7 replies to this topic

[KeJoSa2010]

I have a question about calculating relief load through an orifice for a tube rupture case. In the past, I have seen Crane TP 410 equation 3-21 in combination with the correlations on page A-20 used to determine the relief rate through an orifice (which would then represent the relief rate used to size the PSV).

 

Upon investigation of these equations, it does not appear to me that the calculation of the flow coefficient C, on page A-20 is representative of a tube rupture case. In both cases (flow coefficients for nozzles and square edge orifices)the C value is based on beta which is defined as  the diameter of the nozzle/upstream pipe diameter.....In the tube rupture case I am analyzing, the shell side of the exchanger is the high pressure side (in fact it is much higher pressure). So, I have the diameter of the nozzle/orifice/hole but, there is no upstream piping, only the shell side of the exchanger.

 

How do i calculate the flow coefficient C, through a ruptured tube?

 

Thanks for the help in advance! 

[fallah]

Hi,

 

You can take the C equal to 0.6 based on following judgment:

 

As you know the flow into or out of a broken tube can be modeled as an orifice with small beta ratio because the cross sectional area of the shell as tube bundle space is very larger than that of a single tube. Considering this in mind, if  you take a look at page A-20 the C value for small beta ratio, between 0 to 0.2, is to be specified as 0.6; then it can be a reasonable value covers all tube rupture cases...

[KeJoSa2010]

Thanks Fallah,

 

One question for you though. Is it really the same if flow is coming out of a broken tube rather than going in (i.e. high pressure on tube side rather than shell side)? It seems to me that this would give you an unusually large beta ratio (i.e. >1) and hence a large C value.

Edited by KeJoSa2010, 03 September 2014 - 01:58 PM.

[fallah]

Hi,

 

In either case the beta ratio cannot be higher than 1 and is lower than, let say, 0.2 either tube side would be high pressure side or low pressure side...

[Bobby Strain]

Is this not covered in API recommended practice?

 

Bobby

[latexman]

API-521 5.19, but Fallah has added some detail from other references that is not directly found there.

Edited by latexman, 04 September 2014 - 01:28 PM.

[PingPong]

API-526 5.19

You mean API-521 5.19

[latexman]

Yes, thank you!