Bursting disc sizing

The corresponding relief diameter is 0.059 m, and the next largest pipe size of 0.075 m would be chosen. 

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Bursting discs and relief valves are proprietary items and the vendors should be consulted when selecting suitable types and sizes. 

Pressure relief of a runaway reaction is likely to be via a bursting disc or a safety valve, or a combination of both these items. Further information about these is given in Chapter 9. For relief system sizing, it is important to know the pressure at which a relief device will open. 

Within this Workbook, the maximum pressure required to fully open the pressure relief device will be referred to as the "relief pressure". (Caution some papers on relief sizing refer to "set pressure" but mean "relief pressure"). For a bursting disc, the relief pressure will be the maximum specified bursting pressure and for a safety valve, it will be the set pressure plus 10% overpressure (or whatever percentage overpressure the valve has been certified at). 

The problem is to evaluate the relief size required. Relief is to be via a bursting disc system with an overall length of 12 metres and two 90° bends with a velocity head... 

It is required to size a bursting disc system with a maximum specified bursting pressure of 2.2 barg (3.2 bara) for a reactor of volume 1.5 m3 and design pressure 3 barg (maximum accumulated pressure = 4.3 bara). The frictional resistance of the bursting disc system in this case is equivalent to 4fL/D = 5. The worst case reaction has been identified as a tempered hybrid, and an open system calorimetric test has demonstrated that it will continue to temper until the reaction is complete. For the worst case reaction, the mass in the reactor would be 860 kg. 

The version of the ERM given. by equation (9.4) is used in Fauske s relief sizing method (see A5.3), together with a correction factor for friction if relief is via a bursting disc. Such correction factors are discussed further in 9.6.1. 

Provision should also be made to minimise solids build-up under a bursting disc. If the solid may be present due to freezing, then heat tracing may be a solution. In other cases, it may be beneficial to take the relief system off a liquid inlet nozzle (of suitable size) so that the nozzle is washed clean of solids by the liquid. 

For, single-phase relief, the required relief system size is not affected by whether relief is via a safety valve or a bursting disc. 

However, for tempered systems, relief via a bursting disc may give rise to two-phase relief due to flashing as the reactor depressurises. Although this does not affect the sizing of the relief system, it does increase the mass loss from the reactor and has implications for the disposal system design. Use of a safety valve, rather than a bursting disc, can prevent this. 

A reaction has been characterised as a tempered hybrid system and it has been determined that the system will relieve single-phase gas/, vapour. Relief sizes for both a safety valve and a bursting disc system are required. The reactor contains a charge of 3000 kg. Data for relief sizing have been compiled in Table A6.2. -The type of safety valve selected has a de-rated discharge coefficient under BS 6759131 of 0.87. 

The final safety requirement is a relief line with a relief valve protected by a bursting disc. This disc must be sized according to the Australian Standard AS1 210. 

Pressure bursting discs may rupture, tail gas release, h) Ensure correct sizing on pressure relief... 

Safety features for the tank include a pressure relief-valve system on the tank roof, to be opened when draining or adding to the tank contents. A bursting disc system also allows for pressure release in the event of pressure build-up. Amanhole providesaccessto the tank for internal maintenance. The product inlet line is standard nominal pipe size 1.5, schedule number 40S. This inlet is sized for the maximum production flowrates. The product outlet line is of standard nominal pipe size 6, schedule number 120. This line is sized such that a standard-size road tanker may be filled in 15 minutes. 

Inlet line Nominal pipe size 1.5. schedule number 40S Outlet line Nominal pipe size 6, schedule number 120 Manhole, bursting disc, pressure relief valve on roof No insulation... 

All European valves professionals and organizations are recommended to use tables 6-9 (in Annex II of the Directive), which relate to pressure and size DN (maximum Category III). Safety accessories, however (such as SRVs, CSPRS, bursting disc safety devices, pressure/temperature switches, SRMCR devices, etc.), are classified in Category IV. 

The increased size of components when an expansion tank is present gives the designer some incentive to offset these effects. The use of bursting discs or balanced... 

The minimum net flow area is the calculated net area after a complete burst of the disc with appropriate allowance for any structural or support members that may reduce the net flow area through the rupture disc device. The net flow area for sizing purposes should not exceed the nominal pipe size area of the rupture disc device. 

Rupture discs are typically manufactured to order, where each order represents a lot. The ASME Code defines three mediods of acceptance testing for rupture discs. The most common method requires dial at least two discs from the lot be burst tested at the specified disc temperature. The results of these tests must fall within the rupture tolerance. Table 12-5 shows the changes between the old requirements and the new sizing methodology and certification process. 

Worst-case analysis based on the DSC data, namely, the test with the lowest onset temperature, resulted in a graph showing the relationship between initial temperature and time-to-maximum rate under adiabatic conditions. For an initial temperature of 170°C, it would take 2 hours to reach the maximum rate. Venting simulation tests were undertaken on a larger scale to detect safe venting requirements for the separator and for the MNB hold tank. Several vent sizes were tested. It was found that a 10-cm rupture disc with a burst pressure 1 bar above the operating pressure was adequate. 

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