Rupture discs general

There are two general categories of relief devices (spring-operated and rupture discs) and two major types of spring-operated valves (conventional and balanced-bellows), as illustrated in Figure 8-7. 

Rupture disc provided for decontamination pit failed once due to aging and degradation and was replaced. Generally the decontamination experience in the plant has been satisfactory. 

Larger capacity storage vessels are basically the same double-walled containers, but the evacuated space is generally filled with powdered or layered insulated material. For economic reasons, the containers are usually cylindrical with dished ends, approximating the shape of a sphere, which would be expensive to build. Containers must be constructed to withstand the weights and pressures that will be encountered and adequately vented to permit the escape of evaporated gas. Containers also should be equipped with rupture discs on both inner and outer vessels to release pressure if the safety relief valves should fail. 

PTFE is resistant to liquid chlorine and to both wet and dry chlorine gas up to 200°C. Tantalum, Hastelloy C, PTFE, PVDF, Monel, and nickel are recommended for membranes, rupture discs, and bellows. The materials of construction for heat exchangers and tanks are generally titanium or Ti-clad, rubber-lined carbon steel, PTFE-lined carbon steel to handle wet chlorine gas or aqueous solutions containing chlorine. 

The nature of any safety devices employed can also play a role with respect to uncertainty in the case of a pressure ashing system. For example, serious losses may be incurred if sample constituents are entrained during a pressure blow-off. With an irreversible safety device like a rupture disc such a problem may be immediately apparent, but the activation of a reversible device like a valve generally cannot be documented even though major losses may be excluded by auto-... 

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