Hi. I'm working on the tube external pressure calculation (hand calculation) by using PD5500 code. In order to determine the mean elastic circumferential strain (equation 3.6.2-9), i need to find the ncyl value from Figure 3.6-3. Then i just realise that my L/2R value which is 65 and e/2R value which is 0.06 is out of the chart. So, how to read the ncyl value from the Figure 3.6-3?

Hello Lim

PD 5500 discusses ncyl at section 3.6.2.1(b). You notice that ncyl is chosen to the value of pm a minimum. You also have an equation for pm such that pm = Eeε/R. PV Elite performs the calculation this way:

First select a value for ncyl (=2 the first time round). Then calculate the strain ε from equation 3.6.2-9. Then compute the value of pm. Select the next value of ncyl (= 3 this time), and repeat the calculalation. Keep repeating the calculation with increasing values of ncyl. Check the value of pm each time until you get an ncyl corresponding to the minimimum value of pm. That is your final value of ncyl.

The procedure is very tedious by hand. You really need to write a programme yourself or use a product such as Excel or MathCad to make it easier. We wrote the programme in another language as a check.