Optimising of pipe support concept

Preface

The load of the piping is determined – beside the load cases itself – predominantly by the concept of the pipe supports. In many cases in calculations of piping systems an optimisation of the support concept is sensibly or even necessarily. An optimisation is carried out beneath four fundamental points of view:

  • Reduction of piping loads
  • Reduction of support loads
  • Practicability of the new support concept!!!
  • Load transfer on the structural supports and the building respectively

Optimisation of supports using the example of the TH30-suction side

Picture1 calculation model TH30-suction side with hardware measures

Using the example of a residual heat removal leg (TH30-suction side) of a boiling-water reactor it is shown with the help of a structural dynamic computer program how an optimal pipe support concept can look like. The already builded TH-system is designed for the classical static and dynamical load cases like dead weight, pressure, restrained thermal expansion and earthquake. The support concept was developed stepwise firstly for the static and subsequent for the dynamical load cases. Thereby, beside fixed supports and fixed points in this facility a large number of spring hangers are placed. These require periodic maintenance and testing which mean high costs for the operating company of the power plant.

The optimisation of the support concept happens beneath the linking of the static and the dynamic load cases. That means that the static and the dynamic load cases are calculated iteratively together. In order to exploit the multi functionality of the fixed supports optimally, each support has to be placed on the right place in the piping system to absorb the load from dead weight in an ideal way, to prevent the piping from swinging up due to dynamical excitation and at the same time the piping not to distort by thermal expansion. Moreover the location of the supports within the whole system has to be uniform to achieve a utilisation of allowable loads of all components (pipes and attachments). Through this the number of necessary attachments is limited.


Results of the optimisation

A result of the optimisation is that the number of supports is reduced from 27 in the actual state to 13. The 18 remaining supports are composed of 11 spring hanger and 7 fixed supports. Two of the 7 fixed supports are retrofitted from plain bearings to sliding guides and on two further fixed supports the structural attachment (achorage) is improved.

Picture2 number of supports before and after optimisation

Beside the reduction of supports the optimisation of the support concept for the TH30-suction side also yields to a reduction of the maximum stress ratio in the pipe in the operational and fault load cases. The punctual load increase at 3 supports is intended by the concept. Integrally, the optimised concept of supports leads to a reduction of the support loads (sum of loads) whereupon the loads on the component connections stay nearly the same.