Corrosion Under Insulation (CUI) Guidelines

Revised

S. Winnik

• Publisher: Woodhead Publishing
• Year: 2015
• eBook ISBN: 9780081007396
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Mining Engineering
• Index: Technology & Engineering

Corrosion-under-insulation (CUI) refers to the external corrosion of piping and vessels that occurs underneath externally clad/jacketed insulation as a result of the penetration of water. By its very nature CUI tends to remain undetected until the insulation and cladding/jacketing is removed to allow inspection or when leaks occur. CUI is a common problem shared by the refining, petrochemical, power, industrial, onshore and offshore industries.

In the first edition of this book published in 2008, the EFC Working Parties WP13 and WP15 engaged together to provide guidelines on managing CUI with contributions from a number of European refining, petrochemical and offshore companies. The guidelines are intended for use on all plants and installation that contain insulated vessels, piping and equipment. The guidelines cover a risk-based inspection methodology for CUI, inspection techniques and recommended best practice for mitigating CUI, including design of plant and equipment, coatings and the use of thermal spray techniques, types of insulation, cladding/jacketing materials and protection guards. The guidelines also include case studies.

The original document first published in 2008 was very successful and provided an important resource in the continuing battle to mitigate CUI. Many members of the EFC corrosion community requested an update and this has taken between 18-24 months to do so. Hopefully this revised document will continue to serve the community providing a practical source of information on how to monitor and manage insulated systems.

• Revised and fully updated technical guidance on managing CUI provided by EFC Working Parties WP13 and WP 15
• Contributions from a number of European refining, petrochemical and offshore companies
• Extensive appendices that provide additional practical guidance on the implementation of corrosion-under-insulation best practice, collected practical expertise and case studies

1

Introduction

Abstract

Provides historical background and basic CUI corrosion mechanisms of carbon steel and stainless steel insulated equipment applicable to hot and cold insulation systems. Includes effect of operating environmental conditions.

Keywords

CUI carbon steel

stainless steel dew-point

hot and cold insulation

The term “corrosion under insulation” (CUI) refers to the external corrosion of piping and vessels fabricated from carbon manganese, low alloy, and austenitic stainless steel that occurs underneath externally clad or jacketed thermal or acoustic insulation primarily due to the penetration of water. By its very nature CUI tends to remain undetected until the insulation and cladding/jacketing is removed to allow inspection or when leaks to atmosphere occur. CUI is a major problem worldwide and is shared by all of the Oil&Gas (both onshore and offshore), Chemical processing industries (CPI), and related industries. It is not a new problem, but it can be a serious problem. CUI has been responsible for many major leaks that have led to safety, health, and environmental (SHE) related incidents, to lost production, and is responsible for the large maintenance budgets that are often required to mitigate the problem.

Corrosion of austenitic stainless steels is localized and usually a combination of pitting and chloride external stress corrosion cracking (Cl-ESCC). Although Cl-ESCC¹ of insulated austenitic stainless steel was first reported in 1965, very limited published information was available on the CUI of carbon manganese and low alloys steels and Cl-ESCC of austenitic stainless steels up to 1980 when a meeting was held in the November of that year.² Richardson³ provided a review of this very successful, 2-day meeting during a combined ASTM/NACE/MTI sponsored symposium held in 1983.⁴ When reviewing the literature from that meeting today, it would appear that the problems reported in 1980 mirror the experiences currently being reported.

Although numerous instances of CUI are reported annually, this has not been reflected in the current industry standards for insulation or other measures used to mitigate CUI. The first ASTM standard on thermal insulation materials relevant to CUI was only adopted in 1971.⁵ The NACE Task Group T-6H-31 first issued a report on CUI⁶ in 1989 and later NACE Task Group T-5A-30 became an open forum for industry CUI problems and solutions. This led to the publication of a NACE recommended practice RP0198⁷ in 1998. RP0198 was revised in 2004⁸ and republished in 2010 as a standard practice SP0198 in 2010.⁹ Other conferences and initiatives covering CUI and insulation materials have taken place since 1983 but the problem remains unresolved. It would seem that the incidence of CUI examples is not diminishing and would appear to be increasing given the number of instances being reported. A NACE conference in 2003 reviewed similar topics first discussed in 1983, which was well illustrated by Delahunt¹⁰ who presented an excellent historical perspective of the occurrence of CUI. A conference held in the UK in 2004¹¹ had a similar theme and again suggested that CUI had not been mitigated and that instances of CUI where actually increasing. These instances led to the formation of an informal group based in the UK (UK CUI Forum)¹² by corrosion and materials engineers from a number of major oil and gas producers in the UK specifically to share CUI related information. The Forum has since expanded and now includes representatives from other industries. Collaboration between the UK CUI Forum and the European Federation of Corrosion (EFC) led to the development of this document, EFC Number 55 “Corrosion Under Insulation Guidelines (CUI)”¹³ first published in 2008.

Why does CUI occur? CUI of carbon manganese and low alloy steel usually occurs when a number of conditions are fulfilled:

• Water or moisture must be present on the substrate in order to allow oxygen corrosion to occur. Water ingress is due to breaks in the insulation cladding/jacketing which may have resulted as a consequence of poor installation, damage during service, or simply as a result of deterioration over time. The principle sources of water are:

– External sources, which include rainwater, deluge systems, and process liquid spillage, and

– Condensation

This water may be retained depending on the absorption properties of the insulation material and the operating temperature. Depending upon process conditions, saturated insulation may never have the opportunity to dry out completely.

Generally CUI is classified into one of four categories:

• Low temperature (cold or cryogenic)

• Sweating service (below dew point)

• High temperature

• Cyclic temperature

All of the four CUI categories are influenced by location or geography and prevailing local climatic conditions. This is especially pertinent for equipment operating below ambient temperature or in sweating service with the CUI rate being influenced by the average ambient temperature and humidity. The temperature and humidity controls the dew point and it is the dew point that controls the degree of wetness. Figure 1.1 shows the dew point annual variation in three different regions and clearly illustrates the influence of dew point on the degree of wetness and possible CUI for equipment operating at the same temperature.

Figure 1.1 Influence of annual variation in temperature and dew point in different regions on the degree of wetness.

Contaminants that can cause problems on both carbon manganese and low alloy steel as well as austenitic stainless steel need to be present. Chlorides and sulfides make up the bulk of the contamination and generally increase the corrosivity of the water. The source of the contaminants can be external, such as...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Volumes in the EFC series
• Introduction
• 1: Introduction
• 2: Economic consideration
• 3: Ownership and responsibility
• 4: The risk-based inspection methodology for CUI
• 5: Inspection activities/strategy
• 6: Nondestructive examination and testing techniques for CUI
• 7: Recommended best practice to mitigate CUI
• 8: Design for the prevention of CUI
• Appendix A: Cost: Economic evaluation
• Appendix B: Quality assurance
• Appendix C: Additional guidelines on the implementation of CUI best practice
• Appendix D: Coatings
• Appendix E: Application of thermal sprayed aluminum
• Appendix F: Insulation material types and forms
• Appendix G: Cladding/jacketing materials
• Appendix H: Use of protection guards
• Appendix I: NDE/NDT techniques
• Index
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