Fabrizio Paolacci, Md Shahin Reza**, Oreste S. Bursi2
1University Roma Tre, Department of Engineering, Rome, Italy

**University of Trento, Department of Civil, Environmental and Mechanical Engineering

Abstract

Piping systems are of paramount importance to many industries, e.g. refinery, oil & gas and petrochemical plants, where they are

often employed to transport raw and refined materials,
e.g. oil and gas, from one point to another connecting several components, such as tanks, dis-tillations columns, furnaces and pressure vessels. Recent studies showed that such structures
are quite vulnerable under earthquakes, and reported many damages of piping systems and their components which led to catastrophic accidents.

Therefore, particular attention must be paid to safeguard them against seismic events. However, there exists a clear lack of proper seismic design guidelines for piping systems, whereas researchers have confirmed the inadequacy of available standards. As a result, in-depth research is required to understand better the seismic design and analysis criteria of piping systems. Along this line, this paper studies the main issues related to the analysis and design of refinery piping systems through a realistic case study. Initially, seismic analysis and component design methods of refinery piping sys-tems is analysed. A review of the current design approaches according to European (EN13480 - 3) and American (ASME B31.1 & B31.3) standards is illustrated by using a typical refinery piping system as a case study.

The analysis permitted to identify the limits of design standards and some critical aspects of the problem, e.g. dynamic interaction between pipes and rack, correct definition of response factors and strain versus stress approach. Finally, a discussion on the main results of an experimental activity carried out on flange joints under strong cyclic loading is presented, which allowed to highlight some limitations of current standards in terms of conservativeness.

1. INTRODUCTION
The piping systems typically found in a refinery complex contain various components and support structures and operate in a broad range of working environments. Some common components usually used in piping systems include straight pipes, elbows, Tee-Joints, various valves, flanged joints, pressure vessels, tanks, strainers and reducers. Depending on the nature of the working fluids, piping systems are designed to work over a wide range of temperature and pressure. A typical piping
system is presented in Fig. 1.

Currently, both European and American codes are available for the design of piping sys-tems in seismic-prone zones. The main European contribution is chiefly represented by the standard
EN13480, dedicated to metalling piping systems [1]. The Eurocode 8 - Part 4, the European seismic code for industrial components, is also devoted to pipelines, but only of aboveground type, which differs from metallic piping system for many aspects, and then use-less. American experience on piping system is instead very rich, especially in terms of design standardization and seismic design calculation, and the long list of standards and codes avail-able it is a clear demonstration of it.

The main standard is represented  by ASME B31.3 [2], but many other contributions and guidelines are also available [3, 4]. The seismic analysis of a piping system involves several basic steps that allow defining the proper seismic action, the suitable numerical model and analysis method and the verification format to be used. The European (EN13480:3-2002) and the American standards (ASME B31.3-2006) for piping systems differ for several of these aspects.

Thus, in order to under-stand these differences and the consequences on the seismic response evaluation, in the fol-lowing both European and American standards are applied to a representative case study. It is necessary to stress that the American Standard does not contain explicit indications on the seismic analysis of piping systems, but rather refers to the American standard for seismic analysis of structure ASCE7-05, which includes all the required prescriptions.

On the contrary the European Standard contains an entire Annex (A) dedicated to the dynamic and seismic analysis of piping systems, but does not contains explicit quantification of the seismic action. At this end the Eurocode 8 (prEN1998:1 2004) should be used.

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