Updated May 27th, 2020

By: Fred Addington, Principal of Corrosion Technology, Pinnacle

Integrity Operating Windows (IOWs) are limits and ranges placed on key process variables (i.e. temperature, pressure, velocity and process stream constituents), designed to ensure equipment integrity and maintain safe operations. Put simply, IOWs provide parameters in which assets can operate within, in order to 1) create predictable reliability, 2) avoid loss of containment / unplanned failures, and 3) achieve desired product quality.

The American Petroleum Institute (API) Recommended Practice 584 defines Integrity Operating Windows as “established limits for process variables that can affect the integrity of equipment if the process operation deviates from the established limits for a predetermined amount of time.”

While using predictive damage models aid in the development of a robust asset integrity program, variable processes or operating conditions (i.e. fluctuating contaminant levels, temperatures, pressures, etc.) have the potential to introduce new damage mechanisms or accelerate predicted damage mechanisms. Thus, operating outside of IOWs can lead to otherwise avoidable degradation and/or failure. While operations should remain flexible in operating the unit to meet production goals, operating outside of the inspection department’s prescriptions can result in unpredictable asset performance and lead to unplanned loss-of-containment scenarios.

Overall, IOWs are:

  • Operating parameters that are both measurable and controllable.
  • Values related to integrity risks.
  • Boundaries that require an action.

Where do IOWs come from?

By identifying potential damage mechanisms and identifying critical integrity process variables across a unit, you can determine acceptable upper and lower operating thresholds to establish your IOWs. Some equipment and process variables that are useful in determining IOWs are listed below (see Figure 1).


Max Operating Pressure

Max Design Temperature

Minimum Thickness

Minimum Allowable Operating Temperature



Boiling Range

Operating Pressure

Operating Temperature

Production Rate


Water Conservation



Water Pressure Temperature

Shear Stress



Corrosion Inhibitors

How do you find them?

Mechanical Design Limits

  • Maximum Operating Pressure
  • Maximum Operating Temperature

Material Properties

  • Corrosion Environment – derived from process stream qualities
  • Mechanical Environment – shear stress, pressure, vibration, etc.

Unit Control Parameters

  • Reaction Control – exothermic, freeze points, etc.
  • Phase Control – condensation, salt formation, etc.

This information can be gathered from both experienced operators and from stored information, as found in the following sources:

  • Unit corrosion review
  • Unit operations manual
  • Equipment code documentation
  • Unit design information
  • Inspection record
  • Company engineering standards

Establishing the IOWs

When you begin establishing IOWs for your facility, it is imperative to complete each of the following steps:

  • Associate each limit with the plant and system to which it applies.
  • Identify parameter and monitoring location for each limit.
  • Record the value and urgency for each limit.
  • Capture the consequence and justification for each limit.
  • Determine the communication plan for each limit based on urgency.
  • Create response actions for operations.

Challenges you may face when establishing IOWs

As with most initiatives, you should be prepared to face some obstacles when working to establish IOWs at your facility. Common issues include:

Data quality and availability:

If data is poorly managed, you may discover outdated and/or missing information. Additionally, some data may be available electronically, while other data is kept in a hard-copy format. This is why keeping your data clean  is so important.

Availability of experienced personnel:

You will need seasoned operators that have the knowledge, experience, and insight to help develop your IOWS. However, availability for experienced personnel is likely limited due to conflicting priorities. And although the experienced personnel in your facility may be difficult to obtain, the fresh operating staff will simply not have the experience necessary to properly assist in your IOW development. This service can be provided through corporate technology experts or contract specialists.

Misalignment of organizational initiatives:

Initiatives across organizations are often uncoordinated, and misaligned aspects such as corporate risk strategy, business drivers, and system technical requirements may exist. Only facility management can determine the priority of strategic workforce assignments. This support is critical.

The value of IOWs

Although you may face some hurdles, establishing and implementing IOWs can provide significant value to your organization. Established IOWs will help your facility:

Establishing and operating within IOWs, in which damage rates are known and predictable, will help your organization maintain valid assumptions for inspection.Create predictable reliability.

  • By operating within your identified parameters, you will be equipped to predict and control for acceptable damage rates (as there is no such thing a zero corrosion). The ability to predict your damage rates thus enables proactive and strategic repair or replacement—helping your facility avoid unplanned failures and reducing costs associated with reactive maintenance.
  • Establishing and operating within IOWs, in which damage rates are known and predictable, will also help your organization maintain valid assumptions for inspection.

Avoid loss of containment (failure is not an option).

Again, by predicting and controlling for acceptable damage rates through IOWs, you will avoid loss of containment scenarios, thus having a positive impact on:

  • Reduced risk to personnel.
  • Reduced impact on the environment.
  • Reputation of organization.

Produce desirable quality.

  • Managing the process variables through IOWs will allow you to have more control over product specification, helping you to produce quality product(s) on par with your standards.
  • Along with increased product quality, maximum throughput is also achievable through proactive maintenance and increased asset reliability.

With more than 25 years in the industry, Fred Addington serves in the role of Principal of Corrosion Technology within Pinnacle Advanced Reliability Technologies’ (PinnacleTM) Engineering Department. As Pinnacle’s foremost corrosion subject matter expert, Fred is responsible for training, advising and disseminating technical knowledge to Pinnacle’s project teams, and developing efficient management processes so team members can deliver quality services and solutions to clients.

Fred’s expertise includes his understanding of processes and equipment in the area of corrosion control and material selection in the upstream and downstream oil and gas, water and petrochemical industries. Specifically, his knowledge includes corrosion and metallurgical analysis, corrosion control and monitoring, material selection, hydrogen permeation technology and mechanical integrity.

He is a member of the National Association of Corrosion Engineers (NACE) and has held various chair positions on technical committees. In addition, he has published multiple papers for NACE on topics including “Aggressive Corrosion of 316 Stainless Steel in an Amine Unit” and “Hydrogen Permeation Application to Crude Unit Overhead Corrosion Monitoring.”

After serving in the United States Navy, Fred went on to graduate from the University of Texas at El Paso with a Bachelor of Science degree in Metallurgical Engineering.