Inspectioneering Journal

The Importance of Integrity Operating Windows in the Process Safety of Pressure Equipment

By John Reynolds, Principal Consultant at Intertek. This article appears in the March/April 2005 issue of Inspectioneering Journal.


One of the more important uses of the “99 Diseases of Hydrocarbon Process Equipment”(1) is to determine how to safely operate process pressure equipment. Such a work process thereby minimizes the impact of any potential degradation mechanisms (the 99 Diseases), by establishing the appropriate boundaries for long and short-term safe process operation. Such boundaries are called

Integrity Operating Windows (IOW’s)

Process Safety Management (PSM) is a many faceted program, involving mechanical integrity assurance, management of change, operator training and procedures, process hazards analysis, along with numerous other elements of a comprehensive process safety-quality management system. This article zeros in on one vital aspect of the mechanical integrity aspect of PSM, that is, the creation and implementation of integrity operating windows (IOW’s) for static pressure equipment.

In earlier years, some groups of operating windows were largely established to simply control the process, meet business premises and produce quality hydrocarbon products. Subsequently, integrity operating windows started to play a larger role in establishing operating windows for safe, environmentally sound process control.

In The Beginning....

Soon after the turn of the millennium, Shell US refining sites implemented ten process safety initiatives designed to increase process safety by implementing common work process systems across all of its operating facilities. Four of those initiatives facilitated the improvement of the integrity operating windows (IOW’s) in Shell’s US refining system. These initiatives included:

  • A Pressure Equipment Integrity Initiative, where IOW’s are created;
  • A Monitor and Control Conditions Initiative, where IOW’s are implemented and monitored;
  • A Management of Change Initiative, which is the process in which any changes needed for IOW’s are systematically controlled; and the
  • An Operator Training Initiative, which is the process by which IOW knowledge is transferred to operators that need to know about IOW’s.

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