Mitigating Processes 1

[Bill3752]

I am evaluating a tube rupture RV case. Due to the tube size (3") and high pressure diffential, the calculated flow is huge. The calculated RV size is 24", which is larger than any nozzle. I am hoping that one of the forum members might have encounted this problem. Does ASME allow for mitigation via upgraded preventive/predictive maintenance?

Thanks in advance.

 

[ggordil]

Bill3752,

I have one question. Did you use the hydrotest pressure of the shell as your low pressure? This may help reduce your required rate.

In addition, API 521 also allows credit for the normal volumetric capacity of the system. This is based on the assumption that as soon as the tube ruptures, the normal flow will stop, and all that will be going downstream is from the high pressure side.

 

[djack77494]

Bill,
Tube rupture is a rare phenomena and you're talking about a huge (probably bigger even than is commercially available) PSV. Why not go with a rupture disk which anyway will offer better protection from a rapidly acting pressure surge such as the tube rupture scenario. If you do use one or more RD's, put one in the center of the tube bundle; for several, space them around the center of the tube bundle.

 

[Bill3752]

Thanks for the input. There are several exhangers that are involved. I am assuming the the high pressure flow is the only flow. Rupture disks are being used, not RV's (except in a couple of cases as extra protection). Grasping at straws, but wondering if one looks at likelihood of event, plus takes extra predictive maintenance measures, that he could install instead a smaller RD based on a much more likely case.

 

[djack77494]

I think the answer is "NO". Though unlikely, tube rupture is considered a valid relief scenario and must be provided for. There are no mitigating circumstances that can justify anything less than the full relief scenario.

 

[Bill3752]

Thanks Jack, you pretty much confirmed what I knew (but wished I was wrong - lol).

 

[maddocks]

You may be able to look at the design pressures of the system -if the low side design pressure is 66% of the highside, there are some provisions for not requiring tube rupture protection....