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Design Pressure As Credit


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#1 m42364236k

m42364236k

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Posted 31 October 2014 - 01:19 PM

Dear friends

 

Can we consider the design pressure of the vessel as credit instead of the PRESSURE SAFETY VALVE.

is it applicable as pre ASME SECTION 8

Instead of considering the psv ,increasing the design pressure of the vessel

I know that this solution is not good choice and have big cost impact but I want to know that is it correct or not?

in the P&ID I see for heat exchanger vendor did not consider the psv for tube rupture and also thermal expansion .

When we ask them they said that we increase the design pressure and in this case no need to consider the psv 

 

Thanks

mike



#2 fallah

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Posted 31 October 2014 - 02:15 PM

mike,

 

Increasing the vessel DP to upstream overpressure source in orger to ignore considering PSV, especially in blocked outlet case, is an acceptable method; but in the case you mentioned appears the DP of the low pressure side of the exchanger has been increased to remove credibility of the tube rupture case which can be acceptable as well...



#3 Puneet arora

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Posted 02 November 2014 - 03:23 AM

I have a doubt on increasing the DP of low pressure side of heat exchanger. I know this is acceptable but what about the connecting piping of the low pressure side. I have seen that the DP of the connecting piping is not increased and the relief valve datasheets on the connecting piping do not cover the tube rupture case. So when there is a tube rupture how is the connecting piping able to handle the overpressure?



#4 fallah

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Posted 02 November 2014 - 03:49 AM

Hi,

 

As per the current engineering practices the DP of the piping around an equipment such as a heat exchanger at least should be equal to that of the equipment up to the first isolation valve in either side. Then if the DP of low pressure side of a heat exchanger is increased to remove the tube rupture scenario, the DP of the piping connections to that side till the first isolation valve, should be increased as well. in such cases the PSV on the connecting piping before isolation valve would handle the thermal expansion case for blocked-in liquid.

Obviously, if the DP of the piping downstream of the isolation valve can't handle the over pressure due to tube rupture case, the PSV at the downstream equipment would do the job properly...






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