Review
Evaluation of the cathodic disbondment resistance of pipeline coatings – A review

https://doi.org/10.1016/j.porgcoat.2020.105728Get rights and content

Highlights

  • Understanding of different mechanisms of cathodic disbondment of pipeline coatings.

  • Recent advancement in both ex-situ and in-situ cathodic disbondment test methods.

  • Strategies for mitigating cathodic disbondment and corrosion related.

Abstract

For coated pipelines with cathodic protection, cathodic disbondment has been recognized as the main cause of coating degradation. A thorough understanding of the cathodic disbondment mechanism, a proper evaluation of the coating resistance to disbondment as well as a precise monitoring of the cathodic protection level would minimize the occurrence of cathodic disbondment and help to maintain a pipeline’s long-term integrity. This paper first reviews the various mechanisms proposed in the literature for cathodic disbondment. To provide useful guidance for selecting pipeline coating systems, cathodic disbondment test methods (categorized as standard test methods or modified test methods) that have been developed over the past two decades are then critically reviewed. In-situ techniques for assessing cathodic disbondment of coatings, especially those having promise for field applications, are also discussed. Finally, a brief discussion on the mitigation of cathodic disbondment and the associated corrosion is presented.

Introduction

Pipelines are an integral component of our modern society as they provide the most practical and the safest way of delivering oil and gas [1] to satisfy the energy demands of our daily life. Take Canada for example: approximately 1.2 billion barrels (∼ 190 billion liters) of liquid petroleum products and 5.3 trillion cubic feet (∼ 150 trillion liters) of natural gas are transported by pipelines each year [2]. In 2015, the total economic impact from the operation of all of the energy transmission pipelines in Canada on GDP was estimated to be about $11.5 billion (about 0.7 % of the total GDP) [3]. The long-term integrity of pipelines is therefore of significant economic importance. As steel pipes tend to corrode when exposed to moist soil or wet air, applying coatings on the surface of pipes is the primary approach to defend them against corrosion. Coatings provide a physical and electrochemical barrier between the steel surface of the pipe and the surrounding environment. However, defects in pipeline coatings are unavoidable at every stage of the coating process, the pipe installation and operation of the pipeline. A discontinuity in pipeline coatings is referred to as a “holiday”. Once a holiday exposes bare metal to the surrounding environment, corrosion can occur. This is where cathodic protection (CP) becomes important. CP enforces a cathodic current at the coating defect sites to protect the steel pipe from corrosion so that it cannot become an anode. Therefore, for immersed and buried pipelines in the field, a combination of protective coatings and CP is almost always adopted to defend against corrosion. Nevertheless, depending on the nature of the defect and the surrounding environment’s chemistry, cathodic current provided by CP may result in reaction products that can affect adhesion of the coating around the defect and cause so called cathodic disbondment (CD), which is considered to be the most significant degradation mechanism for organic coatings on submerged steel [4]. Since the performance of a coating system directly affects the integrity of the pipelines it protects, it is essential to evaluate coating performance in conditions encountered during the installation and operational life of pipelines. As a consequence, ex-situ CD tests as well as in-situ CD assessment have been developed through the years to assess coating performance before and after service in the field. Ex-situ CD tests provide a basis with which to judge the resistance of coatings to CD and thus act as a practical tool to select pipeline coatings. In-situ CD assessment offers a way to monitor a coating’s performance non-destructively and is useful in aiding the maintenance of pipelines in the field, such as via the adjustment of applied CP potentials.

In this review, fundamental aspects of CD are first introduced, focusing on a discussion of the proposed mechanisms. Following this, ex-situ CD test methods including both the standard and modified methods are examined. The influence and the significance of test parameters on the disbondment rate is analyzed to reveal the advancement of the standard test methods. The need for developing modified CD test methods as well as their contribution to coating evaluation is discussed. The potential use of these ex-situ CD test methods to compare the disbondment resistance of coatings, e.g., fusion bonded epoxy (FBE) and high-performance powder coating (HPPC) is also presented. The third part of this review introduces various in-situ techniques to monitor the CD behavior of coatings, compares the pros and cons of each technique and addresses the development of two techniques in particular, i.e., electrochemical impedance spectroscopy (EIS) and electrochemical measurement using a wire beam electrode (WBE). As the mitigation of CD as well as ensuring pipeline integrity are the ultimate goals of any research in this field, the final section discusses strategies that have been used to achieve these goals in terms of coating selection and cathodic protection adjustment. This discussion further highlights the importance and necessity of using the proper CD test for a given situation.

Section snippets

The mechanisms of CD

CD occurs on coated metals that are cathodically protected. CD refers to the failure of adhesion at the coating/substrate interface, which is directly related to the application of CP [5,6]. The mechanistic study of CD reveals how the disbondment commences, shedding light on the methods that may mitigate it.

CD is often initiated by the formation of defects due to accidental coating damage during pipeline handling and installation or imperfect application, leading to excessive permeability of a

Ex-situ evaluation of CD resistance of coatings

Once the coatings have cathodically disbonded, corrosive gases, water, and reactive species may enter the disbonded area and cause pipeline corrosion [[31], [32], [33], [34]]. It is therefore essential to evaluate the CD resistance of coatings when selecting them for use on pipelines. CD tests are designed with relevant test parameters to investigate their effects on the rate of coating disbondment and to provide a reliable assessment of the coating quality. This section discusses both standard

In-situ assessment of CD of coatings

CD test methods provide an efficient way of predicting coating performance and therefore offer useful guidance for coating selection. On the other hand, it is important to note that the present CD test methods are all destructive ex-situ laboratory based tests, which have limitations in accurately predicting the disbondment behavior of coatings in service. For field monitoring of coating disbondment, the use of in-situ techniques (non-destructive methods) is preferred, as these are able to

Mitigation of CD and corrosion under the disbonded coating

For cathodically protected pipelines with coatings, an appropriate amount of CP is able to reduce corrosion to less than 0.01 mm per year [92] and a good quality coating can decrease the current required for protection by a factor of 1000 or greater [93]. However, excessive CP can lead to coating CD, and insufficient CP cannot provide effective corrosion protection [94]. Therefore, the coating resistance to disbondment, the applied CP level, as well as the compatibility of coating and CP after

Summary

Protective coatings and CP are used simultaneously on pipelines to prevent them from corrosion. However, CD, i.e., the loss of adhesion of coatings on the metal substrate, appears as an adverse side effect of the combination of coatings and CP. The application of ex-situ CD tests as well as in-situ techniques to assess the performance of pipeline coatings plays a vital role in mitigating CD and helps to guarantee and maintain the pipeline integrity. Fig. 24 illustrates the effects of coating

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

The authors acknowledge funding support from the Natural Sciences and Engineering Research Council (NSERC) of Canada [NSERC CRDPJ 503725-16]. The funding and in-kind support from Shawcor Ltd. and Specialty Polymer Coatings Inc. [Industry portion - NSERC CRDPJ 503725-16] is also greatly appreciated.

References (114)

  • J.J. Perdomo et al.

    Chemical and electrochemical conditions on steel under disbonded coatings: the effect of previously corroded surfaces and wet and dry cycles

    Corros. Sci.

    (2001)
  • Z. Li et al.

    A study on cathodic protection against crevice corrosion in dilute NaCl solutions

    Corros. Sci.

    (2002)
  • S. Shreepathi

    Physicochemical parameters influencing the testing of cathodic delamination resistance of high build pigmented epoxy coating

    Prog. Org. Coat.

    (2016)
  • G.R. Howell et al.

    Characterization of high performance composite coating for the northern pipeline application

    Prog. Org. Coat.

    (2007)
  • V. Upadhyay et al.

    Localized electrochemical characterization of organic coatings: a brief review

    Prog. Org. Coat.

    (2016)
  • B. Reddy et al.

    Breakdown of organic coatings in corrosive environments examined by scanning kelvin probe and scanning acoustic microscopy

    Electrochim. Acta

    (2004)
  • B. Reddy et al.

    Degradation of organic coatings in a corrosive environment: a study by scanning Kelvin probe and scanning acoustic microscope

    Prog. Org. Coat.

    (2005)
  • R. Montoya et al.

    A cathodic delamination study of coatings with and without mechanical defects

    Corros. Sci.

    (2014)
  • F.M. Geenen et al.

    An impedance spectroscopy study of the degradation mechanism for a model epoxy coating on mild steel

    Prog. Org. Coat.

    (1990)
  • F. Mahdavi et al.

    Electrochemical impedance spectroscopy as a tool to measure cathodic disbondment on coated steel surfaces: capabilities and limitations

    Prog. Org. Coat.

    (2015)
  • K. Darowicki et al.

    Assessment of organic coating degradation via local impedance imaging

    Electrochim. Acta

    (2010)
  • M. Stratmann et al.

    A new technique able to measure directly the delamination of organic polymer films

    Corros. Sci.

    (1991)
  • A.Q. Fu et al.

    Characterization of corrosion of X65 pipeline steel under disbonded coating by scanning Kelvin probe

    Corros. Sci.

    (2009)
  • M.A. Hernández et al.

    Mechanism of cathodic delamination control of zinc–aluminum phosphate pigment in waterborne coatings

    Corros. Sci.

    (2004)
  • Q.L. Thu et al.

    Modified wire beam electrode: a useful tool to evaluate compatibility between organic coatings and cathodic protection

    Prog. Org. Coat.

    (2005)
  • B. Ramezanzadeh et al.

    The effects of addition of poly(vinyl) alcohol (PVA) as a green corrosion inhibitor to the phosphate conversion coating on the anticorrosion and adhesion properties of the epoxy coating on the steel substrate

    Appl. Surf. Sci.

    (2015)
  • Z. Mahidashti et al.

    The role of post-treatment of an ecofriendly cerium nanostructure Conversion coating by green corrosion inhibitor on the adhesion and corrosion protection properties of the epoxy coating

    Prog. Org. Coat.

    (2018)
  • G. Williams et al.

    Inhibition of corrosion driven delamination on iron by smart-release bentonite cation-exchange pigments studied using a scanning Kelvin probe technique

    Prog. Org. Coat.

    (2017)
  • R. Naderi et al.

    Effect of zinc-free phosphate-based anticorrosion pigment on the cathodic disbondment of epoxy-polyamide coating

    Prog. Org. Coat.

    (2014)
  • A. Darvish et al.

    The impact of pigment volume concentration on the protective performance of polyurethane coating with second generation of phosphate based anticorrosion pigment

    Prog. Org. Coat.

    (2014)
  • D. Furchtgott-Roth

    Pipelines are safest for transportation of oil and gas

    Manhattan Inst. Policy Res. No.

    (2013)
  • The Canadian Energy Pipeline Association (CEPA)

    Committed to Safety-committed to Canadians, 2015 Pipeline Industry Performance Report

    (2015)
  • Angevine Economic Consulting Ltd., Economic Impacts From Operation of Canada’s Energy Transmission Pipelines

    (2016)
  • O.Ø Knudsen et al.

    Corrosion Control Through Organic Coatings

    (2017)
  • K. Cameron et al.

    Practical Analysis of Cathodic Disbondment Test Methods

    (2005)
  • G. Weber et al.

    Comparison of Cathodic Disbondment Test Methods for Water Infrastructure Coatings

    (2018)
  • C.G. Munger

    Corrosion Prevention by Protective Coatings

    (1984)
  • R. Brousseau et al.

    Distribution of steady-state cathodic currents underneath a disbonded coating

    Corrosion.

    (1994)
  • J.F. Watts et al.

    The application of X-ray photoelectron spectroscopy to the study of polymer-to-metal adhesion. Part 2. The cathodic disbondment of epoxy coated mild steel

    J. Mater. Sci.

    (1984)
  • R.A. Dickie et al.

    Interfacial chemistry of the corrosion of polybutadiene-coated steel

    Ind. Eng. Chem. Prod. Res. Dev.

    (1981)
  • P. Sorensen et al.

    Reduction of cathodic delamination rates of anticorrosive coatings using free radical scavengers

    J. Coat. Technol. Res.

    (2010)
  • E.L. Koehler

    Technical note: the mechanism of cathodic disbondment of protective organic coatings—aqueous displacement at elevated pH

    Corrosion.

    (1984)
  • T. Kamimura et al.

    Mechanism of cathodic disbonding of three-layer polyethylene-coated steel pipe

    Corrosion.

    (1998)
  • J.E. Castle et al.

    Interface chemistry of stoved organic coatings

    Ind. Eng. Chem. Prod. Res. Dev.

    (1985)
  • M. Kendig et al.

    Mechanism of Disbonding of Pipeline Coatings

    (1992)
  • H. Leidheiser

    Towards a better understanding of corrosion beneath organic coatings

    Corrosion.

    (1983)
  • M. Kendig

    Effect of zeta potential on adhesion of organic coatings

    Corrosion.

    (1992)
  • F. Song et al.

    Evaluation of global cathodic protection criteria-part 1

    Criteria and Relevance With Cathodic Protection Theory

    (2012)
  • J. Holub et al.

    Analysis of CDT Methods and Factors Affecting Cathodic Disbondment

    (2007)
  • N. Kamalanand et al.

    Role of hydrogen and hydroxyl ion in cathodic disbondment

    Anti-corrosion Methods Mater.

    (1998)
  • Cited by (28)

    • Emplacement and evolution of zoned plutons: Multiproxy isotopic and geochemical evidence from the peraluminous Laojunshan leucogranite suite, southwestern China, and implications on the regional geodynamic and metallogenic history

      2023, Gondwana Research
      Citation Excerpt :

      The geodynamic setting of peraluminous leucogranites also remains equivocal. Some scholars attribute such magmatism to a back-arc extension (or intra-arc rift) (Xu et al., 2015) or post-collisional extension (Sylvester, 1998), whereas others correlate with compression-extension associated with seafloor subduction and continental collision (de Sigoyer et al., 2014; He et al., 2021; Wu et al., 2020a). Located in the junction of the Simao block, the Yangtze and the North Vietnam blocks (Fig. 1a), the Late Mesozoic granite-related tungsten-tin metallogenic belt in the Gejiu - Bozushan - Laojunshan area (Fig. 1b) is an excellent natural laboratory for studying the petrogenesis of peraluminous leucogranites.

    View all citing articles on Scopus
    View full text