integrity operating windows

Integrity Operating Windows

“… a typical RBI assessment program is particularly ineffective in reducing risk … in the absence of expert input.”

Corrosion-control documents (CCD) are essential inputs into effective mechanical integrity programs and risk-based inspection programs. They are particularly useful for capturing in one document the essential elements of a chemical or refining process that influences corrosion, i.e. materials of construction, process-stream chemistry, operating conditions and damage mechanisms.

The Hendrix Group Inc. has been providing corrosion consulting, corrosion prevention, and corrosion-control services for more than 35 years. Our objectives are:

  • to provide a high quality of service at a reasonable price
  • to develop practical solutions to clients' corrosion problems
  • to work with our clients as a team.
  • The Hendrix Group offers proven expertise in developing corrosion-control documents for specific industry applications.

    Variations of corrosion-control documentsCorrosion-control documents have been referred to by different acronyms, including Material Operating Envelopes (MOEs); Critical Process Variables (CPVs); Corrosion Manuals; Corrosion Control Documents, Corrosion Circuits, Corrosion Reports, Corrosion Loops, etc. They can be combined in a risk-based inspection program implementation or can be stand-alone documents.

    Why corrosion-control documents are important

    Semi-quantitative, risk-based inspection assessments and the various RBI software tools are very useful for capturing and presenting large amounts of equipment data, for facilitating the structured assignment of risk to equipment, and for setting inspection intervals. However, RBI programs and software are not particularly useful for identifying the damage mechanisms in a unit and do not address upset or startup/shutdown damage mechanisms at all. In fact, one could argue that a typical RBI assessment program is particularly ineffective in reducing risk - and largely a poor use of personnel and money - in the absence of expert input into a unit’s damage mechanism and where those mechanisms are likely to exist.

    Download our CCD Presentation from the API Inspection Summit

    Download the CCD presentation from the 2011 API Inspection Summit and Expo (PDF).

    Corrosion-control document contents

    A corrosion control document:

    • Describes the unit process
    • Provides rationale for materials of construction
    • Defines corrosion circuits
    • Defines damage mechanisms in each circuit:
    • Includes critical locations
    • Includes integrity operating windows
    • Provides start up, shut down and upset operation influences
    • Includes predicted (or actual) corrosion rates and environmental cracking tendencies

     Uses of corrosion-control documents

    CCD’s have several uses including:

    • A training tool for new materials and corrosion engineers and unit inspectors
    • TML and CML placement tool
    • Input into RBI inspection programs
    • Inspection Planning
    • Optimizing inspection techniques
    • Establish integrity operating windows
    • The essential information for an individual corrosion circuit is typically summarized in a tabular, easy to understand format (PDF).

    Integrity operating windows (IOW’s) and CCD’s

    As an essential component of a CCD, Integrity operating windows (IOW’s) are gaining recognition as a valuable input into a corrosion control document. What are IOWs? The American Petroleum Institute (API) has a new recommended practice in the ballot stage (API RP 584) that discuss the need to establish operating limits that address the controls necessary for process variables that might affect the integrity or reliability of the process unit. An example of an IOW is the establishment of furnace tube temperature limits to avoid premature rupture. At some established limit, say 800F, a furnace tube designed for 775 F would have a shortened service life, so operators would understand the need to maintain control of furnace firing to remain below the 775F limit. That limit of 775F would be an IOW limit for the furnace tubes.

    The Hendrix Group has developed corrosion-control documents for the following processes:

    • Diesel Hydrotreater units (DHT)
    • Naphtha Hydrotreater units (NHT)
    • FCC Naphtha Hydrotreater (CDTECH)
    • CBI/Lummus Delayed Coker
    • Saturation gas units (SAT)
    • Gasoline Stabilization Units
    • Natural gas plants
    • Fluid Catalytic Cracking units (FCC)
    • Gas Concentration Units (GCU)
    • Merox units
    • Mericham NAPFINING unit
    • Sulfur Recovery Units (SRU)
    • Sour Water Stripper units (SWS)
    • Syngas/PSA Hydrogen units
    • CO boiler
    • Amine units
    • Methanol unit
    • Acetic acid unit
    • Vinyl acetate monomer unit

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Related Downloads

CCD Presentation

Download the CCD presentation from the 2011 API Inspection Summit and Expo (PDF).


The safe operation of oil refineries in the United States is under constant more
When: January 30, 2017 - February 2, 2017 Where: Galveston Island more

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