Oil Industry installation seismic design

Introduction

Regarding to the seismicity of the country and the positioning area of seismic hazards and the possibility of irreparable human, economic and environmental damages caused by earthquakes, designing of seismic design and the related structures in the oil industry is very important The purpose of this article is to provide a general overview about the seismic design criteria for installation structures in the oil industry, in such a way to minimize the possibility of disruption and inefficiency in microseism and moderate earthquakes as well as the possibility of extensive damages in strong earthquakes LINKRAN’s design and technical team effort is to use the rules of seismic design criteria so that the components behave linearly in mild to moderate earthquakes, and to have the desired formability and minimize damages in strong earthquakes In this article, we review the design methods of seismic support for mechanical and electrical equipment of the oil industry

Description

As we know, mechanical and electrical equipment are components that are attached to floors or ceilings or structural walls and may be subjected to significant lateral forces in the earthquake. In installation supports design, the required capacity of the components should be calculated and then the specific seismic criteria for mechanical and electrical components should be applied to them according to the relevant regulations In fact, in simpler terms, the load-bearing capacity of the components and the amount with lateral seismic and gravitational loads on different components and connections should be calculated and the proper reliability factor should be applied for the resistance of these systems against earthquakes

Different methods of considered load combination usage in the relevant design regulations are essential It is recommended that the retaining structure and its components be modeled as a complex with full engineering conditions and dynamic analysis shows the effects of component interaction on support with support itself. However, the regulations allow using the mentioned analytical methods for analyzing the independent Non-structural part from the maintenance structure Analytical methods for calculating the seismic force on mechanical and electrical installations in the oil industry are as follows

1. Equivalent lateral load method
2. Simplified interaction method
3. Class spectrum method

1. Equivalent lateral load method

In this method, the following formula is used to calculate the seismic force on the system. Earthquake force must enter to the system in two independent horizontal directions or in a critical horizontal direction of a hypothetical degree of free-standing and be distributed in proportion to the mass

S_DS : Acceleration parameter design spectrum a_p : Reflection coefficient according to the tables of the regulations I_p : Coefficient of importance W_p : Operating weight R_P : Behavioral coefficient according to the tables of regulations : The height of the connection point to the structure to the base level ℎ : The average height of the roof of the structure to the base level

2. Simplified interaction method

This method has been developed for analyzing non-structural components based on the simplification of the analytical relations of secondary systems in interaction with the support structure. Internal forces should be used in the design based on the distribution of lateral force, which is calculated based on the following formula

F_pi : The force acting on the center of mass V_P : Base cut C_p : Magnification coefficient S_a: Spectral acceleration

3. Class spectrum method

Class spectrum method is recommended if more precision is required to determine the acceleration or displacement at the component installation

point or on the desired floor

a_i : Combination of the spectral accelerations of moody level

A_x : Structural torsion magnification coefficient

The application of equivalent lateral load and class spectrum method is limited to electrical and mechanical components that can be modeled as a degree of free-standing, otherwise the simplified interaction method should be used.

Studying the lateral displacement

D_Pi  or proportional  displacement of seismic design is obtained from the D_P in the coefficient of importance of the structure. The calculated D_P of proportional displacement is as follows:

and : The lateral displacement of the structural design in and level

ℎ and ℎ : Height of two consecutive sequential to the structure in and level

Δ : Allowed proportional lateral displacement of the floor

ℎ  : The height of the floor to the floor of which the non-structural component

is connected to

The mechanical and electrical equipment supports and connections shall be designed for the proportional displacement of seismic and the seismic forces according to the above-mentioned formulas. These supports include the structural component, supports, frames, steel axis, cables and other components which are connected to equipment or are made as part of equipment support. Also, equipment connections to the support must be designed for force and seismic displacement, unless they are integrated with the equipment.

It is not necessary to calculate the force and displacement of the seismic for ducts with a smaller or equal dimension of 65 mm, as well as in hangers with a height of less than 300 mm.

If the support point does not have sufficient strength and stiffness to transmit the seismic force, suitable metal washers should be used at the screw connections in screw installation points.

The equipment on vibration isolators must have the appropriate supports or stroke absorber in each horizontal direction and vertical supports must be used in places where equipment can be overturned. To reduce the impact of stroke, between the stroke absorber and the equipment, viscoelastic pads or similar materials pads with appropriate thickness can be used.

There are exceptions to seismic design for canals, trays, and pipes, so according to these exceptions; there is no need for seismic design for equipment except in the specific cases listed in the related regulations.

LINKRAN Company is a manufacturer of various profiles and supports and installation connections, vibration isolators, elastomeric insulators, spring hangers, etc. It is ready to cooperate with oil and petrochemical projects in the country to support mechanical and electrical equipment.