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Furnace Tubes

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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

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...

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November/December 2017 Inspectioneering Journal

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...

Authors: James R. Widrig
September/October 2016 Inspectioneering Journal

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November/December 2014 Inspectioneering Journal

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January/February 2014 Inspectioneering Journal

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July/August 2012 Inspectioneering Journal

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...

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January/February 2010 Inspectioneering Journal

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...

July/August 2004 Inspectioneering Journal

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...

Authors: John Reynolds
March/April 2004 Inspectioneering Journal

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...

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July/August 2003 Inspectioneering Journal

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...

Authors: John Reynolds
July/August 2003 Inspectioneering Journal

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...

Authors: John Reynolds
May/June 1998 Inspectioneering Journal

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...

January/February 1998 Inspectioneering Journal

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May/June 1995 Inspectioneering Journal

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