Enhanced seismic criteria for piping

Abstract

In situ, or laboratory, experience have shown that piping systems exhibit a very satisfactory seismic behavior. Seismic motion do not achieve to significantly damage piping systems unless large differential motions of anchorage are imposed. Nevertheless, present design criteria for piping are very severe and lead to require a large number of supports, which overly rigidify the piping systems. CEA, in collaboration with EDF and FRAMATOME, are working on proposals for enhanced design methods, less severe, but still conservative, and compatible with defect justification during operation. Our approach is based on the difference between the real behavior (or the computed one) with the codified methods. Criteria are applied on an elastically calculated behavior that can be significantly different from the real one : the effect of plasticity may be very meaningful, even with low incursion in the plastic domain. Moreover, and particularly in piping systems, the elastic follow-up effect affects stress distribution, for both seismic and thermal loads. For seismic load, we have proposed to modify elastic moment limitation, based on the interpretation of experimental results on piping systems. The methods have been validated on more industrial cases, and some of the consequences of the changes have been studied : modification of the drawings and of the number of supports, global displacements, efforts in the supports, stability of potential defects... The basic aim of the studies undertaken is to make a decision on the stress classification problem, that is not limited to seismic induced stresses and to propose simplified method to cope with.

Performance-based earthquake evaluation of a full-scale petrochemical piping system

“…All these tests displayed a favourable performance of piping systems which remained below yield limits under design level earthquakes; failure of supports or connections to other linked components occurred prior to the failure of the pipe itself. Other authors confirmed an over-conservativeness of relevant design standards; see, among others, Touboul et al (2006), Paolacci et al (2011Paolacci et al ( , 2013b, Hosseinzadeh et al (2013) and Nakamura (2013). Hence, a need for deep numerical and experimental investigations of piping systems and support structures under realistic seismic loading is evident.…”

Main Issues on the Seismic Design of Industrial Piping Systems and Components

“…Studies have shown that the present Standards for piping system design under seismic loads are over conservative and modifications have been proposed to relax this over conservatism [19,20]. For example, [20] has applied the present Codes to calculate the stress limit on piping systems and experimental results showed significant discrepancy from the real behavior.…”

“…For example, [20] has applied the present Codes to calculate the stress limit on piping systems and experimental results showed significant discrepancy from the real behavior. This aspect has been treated for example in [21].…”

“…The attempt of some researchers to modify Eq. (1) [19,20] is not enough to fully exploit the plastic properties of pipes. In this sense the strainbased approach is more promising, especially if the Performance-Based approach would be used to design new pipelines or to assess the seismic behavior of existing ones.…”

Dynamic analysis of a cabinet of a reactor protection system

“…They applied these methods to the seismic qualification analysis of a perforated horizontal tube in a nuclear reactor [18]. Touboul et al [19] studied non-linear behaviour of piping systems under seismic loading and proposed simplified methods to solve seismic induced stresses. Sigrist et al [20] presented seismic analysis of a prototype nuclear reactor with fluid-structure interaction modelling and showed that added mass effects have a significant influence on the dynamic response of the nuclear reactor.…”