Abstract

Operating plants can be as old as 40 years and are always updated in time with the possible introduction of additional equipment and/or treatment facilities. In addition, plants could also be updated in order to accommodate the additional production of nearby gas discoveries that can be tied-in over the years and the consequently modify the operating conditions caused by the simultaneous depletion of older wells.

All these modifications may lead to significant changes to the plant from its original greenfield design configuration and operating conditions.

Whilst it is assumed that the new installations and/or modifications are carried out in accordance with the best industry and engineering practices and standards, it may not be so obvious that the operation of the overall plant in such new conditions is still sound. Thus, a structured Overall Process Hazardous Assessment (OPHA) of the systems shall be carried out for this purpose.

As first step, an updated plant as-built documentation package shall be prepared, if needed, to incorporate all the plant modifications occurred during the previous years.

As second step, the complete set of safety studies (FERA, blowdown, etc.) shall be updated to reflect the new conditions and assess the status of the physical barriers in place.

Finally, a Hazardous Operation (HAZOP) review shall be carried out to assess the status of the updated plant in the new operating conditions.

Being relevant to an operating plant, the management of the outcomes of the HAZOP review is particularly complex and challenging, as it may imply capital expenditure, interventions in already congested areas and/or, most importantly, potential production loss. The possible unavailability of data in such old assets designed and built in the paper era and the co-existence of equipment designed, built and installed in accordance with an evolving set of codes and standards are additional factors contributing to increase the complexity.

This paper provides insights about the documentation required as input for the activity and it focuses on the most common outcomes of the OPHA, addressing how to handle and eventually close them, minimising plant shutdown without compromising on safety.

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