(149b) Plant Equipment Overdesign | AIChE

(149b) Plant Equipment Overdesign


Many Engineers overdesign plant equipment, valves and pipes  to account for uncertainty even though they have designed the same equipment a hundred times. An acceptable and encouraging name is given to the overdesign factor for example, safety margin or design factor. It starts with the proponent (operating company), through the design contractor and finally the vendor.  It is the mentality of, “the bigger the better.” If it is oversized, it will work. However, if it is undersized, it will not work and everyone will hear about it and it will be a lesson learned to everyone.

One of the main reasons for overdesign factor is attributed to the lack of clear guidelines and instruction from the proponent to take responsibility of not adding this factor.

The design factor increases the operating costs and consequently reduces the plant profitability. It also affects the plant safety. Liquid hammering in the plant could be attributed to pipes overdesign.

 In this paper we will discuss the reasons for adding an overdesign factor and the consequences of overdesigning the plant equipment, pipes and valves with real life case studies. Oversizing the crude charge pump in one of the Gas Oil Separating Plant (GOSP) will be discussed in details. The oversizing did not only waste energy, but it also  interrupted the plant operation and caused the continuous opening of off-spec valves.