The basic function of the surveillance system is to report when moisture has entered the insulation and show how the fault has developed over time. Surveillance systems can be designed after very different principles: • Passive system. Manual measurements of the system by a measuring technician at set intervals e.g. once or twice a year. No active surveillance of the system between these measurements. Fault location, if any, is done by the measuring technician. • Active system based on the resistance measuring principle with information about whether there is moisture in the insulation or not. Further analyses of the insulation resistance values and galvanic voltage can be performed to establish whether the insulation is wet or dry and whether any moisture enters from the service pipe or from the outside. Fault location, if any, is done by the measuring technician. • Active system based on the impedance principle. In addition to above possibilities, the system can locate any fault in the system. As regards asset management the recommendation obviously is to establish an active surveillance system, which makes it possible continuously to monitor and analyze the condition of the pipe system. This enables due intervention as regards any damage before it evolves and spreads in the system. In this way, the surveillance system forms the basis for obtaining at least the expected service life at a minimum of costs. REQUIREMENTS TO CONTRACTORS Even if the products are of the highest quality, if the installation is not carried out according to the instructions, the system will not be faultless, and repairs will be necessary. It is therefore important to make requirements to the contractor prior to the installation. For the pre-insulated system, the welding of the steel pipes and the installation of casing joints are decisive for a faultless system during the operational period. For many years, there have been very well-defined requirements to steel welds, and it is a tradition to prescribe these. For the installation of casing joints, it ought to be a fundamental requirement that the fitters are trained to do so, but this is not always the case. In fact, they often have no training in installing these. The energy companies ought to require that casing joint fitters have attended a course at the pipe supplier’s and have been certified at regular intervals to install the casing joint type in question. In addition, the energy company should require that the course gives the fitter a theoretical as well as a practical training in installing the relevant casing joints. It would be a big step for the DH trade to raise the requirement to casing joint installation to the same level as the requirement to steel welds.
As for the surveillance system, an uncertainty often exists about the acceptance criteria for the finished system. It is recommended to require that the acceptance criteria for the insulation resistance in the surveillance system follow the specifications of the supplier of the pre-insulated pipe system. The contractor must then document this on handover, and it will be a precondition for a good starting point in the asset management during the operational period. Most faults appear by far in the first years after putting the system into operation. With an active and well-functioning surveillance system these faults will be found within the guarantee period of the supplier and contractor, and in this way the energy company ensures that there is a sponsor for repairing the damages. NEW PIPE SYSTEMS: THE CONSTRUCTION PHASE Trust is good, but control is necessary. It is decisive for the pre- insulated pipe system being installed without built-in faults after the instructions that an active inspection is performed in the construction phase. Unfortunately, this is often neglected. With an active supervision, potential faults are stopped in due time, and the basis for a faultless system for the part of the asset management belonging to the operational period will be good. It is therefore recommended that the energy company is trained to supervise casing joint installation and surveillance systems at the pipe supplier’s. OPERATIONAL PERIOD In established district heating networks, the active surveillance system must be monitored continuously, and you must react to the information you receive. The energy company can monitor the surveillance system, but it is also possible for the pipe supplier to offer this service.
D I S T R I CT ENERGY - SUS TA I NAB L E C I T Y T RANS FORMAT I ON
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