7/23/2014 Fatigue Analysis in Caesar II | What is Piping

http://www.whatispiping.com/case-study-for-fatigue-analysis 1/8

I have taken up this topic to explain the fatigue analy sis (Click here to read the basic

article on Fatigue Analy sis) methodology using caesar II with an example problem of a

ty pical piping sy stem. To perform fatigue analy sis we need to calculate the thermal and

pressure fluctuations the piping sy stem will undergo in its design life. We have to

calculate the worst possible cy cles from preliminary data prov ided by process/operation

department. Lets assume we received the following data from process for a ty pical piping

sy stem.

Operating cy cle from ambient (40C) to 425C (400,000 cy cles anticipated)

Shutdown external temperature variation from ambient (40C) to -20C (300,000

cy cles anticipated)

Pressurization to 5.5 Bars (400,000 cy cles anticipated)

Pressure fluctuations of plus/minus 1 .5 Bars from the 5.5 Bars (1 ,000,000 cy cles

anticipated)

Now, in order to do a proper fatigue analy sis, these should be grouped in sets of load

pairs which represent the worst-case combination of stress ranges between extreme

What is PipingAn attempt to explain process piping engineering basics in detail to help all the process

piping engineering professionals around the world.

HOME ABOUT US PIPING STRESS PIPING SUPPORTS PIPING DESIGN

FORUM PRIVACY POLICY CONTACT US MISC.

25th Nov ember 201 3 Anup Caesar II 3 Comments

Case Study for Fatigue Analysis in

Caesar II for a typical piping system

0Like 0

7/23/2014 Fatigue Analysis in Caesar II | What is Piping

http://www.whatispiping.com/case-study-for-fatigue-analysis 2/8

states which we can do in the following way (Refer Attached Figure, Fig.1 for proper

understanding):

Fig. 1 : Explanation of worst case cy cle combination for fatigue analy sis

From -20C, 0 Bars to 425C, 7 Bars. 300,000 Cy cles

From 40C, 0 Bars to 425C, 7 Bars.: 100,000 Cy cles

From 425C, 4 Bars to 425C, 7 Bars: 600,000 Cy cles

From 425C, 4 Bars to 425C, 5.5 Bars: 400,000 Cy cles

So in Caesar II we can define the above data as follows (Refer Fig. 2):

T1= 425C; T2= -20C

P1= 5.5 Bar; P2= 4 Bar and P3= 7 Bar

Fig.2: Caesar II spreadsheet explaining the input requirement

Now go to the load case editor and define load cases as shown in Fig.3 for fatigue analy sis.

Click on load cy cles button to input the number of cy cles calculated above.

7/23/2014 Fatigue Analysis in Caesar II | What is Piping

http://www.whatispiping.com/case-study-for-fatigue-analysis 3/8

Fig.3: Load cases for Fatigue Analy sis

Dont forget that all load cases with stress ty pe FAT (for fatigue) must have their expected

number of Load Cy cles specified.

After load cases are prepared run the analy sis and find out the results from output

processor. Part of the output results are prov ided in the below attached figures for y our

reference (Fig. 4 and Fig. 5)

The fatigue stress range (Maximum Stress Intensity as calculated in Expansion stress

case) may be checked against the fatigue curve allowable for each fatigue load case as

shown in Fig 4.

Fig 4: Output Screen showing stress range

However, this is not a true evaluation of the situation, because it is not a case of either-

or. The piping sy stem is subjected to all of these load cases throughout its expected

design life, not just one of them. Therefore, we must rev iew the Cumulative Usage report,

which shows the total effect of all fatigue load cases (or any combination selected by the

user) on the design life of the sy stem. Refer Fig 5 for example.

7/23/2014 Fatigue Analysis in Caesar II | What is Piping

http://www.whatispiping.com/case-study-for-fatigue-analysis 4/8

Fig. 5: Output Screen showing Cumulative usage factor

This report lists for each load case the expected number of cy cles, the allowable number

of cy cles (based upon the calculated stress), and the Usage Ratio (actual cy cles div ided

by allowable cy cles). The Usage Ratios are then summed for all selected load cases; if this

sum exceeds 1 .0, the sy stem has exceeded its fatigue capabilities.

Please prov ide y our inputs in comments section.

Related Posts:

1 . Step by Step Method of Fatigue Analy sis of a Piping Sy stem Using Caesar

II

2. Basics for Fatigue Analy sis of Piping Sy stem using Caesar II

3. Stess Analy sis of PSV connected Piping sy stem s using Caesar II

4. Step by Step Methods for WRC 107 and WRC 297 Checking in Caesar II

5. ST ORAGE T ANK PIPING ST RESS ANALYSIS AS PER API 650 USING

CAESAR II

6. Co-Efficient of Friction for pipe supporting during Stress Analy sis using

Caesar II

7 . 10 points to keep in m ind while using project specific pressure vessel

nozzle load tables during stress analy sis.

More In Caesar II

Co-Efficient of Friction for pipe supporting during Stress Analysis

using Caesar II

All piping stress engineers must be aware that while modeling supports or restraints in

Caesar II input spreadsheet we have to enter the frictional co-efficient.read more

7/23/2014 Fatigue Analysis in Caesar II | What is Piping

http://www.whatispiping.com/case-study-for-fatigue-analysis 5/8

Stress Analysis of Vertical Reboiler Piping using

Caesar II: Part 3 of 3

Continued from Part 2... Supporting Arrangement: Reboilers may

be supported from column or by making a independent structure.

In both of the cases there isread more

Basics for Fatigue Analysis of Piping System

using Caesar II

Introduction: Fatigue is the progressive and localized structural damage that occurs

when a material is subjected to cy clic loading. Continued cy cling of high

stressread more

This article has 3 comments

superdry

Thursday 19 December 2013, 6:21 am

Terrific article! That is the typpe of information that are meant to

be shared across the internet.

Reply

PANKAJ TRIPATHI

Friday 10 January 2014, 2:35 pm

Dear sir

as per your example pressure variation you have taken From 425C, 4 Bars to

425C, 7 Bars: 600,000 Cycles

i think you it should be 1000,000 and other pressure case need not to be take care.

Reply

David Diehl

7/23/2014 Fatigue Analysis in Caesar II | What is Piping

http://www.whatispiping.com/case-study-for-fatigue-analysis 6/8

Prev ious Next

Leave a Reply

Name*

Email*

Website

Submit Comment

Search this Website

Popular posts

Monday 17 March 2014, 7:12 pm

Your Figure 5 is not a Cumulative Usage Report.

Reply

Search

7/23/2014 Fatigue Analysis in Caesar II | What is Piping

http://www.whatispiping.com/case-study-for-fatigue-analysis 7/8

Step by Step Methods for WRC 107 and WRC 297 Checking in Caesar II

11 most important questions & answers from ASME B 31 .3 which a Piping stress

engineer must know

Stess Analy sis of PSV connected Piping sy stems using Caesar II

Stress Analy sis of Pump Piping (Centrifugal) Sy stem using Caesar II

STORAGE TANK PIPING STRESS ANALY SIS AS PER API 650 USING CAESAR II

Must have Load cases for stress analy sis of a ty pical piping sy stem using Caesar II

Methods for flange leakage checking by Pressure Equivalent Method using Caesar II

Spring hanger selection and design guidelines for a Piping engineer using Caesar II

Trunnion Checking or Dummy Checking during stress analy sis of a piping sy stem

Huge Openings with Foster Wheeler for all Oil and gas professionals in Japan,

Netherlands and Sharjah

Piping Stress Job Interv iew questions for y ou: Part 1

Stress Analy sis of Column piping sy stem using Caesar II

Nozzle Loading of Various Equipments and means for reducing them

Flange Leakage Evaluation based on NC 3658.3 Method method using Caesar II

Case Study for Fatigue Analy sis in Caesar II for a ty pical piping sy stem

Subscribe by Email to get updates

Enter y our email address:

Subscribe

Delivered by FeedBurner

Archives

Select Month

Categories

Select Category

Sitemap

SiteMap

7/23/2014 Fatigue Analysis in Caesar II | What is Piping

http://www.whatispiping.com/case-study-for-fatigue-analysis 8/8

WordPress Theme Theme by WPExplorer