MAWP & Design Pressure: Understand the Difference

[balanar]

Hi All,

I have a question regarding the design of the pressure vessel.

What is the Maximum allowable working pressure (MAWP)?
What is the Design pressure?
What are the differences between MAWP and design pressure?

I know their definition but i am struggling to understand.

For example, let's say the operating pressure of the pressure vessel is 100 psi.
So how to determine the MAWP and design pressure?

Thanks!

 

[Q_Goest]

Hi balanar, The term MAWP is one used by ASME code. When you design a vessel per the code, it will be designed to an MAWP which is the pressure you will use in calculations. When performing those calculations, you will always compare the stress levels at the MAWP to the maximum stress allowables provided by the code. So if you had a vessel made of austenitic stainless steel for example, with a stress allowable of 20 ksi, the calculations you perform per ASME code will give you the pressure the vessel can be rated for which is the MAWP. The MAWP is the maximum pressure the vessel is allowed to be exposed to under most conditions, so the code requires you to put a relief valve on the vessel which is set at the MAWP. Realistically, you can't therefore use a vessel at the MAWP since you could easily pop a relief valve or exceed that pressure.

The term design pressure is generally meant to be MAWP but sometimes meant to mean a pressure slightly below MAWP. You may have to infer the meaning by context. Operating pressure however is generally meant to mean the maximum pressure the vessel is exposed to on a regular basis, so operating pressure is lower than MAWP such that MAWP is 110% of the operating pressure (ie: MAWP is 10% higher than operating pressure).

 

[balanar]

Thanks for your reply, Goest.

I am using PV Elite to design the pressure vessel:

Let's say:
Operating pressure: 0.1bar
Operating temperature: 34degC
Material: SS316L

And i need to input the following data into the software:
-Design pressure
-Design temperature
-Minimum design metal temperature

So, how could i calculate/get the above data?

 

[Nidum]

A baked bean tin would be overdesigned for a pressure of 0,1 bar .

Please tell us more about what you actually want to do in case there are special design requirements to be considered .

 

[balanar]

Actually pressure of 0.1bar was an example only.

My purpose is want to know how to determine/calculate the following when operating pressure and temperature are given:
-Design pressure
-Design temperature
-Minimum design metal temperature

 

[Q_Goest]

Hi balanar. The design temperature is generally determined from the process the vessel is going into. Similarly, the design pressure and MAWP are also determined from the process. A vessel designer then takes that information along with things such as material requirements and designs a vessel per the applicable design rules. In the US and many other countries, vessels are designed per the ASME pressure vessel code, though there are more than one variations of the code called "divisions".

Here's a couple web sites that might help explain more:
https://www.asme.org/shop/standards/new-releases/boiler-pressure-vessel-code-2013
http://www.engineeringtoolbox.com/asme-boiler-vessel-code-d_8.html