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Relief Valve Sizing: Steam Trap Failure


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#1 Chemitofreak

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Posted 08 October 2019 - 03:45 AM

Hi All,

 

Is operation of steam trap considered reliable while considering relief/over pressure scenario.

 

Thanking you in advance.

 

Regards



#2 CH3CH2OH

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Posted 08 October 2019 - 10:57 AM

Typically no, at least following my company's philosophy -- we treat relief devices as a SIL-2 quality device (to protect in a case that requires such a level of risk reduction), so in order say a control device (such as a block valve, control valve, or steam trap in this case) is reliable enough to prevent an overpressure case that would typically require a PSV, that control device would also need to be at least SIL-2 quality which a steam trap will not meet.

 

API 521 goes into it a bit more, and it looks like for an ASME Sec VIII vessel where a relief device is typically required by code, SIL-3 quality performance may be needed (per API 521 section 4.2.6).

 

Are you depending on the steam trap to protect upstream equipment, downstream equipment, or both?



#3 fallah

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Posted 08 October 2019 - 11:18 AM

 

Is operation of steam trap considered reliable while considering relief/over pressure scenario.

 

Hi,

 

Normally no, but having a sketch of the system for which you are specifying its over pressure scenarios will help to submit specific response...



#4 Chemitofreak

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Posted 09 October 2019 - 01:09 AM

Thanks for your response guys.

 

PFA the sketch of the system for your reference

 

Regards

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#5 CH3CH2OH

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Posted 09 October 2019 - 11:24 AM

It looks like you could overpressure your condensate tank through steam trap failure, steam through steam trap bypass valve if left open or leaking, and you could possible get flash steam generation if your condensate out of the steam trap is greater than 6 barg.



#6 Chemitofreak

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Posted 10 October 2019 - 12:38 AM

It looks like you could overpressure your condensate tank through steam trap failure, steam through steam trap bypass valve if left open or leaking, and you could possible get flash steam generation if your condensate out of the steam trap is greater than 6 barg.

 

Bingo...!

 

Generally we consider the bypass valve failure as remote contingency.

 

So, if I do not take credit of the steam trap the relief rate during the remote contingency will double and the relief valve on the condensate drum is inadequate for handling this load.

 

Regards,






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