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District Heating Network Stress Analysis

A key part of our technical support services for the Hiline pre-insulated district heating pipe system range is advanced stress analysis service to ensure that a network’s design is optimised for the day-to-day thermal expansion that a system encounters during its many decades of operation.

stress analysis service screen 400When designing and installing district heating pipe networks, stress analysis is a critical part process and one which should be carried out by default. To illustrate the importance of stress analysis, something as simple as adding in an unplanned branch connection can seriously impair a system’s ability to cope with the huge forces exerted on the pipe from thermal expansion. To put it into context, a 200-metre length of buried DN250mm pre-insulated steel pipe, heated to an operating temperature of 120°C will expand by around 150mm – exerting stress of some 171MPa – the equivalent of 52 tonnes. This clearly needs to be dealt with in a way that does not impede the life expectancy of the network and ensure a long and trouble-free operation in delivering heating and hot water to consumers.

sisKMR Software

CPV Ltd is a certified licensed holder of sisKMR software and our design team has several fully-trained engineers to carry out the calculations, offering expert advice in all aspects of stress analysis.

By evaluating the proposed pre-insulated district heating network and using a combination of our engineers’ experience, rules of thumbs and the sisKMR software, pipe systems can be modelled and stresses calculated to the design principles and parameters according to standard EN 13941, Design and installation of pre-insulated bonded pipe systems for district heating.

pre insulated steel bends 300x450Pipe static calculation against proposed district heating network design and routing:

The service covers the pipe initial static calculation for the entire district heating network including modelling the pipework geometry of buried pre-insulated pipework within sisKMR software and according to the proposed design and routing as provided by our client. CPV will model and undertake the analysis to be able to confirm the proposed design is acceptable. 
Where necessary, CPV will propose pipe arrangements, alternative pipe routing and other measures in mutual agreement with the client in order to establish an acceptable technical design solution. Having finalised the design and completed the analysis CPV Ltd shall issue the full stress analysis report together with supporting pipe route drawings.

During Installation - Pipe Static calculation against variations

CPV can provide technical design support for the duration of the installation of the district heating network making recommendations and providing subsequent qualification through stress analysis.

Variations will be remodelled within the sisKMR software to demonstrate compliance. These services do not cover routing modifications that are not based on static requirements

Pipe static calculation against ‘as installed’ district heating network

On completion of the installation of the pre-insulated district heating network and using ‘as-installed’ drawings, our engineers can again model the installed pipework geometry within sisKMR software and complete a final stress analysis to qualify and demonstrate full compliance of the installed network, issuing the final stress analysis report together with supporting pipe route drawings.

Further Information

To find out more, please contact our technical support team by calling +44 (0)1794 322 884 or emailing This email address is being protected from spambots. You need JavaScript enabled to view it.

Details of the sisKMR software

sisKMR is a software programme designed for the static calculation of buried and above-ground pipe systems. It is able to calculate stresses imposed on hot buried pre-insulated bonded pipe systems as well as all kinds of open-air 3-dimentional pipe systems for district heating applications, due to the loads imposed by thermal expansion. The software is based on a beam-element programme with which the sections of 3-dimensional pre-insulated bonded pipe systems with any number of branches can be calculated taking non-linear reactions of the soil and expansion cushions into consideration

In addition sisKMR contains standard modules for the fast calculation of common practical situations including:

  • L-System
  • Z-System
  • U-System
  • Deviation with expansion cushions
  • Curved pipe
  • Reduced Tee Branch
  • Parallel Tee Branch

Alternatively, the stress analysis can be calculated according to the following standards:

  • EN 13480
  • EN 13941
  • AGFW-Worksheet FW 401
  • ASME : AD-S2
  • ASME : AD2000-S2

The following modules are available for fast pre-dimensioning:

  • Pipe bending (during excavation)
  • One-time (start-up) compensator
  • Strain reduction element (System 4)
  • Maximum admissible laying length

With sisKMR the latest research results are included in the calculations:

  • Cold installation
  • Installation without expansion cushions
  • Superimposed installation
  • Pressure bends
  • Mechanical pre-stressing of expansion cushions
  • Subsequent burial of expansion cushions
  • Horizontal branches

This technology is in line with the German Energy Efficiency Association for District Heating (AGFW) research programme, Innovative Heat Distribution

Typical supports implemented in all types of open air 3-dimensional pipe system design and construction can be considered including:

  • Fixed point (anchors)
  • Axial holding point
  • 3-way axial holding point
  • Suspension or pendulum support
  • Sliding bearing bracket
  • Axial roller bearing support
  • Roller bearing with separate roller tracks for u- and v- directions
  • Single roller bearing
  • Spring bearing effective in w-direction

For calculating admissible system limits using:

  • Fixed points
  • Free system limit with free axial displacement and rotation
  • Free system limit with all displacement and rotation possibilities

Other possible considerations that can be taken into account include:

  • Bearing tolerance
  • End displacement
  • Different friction values for axial and lateral displacement
  • Local pre-stressing

In the calculation of load case histories, pre-displacements in the bedding and bearing points are taken into account so that friction and bedding reversal effects can be registered and included in the calculation of the load variation ranges, which are most important for the fatigue analysis of the system.

Complex 3-dimensional systems, also with one-time compensators and strain reducers (bellows), can be calculated together as one entity

sisKMR features comprehensive pre-installed material databases and nominal dimension tables which can be edited and extended by the user.
New databases for different pipe manufacturers and different pipe materials can be created to suit the user’s requirements.

The system features powerful graphics including:

  • XY-/XZ-YZ-View / 3D-View
  • Contour mapping
  • Crosshair cursor
  • Scale for all axis directions
  • Zoom function with mouse driven frame
  • Display of the expanded system with different coloured loaded cases
  • Either in steps or direct distortion of expansion cushion thickness and systems expansion
  • System geometry can be displayed while entering data
  • Clear output of calculation results with tables and graphics

The design parameters of most commonly used compensators can be calculated including:

  • Axial compensator
  • Angular compensator
  • Lateral compensator
  • Strain reduction element (axial compensator with a limit stop)

The calculation results are summarised in special bearing and compensator tables forming part of the final stress analysis report and is able to calculate:

  • Point mass
  • Single load
  • Additional sectional loading in all directions (including wind and snow loads)

sisKMR at a glance:

  • Static calculation of pre-insulated pipe systems (above and below ground)
  • User friendly interface
  • Leading stress calculation software in the district heating industry
  • Simple to use, quick data input, exact results
  • Any bearing condition calculable
  • Calculation capabilities of branched, topological piping system
  • End point displacements and pre-stressing is feasible
  • Comfortable calculation of loading case history
  • Clear orientation by using a local co-ordinate system
  • Visible graphic result while entering pipe geometry
  • Clear layout of results, either in simple or comprehensive reports


To find out more, please contact our technical support team by calling +44 (0)1794 322 884 or emailing This email address is being protected from spambots. You need JavaScript enabled to view it.


Tags: district heating, heat networks, code of practice, pre-insulated pipe, stress analysis, sisKMR