Corrosion Under Insulation (CUI) Guidelines

Technical Guide for Managing CUI

Gino De Landtsheer

• Publisher: Woodhead Publishing
• Year: 2020
• eBook ISBN: 9780128233368
• Edition: 3
• Topic: Technology & Engineering
• Subtopic: Chemical & Biochemical Engineering
• Index: Technology & Engineering

Corrosion Under Insulation (CUI) Guidelines: Technical Guide for Managing CUI, Third Edition, Volume 55 builds upon the success of the first two editions to provide a fully up-to-date, practical source of information on how to monitor and manage insulated systems. 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 were intended for use on all plants and installations that contain insulated vessels, piping, and equipment, and cover a risk-based inspection methodology for CUI, inspection techniques, and recommended best practices for mitigating CUI.The guidelines include design of plant and equipment, coatings and the use of thermal spray techniques, types of insulation, cladding/jacketing materials, and protection guards. 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.- Provides revised and updated technical guidance on managing CUI provided by EFC Working Parties 13 and 15- Discusses the standard approach to risk based inspection methodology- Presents the argument that CUI is everywhere, and looks at mitigating actions that can be started from the onset- Includes a wide array of concepts of corrosion mitigation

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

Chapter outline

• 1.1 Purpose of the document
• References

Corrosion-under-insulation (CUI) refers to the external corrosion of piping and vessels, fabricated from carbon-manganese, low-alloy and austenitic stainless steels, that occurs underneath externally clad or jacketed insulation owing to the penetration of water.

By its very nature, CUI tends to remain undetected until the insulation and cladding or jacketing are removed, to allow inspection or when leaks to atmosphere occur. CUI is a major common problem on a worldwide basis that is shared by all the refining, petrochemical, power, industrial, onshore and offshore industries.

It is not a new problem, but it can be a serious problem. CUI has been responsible for many major leaks that lead to health and safety incidents, result in lost production and are responsible for the large maintenance budgets, which are required to mitigate the problem.

Corrosion of austenitic stainless steels usually manifests itself as chloride external stress corrosion cracking (CI-ESCC). Although Cl-ESCC [1] was first reported in 1965, not many references are available on the CUI of carbon‑manganese steels and low-alloy steels up to 1980 when a meeting was held in November 1980 [2]. A review of this very successful 2 day meeting was given by Richardson [3] during a symposium which was held in 1983 [4], and was sponsored by the Association for Testing and Materials (ASTM), the National Association of Corrosion Engineers (NACE) and the Materials Technology Institute (MTI). It would appear that, when reviewing the literature from that meeting today, the problems reported in 1980 still mirror the experiences currently being reported today.

Although numerous instances of CUI are reported annually, this has not been reflected in the production of many industry standards for insulation or measures to mitigate CUI.

The first ASTM standard on thermal insulation materials relevant to CUI was adopted in 1971 [5]. NACE Task Group T-6H-31 first issued a report on CUI [6] in 1989 and later Task Group T- 5A-30 was formed, which became an open forum for CUI problems and solutions. This led to the publication of a NACE recommended practice RP0198-98 [7] which was revised in 2004 [8].

A number of conferences and initiatives covering CUI and insulation materials have taken place since 1983, but the problem still 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.

An NACE conference in 2003 reviewed similar topics covered back in 1983 which were illustrated by Delahunt [9] who presented an excellent historical perspective of the occurrence of CUI.

A conference held in the UK in 2004 [10] had a similar theme and again suggested that CUI had not been mitigated and that instances of CUI were actually increasing.

These instances led to the formation of an informal group (UK CUI Forum) [11] 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, which is continuously updated to reflect any major advances in the mitigation of CUI.

Why does CUI occur?

CUI of carbon‑manganese steels and low-alloy steels 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 or jacketing which may have resulted as a consequence of poor installation or damage during service or simply be a result of deterioration over time. The principal sources of water are as follows:
  1. o External sources which include rainwater, deluge systems and process liquid spillage.
  2. o 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.

Contaminants that can cause problems on both carbon‑manganese steels and low-alloy steels as well as on austenitic stainless steels need to be present. Chlorides and sulfur species (such as sulfuric acid) 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 environmentally borne chloride sources include sites situated in a marine environment (e.g. offshore), or windborne salts from cooling tower drift, or from periodic testing of firewater deluge systems.

Contaminants can also be produced by leaching from the insulation material itself. Additionally, laboratory studies have shown that higher contaminant concentrations will be found when insulations are thermally aged. But it needs to be highlighted that this observation is only applicable for some insulation materials as other type of insulation materials seems to have better/superior thermal stability. This is quite important when looking to the properties as specified at their product data sheets as they tend to be tested as fresh/new materials without these thermal degradation phenomena.

In the presence of an applied or residual stress and temperatures exceeding 60 °C (140 °F), high chloride contents of water contribute to Cl-ESCC.

The operating temperature range of the piping or vessels for having CUI to occur should be between − 4 °C (25 °F) and 175 °C (347 °F). This temperature range reflects the experience from the contributors to this document and is meant as guide to enable mitigation procedures to be developed.

It needs to be noted that CUI problems have been reported outside this range, but the majority of CUI occurrences are, however, within the specified range from − 4 °C (25 °F) to 175 °C (347 °F). In general, the metal temperature will be approximately the same as the process operating temperature (for insulated equipment). However, if the insulation is damaged and/or highly humid conditions commonly exist, a process temperature significantly above 121 °C (250 °F) can result in metal temperatures low enough to cause CUI; therefore the CUI range is extended to 175 °C (347 °F).

In addition, equipment subject to cyclic temperatures even outside this range (e.g. regeneration equipment) or dead legs (including ‘cold’ dead legs nominally operating below − 4 °C and warming up to ambient temperatures) should be cons...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• European Federation of Corrosion (EFC) publications: Series introduction
• Volumes in the EFC series list
• 1: Introduction
• 2: Economic consideration
• 3: Ownership and responsibility
• 4: The risk-based inspection methodology for CUI
• 5: Inspection activities and strategy
• 6: Non-destructive examination and testing screening techniques for corrosion-under-insulation
• 7: Recommended best practice to mitigate CUI
• 8: Design for the prevention of corrosion-under-insulation
• Appendix A: Cost-economic evaluation
• Appendix B: Quality assurance
• Appendix C: Additional guidelines on the implementation of CUI best practices
• Appendix D: Coatings
• Appendix E: Application of thermally sprayed aluminum
• Appendix F: Types and forms of insulation material
• Appendix G: Cladding and jacketing materials
• Appendix H: Use of protection guards
• Appendix I: Non-destructive examination and testing techniques
• Appendix J: Case studies
• Index