PSV Required? Thermal Relief Sizing?

[TiCl4]

Forward: I work in a state that does not require ASME Section VIII, Div 1 to be followed, but am asking these questions in order to do what is right, not what is required.

We have a ~560 gallon carbon bed that will soon be installed and used for filtering water. The tank is "rated" (no stamp) to 75 psig. In case you were wondering, I did not specify this equipment. This equipment specification and purchase came from an engineer that is no longer with our company.

ASME code allows for exemptions from code based on the following.

(f) a vessel for containing water under pressure,
including those containing air the compression of which
serves only as a cushion, when none of the following limitations are exceeded:

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(-1) a design pressure of 300 psi (2 MPa);

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(-2) a design temperature of 210°F (99°C);

First question: Is the presence of the carbon in the vessel a disqualifying factor for that exemption? I assume the vessel was created under this exemption.

This vessel only has 1 over-pressure case - it is outside, and will have an inlet and outlet valve. There does technically exist the possibility of a blocked inlet/outlet case with direct sunlight exposure leading to over-pressure.

Second question: For any vessel that has valves on all ports (which seems to be many/most of them!), do I have to automatically assume that a blocked inlet/outlet case exists?

Third question: The only way I know to size this is to evaluate the volume of the water in the tank, the gain from ambient heat transfer and solar gain, and use the volume expansion with temperature to calculate a relieving rate in order to size a PSV. Is there another way to do this? In my experience with cases like this, a 1/2" relief valve is usually more than an order of magnitude oversized for such a case.

 

[mk3223]

IMO, if the Code doesn't need to be followed by the State Law, you don't need to follow the exemption rules as stated in ASME Code.

First, this is a carbon bed/filter vessel, not a simple water vessel. IMO, this ASME exemption rule isn't suitable for your vessel.

Second and third, the PSV may not be suitable for the carbon solution, since the valve could be leaking as carbon particle stuck on the valve seat. I saw the system uses the rupture disc for the overpressure protection, similar to the link below.

https://www.calgoncarbon.com/app/uploads/DS-MODEL817-EIN-E1.pdf