Help with PD and MAWP (ASME Sec. VIII div. 1) 1

[Lebpower]

Hello,

I'm very confused about these 2 and I really need your help.

Pressure Design: If I got the Presure and Tempeture (Operation) how can I calculate the Pressure Design? and Where I can Find this equation in ASME Sec. VIII.

MAWP: In UG-27 (ASME Sec. VIII div. 1) they give this ecuation: P= SEt/R+0.6t and P= SEt/R+0.4t but I'm not sure if that's the MAWP.

I read on another thread of this forum that one you use any of the above equations, then you have to subtract the static liquid pressure from this maximum pressure to get the MAWP. But I'm not sure about how to "subtract the static liquid pressure".

But in UG-98 the paragraph says:
"The maximum allowable working pressure for a
vessel part is the maximum internal or external pressure,
including the static head thereon"

So I'm more than confused... Can Anyone please give me an example incluiding the equations to get the MAWP of a Vessel please?

 

[marty007]

There is no one equation that will give you the MAWP.

When designing an ASME vessel, there are three common pressures that have meaning:
[ol 1]
[li]Operating pressure - This is the pressure that the vessel will see during normal operation. This is defined by the process design, and can sometimes have multiple values if the vessel cycles over time.[/li]
[li]Design pressure - This is the pressure given to the vessel manufacturer as the design pressure for the equipment. This pressure must be set sufficiently above the operating pressure to account for many different aspects of operation (upset cases / pressure relief scenarios / etc.). It is not a trivial matter to select an appropriate design pressure. Often this requires a detailed relief study that includes analysis of piping layouts and HAZOP studies.[/li]
[li]Maximum allowable working pressure (MAWP) - This is the maximum pressure that the equipment is allowed to see, and is often a calculated value based on the detailed vessel mechanical design. Normally a fabricator starts with the design pressure, and generates a design that meets all of the requirements of ASME VIII-1. This will lead to some materials being being thicker than required by code. For example, if the code requires 0.47" for the shell thickness, a designer will select 0.5" plate. This additional material means that the vessel can actually handle a higher pressure than the design pressure. To determine the MAWP, the designer must back-calculate the allowable pressure of every component of the vessel (shell/heads/nozzles/nozzle reinforcement/flanges/etc.). There is no one formula for calculating the MAWP, you must consider all aspects of the vessel. [/li]
[/ol]

Regarding static head, this must be considered in all aspects of design. The MAWP is defined to occur at the very top of the vessel. So, if your vessel is filled with a liquid, then every component must be able to withstand the MAWP+static head for the depth of the component.