Rated vs Actual vs Design rate ?

[hniaboujemaa]

Hi guys,

Any thoughs about the difference between rated / actual / design rate for PSV, I have seen many definitions through API and ASME.

Thanks in advance

Mouss

 

[CJKruger]

Okay, let me take a stab at it:

Design = Required flow rate from your relief scenarios.
Rated = Certified flow rate based on full open valve.
Max = 1.1 times Rated flow (as ASME derate by 10%).

"Actual" I assume is whatever happens in a real relief case.

 

[hniaboujemaa]

Thanks CJKruger for your clarif
the design and actual are quite clear but the rated one is still not.

regards,

 

[CJKruger]

Rated flow = Design flow * (Full open area / Design area).

Sequence of calculations are as follows:
- Calc required relief flow from scenarios (design flow).
- Calc design orifice area from design flow.
- Select a standard relief valve with full open area larger than design area.
- Calc rated flow based on flow through fully open valve.

 

[sheiko]

hniaboujemaa,

In API standard, only the "rated relieving capacity" is mentionned, which is the flowrate provided by the manufacturer.

So I tend to think that "Actual", "Design", "Calculated" or "Required" flowrates are actually the same, that is the one you calculate from overpressure contingencies.

"We don't believe things because they are true, things are true because we believe them."