Inspectioneering

Damage Mechanisms

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Damage Mechanisms (also referred to as degradation mechanisms) is a general term referring to any cause of problems or failures within process equipment. These can range from corrosion, to cracking, to heat damage, and everything in between.

When assessing damage mechanisms, one must take into account the current state of the equipment, as well as any potential damage the mechanism may cause later. Equipment’s susceptibility to a particular damage mechanism is affected by a number of variables, including materials of construction, process fluids, operating conditions, external environment, etc. A good understanding of the variety of damage mechanisms that exist is a must for any mechanical integrity program.

A thorough damage mechanisms review is essential for creating an effective inspection strategy. Once damage mechanisms and morphology are understood, inspection strategists can use this information to select inspection methods with the highest probability of detecting, characterizing, and measuring potential damage. Furthermore, inspection intervals can be established using industry codes and standards such as API 510, 570, 653, API RP 579 for fitness-for-service, and API 580 and 581 for risk-based inspection.

Some of the most common damage mechanisms in the refining and chemical processing industries are:

  • Corrosion Under Insulation (CUI), which occurs when moisture builds up on the surface of insulated equipment.

  • Sulfidation Corrosion, a type of corrosion that occurs at temperatures above 500 °F (260 °C) due to sulfur compounds in crude.

  • High Temperature Hydrogen Attack (HTHA), a mechanism that can affect equipment that is exposed to hydrogen at elevated temperatures (at least 400 °F or 204 °C)

  • Wet H2S Damage, which can occur when atomic hydrogen from wet H2S corrosion reactions enters and weakens the steel.

  • CO2 Corrosion, which is a form of degradation that occurs when dissolved CO2 in condensate forms carbonic acid, which corrodes steels.

  • Hydrogen Embrittlement, which happens when atomic hydrogen infuses into certain higher strength steels and causes them to become brittle

  • Brittle Fracture, which is the sudden, very rapid fracture under stress where the material exhibits little or no evidence of ductility or plastic degradation before the fracture occurs.

  • Phosphoric Acid Corrosion is an acidic environment "disease" largely associated with polymerization units using phosphoric acid as a catalyst. Dry phosphoric acid catalyst is not corrosive to carbon steel, but wet phosphoric acid can corrode carbon at thousands of mils per year. This type of corrosion can often be found in dead zones and crevices where wet acid can drop out. In places where water is present, upgrading to 304L, 316L, or Alloy 20 may be necessary to prevent this type of corrosion, depending on the temperature.[1]

Damage mechanisms are detailed and covered at length in API RP 571, Damage Mechanisms Affecting Fixed Equipment in the Refining Industry. This document provides an in-depth look at over 60 different damage mechanisms that can occur to process equipment in refineries. It includes a general description of the damage mechanism, susceptible materials of construction, critical factors, inspection method selection guidelines, and control factors.

References

  1. 99 Diseases of Pressure Equipment: Phosphoric Acid

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Articles about Damage Mechanisms
March/April 2022 Inspectioneering Journal

This study found that a machine learning model was able to predict degradation rates for a hydrocracker unit more accurately and with a smaller margin of error compared to current industry practices.

March/April 2022 Inspectioneering Journal

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January/February 2022 Inspectioneering Journal

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January/February 2022 Inspectioneering Journal

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May/June 2021 Inspectioneering Journal

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May/June 2021 Inspectioneering Journal

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March/April 2021 Inspectioneering Journal

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March/April 2021 Inspectioneering Journal

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January/February 2021 Inspectioneering Journal

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January/February 2021 Inspectioneering Journal

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November/December 2020 Inspectioneering Journal

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September/October 2020 Inspectioneering Journal

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July/August 2020 Inspectioneering Journal

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March/April 2020 Inspectioneering Journal

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January/February 2020 Inspectioneering Journal

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September/October 2019 Inspectioneering Journal

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January/February 2019 Inspectioneering Journal

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July/August 2016 Inspectioneering Journal

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November/December 2015 Inspectioneering Journal

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November/December 2015 Inspectioneering Journal

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September/October 2015 Inspectioneering Journal

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November/December 2014 Inspectioneering Journal

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September/October 2014 Inspectioneering Journal

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July/August 2014 Inspectioneering Journal

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January/February 2014 Inspectioneering Journal

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November/December 2013 Inspectioneering Journal

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September/October 2012 Inspectioneering Journal

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July/August 2012 Inspectioneering Journal

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March/April 2012 Inspectioneering Journal

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November/December 2010 Inspectioneering Journal

High Temperature Hydrogen Attack (HTHA) is a long known and still occurring degradation issue for fixed equipment construction materials in the hydrocarbon process industry where hydroprocess plants (hydrogen plus hydrocarbons) are in service....

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November/December 2010 Inspectioneering Journal

The following references are from the American Petroleum Institute. They are widely used in the petroleum refining and petrochemical industries for managing equipment in HTHA service and are available in the public domain.

September/October 2008 Inspectioneering Journal

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March/April 2007 Inspectioneering Journal

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January/February 2007 Inspectioneering Journal

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Authors: John Reynolds
May/June 2006 Inspectioneering Journal

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January/February 2006 Inspectioneering Journal

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September/October 2005 Inspectioneering Journal

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September/October 2005 Inspectioneering Journal

Strain-aging problems are another form of metallurgical degradation and thankfully are not very common and becoming less so; but since strain-aging does still occasionally occur, it still makes the list of one of the “99 diseases of pressure...

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September/October 2005 Inspectioneering Journal

Another form of metallurgical degradation at higher temperatures is called sigma phase embrittlement. As the name implies, a metallurgical phase change occurs in some stainless steels when they are heated above about 1000F (540C).

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September/October 2005 Inspectioneering Journal

Titanium (Ti) hydriding is another somewhat unusual metallurgical degradation phenomena that can result in brittle fracture. Unlike many other steel embrittlement phenomena, this one most often occurs in thin wall Ti tubes that have been selected...

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September/October 2005 Inspectioneering Journal

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....

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September/October 2005 Inspectioneering Journal

Spheroidization is a rather technical term that describes a metallurgical aging phenomena that results in loss of mechanical and creep strength. It occurs when carbon and low alloy steels are exposed to temperatures in the range of 850F - 1400F...

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July/August 2005 Inspectioneering Journal

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May/June 2005 Inspectioneering Journal

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May/June 2005 Inspectioneering Journal

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May/June 2005 Inspectioneering Journal

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May/June 2005 Inspectioneering Journal

MIC is caused by biological growth, i.e. organic slime (typically bacteria, algae, and fungi) in water under low flow or stagnant conditions. The industry experiences it in cooling water systems, piping, vessels and storage tank bottoms where the...

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May/June 2005 Inspectioneering Journal

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January/February 2005 Inspectioneering Journal

Polythionic Acid Stress Corrosion Cracking (PASCC) is an affliction of many refineries processing sulfur containing feedstocks, and since that is the norm these days, most refiners reduce their susceptibility to PASCC by selecting resistant alloys...

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January/February 2005 Inspectioneering Journal

Hydrogen stress cracking occurs when corrosion from acids like wet hydrogen sulfide or hydrofluoric acid (HF) cause atomic hydrogen to penetrate hardened or higher strength steels and cause stress cracking.

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January/February 2005 Inspectioneering Journal

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January/February 2005 Inspectioneering Journal

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November/December 2004 Inspectioneering Journal

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September/October 2004 Inspectioneering Journal

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Authors: John Reynolds
September/October 2004 Inspectioneering Journal

Corrosion in the refining industry from HFA is not as widespread a problem as it is with HCl because it is only associated with HF Alkylation Units, which are usually fairly carefully controlled in order to avoid potential for a toxic HFA cloud...

Authors: John Reynolds
September/October 2004 Inspectioneering Journal

Problems with naphthenic acid corrosion (NAC) are nearly as old as the refining industry. The first paper on the topic that I knew about was written by one of my early industry supervisors over 40 years ago.

Authors: John Reynolds
September/October 2004 Inspectioneering Journal

Unlike NAC where we’re still on a learning curve, the knowledge of corrosion by sulfuric acid has not changed much in the last quarter century, and there are many good references for it included in API RP 571.

Authors: John Reynolds
Partner Content

Tri-Lateral Phased Array is a novel robotic phased array ultrasonic testing technique for the on-stream inspection of fixed equipment in wet hydrogen sulfide (H2S) service. TriLat identifies and quantifies wet H2S damage in the base metal of...

September/October 2004 Inspectioneering Journal

Corrosion from phosphoric acid is another “old knowledge” corrosion issue that effects only a few processes in the chemical and hydrocarbon process industry.

Authors: John Reynolds
July/August 2004 Inspectioneering Journal

Catastrophic oxidation can occur when certain contaminants are present in a high temperature environment, i.e. inside furnace fireboxes, in our industry. Those contaminants are typically vanadium pentoxide with sulfur oxide or sodium sulfate.

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
July/August 2004 Inspectioneering Journal

Metal dusting is simply a severe form or extension of carburization in which the extensive carbides that form as a result of carburization lead to grains of metal falling out of the tube or piping and being swept away by the process...

Authors: John Reynolds
May/June 2004 Inspectioneering Journal

Chloride cracking of austenitic stainless steels (300 series SS) is an off-shoot of CUI, and there’s nothing really magical about it. If you have insulated solid stainless steel equipment operating in the CUI temperature range you are likely to...

Authors: John Reynolds
May/June 2004 Inspectioneering Journal

For purposes of this article, external (atmospheric) corrosion is what afflicts process equipment and structural members that are not insulated and exposed to moisture associated with atmospheric conditions, ie rain, condensation from humidity,...

Authors: John Reynolds
May/June 2004 Inspectioneering Journal

Soil corrosion (underground corrosion) is another one of those extensively researched and documented types of corrosion, since so many pipes and pipelines are buried and nearly all storage tanks rest on the soil. An entire industry/ technology is...

Authors: John Reynolds
May/June 2004 Inspectioneering Journal

CUI may be the most well known and widespread corrosion phenomena in our industry. It’s also one of the most difficult to prevent because by and large no matter what precautions we take, water eventually gets into the insulation and begins...

Authors: John Reynolds
March/April 2004 Inspectioneering Journal

API Recommended Practice 571, Damage Mechanisms Affecting Fixed Equipment in the Refining Industry

January/February 2004 Inspectioneering Journal

Casting defects are an age old problem for our industry that seems to be getting worse as foundries in the older industrialized world shutdown for economic reasons.

Authors: John Reynolds
January/February 2004 Inspectioneering Journal

Speaking of stress raisers, they are another insidious type of flaw that can and do lead to equipment failures. Stress raisers (aka stress intensification sites) can be mechanical or metallurgical notches. Undercutting, physical weld flaws,...

Authors: John Reynolds
January/February 2004 Inspectioneering Journal

When we specify that some equipment (vessels, flanges, fittings, etc.) be overlaid with a corrosion resistant alloy, we need to pay attention to making sure that the chemistry of the top layer of alloy welding, that will be exposed directly to...

January/February 2004 Inspectioneering Journal

DMW cracking is another fabrication issue that can and does result in equipment failure. It usually occurs at the weld juncture where carbon steel or low alloy steels are welded to austenitic (300 series) stainless steels in high temperature...

January/February 2004 Inspectioneering Journal

Cracks along the toe of a weld are not uncommon during fabrication, and can occur for a wide variety of reasons involving the metallurgy and process control of the the same issues covered above on repair welds can apply to repair welds on...

Authors: John Reynolds
November/December 2003 Inspectioneering Journal

Liquid Metal Cracking (LMC) (aka "liquid metal embrittlement") is another insidious form of cracking that strikes when you least expect it. It most commonly afflicts austenitic stainless steels, but can afflict other copper, nickel and aluminum...

Authors: John Reynolds
November/December 2003 Inspectioneering Journal

Carbonate cracking (CC) of carbon steel has seen an increase recently in frequency and severity in some refinery cat crackers, especially in fractionator and gas processing overheads. Some gas scrubbing units are also susceptible. CC is a form of...

Authors: John Reynolds
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

Cavitation is the sudden formation and immediate collapse of vapor or air bubbles in a liquid stream when system pressure falls below the vapor pressure of the liquid. The sudden collapse of these tiny bubbles generates enormous, though tiny forces...

Authors: John Reynolds
July/August 2003 Inspectioneering Journal

This is the name given to a form of embrittlement that occurs in 400 series of stainless steels, duplex SS's and less commonly in some 300 series stainless steels containing a metallurgical phase called ferrite. The embrittlement occurs from 600...

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
January/February 2003 Inspectioneering Journal

Now you say, he's got to be putting me on. What is green rot? I didn't invent it. I first read about it in one of the early texts on corrosion engineering by Ughlig or Fontana, the venerable corrosion professors at MIT & Ohio State. But when I...

Authors: John Reynolds
January/February 2003 Inspectioneering Journal

I already mentioned this common affliction in the introduction. Caustic cracking was long called caustic embrittlement, but since no embrittlement actually occurs that name is fading away.

Authors: John Reynolds
January/February 2003 Inspectioneering Journal

Welcome to a new series of articles about the ninety-nine leading types of degradation, flaws and failure that can and do happen to pressure equipment in the hydrocarbon process industry.

Authors: John Reynolds
November/December 1996 Inspectioneering Journal

Petroleum coke production is an important source of revenue for many refineries. While coking units were initially constructed to deal with a waste product, these units are now of significant economic value.

November/December 1995 Inspectioneering Journal

Nelson Curve changes in the late 1980's provided cause for Shell Oil Company to look at more reliable NDE non-destructive evaluation methods for assessment of materials/equipment in high temperature hydrogen service. The primary change motivating...

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        This eBook offers practical guidance for, and real examples of, in-service degradation attributed to corrosion under insulation. It provides a detailed discussion on CUI detection, characterization and evaluation, and mitigation or remediation.

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        This eBook offers practical guidance for, and real examples of, in-service degradation attributed to thermal fatigue. It provides a detailed discussion on thermal fatigue detection, characterization and evaluation, and mitigation or remediation.

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        This checklist serves as a companion piece to the Inspectioneering webinar, CUI: A Proactive Approach, and contains some elements to consider when looking for data gaps in your CUI program.

        Asset Intelligence Report

        This Asset Intelligence Report on Sulfidation Corrosion serves as a primer to increase your familiarity with one of the most well-known corrosion mechanisms in the oil refining industry.

        Asset Intelligence Report

        This Asset Intelligence Report on the hydrogen bake-out process serves as a primer to increase your familiarity with this technique used to drive hydrogen out of equipment prior to welding.

        Asset Intelligence Report

        Corrosion Under Insulation (CUI) is one of the most well-known damage mechanisms in the O&G and chemical processing industries, yet CUI still makes up a very large percentage of plant maintenance expenditures.

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        This primer covers the fundamentals of High Temperature Hydrogen Attack (HTHA). Download and learn about this serious damage mechanism.

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