1. SCOPE ………………………………………………………………………..2. REFERENCE DOCUMENTS

3. DEFINITIONS

4. GENERAL ……………………………………………………………………4.1

Response Spectra Method

4.2

Damping

Values

4.3

Computer Model ……………………………………………………….

4.4 Vibration Control

4.5

Hydraulic and Rotary Snubbers

FIGURE

1 Horizontal Design Response, Horizontal Ground Acceleration2 Vertical Design Response, Horizontal Ground Acceleration

TABLE

I Damping

Values

II

Horizontal Design Response Spectra Relative Values of

Spectrum Amplification Factors for Control Points ……………..III Vertical Design Response Spectra Relative Values

of Spectrum Amplification Factors for Control Points

1. Scope

This standard establishes design requirements for piping systems subject to the dynamic effects of

seismic loads and supplements the requirements for ASME B31.1, ASME B31.3, ASME B31.4, and ASME

B31.8.

2. Reference Documents

Reference is made in this standard to the following documents. The latest issues, amendments, and

supplements to these documents shall apply unless otherwise indicated.

SABIC Engineering Standards (SES)

P01-E01 Design Conditions and Basis for Pressure Piping

P01-E02 Design of Piping Systems for Stress and Pressure Criteria

P01-E03 Flexibility, Support, and Anchoring of Piping systems

American Society Of Mechanical Engineers (ASME)

Sect III Division 1 Rules for Construction of Nuclear Power Plant Components, Non-Mandatory

Appendices, Appendix N Dynamic Analysis Methods

Sect III Division 1 Rules for Construction of Nuclear Power Plant Components, Subsection NF,

Component Supports

U.S. Regulatory Commission (NRC)

Regulatory Guide 1.61 – Design Response Spectra for Seismic Design of Nuclear Power Plants

Regulatory Guide 1.92 – Combining Modal Responses and Spatial Components in Seismic Response

Analysis

3. Definitions

Closely Spaced Modes. Two consecutive modes are considered closely spaced if their frequencies differ

from each other by 10% or less of the lower frequency.

Response Spectrum. A plot giving the maximum responses in terms of displacement, stress, or

acceleration, of all possible linear one degree systems due to a given input of ground motion. Usually

plotted with the abscissa of the spectrum as the natural frequency or period of the system and the ordinate

as the maximum response in terms of displacement, stress, or acceleration.

Earthquake Response Spectrum. An empirical response spectrum computed for a particular

earthquake. When combined with other earthquake spectra, it can be used to estimate a proper spectrum

for general design purposes, known as a design response spectrum.

Operating Basis Earthquake. An earthquake which, considering the regional and local geology and

seismology and specific characteristics of local subsurface material, could reasonably be expected to

affect the plant site during the operating life of the plant. It is that earthquake which produces the vibratory

ground motion for which those features of the plant necessary for continued operation without undue risk

to the health and safety of the public are designed to remain functional. Usually considered as having a

much higher probability of occurrence, possibly with a ‘return period’ period of the order of 100 to 200

years, and an intensity which is often taken as half of that of a Safe Shutdown Earthquake. The design is

made at somewhat lower allowable stresses and for somewhat different combinations of conditions.

Owner. SABIC.

Safe Shutdown Earthquake. An earthquake which is based upon an evaluation of the maximum

earthquake potential considering the regional and local geology and seismology and specific

characteristics of local subsurface material. It is that earthquake which produces the maximum vibratory

ground motion for which certain structures, systems, and components are designed to remain functional.

Usually considered a “maximum credible earthquake”, which has only a small probability of occurrence

during the lifetime of the plant, and for which the design is made at yield levels or limit conditions.

Zero Period Acceleration (ZPA). The maximum ground acceleration which corresponds to zero period in

the design response spectra for the site.

4. General

The decision and methodology of using dynamic analysis in piping systems for earthquake applications

shall reside with the Owner’s engineer. Current software programs exist that possess varying capabilities

for performing seismic dynamic analysis. The use of both commercial and proprietary software for

performing seismic dynamic analysis shall be subject to review and approval by the Owner’s engineer.

Dynamic analysis procedures, when used, shall be based on an appropriate ground motion representation,

shall be performed using accepted principles of dynamics, and conform to the criteria applied in this

standard.

4.1 Response Spectra Method

The response spectra method is a dynamic analysis procedure that utilizes the ordinates of a Design

Response Spectra (derived from records of past strong-motion earthquakes) to calculate the peak modal

responses which correspond to the modal periods of the piping system. Only those modes having a

significant contribution to the total piping system response are utilized. The maximum modal contributions

are combined in a statistical manner to obtain an approximate total response of the piping system.

4.1.1 The design response spectra shall be based on the geologic, tectonic, seismologic, and soil

characteristics associated with the specific site. Response spectra, derived from ground motion time

histories developed for the specific site, either individually or in combination, shall be representative of

actual earthquake motions and shall approximate the design response spectra. Design response spectra

developed from site specific data shall be utilized only with the approval from the Owner’s engineer.

4.1.2 In order to ensure that only those vibratory modes of a piping system that have a significant

contribution to the total piping system response are utilized, at least 90% of the participating mass of the

piping system shall be included in the calculation of response in each principal horizontal direction.

4.1.3 The procedure for developing a design response spectra shall follow the requirements set forth in

NRC Regulatory Guide 1.60, Design Response Spectra for Seismic Design of Nuclear Power Plants.

4.1.4 The design response spectra used for a dynamic seismic analysis shall represent the effects of the

vibratory motion of a Safe Shutdown Earthquake (SSE), ½ the Safe Shutdown Earthquake, and the

Operating Basis Earthquake (OBE).

4.1.5 The response spectra method for an earthquake analysis shall consider the representative maximum

values of the piping system response to each of the three components of earthquake motion, namely in the

horizontal (x and z) and vertical (y) directions. The modal responses may be combined in accordance with

the methods outlined in NRC Regulatory Guide 1.92, Combining Modal responses and Spatial

Components in Seismic Response Analysis and shall consist of either the Square Root Sum of the

Squares Method(SRSS) for closely spaced modes, or other choices such as the Group Method, Double

Sum Method, or the 10% Method shall be subject to review by the Owner’s engineer

4.2 Damping Values

Damping values to be utilized in the design of a Safe Shutdown Earthquake and Operating Basis

Earthquake shall be in accordance with ASME Sect III Div 1, Appendix N, Table N-1230-1 (Attachment 1.)

4.3 Computer Model

4.3.1 The computer model of a physical piping system shall represent the spatial distribution of the mass

and stiffness of the piping system to the extent that it is adequate for the calculation of the significant

parameters of its dynamic response. For computer programs which utilize the lumped mass method, half

the mass between two support points is lumped at each support node when node points are located only at

support points. In order to evaluate the vertical component of an earthquake and ensure a more accurate

mass distribution, at least one additional intermediate node point shall be placed at midspan between

supports. For bends, nodes shall be placed at initial, middle, and final locations of the bend.

4.3.2 The computer model of the piping system shall include the support structure of the piping, together

with its mass and damping characteristics. See 4.3.5 below.

4.3.3 The cut off frequency to be used in the response spectra method analysis shall be obtained by using

the frequency projected from the ground acceleration of the design response spectra. In most cases, this

value will be approximately equal to 33 hz. This will increase the likelihood that most of the lower

“amplified” modes which contribute to the bending behavior of the piping system’s response will be

captured.

4.3.4 If the piping system can withstand the maximum acceleration in the design response spectra applied

in any direction, a static seismic analysis shall be considered a sufficient method of analysis.

4.3.5 For piping systems supported from both the ground and from buildings, spectra for both ground and

building shall be developed to account for independent support motion. The range of support nodes

corresponding to each particular shock spectra must be specified.

4.3.6 A visual inspection of the design response spectra shall be made for the purposes of determining

which frictional supports can be considered restraints:

a. The frequency at which the spectral acceleration is less than the coefficient of friction at the

supports in the piping system shall be determined.

b. The natural frequency calculated at the supports from the modal analysis shall be compared to

the frequency in 4.3.6 a).

c.

If the natural frequency calculated at the supports is less than the frequency determined in 4.3.6

a), the frictional resistance will be overcome and a restraint may be required to dampen the system.

d.

If the natural frequency calculated at the supports is greater than the frequency calculated in

4.3.6 a), then the frictional resistance at the support may be treated as a restraint.

4.4 Vibration Control

4.4.1 Vibration due to seismic disturbances may be controlled by the use of a variety of restraints such as

anchors, guides, hold down clamps, rigid struts, sway braces, and hydraulic and mechanical snubbers.

4.4.2 Restraints that require periodic maintenance, such as hydraulic snubbers, shall be located whenever

possible, near platforms for accessibility.

4.5 Hydraulic and Rotary Snubbers

4.5.1 Hydraulic and rotary snubbers shall conform to the requirements established in MSS SP-58 – Pipe

Hangers and Supports – Materials, Design and Manufacturer and ASME Section III, Subsection NF.

4.5.2 Care shall be taken to ensure hydraulic snubbers are installed with reservoir breather filters on top,

reservoirs filled to the proper level, and piston setting set to the required cold piston setting.

TABLE I

Damping Values

Percent of Critical Damping

(1)

Included both material and structural damping. If the piping system consists of only one or two spans,

with little structural damping, use values for small diameter piping.

TABLE II

Horizontal Design Response Spectra Relative Values of

Spectrum Amplification Factors for Control Points

(1)

Maximum ground displacement is taken proportional to maximum ground acceleration and is 36 in

for ground acceleration of 1.0 g.

(2)

Acceleration and displacement amplification factors are taken from recommendations given in

Ref, 1 and discussed in Refs. 2 and 3.

TABLE III

Vertical Design Response Spectra Relative Values

of Spectrum Amplification Factors for Control Points

(1)

Maximum ground displacement is taken proportional to maximum ground acceleration and is 36

in for ground acceleration of 1.0g.

(2)

Acceleration amplification factors for the vertical design response spectra are equal to those for

horizontal design response spectra at a given frequency, where displacement amplification

factors are 2/3 those for horizontal design response spectra. These ratios between the

amplification factors for the two design response spectra are in agreement with those

recommended in Ref. 1 and discussed in Refs. 2 and 3.

FIGURE 1

Horizontal Design Response, Horizontal Ground Acceleration

FIGURE 2

Vertical Design Response, Horizontal Ground Acceleration