Author: M. Vargas

This paper was presented at Corrosion & Prevention 2023.

ABSTRACT

Fabric Maintenance (FM) refers to any type of asset structural maintenance that does not involve mechanical and electrical works, therefore it typically includes coatings, passive fire protection, welding, insulation, and other material and surface protection disciplines. Over the years, FM as a discipline has been purposedly segregated from other maintenance categories to reinforce its importance in the safekeeping of aging oil & gas, petrochemical, marine and energy sector infrastructures, with an ultimate goal of not repeating catastrophic failures from the past. Still, the implementation of effective and efficient FM campaigns proves to be a challenge, often compounded by management neglect, misunderstanding of failure mechanisms, limited human and physical resources, and the lack of sustainable solutions with easy implementation. This overview focuses on discussing sustainable corrosion and surface protection solutions to facilitate the delivery of FM campaigns, including a non-exhaustive summary of current FM solutions. The document concludes with an illustration of a sustainable solution consisting of the easy and cost effective implementation of visco-elastic coatings for mitigation of localised corrosion in widely used stainless steels.

Keywords: Fabric maintenance, sustainable solution, surface protection, visco-elastic coatings

Introduction

Fabric maintenance (FM) intends to restore materials to their intended purpose, whether it is protecting against corrosion and metal loss, or maintaining other materials properties (e.g., mechanical, heat transfer) to avoid failure.

With many of the large scale plants and assets in Oil & Gas, petrochemical, and energy sector infrastructures coming to the end of their originally intended service life, one of the main focuses to FM is to, first and foremost, protect assets that are already in place, but to do it in a sustainable way to ensure a gradual energy transition into new and cleaner technologies.

Over the last few decades, there has been a significant advancement of corrosion and materials knowledge with an important input from global major players mostly from the Oil & Gas sectors. Nonetheless, FM is still considered a burden with the widespread occurrence of corrosion and materials failures. Industry experts may attribute these to the following factors[1, 2]:

• Current drive by corporations to reduce operational expenditure (OPEX) as low as possible, with production outcomes prioritised over FM campaigns, leading to inadequate FM planning. There is a definitive disregard for ISO 4628-3 [3] and ISO 12944-5 [4] which mandate partial repair of assets at rust grade Ri3 (rust in 1% of the surface).
• OPEX cuts also impose extreme restrictions of resources which limit frequency and extent of inspection, and accurate condition assessments and repairs. Inspections are likely conducted beyond the material corrosion allowance. This aspect may also be linked to underestimation of corrosion rates, particularly in severely corrosive environments. As a result, the need for urgent repairs when material reaches its critical metal loss thickness significantly increases FM and operation costs. Ultimately, assets can reach a potential state of disrepair where replacement is the only viable solution.
• Incorrect material and coating specifications can lead to early and extensive fabric damage, requiring quick attention and reallocation of resources for repair.
• There is maintenance priority of pipelines and vessels due to the higher consequence in the case of failure (Figure 1). Structural repairs usually become secondary and even neglected in FM campaigns. For instance, damage of concrete and passive fire protection (PFP) structures can lead to catastrophic failures due to concrete cancer, and the continuous exposure and subsequent loss of reinforcing steel.

• Figure 1: pipeline corrosion in a natural gas liquids plant. Pipe and vessels repair prioritised over structural repairs.

• Even though there is an increasing scrutiny on training and qualifications of applicators and related FM trades, improvement of quality assurance practices and increased effort in supervision in compliance with standards, it only takes ONE deviation from correct application for the early onset of coating failures and corrosion. Application errors are often compounded by limited safe access to site (e.g., the use of scaffolding, rope access, suspended platform, or boat/diving access for offshore installations) and contractual pressures.

• Extensive focus on general and atmospheric corrosion damage with a lot less attention to other corrosion mechanisms such as chloride localised corrosion and pitting affecting austenitic and duplex stainless steels used extensively in processing and seawater systems. Likewise, failures due to corrosion under insulation (CUI) or microbiologically influenced corrosion (MIC) are only becoming more acknowledged and better documented over the last decade.

The list goes on, but these facts exemplify some of the burdens and complexities faced by FM in most plants, with different degrees of criticality. Meaningful opportunities to improve FM delivery must start with decision making based on smart, cost effective, factual, and sustainable solutions offered by corrosion, materials, and asset integrity specialists. These are discussed in subsequent sections.

Sustainable solutions to fabric maintenance

In 1987, the United Nations defined sustainability as “meeting the need of the present without the ability of future generations to meet their own needs” [5], concept supported by 3 basic sustainability pillars: Environmental protection, social development, and economic development [6]. A brief analysis of what these pillars could mean for FM is presented in Table 1.

Table 1: sustainability pillars applied to fabric maintenance

Current developments on sustainable solutions

Over the last decades, there have been very encouraging developments on corrosion control and mitigation that have or potentially can be implemented for improved and sustainable FM campaigns. Some of these solutions are summarised in Table 2:

Table 2: examples of existing sustainable solutions applicable to FM

Example of a sustainable solution: Use of pure polyisobutene visco-elastic coatings to arrest pit growth in stainless steels

Background

Stainless steels (SS) are materials of choice to build the infrastructure for oil and gas (O&G) operations due to their high corrosion resistance compared to carbon steels. The addition of Chromium (Cr) induces the formation of passive oxide films in the form of Cr₂O₃ or CrO. Single phase austenitic alloys (e.g., 304, 316, 316L) are mainly used for utilities, structural and transport applications, whereas higher grades such as duplex and superduplex SS (>22%Cr, >4%Ni) are used for building processing and seawater systems.

Stainless steels, however, prone to localised corrosion and pitting due to the rupture of the passive film, particularly in the presence of acids and high chloride concentrations in offshore facilities, where humidity is usually above 80% RH and corrosive saline droplets (NaCl, MgCl₂) are constantly deposited at the metal surface. Localised corrosion and pitting are also exacerbated at temperatures exceeding 55°C [8], which are typical service temperatures at O&G operational phases.

Given the consequence of any possible failure, the standard industrial practice in O&G plants is to replace any SS pressure equipment undergoing pitting or localised corrosion [9]. Besides this being an extremely expensive approach, it also represents significant down time and production loss. The mitigation of pitting growth has been a matter of significant investigation as this corrosion mechanism costs millions of dollars in production sites worldwide.

The materials and corrosion engineering team at Woodside Energy have been able to implement the use of oxygen and water impervious visco-elastic coatings to mitigate uniform corrosion in carbon and low-grade steels. Woodside embarked in a collaboration with Monash University to trial the effectiveness of the pure polyisobutene visco-elastic coatings in stifling pitting corrosion of austenitic steels. The hypothesis was that an oxygen impervious coating can restrict the electrochemical cathodic reactions at the steel surface, in turn stopping the anodic reactions leading to pit growth [9,10].

Methods and Materials

SS 316L coupons were exposed to 6% ferric chloride (FeCl₃) droplets to get pitting initiated on the surface. The pits were then characterised using high resolution X-Ray computed tomography (CT) with the sample stage being rotated to generate 2D images. Then, the 2D images were processed using Aviso® software to generate 3D X-Ray CT maps of specimens and pits. Similar tests were conducted using lower grade 304L to observe more significant pit growth over short exposures [10]. Complete experimental details are provided elsewhere [9,10].

Once the active pits were characterised, the visco-elastic coating was applied onto some of the specimens while others remained uncoated for control. Coated and uncoated specimens were kept in a humidity chamber (>80% RH) for a prolonged exposure of up to 6 weeks, after which the samples were again characterised by X-Ray CT, both before and after exposure.

Results

The X-Ray CT maps of the uncoated and coated coupons are presented in Figures 2-3.

Figure 2: (a) X-Ray generated image of a pit in 316L formed after exposure to 6% FeCl3droplet after 2 weeks of exposure. (b) X-Ray CTmap of the pit, revealing the morphology of pit beneath the surface of material [9, Courtesy of M.Brameld]

Figure 3: X-Ray CT images of two pits in 316L covered with visco-elastic coating after pit formation. the pits do not show any growth beneath the coating, after 1 day, 30 days and 90 days of ambient exposure. [9, Courtesy of M. Brameld]

The results presented in Figure 3, clearly indicate that there is no pitting growth beneath the coating, whereas there is pit growth and propagation of the uncoated 316L samples. Replication of these tests in 304L samples provided repetitive results, with complete arrest of pit growth in the coated samples.

The hypothesis was proven to be correct, with the visco-elastic coating being able to arrest pit growth by stifling the cathodic reaction at the metal surface. The success of this trial enabled the deployment of the visco-elastic coating on existing stainless steel assets, extending their service life, avoiding material replacement, and saving the business tens of millions of dollars in fabric maintenance.

Conclusions

There is no single solution to the many challenges affecting FM. Rather, the implementation of effective FM comes from a combination of practices appropriately defined under the sustainability pillars: Environmental Protection, Social Development and Economic Development.

The most viable starting point is the protection of the existing ageing infrastructure in a sustainable way, making use of existing technologies and expanding the knowledge by continuous collaboration between asset owners, research institutions, OEMs and stakeholders. In many cases, the problem lies on building confidence in the use of these newer materials and solutions, any technical attempts by research institutions, manufacturers and suppliers need to have full-scale trials and data around their durability. This approach will guarantee a safe and gradual transition into new technologies.

Acknowledgments

Special thanks to Mr Michael Brameld, Chief Technology Materials Engineer at Woodside Energy for his generosity sharing his knowledge and experience. Many thanks to the team at Anti Corrosion Technology and FITT Resources for their continuous support.

References

7. Wilson L. Fabric Maintenance and Asset Integrity. CORRTECH (2020): https://www.linkedin.com/pulse/fabric-maintenance-asset-integrity-lee-wilson/ Last accessed 30 September 2023.
8. Personal Correspondence with Michael Brameld, Chief Materials & Inspection Engineer, Woodside Energy Limited, Perth WA.
9. ISO 4628-3:2016 Paints and Varnishes: Evaluation of degradation of coatings.
10. ISO 12944-5:2019 Paints and Varnishes: Corrosion protection of steel structures by protective paint systems.
11. Definition of Sustainability, United Nations UN Brundtland Commission (1987): https://www.un.org/en/academic-impact/sustainability/ Last accessed 2 October 2023.
12. What is Sustainability, The Welding Institute TWI: https://www.twi-global.com/technical-knowledge/faqs/faq-what-is-sustainability. Last accessed 2 October 2023
13. Sheedy C, Concrete Solutions, Create, Engineers Australia (Editors), Vol 9, No 7 (August 2023)
14. Sedriks AJ. Corrosion of Stainless Steel, 2nd Edition, John Wiley & Sons, Inc., New York, NY. 1996.
15. Brameld M, Thomas S and Malab GS, Collaboration solves long standing corrosion problem, The APPEA Journal 60 (2020).
16. Sander G, Brameld M, Mahbub A, Haque A, Costa C and Thomas S, Arresting active pit growth in stainless steels using an impervious visco-elastic coating. Final Report Woodside Energy- Monash University (2020).

Author Details

Dr M. Vargas is the Engineering Services Manager at Anti Corrosion Technology, a position she has held since 2021. She has over 20 years research, industry, and consulting experience in the areas of corrosion, materials performance, integrity management and failure analysis. She is an SME in the topic of microbiologically influenced corrosion (MIC). As part of her current role, she leads the implementation of corrosion specifications in assets around Australia and is the main consultant in legal failure reports.