful life of district heating pipes: Correlation between natural and accelerated ageing2020In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 175, article id 109117Article in journal (Refereed)
    Abstract [en]

    District heating (DH) systems constitute a smart and environmentally friendly solution for energy distribution in the heat sector in Europe. This technique is still expanding but already faces some issues such as status assessment of the current DH networks and the development of new generation networks for low-temperature DH. Therefore, it is essential to understand the ageing behaviour of pipes under operating conditions and to find the relevant parameters that control the degradation processes. Many factors affect the deterioration of DH pipes, especially the polyurethane foam, which makes it very complex to find a reliable prediction model. Models based on a linear Arrhenius relationship using results from high ageing temperatures seem to be incorrect. For this study, 10 pipes that have been in service for many years in Sweden and Norway were evaluated. The aim was to study the impact of natural ageing on the mechanical adhesion and chemical structure of the polyurethane foam, which affects the pipe's performance. A test method developed at the Research Institutes of Sweden (RISE), called RISE plug method, was used to study the mechanical adhesion strength. In addition, Fourier transform infrared spectroscopy was used to observe any change in the chemical structure. The results were compared with previous analyses of DH pipes exposed to accelerated ageing. This information helps to provide a better comprehension of the deterioration of the current generation of pre-insulated DH pipes and to improve the accelerated ageing methods used nowadays to predict the technical lifetime of DH pipes. Our results suggest that the lifetime of DH pipes has been underestimated when using artificial ageing at relatively high temperatures. The data collected from naturally aged pipes gave confirmatory information about their physical status compared with our laboratory tests. This study also suggests that infrared analyses could be used as an early indication of the degradation of the polyurethane foam at the interface with a steel pipe. 

  • 5.
    Vega, Alberto
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Built Environment, Energy and Circular Economy.
    Yarahmadi, Nazdaneh
    RISE - Research Institutes of Sweden (2017-2019), Built Environment, Energy and Circular Economy.
    Jakubowicz, Ignacy
    RISE - Research Institutes of Sweden (2017-2019), Built Environment, Energy and Circular Economy.
    Optimal conditions for accelerated thermal ageing of district heating pipes2018In: Energy Procedia, ISSN 1876-6102, Vol. 149, p. 79-83Article in journal (Refereed)
    Abstract [en]

    Technical lifetime prediction of polymeric materials is often based on accelerated ageing tests at elevated temperatures. Samples are exposed to relatively high temperatures to accelerate the natural degradation processes. For district heating pipes, accelerated thermal ageing is the ordinary method used to determine the lifetime of pipes. According to the Standard EN 253:2009 + A1:2013, the district heating pipes shall be subjected to an accelerated thermal ageing for a long period of time at 160 °C or 170 °C. The lifetime is determined by extrapolation using the Arrhenius relationship. However, papers published recently have questioned this method, especially the high temperatures used for ageing of the pipes and the use of Arrhenius equation to describe the complicated degradation mechanisms, which can result in the erroneous estimation of the technical lifetime. Our investigation has shown the complexity of the pipe's degradation mechanisms. The behaviour of mechanical shear strength at elevated temperatures (T > 130 °C), suggests an alteration rather than an acceleration of the degradation mechanisms. Accelerated ageing tests should reproduce the proper natural ageing mechanisms. The analyses of PUR's thermal conductivity and its chemical structure by FTIR confirmed the degradation patterns

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  • 6.
    Vega, Alberto
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Built Environment, Energy and Circular Economy.
    Yarahmadi, Nazdaneh
    RISE - Research Institutes of Sweden (2017-2019), Built Environment, Energy and Circular Economy.
    Jakubowicz, Ignazy
    RISE - Research Institutes of Sweden (2017-2019), Built Environment, Energy and Circular Economy.
    Determination of the long-term performance of district heating pipes through accelerated ageing2018In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 153, p. 15-22Article in journal (Refereed)
    Abstract [en]

    The lifetime of pre-insulated district heating pipes (DHPs) is commonly evaluated using the method described in the normative European Standard EN 253. This lifetime is normally calculated using an Arrhenius equation, which makes use of test results from accelerated ageing tests at elevated temperatures. In this investigation, long-term accelerated ageing tests of DHPs at elevated temperatures were carried out. The ageing behaviour, especially at the interface between steel pipe and polyurethane (PUR) foam, showed several routes of degradation. It is clearly demonstrated using measurements of shear strength, thermal conductivity and alterations of chemical structure by Fourier Transform Infrared spectroscopy that the results of accelerated ageing at 170 and 150 °C significantly diverge from those obtained from the ageing test at 130 °C. It is therefore concluded that accelerated ageing at commonly used high temperatures does not create an acceleration of degradation processes at the steel/PUR interface relevant for the DHP application, but rather a significant alteration in mechanism. This finding is of crucial importance for the use of EN 253 and the development of future methods for lifetime prediction of DHPs.

  • 7.
    Vega, Alberto
    et al.
    RISE Research Institutes of Sweden, Built Environment, Infrastructure and concrete technology.
    Yarahmadi, Nazdaneh
    RISE Research Institutes of Sweden, Built Environment, Infrastructure and concrete technology.
    Sällström, Jan
    RISE Research Institutes of Sweden, Built Environment, Infrastructure and concrete technology.
    Jakubowicz, Ignacio
    RISE Research Institutes of Sweden.
    Effects of cyclic mechanical loads and thermal ageing on district heating pipes2020In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 182, article id 109385Article in journal (Refereed)
    Abstract [en]

    The lifetime of pre-insulated district heating pipes is commonly evaluated by thermal ageing at elevated temperatures and is calculated using the Arrhenius equation. In this investigation, the effects of a repetitive shear stress during thermal ageing of pipes were studied. The degradation of polyurethane foam, especially at the interface with a steel pipe was evaluated from measurements of the adhesion strength and of alterations in the chemical structure of polyurethane by Fourier transform infrared spectroscopy. The main conclusion was that the thermal degradation of mechanically stressed district heating pipes was significantly faster than that of non-loaded pipes aged at the same temperature. It was also shown that the faster degradation of the mechanically loaded pipes is mainly due not to fatigue but to accelerated chemical degradation of the polyurethane foam. The results suggest that this methodology should be considered as an accelerated test method in order to avoid overestimation of the lifetime of district heating pipes and to show better ageing characteristics of mechanically stressed pipes, especially those intended for use in the fourth generation district heating networks 

  • 8.
    Yarahmadi, Nazdaneh
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Jacubowicz, Ignacy
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Vega, Alberto
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Livslängd för fjärrvärmerör : Fas I – Nedbrytningsmekanismer2017Report (Other academic)
    Abstract [sv]

    Dagens standard för prefabricerade fjärrvärmerör SS-EN253 innehåller olika testmetoder och krav där ett av de viktigaste är kravet på livslängd på minst 30 år vid en kontinuerlig driftstemperatur på 120 °C. Bestämningen av tekniska livslängden är baserad på mätningar av förändringar i skjuvhållfastheten efter accelererad termisk åldring. Den beräknade livslängden för ett fjärrvärmerör är baserad på extrapolering med hjälp av Arrhenius ekvation. Det finns en stor enighet kring uppfattningen att Arrhenius modellen inte ger en god överensstämmelse med de observerade åldringsdata och att det följaktligen saknas tillförlitliga metoder för livslängdsbestämning av fjärrvärmerör. Trots många forskningsrapporter finns det fortfarande skilda teorier om hur snabbt PURisoleringar bryts ner och vilka nedbrytningsmekanismer som dominerar. Syftet med det här projektet är att kartlägga de komplicerade sambanden och förstå vilka nedbrytningsprocesser som dominerar under olika betingelser och utifrån denna kunskap utveckla tillförlitliga metoder för livslängdsprediktering. Allt testmaterial utgjordes i denna studie av polyuretan (PUR) cellplastisolering som togs ut från nytillverkade fjärrvärmerör. Accelererad åldring genomfördes i luft och i kväveatmosfär vid 150 °C för upp till 8 veckor. Det visade sig att exponering i kväveatmosfär inte orsakar någon mätbar förändring av egenskaper. En motsvarande åldring i luft orsakar däremot stora förändringar i både dimensioner, viktförlust och färg. IR (infraröd) analys kunde också bekräfta att materialet bryts ner genom termo-oxidativa processer. Termo-oxidativ nedbrytning syns också i analyser av cellgassammansättningen. Materialet efter åldring i luft innehåller betydligt mindre halt cyklopentan samtidigt som fyra nya flyktiga ämnen kunde detekteras. Trots alla indikationer på materialets termooxidativa nedbrytning har böjhållfastheten inte förändrats hos materialet. Detta måste utredas vidare för att kunna förklara mekanismer bakom resultatet. Förutom beständighetsstudier av PUR materialet genomfördes långtidsåldring av fjärrvärmerör vid olika temperaturer. Resultaten av skjuvhållfasthet mätningar indikerar att det åtminstone finns tre olika faser i nedbrytningsprocessen. Initialt sjunker hållfastheten troligen på grund av fysikaliska effekter orsakade av de höga temperaturerna. Därefter ökar skjuvhållfastheten troligen beroende på sidoreaktioner och fortsatt tvärbindning. Det tredje steget är en termo-oxidativ nedbrytning som såsmåningom leder till förlust av vidhäftningen. Även värmeledningsförmågan ökar betydligt som ett resultat av nedbrytningsprocesser. Det finns behov av ytterligare forskning för att kunna föreslå en ny modell för livslängdsberäkningar baserade på experimentella resultat.

  • 9.
    Yarahmadi, Nazdaneh
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Built Environment, Energy and Circular Economy.
    Vega, Alberto
    RISE - Research Institutes of Sweden (2017-2019), Built Environment, Energy and Circular Economy.
    Jakubowicz, Ignacy
    RISE - Research Institutes of Sweden (2017-2019), Bioscience and Materials, Chemistry and Materials.
    Accelerated ageing and degradation characteristics of rigidpolyurethane foam2017In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 138, p. 192-200Article in journal (Refereed)
    Abstract [en]

    The urgent need for revision of the normative test method (EN 253) for the lifetime prediction of district

    heating pipes requires a better understanding of the failure mechanisms involved. Therefore, various

    methods were used to study thermal degradation characteristics of rigid polyurethane (PUR) foam in

    both air and nitrogen atmosphere. Accelerated ageing in nitrogen caused insigni

    ficant changes, whereas

    ageing in air caused signi

    ficant changes in weight, dimensions, chemical structure and cell gas composition,

    indicating importance of the thermo-oxidative type of degradation. A clear indication of the

    thermo-oxidative type of degradation was the formation of new carbonyl groups in PUR together with

    the loss of CH

    2 groups after ageing in air. Another result of ageing in air was the loss of pentane and

    cyclopentane, and the formation of some new volatile compounds in the cells of PUR foam. However,

    despite a large difference in degradation characteristics between the samples aged in air and in nitrogen,

    no signi

    ficant difference in the flexural strength of PUR foam was recorded during the induction stage of

    the degradation process. Furthermore, it is shown that the signi

    ficant drop in shear strength, which

    re

    flects the adhesion force between PUR foam and steel pipe, observed during the early stage of

    accelerated ageing of district heating pipes is not caused by thermo-oxidative degradation.

  • 10.
    Yarahmadi, Nazdaneh
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Built Environment, Energy and Circular Economy.
    Vega, Alberto
    RISE - Research Institutes of Sweden (2017-2019), Built Environment, Energy and Circular Economy.
    Jakubowicz, Ignacy
    RISE - Research Institutes of Sweden (2017-2019), Built Environment, Energy and Circular Economy.
    Determination of essential parameters influencing service life time of polyurethane insulation in district heating pipes2017In: Energy Procedia, Elsevier Ltd , 2017, p. 320-323Conference paper (Refereed)
    Abstract [en]

    Pre-insulated district heating pipes (DHP) have been in use during the last forty years. Many improvements and development have been done in the system. However, life-time prediction is still an uncertain issue. This paper is a part of a bigger project with the objective to determine mechanisms related to the deterioration of the mechanical and insulation properties of pre-insulated heating pipes as a result of ageing. The focus in this project is on degradation mechanisms of the PUR material at high temperatures. In this paper some results of the two types of exposure are presented. The first type comprises a condition where the new pipes are subjected to accelerated ageing at three different temperatures. The second type comprises condition, when the PUR material itself is aged in different atmospheres in order to identify different degradation mechanisms. The chosen ageing temperatures in the first condition were 130°C, (close to the supply temperature), 150°C and 170°C, (accelerated ageing temperature in EN 253 [1]). Changes in thermal insulation and the adhesion force between the PUR and the steel pipe were evaluated using the transient plane source (TPS) technique and the SP plug method respectively. The results of ageing show that the degradation of PUR is a multi-stage process composed of a rapid change in properties followed by a plateau phase which changes later to a gradual deterioration of the properties. The results of the PUR material exposure at 150°C in air and in nitrogen showed significant differences in the degradation characteristics between the two environments as were revealed by DSC and FTIR methods. © 2017 The Authors. Published by Elsevier Ltd.

  • 11.
    Yarahmadi, Nazdaneh
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Built Environment, Energy and Circular Economy.
    Vega, Alberto
    RISE - Research Institutes of Sweden (2017-2019), Built Environment, Energy and Circular Economy.
    Jakubowicz, Ignacy
    RISE - Research Institutes of Sweden (2017-2019), Bioscience and Materials, Chemistry and Materials.
    Livslängd för fjärrvärmerör: Fas 1 - Nedbrytningsmekanismer2017Report (Other academic)
    Abstract [sv]

    Dagens standard för prefabricerade fjärrvärmerör SS-EN253 innehåller olika testmetoder och krav där ett av de viktigaste är kravet på livslängd på minst 30 år vid en kontinuerlig driftstemperatur på 120 °C. Bestämningen av tekniska livslängden är baserad på mätningar av förändringar i skjuvhållfastheten efter accelererad termisk åldring. Den beräknade livslängden för ett fjärrvärmerör är baserad på extrapolering med hjälp av Arrhenius ekvation. Det finns en stor enighet kring uppfattningen att Arrhenius modellen inte ger en god överensstämmelse med de observerade åldringsdata och att det följaktligen saknas tillförlitliga metoder för livslängdsbestämning av fjärrvärmerör. Trots många forskningsrapporter finns det fortfarande skilda teorier om hur snabbt PUR-isoleringar bryts ner och vilka nedbrytningsmekanismer som dominerar. Syftet med det här projektet är att kartlägga de komplicerade sambanden och förstå vilka nedbrytningsprocesser som dominerar under olika betingelser och utifrån denna kunskap utveckla tillförlitliga metoder för livslängdsprediktering.

    Allt testmaterial utgjordes i denna studie av polyuretan (PUR) cellplastisolering som togs ut från nytillverkade fjärrvärmerör. Accelererad åldring genomfördes i luft och i kväveatmosfär vid 150 °C för upp till 8 veckor. Det visade sig att exponering i kväveatmosfär inte orsakar någon mätbar förändring av egenskaper. En motsvarande åldring i luft orsakar däremot stora förändringar i både dimensioner, viktförlust och färg. IR (infraröd) analys kunde också bekräfta att materialet bryts ner genom termo-oxidativa processer. Termo-oxidativ nedbrytning syns också i analyser av cellgassammansättningen. Materialet efter åldring i luft innehåller betydligt mindre halt cyklopentan samtidigt som fyra nya flyktiga ämnen kunde detekteras. Trots alla indikationer på materialets termo-oxidativa nedbrytning har böjhållfastheten inte förändrats hos materialet. Detta måste utredas vidare för att kunna förklara mekanismer bakom resultatet.

    Förutom beständighetsstudier av PUR materialet genomfördes långtidsåldring av fjärrvärmerör vid olika temperaturer. Resultaten av skjuvhållfasthet mätningar indikerar att det åtminstone finns tre olika faser i nedbrytningsprocessen. Initialt sjunker hållfastheten troligen på grund av fysikaliska effekter orsakade av de höga temperaturerna. Därefter ökar skjuvhållfastheten troligen beroende på sidoreaktioner och fortsatt tvärbindning. Det tredje steget är en termo-oxidativ nedbrytning som såsmåningom leder till förlust av vidhäftningen. Även värmeledningsförmågan ökar betydligt som ett resultat av nedbrytningsprocesser. Det finns behov av ytterligare forskning för att kunna föreslå en ny modell för livslängdsberäkningar baserade på experimentella resultat.

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