Integrity Operating Windows (IOW) and Design Operating Windows (DOW) are industry terms that relate to the operating limits of process equipment. These are the important limits within which this equipment can be safely operated without the risk of harming its physical integrity (IOW) or resulting in its complete failure (DOW). An IOW plan should be established for each piece of process equipment using the API publication API RP 584 as a guideline.
You can think of IOW and DOW as two concentric shapes placed on a grid of temperature, pressure, acidity, vibration, liquid level, or any other measurable quantity. Operating within the IOW limits maintains the integrity of the process equipment, and insures the expected lifespan of the equipment will be met.
Excursions outside of the IOW, but inside of the DOW, can shorten the expected lifespan resulting in higher maintenance costs. The operator, if properly notified, has the opportunity to bring the system back within the IOW before serious damage can occur.
Excursions outside of both the IOW and DOW can result in immediate and catastrophic failure. Often there is very little time for an operator to correct this situation before serious damage occurs.
Being aware of the IOW and DOW in a process facility and managing the process conditions to remain within these limits is important for maintaining the integrity of the equipment, the efficiency of the process and the safety of the workers. This is why the Universal Tag Locator (UTL) software solution from AIS is used at process facilities around the world. UTL provides IOW/DOW and alarm reports across multiple instrumented systems within a single facility.