The ASME section viii division 1 provides two equations for calculating the thickness of the cylindrical shell for the thin walled pressure vessel. But before going to the ASME section 8 div. 1 equations and their application for our example, refer the input data and the pressure vessel sizing calculation example for better understanding this part of the tutorial.

**Pressure Vessel Cylindrical Shell Thickness Calculation **

* *

*Input data:*

Internal pressure for the pressure vessel, **P=75 Pa = 0.000075 MPa** (Refer Part-1)

Inside radius of the thin walled pressure vessel, **Ri=1350 mm** (Refer part-2)

Corrosion allowance, **C=0.02 mm** (Assumed)

So, the inside radius after adjusting the corrosion allowance, **Ri1=Ri-C=1349.98 mm**

Weld efficiency of the seams, **E=85%=0.85** (Assumed)

Material for the pressure vessel shell=**AISI 304 SS**

Allowable stress for AISI 304SS, **S** = **103 MPa**

Liquid to be stored inside the pressure vessel= **Water**

*Necessary equations:*

The required equations from ASME Sec. Eight Div.1 are,

- Minimum required thickness at the longitudinal seam welds,

**ta=P*Ri1/(S*E-0.6*P)……………………Eq.1**

** **

- Minimum required thickness at the circular seam welds,

**tb=P*Ri1/(2*S*E+0.4*P)……………………Eq.2**

Where,

All the symbols are explained in the input section above.

And, the **minimum required design thickness** for the vessel shell will be **tr=Maximum of (Eq.1, Eq.2)+C ………………………………………..Eq.3**

** **

** **

** **

*Solution:*

By using the input data to the **Eq.1**, we get,

**ta= 0.001156465 mm**

** **

By using the input data to the **Eq.2**, we get,

**tb= 0.000578232 mm**

Now, from the **Eq.3, **we get,

**Minimum required design shell thickness, tr= 0.021156465 mm**

** **

For the pressure vessel design tutorial example, we have **initially assumed the shell thickness, t = 6mm **(refer Part-2)

And, as **t>tb** so our assumed shell thickness is safe for the application example.

That’s it for shell thickness, I will discuss the maximum allowable pressure calculation according to the ASME Section viii division i codes.

### Shibashis Ghosh

Disclaimer: I work for Altair. mechGuru.com is my personal blog. Although i have tried to put my neutral opinion while writing about different competitor's technologies, still i would like you to read the articles by keeping my background in mind.

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Hi,

My team has designed a pressure vessel, and we’ve assumed the thickness to be 10mm. 8mm thickness + 2mm corrosion allowance. The equation gave us .2mm as minimum thickness, but our supervisor refuses to acknowledge the design at 10mm thickness because there is no reference regarding why we sized up our thickness to 10mm. We’ve tried explaining that the equation only gives the minimum thickness, and that .2mm is an unrealistic thickness, but he wont give in until we can get a proper reference as to why we sized it up from .2mm. Any ideas on how we should go about this??

Hi,

My team has designed a pressure vessel, and we’ve assumed the thickness to be 10mm. 8mm thickness + 2mm corrosion allowance. The equation gave us .2mm as minimum thickness, but our supervisor refuses to acknowledge the design at 10mm thickness because there is no reference regarding why we sized up our thickness to 10mm. We’ve tried explaining that the equation only gives the minimum thickness, and that .2mm is an unrealistic thickness, but he wont give in until we can get a proper reference as to why we sized it up from .2mm. Any ideas on how we should go about this??

Hi, I found your description of calculating shell thickness useful (ref applyinf ASME equations) But I think there is an error in the ta and tb values calculated they are shown as fractions of a millimetre ie 0.00057mm

this would be a thin foil unlikely to support its own weight. Appreciate it is just computer error and it does not change the concept but need to check figures to make sure they make sense.

I think there is no error,it is the design pressure which is too small actually contradicting the purpose,i.e not a pressure vessel.

we have fabricated a vesssel which consists of two shells and one has a height of 470mm. is thre any specific requirement in ASME for shell height, if yes wat should be the minimum height????

sir, how do we derive the equation you used from basic eq : ta = P*R/S*E