Creep is the time-dependent deformation of a material under load. It is a generally slow developing form of degradation occurring in metals under stress and higher pressures. The amount of creep deformation that will be experienced is highly dependent upon the level of stress, level of temperature, and material properties of the metal. Deformations caused by creep evenutally cause damage that may result in a rupture of the affected equipment components. Commonly susceptible equipment includes nozzles and other components with high tri-axial loading on some catalytic reformers, furnace components, and dissimilar metal welds.
Inspection for creep damage is not straight-forward and may require several techniques to be used in combination. While the use of ring gauges for bulges in furnace tubes is fairly widespread, in other cases, a combination of surface and volumetric NDE may be required, along with metallographic samples (destructive & non-destructive) to verify the presence of creep damage.
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September/October 2017 Inspectioneering Journal
By Arun Sreeranganathan at Stress Engineering Services Inc., and John Norris, P.E. at Stress Engineering Services
Fired heaters are among the most critical equipment in refineries and chemical plants, and failure of heater tubes presents significant safety and financial concerns. This article provides an overview of what a fired heater tube mechanical integrity program should include. |
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July/August 2016 Inspectioneering Journal
By Mark Geisenhoff at Flint Hills Resources, Jonathan D. Dobis at The Equity Engineering Group, Inc., Phillip E. Prueter at The Equity Engineering Group, Inc., and Dr. Michael S. Cayard at Flint Hills Resources
This article summarizes a recent finite element analysis (FEA)-based study that employs creep simulation techniques to investigate the elevated temperature response of piping with peaked longitudinal weld seams. |
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January/February 2015 Inspectioneering Journal
By Pamela Hamblin at Thielsch Engineering, Inc.
Avoiding cracking under pressure when managing high-energy piping systems is common subject matter in the power industry. Just as high-energy piping can give way to pressure, stress and fatigue, so can the people in charge of operating them when trying to determine what to inspect, where to inspect, and what to do with those inspection results once they have them. |
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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. |
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September/October 2005 Inspectioneering Journal
By John Reynolds at Intertek
Metals will slowly deform under stress and higher temperatures by the mechanism known as creep. The amount of creep deformation that will be experienced is highly dependent upon the level of stress, level of temperature and material properties. It is vital that any component operating in the creep range have Integrity Operating Windows (IOW’s) established where upon operators are required to make adjustments if certain temperatures are reached. |
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November/December 1999 Inspectioneering Journal
By Richard D. Roberts at Quest Integrity Group
Steam reformers are an integral part of ammonia, methanol, hydrogen, and gas process plants around the world. THey are one of the highest cost, both in capital and maintenance, pieces of equipment in the plant. Typically, reformers contain several hundred vertically oriented straight tubes, referred to as catalyst tubes. These tubes represent a significant cost for replacement and can be a major source of plant unavailability if unplanned failures occur. |
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May/June 1997 Inspectioneering Journal
By John Brear at ERA Technology Ltd., John Williamson at ERA Technology Ltd., and Bobby Wright, P.E. at Stress Engineering Services
Reformer catalyst tubes are commonly manufactured from high strength, creep and corrosion resistant alloys. They are relatively thick walled and are usually produced by centrifugal casting. Their lives are limited by creep, driven by a combination of internal pressure and through-wall thermal stresses generated by operational transients. The typical composition for alloys for reforming service is 25/20 Cr/Ni with the generic reference HK40. |
