Operating Limits (Operating windows) and IOWs ?

In order to operate any process unit, a set of operating ranges and

limits needs to be established for key process variables, to achieve the

desired results (i.e. product within specification, safe operation, reliability,

etc.).  These limits are generally called operating limits (windows) or

operating envelopes.   

However, IOW’s are a specific subset of these key operating limits that

focus only on maintaining the integrity or reliability of process

equipment. 

Integrity operating windows (IOWs) are those preset limits on process

variables that need to be established and implemented in order to prevent

potential breaches of containment that might occur as a result of not

controlling the process sufficiently to avoid unexpected or unplanned

deterioration or damage to pressure equipment.    

Typically IOW’s address issues that involve process variables that, when not

adequately monitored or controlled, can impact the likelihood and rates of

damage mechanisms, which may result in a loss of containment which is an

incident not acceptable in any process industry.