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.
FREE RESOURCE: Click here to download a more detailed overview of CUI.
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.
We welcome updates to this Integripedia definition from the Inspectioneering community. Click the link below to submit any recommended changes for Inspectioneering's team of editors to review.
Contribute to Definition|
May/June 2021 Inspectioneering Journal
By Phillip E. Prueter at The Equity Engineering Group, Inc.
In this article, FFS assessment methods are summarized and practical guidance is offered for qualifying CUI damage on carbon and low-alloy steels. |
|
March/April 2021 Inspectioneering Journal
By Phillip E. Prueter at The Equity Engineering Group, Inc.
Corrosion under insulation is a form of external corrosion that is caused by trapped water on insulated surfaces. It is an industry problem affecting equipment in the oil and gas, petrochemical, specialty chemical, fertilizer, and related industries. |
|
Blog
March 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. |
|
May/June 2020 Inspectioneering Journal
By 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. |
|
January/February 2020 Inspectioneering Journal
By 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. |
|
November/December 2019 Inspectioneering Journal
By 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. |
|
September/October 2019 Inspectioneering Journal
By 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. |
|
July/August 2019 Inspectioneering Journal
By Ana Benz at IRISNDT
Tanks are ubiquitous and essential in industrial societies. When they fail, the consequences can be dire if products/volumes they store are explosive and/or toxic. |
|
May/June 2019 Inspectioneering Journal
By 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. |
|
May/June 2019 Inspectioneering Journal
By 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. |
|
November/December 2017 Inspectioneering Journal
By 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... |
|
May/June 2017 Inspectioneering Journal
By Justin Nickel at PK Technologies
Are you giving CUF the attention it deserves? Learn the vital role fireproofing plays in maintaining the integrity and reliability of what it protects as well as what's needed for managing potential CUF issues. |
|
March/April 2017 Inspectioneering Journal
By 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... |
|
November/December 2016 Inspectioneering Journal
By Adam Gardner at Pinnacle
Beyond the financial hits, undetected degradation from corrosion can also lead to critical safety risks. To effectively manage mechanical integrity, organizations need reliable methods of identifying the current states of corrosion occurring within... |
|
September/October 2016 Inspectioneering Journal
By John Reynolds at Intertek
Did you ever wonder where you fit into the entire hierarchy of a fixed equipment asset integrity management (FE-AIM) program? Or who is responsible and accountable for what aspects of FE-AIM at your site? All the way from top management down to... |
|
Blog
December 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... |
|
Blog
September 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. |
|
July/August 2014 Inspectioneering Journal
By 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. |
|
Blog
June 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. |
|
Partner Content
In this interim report, Pinnacle analysts take data from the oil refining industry and dive into how that key sector is being affected by reliability today. Download your free copy! |
|
Blog
March 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. |
|
November/December 2013 Inspectioneering Journal
By 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). |
|
Blog
July 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. |
|
July/August 2010 Inspectioneering Journal
By 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... |
|
January/February 2005 Inspectioneering Journal
By 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... |
|
September/October 2004 Inspectioneering Journal
By 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... |
|
May/June 2004 Inspectioneering Journal
By 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... |
|
May/June 2004 Inspectioneering Journal
By John Reynolds at Intertek
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... |
|
March/April 2001 Inspectioneering Journal
By Deal Moore at NDE Seals, Inc.
Determination of the mechanical integrity of pipe and equipment in US process industries has evolved from day to day business to federal mandate (OSHA 1901.119) to a part of industry best practice. Insulated pipe and equipment pose specific... |
|
September/October 2000 Inspectioneering Journal
By John Reynolds at Intertek
This article continues to outline the 101 essential elements that need to be in place, and functioning well, to effectively and efficiently, preserve and protect the reliability and integrity of pressure equipment (vessels, exchangers, furnaces,... |
|
January/February 1999 Inspectioneering Journal
By 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? |
|
November/December 1996 Inspectioneering Journal
By Michael Twomey at CONAM Inspection Inc.
Corrosion under insulation (CUI) is a real threat to the onstream reliability of many of today's plants. This type of corrosion can cause failures in areas that are not normally of a primary concern to an inspection program. The failures are often... |
|
July/August 1996 Inspectioneering Journal
By 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. |
|
September/October 1995 Inspectioneering Journal
By Dr. Nand K. Gupta at Omega International Technology, Inc.
In May 1995, Omega International Technology, Inc., began testing a new system to measure pipe wall thicknesses using digital radiography (RT) scanning. This new system has the potential for being faster, less labor intensive, and shown improved... |
|
May/June 1995 Inspectioneering Journal
By Greg Kobrin
Corrosion is one of those "equal opportunity" hazards that affects all industries indiscriminately, to the tune of billions of dollars annually in repair and replacement costs. Some types of corrosion are readily apparent, such as rusting of... |
Inspectioneering teams up with Johns Manville for the webinar, Mechanical Integrity Considerations for Your Insulation System. This webinar provides an overview of insulation systems, industry documents, insulation considerations, and more.
Although CUI is widely recognized as a primary driver for damage in the petrochemical industry, the solutions often lack the sophistication devoted to other damage mechanisms.
