Equivalences among the discharge coefficients depending on the standards

[Garlik]

Hello,

The standards AD2000 and TRD421 talk about the discharge coefficent α_w.
The standard EN 4126-5 talks about the discharge coefficient K_d and the de-rated discharge coefficient K_dr. And K_dr=0.9*K_d
The standards ASME VIII and API RP 520 talk about the discharge coefficient K_d.
α_w and K_dr are used for sizing safety valves.

With the statements above, can anyone tell me if the following is true?
Can I assume that the value of α_w (AD2000 and TRD421) is the same as K_dr (EN 4126-5)? Or is there any conversion?
The same for the coefficients of the American standards. Are there any equivalences?

Thanks.

 

[don1980]

In all relief design codes/standards the coefficient of discharge is a ratio of the orifice's tested capacity to it's theoretical capacity. In that sense, the ASME Kd and the ISO 4126 Kd (actually Kdr) are the same. The difference is the test conditions under which the valves capacity is determined. ASME defines specific requirements for this testing (valve set-up and other conditions) to be sure everyone is playing by the same rules. ASME used the National Board as the independent certification body for this testing.

Is the ASME testing protocol exactly the same as the ISO 4126 protocol? They're pretty close to being the same, but I can't say if they're exactly the same. In both cases the valve's capacity is determined at 10% overpressure, but I don't know if the valve set-up conditions (e.g. blowdown ring setting, etc) are exactly the same. So, there's possibly a small differences between an ISO Kdr valve and an ASME Kd value for the same valve, but I would not expect to see a significant difference.

The bottom line is that you use ASME Kd for sizing valves in ASME jurisdictions, and you use ISO Kdr in European PED jurisdictions.

AD2000 is a legecy German code that predated the harmonization of European pressure vessel rules (PED). I know that AD2000 was updated in the early 2000's to align it with PED, but I don't know if it's exactly the same as ISO 4126. However, the whole point of European harmonization was to get away from country-specific rules, so it seems to me that AD2000 is essentially redundant and unnecessary. In today's Europe, you're free to apply the ISO harmonized standards in Germany, rather than following AD2000.

 

[e43u8]

Garlik,

As far as i know there is no equivalences or conversion factors among all coefficient of discharges in the standards/codes you mentioned. They are obviously are different values as per relevant standards/codes due to difference in their test conditions and/or orifice area; but the only thing can be said is that all of them are adjusted to be able to handle the nameplate capacity of the relevant PSVs and the difference can, in one hand, be due to difference in orifice area and on the other hand, due to the degree of conservatism has already been considered in the relevant test conditions...