An unexpected or unwanted failure in industrial processes – due to the stored energy – creates high risks for personnel and potentially for the public. Additionally, the uncontrolled loss of a containment may affect return on investment and the efficiency of the processing plant.
Legislative standards apply where strict demonstration of compliance with mandatory requirements are provided, prior to allowing the equipment to be put in service. There are certified design and manufacturing standards that need to be met. These include: stress resistance under operating pressures and at operating temperatures, selection and qualification of applied materials of construction as well all applied methods of manufacturing (such as welding). To provide the required minimum level of quality of products, components and workmanships specific (destructive and/or non-destructive) test methods are defined.
Traditionally, as a final step often specified in legislative construction codes, it is common to apply a test pressure (either hydraulic or pneumatic) to the equipment. This is especially important where individual subcomponents are assembled into a unique assembly.
Industry recognized global standards will accept pressure testing, where a test pressure higher than the intended working pressure needs to be applied and further leakage of equipment must be avoided. Pressure testing is however considered as a high-risk activity. There are risks associated with the use of compressible media (gas or air), as high energy will be stored, safe handling needs to be ensured.
When applying stored energy to an assembly, especially where it exceeds the intended maximum working pressure, there is potential for a sudden unintended or premature release of pressure while people are in a dangerous zone. The amount of stored energy is directly related to the test media: a liquid (typically water) is virtually non-compressible whereas gases will compress under pressure. As a result, the stored energy when testing with a compressible media – e.g. in the case of pneumatic testing – will be considerably high as will the hazards. For this reason, all testing is preferably executed with (non-compressible) liquids and the volume of pressurized fluid used should be minimized.
The sudden unintended release of pressure can cause:
- Test equipment to rupture, creating flying debris
- Failure of individual components, creating missiles
- Test hose connection failure resulting in hose whips (striking people or other equipment)
- Sudden uncontrolled discharge of test media causing injuries
Therefore, under all conditions, the necessary caution and procedures need to be applied to avoid the occurrence of such sudden release of pressure. Special attention is required when periodic testing of the equipment is scheduled. All equipment should undergo regular inspection and potentially pressure tested to assure their fit-for-purpose level after some time in service. Where inspection methods applied result in the potential of stored energy, the use of suitable pressure relief devices is required.
The use of simple, highly reliable pressure relief devices which cannot be tampered with will provide best long-term safety to people, investments and the environment. Rupture (or bursting) disc devices have a long-standing reputation to offer uncompromised safety against hazardous pressures in all industrial environments. They do not require specific maintenance or external energy to operate making them highly preferred by most designers and users.