Q: Tuan IR. Mursyidi, i have a problem. How to score good grade in calculations? Do you have a solution? Mind to share with us?
A: Thanks for asking. I understand, some of us having this problem. Some of us are not. But, it doesn’t mean that you have no problem at all especially when you’re in exam mode. That’s why, i come up with this simple explanation in order to help you understand the basic of calculation.
Okay, calculations are usually the most favoured one in any API exams. Most candidates find calculations easier than theoretical questions which require some memorization.The key to answering calculations correctly and timely is:
- Know the step by step.
- Know how to find the relevant information QUICK.
- Show your calculations (on the given sketch board).
Now remember, practice makes perfect!
CALCULATION – tmin
The formula, UG-27 (c) (1) – internal pressure.
a. R is the inside radius:
-Radius is 1/2 of the diameter.
b. P is the design pressure:
-the pressure on the part.
-includes static head.
c. The P formula calculates the shell MAWP:
-Part MAWP.
-Not the vessel MAWP.
CALCULATION EXAMPLE – tmin
A vessel shell has an internal radius of 35.0″. At the design temperature, the material’s allowable stress is 15 000 psi. The pressure on the shell (including static head) is 185 psi. Nameplate states RT-1 (type-1). Determine the minimum required thickness.
CALCULATION PRACTICE – tmin
A vessel shell has an internal radius of 38.0″. At the design temperature, the material’s allowable stress is 12 500 psi. The pressure on the shell (including static head) is 155 psi. Nameplate states RT-3. Determine the minimum required thickness.
A vessel shell has an internal radius of 38.0″. At the design temperature, the material’s allowable stress is 12 500 psi. The pressure on the shell (including static head) is 155 psi. Nameplate states RT-3 (type-1). Determine the minimum required thickness.
To be continued (part ii)…
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