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Overview of Corrosion Under Insulation (CUI)

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 the 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.

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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Articles about Corrosion Under Insulation (CUI)
  • 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 and applies it to some sample NDT methods.

  • 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 asset’s reliability or performance.

  • November/December 2016 Inspectioneering Journal
    By Adam Gardner at PinnacleART

    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 their assets.

  • 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 those doing the work at the field level? That’s what I will try to address in this article.

  • Partner Content

    Properly anticipating and finding the damage in your facility is no small task, and spending millions of dollars on inspection may not be getting you anywhere if it’s not the right inspection processes. PinnacleART can use industry best practice models and corrosion expertise to proactively identify damage types, locations and magnitudes so you can ensure you’re performing the right inspections at the right times. Visit us at pinnacleart.com to learn more.

  • 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 studied and because of that, there exist several good resources on it, and we at Inspectioneering are dedicated to bringing those resources to you.

  • 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. I've limited the list to these three mechanisms for the sake of brevity, but keep in mind that there are nearly a hundred different damage mechanisms that affect fixed equipment mechanical integrity in the oil & gas and chemical industries.

  • 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, and is particularly difficult to prevent, track, and mitigate. Corrosion under insulation (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.

  • 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.

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  • 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

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  • 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. As I have said previously, this information is based off a series of articles I did on PEI&R MS, which you can reference here. Here are the next four...

  • 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 downs or even the whole facility shut down for emergency repairs.

  • 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 the longitudinal guided wave mode introduced into the pipe with a coil wrapped around the steel pipe with a coil wrapped around the steel pipe and a number of large magnets setting up an axially oriented magnetic baising field in the area of the coil. The longitudinal mode worked well for dry, unfilled pipe. However, in liquid filled pipes, the longitudinal mode didn't work well because it interacts with the liquid, producing extraneous signals that, in turn, cause difficulty in analyzing data.

  • 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 recently and what he feels are some of the biggest challenges ahead for the Inspectioneering® community.

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  • 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 eventually experience External Chloride Stress Corrosion Cracking (ECSCC).

  • 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 to do it’s dirty work, sometimes sight unseen until process leakage occurs. And it’s not isolated to just insulation. Corrosion under fire-proofing (CUF) is also prevalent in our industry and requires the same type of inspection planning, design prevention, and mitigation that is required for CUI.

  • 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 challenges for the examination effort. This article is an attempt to review the regulations that are driving these efforts and the innovations designed to address these challenges. Understanding both will enhance the value added services offered by the insulation industry.

  • 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, boilers, piping, tanks, relief systems) in the refining and petrochemical industry.

  • 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?

  • Partner Content

    Join Pro-Surve and ProSource us at SynGas 2018 from April 16 - 18 at the Tulsa Marriott, Southern Hills. We will be at Booth 77 with our sister company Calculated Controls. Come discuss resolution of your inspection, NDT, Engineering, PSM and data management needs. In addition, we encourage you to attend the discussion session on Mechanical Integrity as Pro-Surve will help facilitate the session.

  • 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 the result of localized corrosion and not general wasting over a large area. These failures can be catastrophic in nature, or at least, have an adverse economic effect in terms of downtime and repairs.

  • 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 accuracy over traditional ultrasound testing, and at a lower cost. Perhaps best of all, scanning can be performed while the pipe is in service, insulation in place.

  • May/June 1995 Inspectioneering Journal

    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 unprotected plain carbon steel tanks and piping.

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