Oversizing PSV for HEX tube rupture case

[pastyl]

Dear all

I sized a pressure relief valve for an Heat Exchanger and for tube rupture case.
The problem is that I considered 3 tubes to be ruptured and as result I oversized the relief. I have 2 questions:

1) Is forbidden from API to consider 3 tubes ruptured and you have to consider only one ?

2) Were is the problem if I oversized the relief and it can handles more mass flow than the minimum required ?

Because my client complained about the above problem I really appreciate a quick response

Best Regards

 

[ggordil]

From what I understand, usually only one tube is considered to break. It is not forbidden, but it may be too conservative.

The biggest problem with oversizing relief valves, is the cost. API recommends less than 3% inlet loss at capacity for all overpressure scenarios. If your valve is really large for tube rupture, the inlet piping may have to be quite large.