OscarGr
Nuclear
- Mar 24, 2015
- 5
Hi,
I am an engineer from Sweden and I am used to working with swedish national standardization when it comes to overpressure protection. However I am now facing a case where I need to construct a safety valve installation according to the ASME code. When doing this, a question about the 110 % allowable overpressure as compared to the system design pressure under relief conditions has arisen. I hope somebody with experience in using the ASME code in the United States could clarify how the 110 % evaluation should be carried out.
I am protecting a vessel against overpressure from another upstream high pressure vessel. Between the high pressure vessel and the vessel I will protect a control valve is installed. I have calculated the maximum possible inflow thorugh this control valve in the fully open position (100 000 lbs/hr of water at 60 Farenheit). The vessel I am protecting has a design pressure of 300 psig. My initial plan was to set my relief valve at 300 psig. According to the manufacturer the valve will have a certified capacity of 105 000 lbs/hr at 10 % overpressure. In other words at 330 psig which is 110 % of the designpressure the relief valve will have sufficient capacity!
Now to the question which has arisen:
I have calculated the inlet losses in the relief piping between my vessel and the relief valve to 8 psi which is somewhat less than 3 % of the set pressure (the ASME code tells me that my inlet line losses must be less than 3%). One of the other design engineers at the plant has told me that when constructing according to ASME code I have to consider this inlet line loss when determining that the vessel will be protected at 110 % of the design pressure, that I have to set the valve at a lower pressure to account for the inlet line loss (<3 % of the set pressure).
Therefore I have two options, which one would be considered the standard way to set the relief valve when fullfilling the ASME code?
OPTION 1:
P_design,vessel = 300 psig
P_maximum_allowable_vessel_accumulation = 330 psig
Set the relief valve at Pset = 300 Psig
Make sure that the valve has enough certified capacity at 10 % overpressure (30 psi).
Make sure that the inlet line loss does not exceed 3 % (9 psi).
or
OPTION 2:
While the inlet lines loss is 9 psi I have to set the valve lower than 300 psi in order not to exceed 110 % of the design pressure (330 psig).
Therefore
P_design,vessel = 300 psig
P_maximum_allowable_vessel_accumulation = 330 psig
Pset = 291 psig (while Pset + Poverpressure + Pinletline loss should be less than P_maximum_allowable_vessel_accumulation)
Make sure that the valve has enough certified capacity at 10 % overpressure (29,1 psi).
Make sure that the inlet line loss does not exceed 3 % (9 psi).
Which one is the ASME (American way)? Your help would be greatly appreciated. In Sweden we would use option 1.
Thanks!
I am an engineer from Sweden and I am used to working with swedish national standardization when it comes to overpressure protection. However I am now facing a case where I need to construct a safety valve installation according to the ASME code. When doing this, a question about the 110 % allowable overpressure as compared to the system design pressure under relief conditions has arisen. I hope somebody with experience in using the ASME code in the United States could clarify how the 110 % evaluation should be carried out.
I am protecting a vessel against overpressure from another upstream high pressure vessel. Between the high pressure vessel and the vessel I will protect a control valve is installed. I have calculated the maximum possible inflow thorugh this control valve in the fully open position (100 000 lbs/hr of water at 60 Farenheit). The vessel I am protecting has a design pressure of 300 psig. My initial plan was to set my relief valve at 300 psig. According to the manufacturer the valve will have a certified capacity of 105 000 lbs/hr at 10 % overpressure. In other words at 330 psig which is 110 % of the designpressure the relief valve will have sufficient capacity!
Now to the question which has arisen:
I have calculated the inlet losses in the relief piping between my vessel and the relief valve to 8 psi which is somewhat less than 3 % of the set pressure (the ASME code tells me that my inlet line losses must be less than 3%). One of the other design engineers at the plant has told me that when constructing according to ASME code I have to consider this inlet line loss when determining that the vessel will be protected at 110 % of the design pressure, that I have to set the valve at a lower pressure to account for the inlet line loss (<3 % of the set pressure).
Therefore I have two options, which one would be considered the standard way to set the relief valve when fullfilling the ASME code?
OPTION 1:
P_design,vessel = 300 psig
P_maximum_allowable_vessel_accumulation = 330 psig
Set the relief valve at Pset = 300 Psig
Make sure that the valve has enough certified capacity at 10 % overpressure (30 psi).
Make sure that the inlet line loss does not exceed 3 % (9 psi).
or
OPTION 2:
While the inlet lines loss is 9 psi I have to set the valve lower than 300 psi in order not to exceed 110 % of the design pressure (330 psig).
Therefore
P_design,vessel = 300 psig
P_maximum_allowable_vessel_accumulation = 330 psig
Pset = 291 psig (while Pset + Poverpressure + Pinletline loss should be less than P_maximum_allowable_vessel_accumulation)
Make sure that the valve has enough certified capacity at 10 % overpressure (29,1 psi).
Make sure that the inlet line loss does not exceed 3 % (9 psi).
Which one is the ASME (American way)? Your help would be greatly appreciated. In Sweden we would use option 1.
Thanks!
