Protective Process Safety Interlocks at a DuPont Plant

Protective Process Safety Interlocks at a DuPont Plant 

The Sabine River Works of the DuPont Company Plant in Orange, Texas, shared their process interlock classification and test program in 1988. [26] At that time, this large DuPont chemical complex employed about 2,500 individuals and consists of large singletrain processing units. Most of the units are continuous processes for the manufacture of olefins, polyolefins, and chemical intermediates for nylon. 

Process materials range from mild-mannered substances such as water and air to highly-toxic chemicals and very large inventories of hydrocarbons. Process temperatures were reported to range from —180° F (—118° C) to 1,000° F (540° C). Process pressures were reported to range between a low vacuum and over 30,000 psig (207 MKa). [26] 

The DuPont Sabine River Works had reported between 35,000 and 40,000 instrument installations and more than 5,000 safety interlocks and alarms in 1988. The interlocks and alarms are divided into two classifications the operator aid is used to alert the operator of a nonhazardous abnormal condition that might otherwise be undetected the safety interlock or alarm refers to any equipment whose proper functioning is essential to prevent or signal hazardous process conditions that may threaten personnel or equipment. [26] 

DuPont s Sabine River Works experience shows that it is crucial to segregate the more critical interlocks from the others. A few well-understood, respected interlocks are said to be better than an overwhelming number of interlocks with the critical ones scattered amongst the others. DuPont s system allows a range of required authorizations. At DuPont, a supervisor may bypass less critical interlocks such as lubrication alarms for up to 24 hours for testing and repairs, but some of the more critical alarms may not be bypassed by anyone. 

Testing Safety Critical Process Instruments at a DuPont Plant 

Interlock testing is performed on a periodic basis, usually every 12 months, following detailed written test procedures. The test procedure for each safety interlock defines the actions, including the approval system and the mechanical work required to ensure reliability. These procedures cover the testing activity from the process measurement dc ice to the final element, which is often a control valve. [26] 

Due in part to the complexity of the instrument systems, there are two first-to-final testing methods. These methods are labeled actual tests and simulated tests.  

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Protective process safety interlocks at a DuPont plant... 

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