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. 

This report is a result of the SUSPIPE project. Within SUSPIPE, the water and sewage industry's manufacturers, suppliers and customers collaborate. In this sub-project, the possibilities for better products and methodology for electrofusion of large-dimension polyethylene pipes have been investigated through interviews, measurements, and simulations. When building new water and sewage pipe networks of polyethylene pipes, the network owners should demand that the work complies with “AMA Anläggning 20,” that the welders have training with an EWF certificate and that procedure testing is carried out before the construction starts. Furthermore, they should have inspectors present at the construction sites. The members of INSTA-CERT should review the certification regulations regarding requirements for ovality and indirect methods for measurements of residual internal stresses in polyethylene pipes for water and sewage. To achieve good quality joints in polyethylene pipes, rotating scraping tools, fixing tools and rounding clamps must be used. Furthermore, the trenches must be wide and long enough for fitting equipment and personnel and for adjusting the positions of the pipe ends.  

This report is a result of the SUSPIPE project. Within SUSPIPE the water and sewage industry's manufacturers, suppliers and customers collaborate. In this sub-project, solutions for connecting concrete manholes to structured wall pipes in plastic have been investigated. The project has also analysed conditions in the field, interviewed customers, contractors and inspectors and tried to understand the origin and cause of the perceived problems with leaking joints. Different types of joints between concrete manholes and plastic pipes have been identified. The new edition of “AMA Anläggning 20” requires seals to be used at the joints, but there is always some lag to implement new editions in procurements. To have consistent requirements for seals, supplementary wording from this report should be introduced in “AMA Anläggning” under PB, PC and PD. In this report, efforts have also been made to formulate requirements for materials and tightness testing, which customers can use in procurements or project instructions to improve the quality of their joints. However, further work will be required to link these to appropriate standards at the system level. The requirements for vulcanized rubber and, also thermoplastic elastomers in applicable standards need to be tightened, but this is a long-term process. A proposal from a previous project is adopted in this report, which is to perform relaxation tests for longer time periods. The report's proposal for requirements for verification of joint seals is based on product standards for concrete manholes and unpressurized plastic pipes, as well as a general standard for unpressurized piping systems. However, there is no standard or similar where these requirements can be set. Optionally, a voluntary labelling could be applied. Plastic pipes are marked in the Nordic countries with Nordic Poly Mark and for some other products, P-marking has been introduced through SP / RISE. Furthermore, the report states six success factors for water tight unpressurised piping systems, which include favourable contractor conditions, that accuracy in pipe laying is applied, that correct joint seals are used, that the supplier's instructions are followed, that on-site inspections are carried out and that leakage tests are carried out. 

Large parts of the existing pre-fabricated district heating pipe networks are close to reaching their technical life. There is a need to assess the status of the district heating pipes in order to plan maintenance and replacements of pipes. A first step towards developing a simple and cheap method for technical status assessments of existing pipes without shutting the pipes down has been taken. The proposed mechanical field method is based on that the district heating pipes are uncovered and cylindrical samples still attached to the service pipes are created by removing material around them by use of hole drills. Laboratory equipment for pulling or turning the cylindrical samples off, while measuring load and deformation, has been developed.

This report concerns part 2 of a project with the aim to propose protective measures for cables and pipelines for bio and natural gas. Part 1 was previously reported in SGC Rapport 2011:239. The wish is to be able to increase the pressure in the distribution networks from 4 to 10 bar without having to retain the safety distances valid for 80 bar pipelines. Polymer, concrete and steel protective plates, and deep digging are the physical measures considered. In part 1 a survey was made, in part by an enquiry, of the frequency, causes and consequences of incidents where pipelines were hit by excavators. Further, the rules and standards were investigated in countries where 7–10 bar pipelines are already in service. Here, in part 2 the perspective was widened to include, apart from gas pipelines, also all kinds of buried pipelines and cables. Now a visit to a supplier in France is reported, as well as an vestigation of costs and environmental impacts of the different protective measures, and an analysis of the strength of protective plates and of how they can best be positioned in the ground in relationship to the pipeline. The main result from the study visit to France was that new regulations mean that both new and existing pipelines have to be satisfactorily protected. For the physical point of view these plastic protective plates play an important part, and there are commercially available building systems of plates for which the strength and durability have been verified by tests. In the full scale experiments done in, e.g., France, it can be concluded that the plastic (HDPE) plates can wit stand high loads which are applied by use of a bucket with teeth mounted on an excavator. In some cases penetration of teeth occurs, but the plates will in that case either come up and alert the operator or stay in the ground and still protect the buried cable or pipeline. Concrete plate can also break, but the pieces are held together by the steel reinforcement. The analysis of costs and environmental impacts shows that plastic plates are preferred with regard to both aspects. In addition they have a very good signalling effect being produced in a bright yellow colour. Also deep digging can be effective taking into account costs and environmental aspects, but the risk reduction will according to literature be less than for the plates. Plastic plates are shown, in the literature surveyed, by full scale experiments to have at least as good, and sufficient, resistance to impact as concrete ones. This is verified by in-house numerical analyses. The finite element analyses show that the plastic plates deforms but do not break. The arching action of the backfill protects the buried pipe, and the stresses become only somewhat higher when using plastic plates instead of using stiff plates of steel or concrete. There may be unfavourable cases when the plastic plates cannot by themself stop forces and stresses passing down through soil layers acting on the buried pipe.

This report concerns part 2 of a project with the aim to propose protective measures for cables and pipelines for bio and natural gas. The wish is to be able to increase the pressure in the distribution networks from 4 to 10 bars without having to retain the safety distances valid for 80 bar pipelines. Polymer, concrete and steel protective plates, and deep digging are the physical measures considered. In part 1 a survey was made, in part by an enquiry, of the frequency, causes and conse-quences of incidents where pipelines were hit by excavators. Further, the rules and standards were investigated in countries where 7-10 bar pipelines are already in service. Now a visit to a supplier in France is reported, as well as an investigation of costs and environmental impact of the different protective measures, and an analysis of the strength of protective plates and of how they can best be positioned in the ground in relationship to the pipeline. The main result from the study visit to France was that new regulations mean that both new and existing pipelines have to be satisfactorily protected. For the physical part of these plastic protective plates play an important part, and there are commercially available building systems of plates for which the strength and durability have been verified by tests. The analysis of costs and environmental impact shows that plastic plates are to prefer with regard to both aspects. In addition they have a very good signalling effect being produced in a bright yellow colour. Also deep digging can be effective taking into account environmental and costs aspects, but the risk reduction will according to literature be less than for the plates. Plastic plates are shown, in the literature surveyed, by full scale experiments to have at least as good, and sufficient, resistance to impact as concrete ones. This is verified by in-house numerical analyses. A discussion is presented of how well the geometric design of pipeline and protective plate protects the pipeline against some digging scenarios with excavators of different sizes. Since the regulations are differing between countries and comprise a mix of administra-tive and physical protective measures in a way that is not quite evident, it was also found worthwhile to make a note, for possible further use, on how risk analysis can, and has been, used in connection with the establishment of major pipelines for optimization of protective measures.