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  1. Tank Relief Philosophy

    Storage Tank Relief Calculation Philosophy
    for Chemical Processing Plant Storage Facilities


    Relief Cases

    When determining the relief requirements for atmospheric storage tanks there are seven independent cases. They are:

    1. Inflow
    2. Outflow
    3. External Fire
    4. Steam Coil Rupture
    5. Liquid Overfill
    6. Chemical Reaction
    7. Steam Out

    The following are contributions that are used in combination to determine the loads required for each case:

    1. Liquid Movement In
    2. Liquid Movement Out
    3. Thermal Out Breathing
    4. Thermal In Breathing
    5. Fire Exposure
    6. Pressure Transfer Blow-through
    7. Fail Open the Nitrogen Padding System
    8. Failure or loss of Control of Heat Transfer Devices; loss of heating/cooling utility or instrument air.
    9. Failure of Internal/External Heating/Cooling Coils
    10. Failure of Vent Vapor Collection System
    11. Chemical Reaction
    12. Steam Out

    Table 1 shows which contributions need to be considered when calculating each Case.


    Relief Devices

    1. Conservation Vents - These are Pressure Vacuum breather valves. They may be used as final pressure and/or vacuum relief or for normal pressure control on atmospheric tanks.

    2. Emergency Vents - These devices are like conservation vents except that they only have the pressure side. They may be used to supplement the conservation vent(s) when additional capacity is needed to meet a large pressure relief load while additional vacuum relief is not needed. They can take the inexpensive form of simple, weighed blind flanges on top of a tank roof nozzle; the blind cover flange is often hinged or chained in order to avoid a hazard with the cover being expelled.

    3. Fire Hatches - These devices may be used in the same cases as Emergency Vents. These devices are usually weighed down and swing open when over-pressured. They will not re-seal after the relief venting is complete. Because of this feature, their relief capacity is restricted to mitigate the Fire, Coil Failure, and Chemical Reaction contributions. Other devices must be available to provide relief for all of the other contributions.

    4. Pipe Away Vent Valves - These are like Emergency or Conservation Vents with a piping flange on the outlet. They are used to connect tanks to environmental control devices where the pressure in the tank is the driving force pushing the vapors through the piping and environmental control device. These devices are usually not considered as relief devices; however, their capacity can be considered as contributing to a relief scenario if there are no block valves or control valves between the Pipe Away Vent Valve and the atmosphere or all block valves are locked open and there are no control valves. If their capacity is considered, calculations will need to be made to de-rate the capacity due to back pressure effects of the down stream piping and other equipment.


    Table 1
    Pressure Relief Cases for Atmospheric Storage Tanks

    Case:
    1 2 3 4 5 6 7
    Inflow
    (Pressure) Outflow
    (Vacuum) Fire Coil Rupture Liquid Overfill Chemical
    Reaction Steam Out (Vacuum)
    Contributions:
    1. Liquid / Vapor In Yes Yes Yes Yes
    2. Liquid Out Yes
    3. Out Breathing Yes Yes Yes Yes
    4. In Breathing Yes
    5. Fire Exposure Yes
    6. Pressure Transfer Yes Yes Note 3
    7. N2 Regulator Failure Yes Yes
    8. Loss Heat Transfer 8.b) & c) 8. a) & d) Note 1
    9. Coil Failure 9.a) 9.b)
    10. Vent System Failure 10.b) 10.a) Note 2
    11. Chemical Reaction 11.a) 11.b) 11.b) 11.c)
    12. Steam Out Yes

    Notes:
    1. Controls Fail to maintain full heating and results in no cooling.
    2. Vent valve Fails in Closed Position and prevents any vent going to a vent collection system.
    3. Rate as Liquid.



    Calculating Contribution Loads


    1. Liquid Movement In

    The liquid movement into a tank is the lesser of the following:

    a) Determine the Maximum flow, at the horse power limit, for each pump that can be lined up to the tank. Consider the motors service factor (usually 1.15) when determining the horse power limit.

    For sources that are not pump driven, calculate the maximum flow for the flow limiting element. For control valves use the largest trim for the valve body and add the capacity of any bypass valves. An alternate to using the largest trim for a control valve, is to use the actual trim size and affix a metal tag to the valve indicating that a safety device rating is dependent on the trim size. The total inflow is the sum from all of these sources. The total inflow can be reduced if engineering judgment indicates that it is unlikely that all of the sources will be feeding into the tank simultaneously.

    b) Determine the maximum flow that the piping between the inlet manifold and tank can handle at the highest available pressure drop. The highest available pressure drop is the highest-pressure sources deadhead gauge pressure.

    For tanks that have multiple liquid inlets, each inlet can be considered independently using the flow calculated by method (a) or (b). Sum the flows for each inlet line to get the total for the tank.

    Once the total liquid inflow is determined, multiply the flow by the appropriate factor as per API-2000 based on the flash point and normal boiling point of the material stored. API-2000 has a logic error in the sections covering the selection of the factor (2.4.2.2.1 and 2.4.2.3.1). The selection criteria as presented in API-2000 is flash point below 100 oF or boiling point below 300 oF for the more conservative factor and flash point at or above 100 oF or boiling point at or above 300 oF for the less stringent factor. A fluid with a flashpoint of 113 oF and a normal boiling point of 271 oF will test true for both criteria. In cases such as this fluid, use the more conservative factor. In other words, replace the or in flash point at or above 100 oF or boiling point at or above 300 oF with an and.

    Test Factor, SCFH/GPM
    Flash Point below 100 oF or Boiling Point below 300 oF 17.14
    Flash Point at or above 100 oF and Boiling Point at or above 300 oF 8.57


    2. Liquid Movement Out

    Determine the Maximum flow, at the horse power limit, for each pump that can take suction from the tank. The total liquid outflow is the sum of all of these, including installed spare(s). Consider the motors service factor (usually 1.15) when determining the horse power limit.

    Once the total liquid outflow is calculated, multiply it by the API-2000 factor of 8 SCFH/GPM to determine the vent rate.


    3. Thermal Out Breathing

    Table 2A in API Standard 2000 (5th Edition, April 1998) is used to determine the thermal out breathing based on the capacity of the tank. For tanks less than 840,000 gal capacity, a factor can be used that is based on the flashpoint and normal boiling point of the material stored. API-2000 has the same logic error in Table 2 as discussed in Liquid Movement In above. The factors for tanks with a capacity up to 840,000 gal are presented below.

    Test Factor, SCFH/MGAL
    Flash Point below 100 oF or Boiling Point below 300 oF 23.81
    Flash Point at or above 100 oF and Boiling Point at or above 300 oF 14.29

    For tanks larger than 840,000 gal, refer to Table 2 in API-2000.


    4. Thermal In-Breathing

    Per API 2000. Table 2 in API-2000 is used to determine the thermal in breathing based on the capacity of the tank. For tanks less than 840,000 gal capacity, the factor is 23.81 SCFH / MGAL. For tanks larger than 840,000 gal, refer to Table 2 in API-2000.


    5. Fire Exposure

    Per API 2000


    6. Pressure Transfer Blow-through

    a) For tanks that are not expected to be unloaded into, the vapor rate is the flow capacity of two (2) 1 by 20 foot utility hoses with a pressure drop of the maximum nitrogen header gauge pressure. One 1 (3/4 ID) by 20 utility hose can pass 18,825 SCFH of nitrogen.

    b) For tanks where unloading is expected, use the greater of (a) above or the sum of one (1) 1 by 20 foot long utility hoses with a pressure drop of the maximum nitrogen header gauge pressure and the unloading line size with the pressure drop as the maximum gauge pressure rating of the shipping container to be used.


    7. The Nitrogen Padding System Feed Valve Fails Open

    Calculate the flow capacity of the flow limiting device using the maximum nitrogen header gauge pressure for the pressure drop. For padding systems that have a step down regulator, the step down regulator will almost always be the flow limiting device.


    8. Failure or loss of Control Heat Transfer Devices; loss of heating/cooling utility or instrument air.

    This contribution covers loss of heating, excessive heating, loss of cooling, or excessive cooling and must be determined on a tank by tank basis. These failures can be caused by failures in the control systems, measurement instruments, control valves, instrument air, and the loss of the heating or cooling utility.

    a) Loss of heating - determine the in breathing required if heating were lost. This will probably be a transient inflow until equilibrium is reached.

    b) Excessive heating - determine the out breathing required at full heating. The steam control valve usually limits this. This will probably be a continuous condition.

    c) Loss of Cooling - determine the out breathing required if cooling were lost. This could be a transient and continuous condition.

    d) Excessive Cooling - determine the required in breathing if the cooling were to fail to maximum. This will probably be a transient inflow until equilibrium is reached.


    9. Failure of Internal/External Heating/Cooling Coils

    This contribution covers a mechanical failure of a heat transfer device.

    a) For tanks with heating coils, determine the flow capacity of the flow-limiting device fully open. If the flow-limiting device is a control valve, use the largest trim available for the valve body. Also, add the capacity of any bypass valves. An alternate to using the largest trim for a control valve is to use the actual trim size and affix a metal tag to the valve indicating that a safety device rating is dependent on the trim size. Determine the vapor generated by vaporization of the product or by the steam itself - whichever is greater.

    b) For tanks with cooling coils, determine the flow capacity of any flow-limiting devices. If there are no flow-limiting devices perform a reasonable pipe pressure drop calculation, taking into consideration that the return line can potentially contribute to the inflow.


    10. Failure of Vent Vapor Collection System

    a) For vacuum relief, this pertains to any failure in a vapor collection system that can cause the system to pull excessive vapors from the tank. Calculate the flow capacity of the flow-limiting device. For systems that vent through a vacuum device that can pull down below the vacuum rating of the tank, calculate the vapor flow at the pressure where the capacity of the vacuum device equals the full open capacity of the vent valve. Use Atmospheric pressure for the upstream pressure of the vent valve. Do not take credit for pressure losses in the piping or any nitrogen from a padding system.

    b) For pressure relief, if the vacuum-producing device discharges into a header that can have a pressure higher than the pressure rating of the tank, the back flow case must be considered in the event of the failure of the vacuum-producing device. For this case calculate the capacity of the vent valve using the maximum anticipated vacuum producing device discharge header gauge pressure as the pressure drop. Do not take credit for check valves or piping losses.


    11. Chemical Reaction

    A chemical reaction in a tank can be caused by exposure to heat, incomplete reaction in a reactor, or by reaction of the tank contents with some contaminant.

    a) Thermal runaway reaction. This issue must be considered on a tank by tank basis. For tanks where the product decomposes before it reaches a normal boiling point, the runaway case is not considered since it would result in a relief device as large as the tank.

    b) A reaction can take place if two materials are contacted unintentionally. This issue must be considered on a tank by tank basis. The primary cause is due to water contamination as a result of the failure of a heat transfer device. Heat of mixing should also to be considered.

    c) This contribution covers the possibility of incomplete reaction in a reaction system. This issue must be considered on a tank by tank basis and will rarely need to be calculated.


    12. Steam Out

    This case covers the steaming out of a storage tank for tanks that are steamed out during normal product switchovers or for maintenance and inspection reasons. OSHA mandates, for good human safety reasons, that all vessels should be cleaned and purged free of any chemicals or substances hazardous to subsequent entry by humans. Steaming achieves a lot of the gross residual chemicals removal in a tank. However, in the process of steaming a tank out, a sudden rain shower may develop a dangerous situation where the internal steam is quickly condensed and the tank collapses due to a vacuum produced internally by the condensed steam. Proper nozzle sizes should be ensured for atmospheric air to enter the tank in that event such that sonic velocity is not achieved prior to breaking the vacuum. For tanks that are designed for a steam out case, a placard is to be affixed to the tank stating Vacuum Breakers are Sized for Steam Out.

    a) For tanks up to 20,000 gal the steam inflow rate is assumed to be one 3/4 ID hose by 20 ft long with a differential pressure is 40 psi gauge to atmospheric pressure. A material and energy balance must be done to determine the vacuum relief due to a hard sudden 40 oF rain.

    b) For 20,000 gal tanks up to and including 70,000 gal the steam inflow rate is assumed to be three parallel 3/4 ID hose by 20 ft long with a differential pressure is 40 psi gauge to atmospheric pressure. A material and energy balance must be done to determine the vacuum relief due to a hard, sudden 40 oF rain.

    c) For tanks larger than 70,000 gal, the steam inflow rate is assumed to be one 3/4 pipe by 50 ft long. The differential pressure is 250 psi gauge to atmospheric pressure. A material and energy balance must be done to determine the vacuum relief due to a hard, sudden 40 oF rain.

    Arts Note: This tank collapse (A.K.A. suck-in in the Texas Gulf Coast) has been personally witnessed by me and the results have also been seen out in the field. Some of the steam-out vacuum failures have resulted because of a proven lack of flow capacity in the tanks venting nozzle i.e., the nozzle reached a maximum sonic velocity capacity which was not enough for the scenario and the tank immediately sucked-in.


    See More: Tank Relief Philosophy

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  3. Re: Tank Relief Philosophy

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    Quote Originally Posted by real_chinner View Post
    Storage Tank Relief Calculation Philosophy
    for Chemical Processing Plant Storage Facilities


    Relief Cases

    When determining the relief requirements for atmospheric storage tanks there are seven independent cases. They are:

    1. Inflow
    2. Outflow
    3. External Fire
    4. Steam Coil Rupture
    5. Liquid Overfill
    6. Chemical Reaction
    7. Steam Out

    The following are contributions that are used in combination to determine the loads required for each case:

    1. Liquid Movement In
    2. Liquid Movement Out
    3. Thermal Out Breathing
    4. Thermal In Breathing
    5. Fire Exposure
    6. Pressure Transfer Blow-through
    7. Fail Open the Nitrogen Padding System
    8. Failure or loss of Control of Heat Transfer Devices; loss of heating/cooling utility or instrument air.
    9. Failure of Internal/External Heating/Cooling Coils
    10. Failure of Vent Vapor Collection System
    11. Chemical Reaction
    12. Steam Out

    Table 1 shows which contributions need to be considered when calculating each Case.


    Relief Devices

    1. Conservation Vents - These are Pressure Vacuum breather valves. They may be used as final pressure and/or vacuum relief or for normal pressure control on atmospheric tanks.

    2. Emergency Vents - These devices are like conservation vents except that they only have the pressure side. They may be used to supplement the conservation vent(s) when additional capacity is needed to meet a large pressure relief load while additional vacuum relief is not needed. They can take the inexpensive form of simple, weighed blind flanges on top of a tank roof nozzle; the blind cover flange is often hinged or chained in order to avoid a hazard with the cover being expelled.

    3. Fire Hatches - These devices may be used in the same cases as Emergency Vents. These devices are usually weighed down and swing open when over-pressured. They will not re-seal after the relief venting is complete. Because of this feature, their relief capacity is restricted to mitigate the Fire, Coil Failure, and Chemical Reaction contributions. Other devices must be available to provide relief for all of the other contributions.

    4. Pipe Away Vent Valves - These are like Emergency or Conservation Vents with a piping flange on the outlet. They are used to connect tanks to environmental control devices where the pressure in the tank is the driving force pushing the vapors through the piping and environmental control device. These devices are usually not considered as relief devices; however, their capacity can be considered as contributing to a relief scenario if there are no block valves or control valves between the Pipe Away Vent Valve and the atmosphere or all block valves are locked open and there are no control valves. If their capacity is considered, calculations will need to be made to de-rate the capacity due to back pressure effects of the down stream piping and other equipment.


    Table 1
    Pressure Relief Cases for Atmospheric Storage Tanks

    Case:
    1 2 3 4 5 6 7
    Inflow
    (Pressure) Outflow
    (Vacuum) Fire Coil Rupture Liquid Overfill Chemical
    Reaction Steam Out (Vacuum)
    Contributions:
    1. Liquid / Vapor In Yes Yes Yes Yes
    2. Liquid Out Yes
    3. Out Breathing Yes Yes Yes Yes
    4. In Breathing Yes
    5. Fire Exposure Yes
    6. Pressure Transfer Yes Yes Note 3
    7. N2 Regulator Failure Yes Yes
    8. Loss Heat Transfer 8.b) & c) 8. a) & d) Note 1
    9. Coil Failure 9.a) 9.b)
    10. Vent System Failure 10.b) 10.a) Note 2
    11. Chemical Reaction 11.a) 11.b) 11.b) 11.c)
    12. Steam Out Yes

    Notes:
    1. Controls Fail to maintain full heating and results in no cooling.
    2. Vent valve Fails in Closed Position and prevents any vent going to a vent collection system.
    3. Rate as Liquid.



    Calculating Contribution Loads


    1. Liquid Movement In

    The liquid movement into a tank is the lesser of the following:

    a) Determine the Maximum flow, at the horse power limit, for each pump that can be lined up to the tank. Consider the motors service factor (usually 1.15) when determining the horse power limit.

    For sources that are not pump driven, calculate the maximum flow for the flow limiting element. For control valves use the largest trim for the valve body and add the capacity of any bypass valves. An alternate to using the largest trim for a control valve, is to use the actual trim size and affix a metal tag to the valve indicating that a safety device rating is dependent on the trim size. The total inflow is the sum from all of these sources. The total inflow can be reduced if engineering judgment indicates that it is unlikely that all of the sources will be feeding into the tank simultaneously.

    b) Determine the maximum flow that the piping between the inlet manifold and tank can handle at the highest available pressure drop. The highest available pressure drop is the highest-pressure sources deadhead gauge pressure.

    For tanks that have multiple liquid inlets, each inlet can be considered independently using the flow calculated by method (a) or (b). Sum the flows for each inlet line to get the total for the tank.

    Once the total liquid inflow is determined, multiply the flow by the appropriate factor as per API-2000 based on the flash point and normal boiling point of the material stored. API-2000 has a logic error in the sections covering the selection of the factor (2.4.2.2.1 and 2.4.2.3.1). The selection criteria as presented in API-2000 is flash point below 100 oF or boiling point below 300 oF for the more conservative factor and flash point at or above 100 oF or boiling point at or above 300 oF for the less stringent factor. A fluid with a flashpoint of 113 oF and a normal boiling point of 271 oF will test true for both criteria. In cases such as this fluid, use the more conservative factor. In other words, replace the or in flash point at or above 100 oF or boiling point at or above 300 oF with an and.

    Test Factor, SCFH/GPM
    Flash Point below 100 oF or Boiling Point below 300 oF 17.14
    Flash Point at or above 100 oF and Boiling Point at or above 300 oF 8.57


    2. Liquid Movement Out

    Determine the Maximum flow, at the horse power limit, for each pump that can take suction from the tank. The total liquid outflow is the sum of all of these, including installed spare(s). Consider the motors service factor (usually 1.15) when determining the horse power limit.

    Once the total liquid outflow is calculated, multiply it by the API-2000 factor of 8 SCFH/GPM to determine the vent rate.


    3. Thermal Out Breathing

    Table 2A in API Standard 2000 (5th Edition, April 1998) is used to determine the thermal out breathing based on the capacity of the tank. For tanks less than 840,000 gal capacity, a factor can be used that is based on the flashpoint and normal boiling point of the material stored. API-2000 has the same logic error in Table 2 as discussed in Liquid Movement In above. The factors for tanks with a capacity up to 840,000 gal are presented below.

    Test Factor, SCFH/MGAL
    Flash Point below 100 oF or Boiling Point below 300 oF 23.81
    Flash Point at or above 100 oF and Boiling Point at or above 300 oF 14.29

    For tanks larger than 840,000 gal, refer to Table 2 in API-2000.


    4. Thermal In-Breathing

    Per API 2000. Table 2 in API-2000 is used to determine the thermal in breathing based on the capacity of the tank. For tanks less than 840,000 gal capacity, the factor is 23.81 SCFH / MGAL. For tanks larger than 840,000 gal, refer to Table 2 in API-2000.


    5. Fire Exposure

    Per API 2000


    6. Pressure Transfer Blow-through

    a) For tanks that are not expected to be unloaded into, the vapor rate is the flow capacity of two (2) 1 by 20 foot utility hoses with a pressure drop of the maximum nitrogen header gauge pressure. One 1 (3/4 ID) by 20 utility hose can pass 18,825 SCFH of nitrogen.

    b) For tanks where unloading is expected, use the greater of (a) above or the sum of one (1) 1 by 20 foot long utility hoses with a pressure drop of the maximum nitrogen header gauge pressure and the unloading line size with the pressure drop as the maximum gauge pressure rating of the shipping container to be used.


    7. The Nitrogen Padding System Feed Valve Fails Open

    Calculate the flow capacity of the flow limiting device using the maximum nitrogen header gauge pressure for the pressure drop. For padding systems that have a step down regulator, the step down regulator will almost always be the flow limiting device.


    8. Failure or loss of Control Heat Transfer Devices; loss of heating/cooling utility or instrument air.

    This contribution covers loss of heating, excessive heating, loss of cooling, or excessive cooling and must be determined on a tank by tank basis. These failures can be caused by failures in the control systems, measurement instruments, control valves, instrument air, and the loss of the heating or cooling utility.

    a) Loss of heating - determine the in breathing required if heating were lost. This will probably be a transient inflow until equilibrium is reached.

    b) Excessive heating - determine the out breathing required at full heating. The steam control valve usually limits this. This will probably be a continuous condition.

    c) Loss of Cooling - determine the out breathing required if cooling were lost. This could be a transient and continuous condition.

    d) Excessive Cooling - determine the required in breathing if the cooling were to fail to maximum. This will probably be a transient inflow until equilibrium is reached.


    9. Failure of Internal/External Heating/Cooling Coils

    This contribution covers a mechanical failure of a heat transfer device.

    a) For tanks with heating coils, determine the flow capacity of the flow-limiting device fully open. If the flow-limiting device is a control valve, use the largest trim available for the valve body. Also, add the capacity of any bypass valves. An alternate to using the largest trim for a control valve is to use the actual trim size and affix a metal tag to the valve indicating that a safety device rating is dependent on the trim size. Determine the vapor generated by vaporization of the product or by the steam itself - whichever is greater.

    b) For tanks with cooling coils, determine the flow capacity of any flow-limiting devices. If there are no flow-limiting devices perform a reasonable pipe pressure drop calculation, taking into consideration that the return line can potentially contribute to the inflow.


    10. Failure of Vent Vapor Collection System

    a) For vacuum relief, this pertains to any failure in a vapor collection system that can cause the system to pull excessive vapors from the tank. Calculate the flow capacity of the flow-limiting device. For systems that vent through a vacuum device that can pull down below the vacuum rating of the tank, calculate the vapor flow at the pressure where the capacity of the vacuum device equals the full open capacity of the vent valve. Use Atmospheric pressure for the upstream pressure of the vent valve. Do not take credit for pressure losses in the piping or any nitrogen from a padding system.

    b) For pressure relief, if the vacuum-producing device discharges into a header that can have a pressure higher than the pressure rating of the tank, the back flow case must be considered in the event of the failure of the vacuum-producing device. For this case calculate the capacity of the vent valve using the maximum anticipated vacuum producing device discharge header gauge pressure as the pressure drop. Do not take credit for check valves or piping losses.


    11. Chemical Reaction

    A chemical reaction in a tank can be caused by exposure to heat, incomplete reaction in a reactor, or by reaction of the tank contents with some contaminant.

    a) Thermal runaway reaction. This issue must be considered on a tank by tank basis. For tanks where the product decomposes before it reaches a normal boiling point, the runaway case is not considered since it would result in a relief device as large as the tank.

    b) A reaction can take place if two materials are contacted unintentionally. This issue must be considered on a tank by tank basis. The primary cause is due to water contamination as a result of the failure of a heat transfer device. Heat of mixing should also to be considered.

    c) This contribution covers the possibility of incomplete reaction in a reaction system. This issue must be considered on a tank by tank basis and will rarely need to be calculated.


    12. Steam Out

    This case covers the steaming out of a storage tank for tanks that are steamed out during normal product switchovers or for maintenance and inspection reasons. OSHA mandates, for good human safety reasons, that all vessels should be cleaned and purged free of any chemicals or substances hazardous to subsequent entry by humans. Steaming achieves a lot of the gross residual chemicals removal in a tank. However, in the process of steaming a tank out, a sudden rain shower may develop a dangerous situation where the internal steam is quickly condensed and the tank collapses due to a vacuum produced internally by the condensed steam. Proper nozzle sizes should be ensured for atmospheric air to enter the tank in that event such that sonic velocity is not achieved prior to breaking the vacuum. For tanks that are designed for a steam out case, a placard is to be affixed to the tank stating Vacuum Breakers are Sized for Steam Out.

    a) For tanks up to 20,000 gal the steam inflow rate is assumed to be one 3/4 ID hose by 20 ft long with a differential pressure is 40 psi gauge to atmospheric pressure. A material and energy balance must be done to determine the vacuum relief due to a hard sudden 40 oF rain.

    b) For 20,000 gal tanks up to and including 70,000 gal the steam inflow rate is assumed to be three parallel 3/4 ID hose by 20 ft long with a differential pressure is 40 psi gauge to atmospheric pressure. A material and energy balance must be done to determine the vacuum relief due to a hard, sudden 40 oF rain.

    c) For tanks larger than 70,000 gal, the steam inflow rate is assumed to be one 3/4 pipe by 50 ft long. The differential pressure is 250 psi gauge to atmospheric pressure. A material and energy balance must be done to determine the vacuum relief due to a hard, sudden 40 oF rain.

    Arts Note: This tank collapse (A.K.A. suck-in in the Texas Gulf Coast) has been personally witnessed by me and the results have also been seen out in the field. Some of the steam-out vacuum failures have resulted because of a proven lack of flow capacity in the tanks venting nozzle i.e., the nozzle reached a maximum sonic velocity capacity which was not enough for the scenario and the tank immediately sucked-in.

    My threads; real_chinner :


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  5. #3

    Re: Tank Relief Philosophy

    Dear all, the reasons are described very well but the API 2000 is issued in a newer version, 2009,

    [link Point to another website Only the registered members can access] which has more details, like isolated tanks, rules about inertization, and - biggest difference - much higher venting for vacuum case !
    The old formula are still incorporated as Annex, but this is mainly to not force the US oil industry to update thousands of tanks due to newer calculations !
    Hope this finds your interest,
    explosion


  6. #4

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