steam purging for Tanks

[mechmanx77]

Hi Every one
I wan to know if there is any rule dictated by ASME or API codes calling for including the steam purging (S/out) condition in the design of tanks? so is there any rule or relation of design parameters like pressure, temp or thickness or service condition to decide whether to consider steam purging connection?

 

[gr2vessels]

mechmanx77,
There is not specific ASME or API design condition called "steam out". However, the principle of steam condensation creating vacuum in closed environment is also well known, I believe that you are fully aware of this. Generally, the datasheet would specify the "steam out" condition, which implies the request to include in the vessel (or tank) design a vacuum condition. Typically, people used to design the ASME VIII vessel for full vacuum, unless vacuum limiting valves are used or simply use large openings like manways as vacuum breakers during the cleaning operation. Also, as a precaution, the high pressure steam if used for cleaning, the steam saturation temperature is being specified as design temperature, unless other process condition requires higher design temperature. Theoretically, the same can be applied for small API tanks, except careful consideration has to be given for limiting the vacuum to the Code allowed level and considering the feasibility of designing the tank for temperatures above 200F. Practically, it's hard to imagine a steam out condition for large API tanks with large openings, where the operator using a relatively small steam lance, could cause a damaging vacuum.
Cheers,
gr2vessels

 

[JStephen]

API tanks are not normally designed for any significant vacuum. The temperature is not too much of an issue. Designs for temperatures above 200 degrees F have some special provisions, but exceeding that temperature just slightly with the tank out of service shouldn't do much.

 

[mechmanx77]

gr2 and JStephen, thanks for your guidance. In fact,for the vessels, I had seen a design with s/o condition but not with FV design but it was clear that venting and the opening were reliable to avoid the vacuum condition. I am wondering if there is any refrence material indicating a rule that relates design conditions with thickness to indicate the requirement for FV condition for those PVs w specified with s/o.