Rupture discs

Rupture discs on pressure relieve valves and plugs in open ended valves can reduce fugitive emissions. 

A rupture disc may also be used in some cases for proteetion against internal explosion overpressure. However, this is a matter of special design and the appropriate safety group should be consulted. 

Flare staging control valves and rupture discs,... 

An important application of a rupture disc device is at the inlet of a pressure relief valve. The sizing of the pressure relief valve or rupture disc device combination requires that the pressure relief valve first be sized to meet the required relieving capacity. The normal size of the rupture disc device installed at the inlet of the pressure relief valve must be equal to or greater than the nominal size of the inlet connection of the valve to permit sufficient flow capacity and valve performance. The failure modes of rupture discs are [40] ... 

Rupture discs should be removed from service at predetermined intervals for visual inspection. Depending on the condition of the disc and recommendations by the manufacturers, they are either replaced or returned to service. The most common mode of failure is case (c), premature rupture below the minimum bursting pressure. An analysis of this mode of failure indicates that this can be the result of ... 

Incorrect specification of the disc. This includes overlooking intermittent vacuum conditions and other pressure/temperature transients, failure to predict corrosion, or operating at a pressure too close to the rupture disc pressure, resulting in fatigue failure. 

The following provide rupture disc terminology definitions ... 

A rupture disc device is a non-reclosing pressure relief device actuated by inlet static pressure and designed to function by the bursting of a pressure containing disc. 

A rupture disc is the pressure containing and pressure sensitive element of a rupture disc device. 

A rupture disc holder is the structure that encloses and clamps the rupture disc in position. 

The manufacturing design range is a range of pressure within which the marked burst pressure must fail to be acceptable for a particular requirement as agreed upon between the rupture disc manufacturer and the user or his agent. 

The specified disc temperature supplied to the rupture disc manufacturer is the temperature of the disc when the disc is expected to burst. 

A batch of rupture discs are those discs manufacmred of a material at the same time and the same size, thickness, type, heat, and manufacturing process including heat treatment. 

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. 

The coefficient of discharge method (Kj = 0.62) was specified to calculate the capacity of the rupture disc device. However, the validity of this method is limited to a disc mounted close to the pressure vessel and the discharging to atmosphere. The ASME Code provides guidance for the limited use of this method ... 

The resistance to flow method (K[ ), which has been employed by industry for years, has now been adopted by the ASME Code for rupture disc. Sizing is performed on a relief system basis and not by capacity of individual components. The key elements of tills metliod are ... 

The rupture disc is treated as another component in the relief system that provides some resistance to flow. 

Certified resistance factors can be provided by the rupture disc manufacturer for each disc model. 

Significant changes by the ASME Code have been employed that now have direct impact on the use of rupture disc devices. The change to the Code affecting rupture disc manufacturers is the application of the UD Code symbol to rupture discs that meet the requirements of the ASME Code. Authorization to use the UD stamp is based on an audit by an ASME representative of various manufacturing, testing. 

The ASME Code provides requirements for rupture disc performance. The rupture tolerance at the specified disc temperature should not exceed 2 psi for marked pressure up to and including 40 psi and 5% for marked burst pressures above 40 psi. 

The rupture disc must be marked at a pressure within the manufacturing range. The manufacturing ranges available are defined in the product literature for each rupture disc model. 

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. 

Possible vaporizer rupture with further release and blast enecls, worker injured by blast or scalded. Relief valves, rupture discs 3c ... 

Local rapid flashing, rupture disc/relief valve inadvertently open, release to stack Stack height designed to dissipate release 4 ... 

Parallel to the frequency assessment, the consequences of the scenarios were calculated for the effects on the public and plant personnel of chemical release through the rupture disc and fire and explosion. 

These are thin diaphragms held between flanges and calibrated to burst at a specified static inlet pressure. Unlike relief valves, rupture discs cannot reseal when the pressure declines. Once the disc ruptures, any flow into the vessel will exit through the disc, and the disc must be replaced before the pressure vessel can be placed back in service. Rupture discs are manufactured in a variety of materials and with various coatings for concision resistance. 

Rupture discs may be used alone, but they are normally used as a backup to a relief valve set to relieve at approximately 115% MAWR This ensures that the disc ruptures only if the relief valve fails or in the unlikely event that the pressure rises above 110% MAWP and the relief valve does not have enough capacity. 

Rupture discs are also used below relief valves to protect them from corrosion due to ves.sel fluids. The rupture disc bursts first and the relief valve immediately opens. The relief valve reseals, limiting flow when the pressure declines. When this configuration is used, it is necessary to monitor the pressure in the space between the rupture disk and the relief valve, either with a pressure indicator or a high pressure switch. Othei-wise, if a pinhole leak develops in the rupture disk, the pressure would equalize on both sides, and the rupture disk would not rupture at its set pressure because it works on differential pressure. 

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