Overpressure protection plant design

Now let us consider utility failure as a cause of overpressure. Failure of the utility supphes (e.g., electric power, cooling water, steam, instrument air or instrument power, or fuel) to refinery plant facihties wiU in many instances result in emergency conditions with potential for overpressuring equipment. Although utility supply systems are designed for reliability by the appropriate selection of multiple generation and distribution systems, spare equipment, backup systems, etc., the possibility of failure still remains. Possible failure mechanisms of each utility must, therefore, be examined and evaluated to determine the associated requirements for overpressure protection. The basic rules for these considerations are as follows ... 

The European standard EN 12186 (formerly the DIN G491) and more specific the EN 14382 (formerly DIN 3381) has been used for the past decades in (mechanically) instrumented overpressure protection systems. These standards prescribe the requirements for the overpressure protection systems, and their components, in gas plants. Not only the response time and accuracy of the loop but also safety factors for oversizing of the actuator of the final element are dictated by these standards. Independent design verification and testing to prove compliance to the EN 14382 standard is mandatory. Therefore, the users often refer to this standard for HIPPS design. 

Overpressure accidents can not only damage equipment but also cause injury or even death to plant personnel. In order to reduce the potential number of incidents or accidents, it is the job of the process engineer to analyse the process design and to determine the what can go wrong scenarios and either find a way to design out of them or provide protection against catastrophic failure in the event an accident does occur, that is, install an SRV and/or rupture disc. 

When utility lines are connected to process lines or equipment, there is a danger of backflow of process material into the utility system and a danger of overpressurization of one system by the other. All connections of this kind require careful study during design and hazard analysis. Many plants review similar connections as a group and develop standard details. This standardization can include formal requirements for the number of layers of protection for each group. 

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