Integripedia Topic
Corrosion Under Insulation (CUI)
Redirected from External Chloride Stress Corrosion Cracking
Corrosion Under Insulation (CUI) is one of the most well-known phenomena in the process industries, and yet it still makes up an inordinately large percentage of global maintenance expenditures. CUI is a subject that is well-researched and understood; extensive studies have been commissioned to determine the causes, effects, prevention, and mitigation of CUI.
In the simplest terms, CUI is any type of corrosion that occurs due to moisture present on the external surface of insulated equipment. The damage/attack can be caused by one of multiple factors, and can occur in equipment operating at ambient, low, and heated services, depending upon conditions. Moreover, CUI can occur in equipment that is in service, out of service, or in cyclic service.
The corrosion itself is most commonly galvanic, chloride, acidic, or alkaline corrosion. If undetected, the results of CUI can lead to leaks and the shutdown of a process unit or an entire facility.
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External Chloride Stress Corrosion Cracking
External Chloride Stress Corrosion Cracking (ECSCC) is a specific form of CUI that occurs in austenitic stainless steels (300 series SS). Most of those who own solid stainless steel equipment operating in the CUI temperature range are likely to experience ECSCC at some point.
Good coatings, properly selected for the purpose and properly applied will give some protection for a period of time. Unfortunately, the vast majority of coatings will break down eventually and allow chloride laden moisture to contact the surface of the stainless steel. Low chloride insulation and well-applied weather barriers will also help avoid the onset of ECSCC.
The older version of calcium silicate insulation which contained chlorides is especially prone to causing ECSCC. Although the temperature range of 140 °F (60 °C) to 300 °F (150 °C) is likely to be the most active region for ECSCC, there are numerous data points reported outside of that temperature range, both above and below, including severe ECSCC of hydroprocess stainless steel piping operating well above 600 °F (315 °C).
For the most part, 300 series stainless steels are fairly strong, thus it’s likely that equipment made from this material will form a leak before it breaks completely. The leak itself will probably be small as well. Because of this, the potential for a large safety event is small compared to other forms of SCC.
This doesn’t mean catastrophic rupture is impossible. There is always the potential for what is known as “plastic collapse,” and of course, even small leaks can be hazardous or produce an undesirable reliability impact.
When it comes to detecting ECSCC after it’s already occurred, inspection methods for ECSCC are normally relegated to surface techniques such as liquid penetrant (LPT) or specialized eddy current probes. For this reason prevention is usually the best option.
Codes, Standards, and Best Practices
- API 510, Pressure Vessel Inspector Program is an inspection code that covers the in-service inspection, repair, alteration, and rerating activities for pressure vessels and the pressure relieving devices protecting these vessels. It applies to most refining and chemical process vessels that have been placed into service. CUI inspection is covered in section 5.5.6 of the standard (Tenth Edition released April, 2014).
- API 570, Piping Inspection Code - Inspection, Repair, Alteration and Rerating of In-Service Piping Systems provides guidance on how to determine which piping systems are most susceptible to CUI (section 5.2.1), as well as some of the most common locations to find CUI (section 5.4.2) on those systems that are determined to be susceptible to CUI (Third Edition released November, 2009).
- API RP 574, Inspection Practices for Piping System Components discusses inspection practices for piping, tubing, valves (other than control valves), and fittings used in petroleum refineries and chemical plants. In order to aid inspectors in fulfilling their role implementing API 570, this document describes common piping components, valve types, pipe joining methods, inspection planning processes, inspection intervals and techniques, and types of records. CUI is covered in section 6.3.3 (Third Edition released November, 2009).
- API RP 583, Corrosion Under Insulation and Fireproofing covers design, maintenance, inspection, and mitigation practices to address external CUI as it applies to pressure vessels, piping, storage tanks and spheres. It examines the factors that affect the damage mechanisms, and provides guidelines for preventing external corrosion or cracking under insulation, maintenance practices to avoid damage, inspection practices to detect and assess damage, and guidelines for conducting risk assessments onequipment or structural steel subject to CUI (First Edition released May, 2014).
- ASTM STP 880, Corrosion of Metals Under Thermal Insulation provides information on corrosion problems that can occur on thermally insulated plant equipment and piping components if its insulation becomes wet (First Edition released 1985).
- NACE SP0198-2010, Control of Corrosion Under Thermal Insulation and Fireproofing Materials – A Systems Approach (Published July, 2010). This standard is a replacement for NACE RP0198-08 (March, 2004).
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Related Topics
- Amine Stress Corrosion Cracking (SCC)
- Ammonia Stress Corrosion Cracking
- Brittle Fracture
- Carburization
- Caustic Stress Corrosion Cracking (Caustic Embrittlement)
- Cavitation
- Chloride Stress Corrosion Cracking
- Cooling Water Corrosion
- Corrosion Fatigue
- Cracking
- Decarburization
- Embrittlement
- Erosion Corrosion
- Fatigue (Material)
- Graphitization
- High Temperature Hydrogen Attack (HTHA)
- Hydrochloric (HCl) Acid Corrosion
- Hydrofluoric (HF) Acid Corrosion
- Hydrogen Blistering
- Hydrogen Embrittlement
- Hydrogen Induced Cracking (HIC)
- Hydrogen Stress Cracking
- Liquid Metal Embrittlement (LME)
- Metal Dusting
- Microbiologically Induced Corrosion (MIC)
- Naphthenic Acid Corrosion (NAC)
- Phosphoric Acid Corrosion
- Polythionic Acid Stress Corrosion Cracking (PASCC)
- Spheroidization (Softening)
- Stress Assisted Corrosion
- Stress-Oriented Hydrogen Induced Cracking (SOHIC)
- Sulfidation Corrosion
- Sulfuric Acid Corrosion
- Thermal Fatigue
- Vibration-Induced Fatigue
- Wet H2S Damage
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BlogMarch 1, 2021 By Greg Alvarado at Inspectioneering Journal
This retrospective takes a quick look at two of the most popular topics that were covered in Inspectioneering Journal last year: the accuracy of thickness readings and corrosion under insulation.
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May/June 2020 Inspectioneering JournalBy Frode Wiggen at DNV GL
The article describes the results from a recent CUI Joint Industry Project which resulted in an RBI methodology for managing the CUI threat. The methodology assesses 4 CUI barriers: material, coating, water wetting, and design.
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January/February 2020 Inspectioneering JournalBy Jeremiah Wooten at Inspectioneering, LLC.
Inspectioneering and PinnacleART co-hosted their 5th Meeting of the Minds roundtable last November in Atlanta. This meeting’s focus was on notable technologies and how they are changing the MI landscape.
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November/December 2019 Inspectioneering JournalBy Dr. Timothy Black at Quasset, Maurice Fransen at Shell Global Solutions International BV, and Sieger Terpstra at Shell Global Solutions International BV
This article examines multiple trials that entailed testing robotic systems on different non-magnetic surfaces to identify the feasibility of detecting CUI using robotics in combination with NDE technology.
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September/October 2019 Inspectioneering JournalBy Ron King
There are inspection requirements in many construction disciplines, including electrical, welding, coating, and the list goes on, but not for mechanical insulation. The need for a certified mechanical insulation inspection program is long overdue.
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May/June 2019 Inspectioneering JournalBy Nick Schmoyer at Inspectioneering
Inspectioneering and PinnacleART recently hosted a roundtable discussion for a select group of mechanical integrity experts to discuss strategies for managing corrosion under insulation and corrosion under pipe supports, a.k.a. touch point corrosion.
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May/June 2019 Inspectioneering JournalBy Andres Salazar at WorleyParsons
This article details an experience assessing the mechanical integrity of a feed pressure vessel, and describes the methodology carried out for detecting CUI and how results were managed for this pressure vessel.
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November/December 2017 Inspectioneering JournalBy Greg Alvarado at Inspectioneering Journal, and John Nyholt at John Nyholt Consulting, LLC
Thanks to the development of documents such as API RP 571 and API RP 586, as well as the emergence of qualification demonstration testing, we can align NDT techniques and inspection strategies better than ever. This article examines this progression...
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May/June 2017 Inspectioneering JournalBy Justin Nickel at PK Technologies
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March/April 2017 Inspectioneering JournalBy Fernando Vicente at ABB, and Laza Krstin at ABB
Myths, challenges, and good practices related to process piping integrity management activities that help inspection and maintenance managers make the right decisions to develop cost-effective piping inspection plans without compromising the...
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November/December 2016 Inspectioneering JournalBy Adam Gardner at Pinnacle
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September/October 2016 Inspectioneering JournalBy John Reynolds at Intertek
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BlogDecember 8, 2014 By Nick Schmoyer at Inspectioneering
Corrosion Under Insulation (CUI) is an insidious damage mechanism that, despite being incredibly well-known and understood, still makes up an inordinately large percentage of global maintenance expenditures. CUI has been extensively researched and...
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BlogSeptember 15, 2014 By Nick Schmoyer at Inspectioneering
I've crunched some numbers and have come up with the three most popular damage mechanisms, based on the activity of our readers, that Inspectioneering publishes information on.
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July/August 2014 Inspectioneering JournalBy Brian J. Fitzgerald at Stress Engineering Services
As any refining or petrochemical plant manager knows, corrosion can occur on insulated piping at any facility. CUI has been a major challenge for the petrochemical and refining industries since the first pipelines were insulated with wrappings.
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BlogJune 2, 2014 By John Reynolds at Intertek
Three new API standards have been published, and one has been revised and updated to a new edition. The standards are described in this post.
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BlogMarch 3, 2014 By Greg Alvarado at Inspectioneering Journal
In many ways, fertilizer plants are no different than most process industry plants including refineries and petrochemical facilities. Information in documents like API 510, 570, 653 and RPs 580, 581, 571, 577, 579, etc. is essential.
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November/December 2013 Inspectioneering JournalBy Richard Mills at GE, John T. Iman at GE Oil and Gas Measurement & Controls-Inspection Technology, and Martin Sauerschnig at GE Oil and Gas Measurement and Control
Over recent years large strides have been made in application, development, and utilization of Digital Detector Arrays (DDAs) in field radiography environments (an application previously limited to film and computed radiography [CR] techniques).
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BlogJuly 8, 2013 By John Reynolds at Intertek
This week’s post takes up right where last week’s post left off in our discussion on Corrosion Management and Control (CM&C) Management Systems.
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July/August 2010 Inspectioneering JournalBy Santhosh Lukose at Metalcare Inspection Services Inc.
CUI (Corrosion Under Insulation) has always been a challenge for plant operators, quality assurance/reliability engineers and equipment owners. It is hard to identify the problem until it has become an emergency situation, often leading to unit shut...
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January/February 2005 Inspectioneering JournalBy Hegeon Kwun at Southwest Research Institute, and Glenn Light at Southwest Research Institute
Nearly ten years ago the magnetostrictive sensor (MsS) technology was reported in this journal (July/August 1996 Issue, Volume 2 Issue 4) as a method to detect corrosion in insulated piping. At that time, the MsS Technology consisted primarily of...
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September/October 2004 Inspectioneering JournalBy Greg Alvarado at Inspectioneering Journal
Exactly two years ago, an interview with John Nyholt appeared in the “IJ”. New ground will be covered in this interchange. We at the IJ thought it might be valuable to spend some time chatting about his background, challenges he has faced...
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May/June 2004 Inspectioneering JournalBy John Reynolds at Intertek
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...
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Download Pinnacle's Economics of Reliability Report - Refining to see how reliability is affecting profitability.
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May/June 2004 Inspectioneering JournalBy John Reynolds at Intertek
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March/April 2001 Inspectioneering JournalBy Deal Moore at NDE Seals, Inc.
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January/February 1999 Inspectioneering JournalBy Joseph E. Pascente at Lixi, Inc.
One of the greatest challenges facing many of refining, fossil power, and pulp and paper industries is: How to effectively examine their insulated piping?
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November/December 1996 Inspectioneering JournalBy Michael Twomey at CONAM Inspection Inc.
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July/August 1996 Inspectioneering JournalBy Hegeon Kwun at Southwest Research Institute, and Richard L. Lopushanksy at Southwest Research Institute
Engineers and scientists at Southwest Research Institute (SwRI) in San Antonio, Texas, may have found a cost-effective and practical method of detecting ID and OD corrosion of insulated piping systems.
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September/October 1995 Inspectioneering JournalBy Dr. Nand K. Gupta at Omega International Technology, Inc.
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May/June 1995 Inspectioneering JournalBy Greg Kobrin
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