**Click here to read the basic article on Fatigue Analysis**) methodology using caesar II with an example problem of a typical piping system. To perform fatigue analysis we need to calculate the thermal and pressure fluctuations the piping system will undergo in its design life. We have to calculate the worst possible cycles from preliminary data provided by process/operation department. Lets assume we received the following data from process for a typical piping system.

- Operating cycle from ambient (40°C) to 425°C (400,000 cycles anticipated)
- Shutdown external temperature variation from ambient (40°C) to -20°C (300,000 cycles anticipated)
- Pressurization to 5.5 Bars (400,000 cycles anticipated)
- Pressure fluctuations of plus/minus 1.5 Bars from the 5.5 Bars (1,000,000 cycles anticipated)

**Fig. 1: Explanation of worst case cycle combination for fatigue analysis**

- From -20°C, 0 Bars to 425°C, 7 Bars. 300,000 Cycles
- From 40°C, 0 Bars to 425°C, 7 Bars.: 100,000 Cycles
- From 425°C, 4 Bars to 425°C, 7 Bars: 600,000 Cycles
- From 425°C, 4 Bars to 425°C, 5.5 Bars: 400,000 Cycles

**T1= 425°C;**

**T2= -20°C**

**P1= 5.5 Bar;**

**P2= 4 Bar and**

**P3= 7 Bar**

**Fig.2: Caesar II spreadsheet explaining the input requirement**

**Fig.3: Load cases for Fatigue Analysis**

**Fig 4: Output Screen showing stress range**

**Fig. 5: Output Screen showing Cumulative usage factor**

**Please provide your inputs in comments section.**

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

be shared across the internet.

Dear sir

as per your example pressure variation you have taken From 425°C, 4 Bars to 425°C, 7 Bars: 600,000 Cycles

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

Dear PANKAJ. 6000 cycles that is correct

Your Figure 5 is not a Cumulative Usage Report.

Could anyone please explain the following conditions. I am confused with cycles for each condition.

From -20°C, 0 Bars to 425°C, 7 Bars. 300,000 Cycles

From 40°C, 0 Bars to 425°C, 7 Bars.: 100,000 Cycles

From 425°C, 4 Bars to 425°C, 7 Bars: 600,000 Cycles

From 425°C, 4 Bars to 425°C, 5.5 Bars: 400,000 Cycles