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Overview of Furnace Tubes

Furnaces are critical pieces of equipment that can have a major impact on process unit safety, reliability, and economics. Therefore, Furnace Tube inspection and maintenance are essential activities for effective asset integrity management at any refinery or petrochemical plant.

Furnace tube life and integrity are impacted by several degradation mechanisms depending on the type of service, operating conditions, and the material of construction. In most cases, creep is the mechanism of major concern, especially in areas of heavy coking. However, tube failures are usually associated with a combination of multiple mechanisms, including carburization, oxidation, sulfidation, erosion, low toughness, and sigma phase formation. This last mechanism specifically affects austenitic stainless steel tubes.

Mechanical integrity personnel, including unit inspectors, site inspection authorities, reliability, fixed equipment, and material/corrosion engineers, are responsible for the reliable operation of furnace tubes. Below are some recommendations for inspectors and engineering practitioners to follow as part of their tube inspection/assessment program covering all site furnaces.

  • Gather representative inspection data to set variables impacting remaining life calculations, such as corrosion rates, diametral growth, and time increment during analysis.
  • Perform on-stream monitoring, including routine visual inspection; looking for sagging, flame impingement, broken or missing hangers, broken tubesheets, etc.
  • Perform infrared surveys (IR) based on furnace history and operation, and set intervals using inspection history and engineering assessment. Schedule a survey before each major shutdown.
  • During turnarounds, regardless of tube metallurgy type, perform thorough thickness measurements and bulging checks (visual, lamping, strapping, and/or advance crawlers), especially at locations where IR indicates elevated temperatures. Use a magnet as a quick screen to check for carburization of stainless steel and Incoloy 800/800HT tubes. Use radiograph inspection to check for localized damage from erosion in return bends and outlets. Perform inspections in furnaces tubes of ferritic-to-austenitic dissimilar welds.
  • Become familiar with furnace design and construction, understanding their effects on tube integrity and life span.
  • Identify life limiting degradation mechanisms that might be contributing to shorter tube life.
  • Determine and set reasonable operating limits for heater tube metal temperatures (determination should consider creep, as well as other damage mechanisms such as sulfidation, carburization, embrittlement, etc.).
  • Complete remaining life assessment baseline and readdress whenever thermocouple readings or IR results consistently approach or exceed those limits. Assessment should be considered at least every turnaround interval. Define representative operating conditions for the tubes, which should include past, present, and future expected values of temperature, pressure, and other loads.
  • Select proper material creep strength and ductility information to perform remaining life assessments; use of industry data or literature might not be always the right option, and when it is, it might provide conservative or non-conservative results. Extract samples and perform metallurgical evaluation and mechanical testing when possible.
  • Set a strain limit for sample removal (mechanical testing and metallographic evaluation) and retirement. Consider tube samples and/or advanced NDE on critical furnaces to check for degradation after 10-15 years in service.
  • Keep records of all inspections, modifications, changes, repairs, evaluations, testing, and engineering assessments done.

 

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Articles about Furnace Tubes
  • May/June 2018 Inspectioneering Journal
    By Nayef Alanazi at Saudi Aramco R&D Center, and Muthukumar Nagu at Saudi Aramco R&D Center

    This article presents a case study from a Middle Eastern refinery that explores a heat exchanger that failed unexpectedly after five years in service. There are multiple initiators that can cause under deposit corrosion (UDC) in heat exchangers in addition to sulfur, which is the focus of this article.

  • Blog
    February 19, 2018

    Infrared (IR) thermometry has been used for over forty years to monitor tube metal temperatures in refining and chemical furnaces. Recently, IR thermometry has been criticized in the industry for delivering inaccurate readings; however, this is often due to poorly applied and interpreted results. Several of the most common IR measurement errors include...

  • November/December 2017 Inspectioneering Journal
    By James R. Widrig at Quest Integrity

    In-service equipment failures present a considerable challenge to reliability engineers. This article presents a case study of a convection tube failure in a furnace and the analyses that were performed to understand the root cause and determine the remaining tube life.

  • September/October 2016 Inspectioneering Journal
    By Tim Haugen at Quest Integrity Group

    Although all ultrasonic smart pigging providers claim the ability to detect wall thinning and tube deformations to some degree, the inspection surface coverage, resolution, minimum wall thickness detection and reporting capabilities may vary drastically from one service provider to the next. Knowing your provider’s capabilities is crucial for ensuring the integrity of your assets, as one refinery recently discovered.

  • November/December 2014 Inspectioneering Journal
    By Dr. Noam Amir at AcousticEye

    Tube and shell heat exchangers are required to operate continuously in tough conditions for years, coping with thermal cycling, corrosive fluids on the tube and shell side, vibration and fouling of many different types, all collaborating towards degrading the performance of the unit and causing its eventual failure.

  • Partner Content

    Turnarounds are costly in terms of lost production. In many respects a turnaround can be even more complicated than the initial construction of the facility, so a carefully designed plan will reduce overall costs. After execution, safety reviews, Corrosion Monitoring Program updates, MOC documentation, and PHA Revalidations are a must.

  • January/February 2014 Inspectioneering Journal
    By Antonio Seijas at Phillips 66 Company

    Fired furnaces in the petrochemical and refining industry are critical pieces of equipment that can have a major impact on process unit safety, reliability, and economics. They are complex pieces of equipment, where tubes and other pressure boundary components might fail due to relatively short periods of upset conditions.

  • July/August 2012 Inspectioneering Journal
    By Kent Coleman at Electric Power Research Institute

    Boiler and heat recovery steam generator (HRSG) tube failures have been the primary availability problem for operators of conventional fossil-fueled and combined-cycle power plants for as long as reliable statistics have been kept for each generating source.

  • January/February 2010 Inspectioneering Journal
    By Richard D. Roberts at Quest Integrity Group

    For years refinery and chemical plant operators have utilized ultrasonic-based intelligent pig technology to inspect coils in convection and radiant sections of fired heaters. This proven technology provides accurate inspection data which allows reliability engineers to make critical decisions about the operation and maintenance of fired heaters. Recent advances have increased the capabilities of these tools and extended these benefits to coker heaters containing 3" (76.2mm) nominal piping size and plug headers with radial inserts.

  • July/August 2004 Inspectioneering Journal
    By John Reynolds at Intertek

    Though oxidation and sulfidation are quite prevalent high temperature corrosion mechanisms in many of our process units, we now come to a few that are not very common, but still deserve some attention to make sure they don’t lead to unexpected failures.

  • March/April 2004 Inspectioneering Journal
    By Mark Badrick at Bahrain Petroleum Company

    The title question is often asked and more often than not, impossible to answer. This paper follows on from a previous discussion (Inspectioneering Journal Volume 4 Issue 1 Jan/Feb 1998) relating to the difficulties arising whilst attempting to carry out temperature surveys of furnace tubes using a thermal imager. The issues discussed then i.e. calculation of emissivity and ambient temperatures, reflected heat etc, are still current concerns, but since the writing of that article, an additional equally important challenge has become apparent - "how do we measure the temperature of an externally scaled or fouled tube"? Where the external scale or some other external deposit, such as refractory dust etc. may mask the true tube temperature.

  • Partner Content

    Optimal cleaning to an "inspection clean" status ensures operational efficiency and a longer duration between heat exchanger cleaning requirements. Fouling left behind after inadequate cleaning activities will attract additional fouling at a greater pace once put back into service, leading to reduced heat transfer and a negative impact on production.

  • July/August 2003 Inspectioneering Journal
    By John Reynolds at Intertek

    Thermal shock is another one of those pressure equipment afflictions where communication with operating groups is a vital factor in prevention. Thermal shock failures usually involve sudden quenching of high temperature equipment and furnace tubes with a relatively cooler liquid or saturated steam containing some liquid, but not always.

  • January/February 2003 Inspectioneering Journal
    By John Reynolds at Intertek

    This failure mechanism is unfortunately all too common in our industry. It's also known as stress rupture, and it is usually entirely preventable by proper maintenance and operating procedures. It occurs when equipment, piping or furnace tubes that are designed to operate safely and reliably in one temperature range are suddenly (and sometimes not so suddenly) exposed to higher temperatures.

  • May/June 1998 Inspectioneering Journal
    By Richard D. Roberts at Quest Integrity Group, and Tim Cowling

    Part 1 included a review of current tube inspection practices in convection and radiant sections of heaters/furnaces in the refining and chemical industries. The authors also presented a new inspection device combining laser image mapping of the internal surface of tubes and ultrasonic thickness mapping.

  • January/February 1998 Inspectioneering Journal
    By Mark Badrick at Bahrain Petroleum Company

    The use of Infrared Thermal Imagers, particularly for temperature measurement within an operating furnace environment, is reliant on the accurate evaluation of specific parameters, which the pyrometer requires in order to produce true temperature measurements.

  • May/June 1995 Inspectioneering Journal
    By James L. Doyle at Quest Integrated, Inc.

    Over the past ten years a broad family of laser-based nondestructive testing systems has been in development. These tools are used for the inspection and measurement of internal surfaces of tubes ranging in size from 5/8-inch to 3-inches in diameter.

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    Videos related to Furnace Tubes
    • Published on February 22, 2018

      This webinar discusses the particular aspects involved in obtaining accurate and repeatable infrared temperature measurements of fired heater tubes, as well as a wealth of diagnostic information that may be used to evaluate the performance and reliability of major fired heater parts (e.g. tubes, tube supports, burners, refractory and structural systems).

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