Flow Assurance and Surge Analysis



Flow Assurance refers to the successful, safe and efficient transfer of fluids within a pipeline and although it is commonly a term refered to within the Oil and Gas industry, it is equally applicable to the water, district heating and powers industries.

Surge Analysis is a flow assurance activity and refers to the analysis of pressure changes in pipework. It is usually undertaken on liquid pipelines where fluid compression is negligable and where sudden changes in flow velocity can cause over / under pressurisation of pipework.

Flow assurance and Surge Analysis encompasses a range of objectives, often in different phases of a pipelines' lifecycle and VariSim is an ideal choice for assisting in each of these phases.


In the design phase, complete designs can be simulated for verification of pipeline size, flow and pressure operating conditions and system capacity. The equipment characteristics can be accurately simulated and correctly sized.

In some cases, a system may be very sensitive to certain control parameters. There is no better way of maximising confidence in the overall system design than being able to simulate the complete interaction between the pipe work, the equipment and the control scheme. Pipe work can be correctly sized and rated, control set-points and control parameters can be tuned, system bottlenecks can be identified and surge suppression equipment can be correctly sized.

In the district heating industry, there is additional emphasis on efficient temperature distribution to ensure the delivery of heat to its customers and users.

Surge pressures (or waterhammer as it is also known) are generated in a pipeline whenever there is a sudden change in flow, for example, as a result of a valve opening / closing, pump start up /shutdown or interaction between equipment on a system during normal or abnormal operation, which may cause problems such as:-

  • Unacceptable high and low pressures
  • Severe pipe loads
  • Unwanted trips and shutdowns
  • Pipe movement and vibration
  • Equipment damage
  • Operation of relief valves / bursting discs
  • Pipeline Leaks

The design process may of course be an extension to a current system. It may include a need to study a change of usage or it may involve decommissioning of an existing system. Future objectives for the system can be checked with current configurations to ensure that long-term objectives can be achieved without the need for future expensive retrofit solutions.


In the planning phase, VariSim can be used to consider the effects of future changes to the way equipment may be operated. This may be the establishment of normal start up procedures, planning for equipment maintenance or equipment decommissioning. The user may wish to determine future operating conditions in terms of future flows, pressures, temperatures, product positions or inventory distribution. Understanding future conditions allows the user to prepare and schedule equipment for the next operation well in advance. 


Forecasting tools can be linked with the planning functions that estimate future product demands (such as a consumers gas usage or heat usage) and so the simulator can simulate the entire system supply/demand and its subsequent equipment and dynamic response. This allows the user to prepare or control the future event.

One of VariSims' strengths lies in its ability to quickly and efficienctly study a systems sensitivity to changes in a pipelines' or equipments conditions. It allows a user to set up a sequence of simulations that consider the same base design but vary specific parameters from one simulation to the next. Changes to all equipment parameters can be made to establish the systems sensitivity to the parameters variance.


In the Operating phase, VariSim can be used to troubleshoot current system operating problems. These problems may include: -

  • Overpressurisation and surge related issues
  • System bottlenecking problems
  • Poor temperature distribution in district heating systems
  • Equipment performance issues
  • Product quality issues
  • Gas and air blockage issues in liquid pipelines
  • Liquid drop-out issues in gas pipelines
  • Equipment sizing issues
  • Badly sized surge suppression equipment
  • Incorrect telemetry settings
  • Poor PID tuning and control system interference


VariSim is extremely powerful as a PC based desktop tool if you want to unlock the real power of VariSim, connect it to the real time world and allow it to calculate the current conditions of the pipeline. The availability of VariSims real time information is valuable to the operator and engineer alike and allows the engineer to conduct studies using the current, validated conditions of the pipeline.