Application of Peps in Stress Analysis of Nuclear Piping

doi:10.4236/jamp.2013.16012

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Journal of Applied Mathematics and Physics, 2013, 1, 57-61

Published Online November 2013 (http://www.scirp.org/journal/jamp)

http://dx.doi.org/10.4236/jamp.2013.16012

Open Access JAMP

Application of Peps in Stress Analysis of Nuclear Piping

Rui Liu, Zhiwei Fu, Tieping Li

Nuclear and Radiation Safety Center, Ministry of Environmental Protection, Beijing, China

Email: l i [email protected], [email protected]

Received August 2013

ABSTRACT

According to the nuclear safety regulations, this paper discusses the mechanical analysis method for piping system.

Peps program has advantages of stress analysis and evaluation for nuclear piping. First, this paper introduces the Peps

software, and discusses the process of stress analysis and evaluation for nuclear piping using the general finite element

software; Secondly, taking nuclear class 2/3 piping system as an example, it uses Peps4.0 program to calculate the pip-

ing stress in variety of working conditions, such as weight, pressure, thermal expansion, earthquake, time-histo ry force,

and etc. Finally, the paper calculates the maximum stress and stress ratio according to the ASME.

Keywords: Peps; Nuclear Class 2/3; Piping; ASME

1. Introduction

In recent years, the rapid development of nuclear power

plants has more strict demand for safety. The safety of

nuclear power plants depends mainly on the devices

which perform safety functions. Most of these devices

are treated with radioactive medium. Once leakage oc-

curs, it will result in the loss that can’t be estimated.

Therefore the nuclear power plants must be designed in

accordance with the corresponding regulatory require-

ments. Nuclear piping which provides the important

guarantee for safe operation is important equipment in

nuclear reactor. The purpose of stress analysis for nuclear

piping is to proof that the maximum stress does not ex-

ceed the limits of regulatory requirements under different

working conditions [1].

There are two kinds of methods of stress analysis for

nuclear piping: simplified calculation method and nu-

merical simulation method. Simplified calculation me-

thod based on the empirical formula, which is suitable

for small piping, could not accurately describe the me-

chanical behavior of the piping system. Considering the

high requirements for security, large piping systems with

complex mechanical properties must resort to numerical

simulation method with the aid of computer program [2].

With the development and application of computer

technology, stress analysis of larger piping system can be

achieved. At present, the civilian nuclear piping stress

analysis software are mainly: ADLPIPE, AUTOPIPE,

SYSPIPE, PIPESTRESS, KWUROHR, HROHR2, APA

(AREVA PIPING ADDON), and etc. Peps (PIPE-

STRESS) used in the three-dimensional linear elastic

piping systems analysis and calculation at home and

abroad. This paper takes a nuclear class 2/3 piping sys-

tem model as an example, and uses Peps4.0 program to

calculate the piping stress in variety of working condi-

tions, such as weight, pressure, thermal expansion, earth-

quakes time-history force, and etc. Finally the paper uses

ASME standard to evaluate the mechanical properties

[3-5].

2. Peps Overview

Peps of DST Company in Switzerland is an integrated

package containing PIPESTRESS, the piping analysis

core program, and Editpipe, its pre- and post-processor.

PIPESTRESS is a program for performing linear elastic

analysis of three -dimensional piping systems subject to a

variety of loading conditions. Chemical process piping,

nuclear and conventional power generation piping sys-

tems may be investigated for compliance with piping

codes and with other constraints on system response.

PIPESTRESS plays an important role in the world nuc-

lear industry. Editpipe is the pre- and post-processor of

PIPESTRESS. Here are some outstanding features of

Editpipe: 1) Advanced text editor environment with full

syntax coloring for editing PIPESTRESS free format

input files. 2) Instant visualization of the piping model

defined in the input file, with input error detection. 3)

Integrated database of PIPESTRESS free format input

cards and standard piping fittings. 4) Post-processing

module for visualizing mode shapes and load case dis-

placements, forces and moments. 5) Tabular view of the

data. 6) QuickPipe wizard to generate complete input

R. LIU ET AL.

Open Access JAMP

files in less than 5 minutes. 7) Online help with an exten-

sive description of the PIPESTRESS cards.

3. Stress Analysis and Evaluation Process

The purpose of stress analysis and evaluation for piping

is to prove that the piping will not fail in various working

conditions. Stress analysis of piping includes static anal-

ysis and dynamic analysis. Static analysis typically in-

cludes pressure, sustained load, thermal expansion and

endpoint displacement. Dynamic analysis is usually the

accidental loads, and seismic analysis is an important

part of the dynamic analysis. Seismic loads are divided

into two types: operation basis earthquake (OBE) and

safe shutdown earthquake (SSE). The former is consi-

dered as the design load, while the latter is considered in

accident conditions. The use of Peps for nuclear piping

stress analysis and evaluation ar e mainly in the following

6 steps [6] :

1) Establish the geometric model and finite element

model, simulating the various parameters of the piping

system (such as the piping layout, size, material, quality,

welding, valves etc.).

2) Apply boundary conditions. That is adding pipe

supports and anchoring point constraints. The stress of

piping system and supports installation are closely re-

lated. The effect of boundary conditions and constraints

imposed on the results of stress are far greater than the

pressure and other loads.

3) Apply loads associated with each kind of condition

according to the design requirements. For the piping

stress analysis, a very important step is to determine the

load conditions, which include 6 different restrictions:

designing condition, class A, class B, class C, class D,

and experimental condition. The loads that the class 2/3

piping system to withs tand can be divided into: sustained

load, thermal expansion endpoint displacement, acciden-

tal loads, and etc.

4) Stress analysis. Combine loads for each condition

respectively. Modal analysis is required before dynamic

analysis.

5) Stress evaluation. Calculate the stress for assess-

ment in accordance with the relevant formulas of the

design specifications.

The step of stress analysis and assessment is shown in

Figure 1:

4. Example Analysis

4.1. Piping System Model

One nuclear piping system of class 2/3 is composed of

five lines: L001B、L002B、L003B、L004B, and L005B.

The material for the piping is SA335 Gr P1. Parameters

wer e descr ibed in Table 1. To ensure the accuracy of the

calculation, node 10 to 11 (material is SA333 Gr6), and

node 139 to 140 (material is 312 GR TP304L) simulate

the equipment or penetrations in Figure 1. Peps simula-

tion of piping system arrangement is shown in Figure 2.

This piping system has a 12 pipe supports, and the sup-

port constraints direction (DIR) marked in the Figure 2.

There are two valves weight 260 kg (V1 and V2), and

one valve (V3) weight 9 kg in the Piping sys te m.

4.2. Lo ading Conditions

The design pressure of the piping system is 8.17 MPa,

and the design temperature is 315.6˚C. Weight, pressure,

thermal expansion, time-history force, and seismic loads

should be considered in the piping. The temperature (˚C)

and pressure (MPa) corresponding to thermal expansion

conditions are showed in Table 2. Thermal displacement,

earthquake displacement, and separate non-repeated

Figure 1. Stress analysis and evaluation for nuclear piping of class 2/3.

R. LIU ET AL.

Open Access JAMP

Table 1. Piping parameters.

Piping No. Piping class Aseismic grade Medium Outer diameter (mm) Wall thickness (mm) Safety requirement

L001B class 2 I water 141.3 6.55 yes

L002B class 3 I water 141.3 6.55 yes

L003B class 3 I water 141.3 6.55 yes

L004B class 3 I water 141.3 6.55 yes

L005B non-nuclear safety class I water 33.4 4.55 no

Figure 2. Model of the piping system.

Table 2. temperature (˚C) and pressure (MPa) correspond- ing to thermal expansion.

Piping No.

Designing condition condition 1

(Level A) condition 2

(Level A) condition 3

(Level A) condition 4

(Level B) condition 5

(Level C) condition 6

(Level D)

temp

(˚C) Pre

(MPa) temp

(˚C) Pre

(MPa) temp

(˚C) Pre

(MPa) temp

(˚C) Pre

(MPa) temp

(˚C) Pre

(MPa) temp

(˚C) Pre

(MPa) temp

(˚C) Pre

(MPa)

L001B/L002B 315.6 8.17 277.3 6.27 51.7 0.26 291.7 7.73 300.5 8.75 280 6.27 180 0.26

L003B/L004B

/L005B 315.6 8.17 277.3 6.30 51.7 0.30 291.7 7.76 300.5 8.78 280 6.30 180 0.30

anchor displacement of anchors are showed in Tables

3-5. Time -history force curve and seismic floor response

spectrum curve are showed in Figures 3 and 4.

4.3. Results and Analysis

The maximum stress ratio is equal to maximum stress

divided by the stress limit. If the maximum stress ratio is

not greater than 1, the designing of piping system meet

the specification. Table 6 gives stress combination of the

piping system in different conditions. The result shows

that the piping system meets the stress limits of ASME

Code, and the design is qualified.

5. Conclusions

Application of Peps in mechanical analysis for nuclear

piping system is an important work. On the one hand to

assist design work and ensure that the design of piping

system meets regulatory requirements; On the other hand

R. LIU ET AL.

Open Access JAMP

Table 3. Thermal displacement.

node working condition thermal displacement (mm)

DX DY DZ

10 condition 6(Level D) 22.02 6.76 0.15

condition 1~4( Level A&B) 5.05 1.55 −0.13

Table 4. Earthquake displaceme nt.

node working condition earthquake displacement (mm)

DX DY DZ

SSE-X 10.46 - -

SSE-Y - 13.18 -

SSE-Z - - 8.66

Table 5. separate non-repeated anchor displacement.

node

working condition anchor displacement (mm)

DX DY DZ

140 equipment/penetration settlement - - −6.35

Figure 3. Time history curve.

Figure 4. Floors response spectrum of SSE.

Table 6. Stress combination under different conditions.

working

condition stress

combination

ASME standard

evaluation

formula maximum

stress Maximum

stress ratio

design Design pressure

+ weight (8) 32.28 0.223

Class A&B normal/abnormal

thermal expansion (10) 150.9 0.865

Class A&B normal/abnormal

pressure + thermal

expansion +weight (11) 192.75 0.682

Class A&B separate non-

repeated anchor

displacement (10a) 29.71 0.086

Class B abnormal pressure

+ weight + time-

history force (9) 44.73 0.279

Class C em ergency operating

pressure + weight

+time-history force (9) 33.19 0.172

Class D Accidents operating

pressure + weight

+ earthquake (9) 82.26 0.385

Class D

Accidents operating

pressure + weight

+ earthquake

+time-history force

(9) 87.49 0.409

to provide the interface parameters and basis for the de-

tailed design.

This paper takes nuclear class 2/3 piping system as an

example, and introduces Peps in the nuclear piping anal-

ysis. Peps, as can be seen with easy modeling, computing

capability, intuitive post-processing advantages, com-

bines the major nuclear standards and specifications and

especially suits for complex mechanical analysis of pip-

ing syst ems in nucle ar power e ngineering.

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Open Access JAMP

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