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Rob Francis

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Papers by Rob Francis

Dry Film Thickness: Is More Coating Always Better?

Coatings+, SSPC 2019, Orlando, Florida, February, 2019

Coating thickness is one of the most important parameters influencing durability of a protective ... more Coating thickness is one of the most important parameters influencing durability of a protective coating system. As a general rule-of-thumb, the thicker the coating, the greater the protection. But is there any upper limit to this general rule? This paper looks at durability figures of common protective coating systems for atmospheric and immersion exposure as a function of dry film thickness. The examples are from studies in North America as well as International and Australian standards. While these studies show there is increasing durability with thickness for low overall film thicknesses, there is strong evidence that this improvement flattens out at a total thickness of around 250 microns (10 mils) for atmospheric coating systems, and a somewhat greater thickness for coatings exposed to immersed conditions. The paper discusses some reasons why this behaviour may arise. It also describes some practical hints for ensuring coverage of edges and corners when applying coatings at lower thicknesses.

Thickness of Marine Coatings: Measurements, Standards and Problems

Marine Coatings, 18 April 2013, London, UK, 2013

Dry film thickness (DFT) is probably the single most important measurement made during inspection... more Dry film thickness (DFT) is probably the single most important measurement made during inspection or quality control of protective coating application. The introduction of IMO resolution MSC 215(82) on Performance Standards for Protective Coatings has drawn attention to the importance DFT measurement in achieving the desired durability of protective coatings in marine applications. This document, along with DFT standards from ISO in Europe and SSPC in the USA, provide the coating specifier, applicator and inspector with information on measuring techniques, acceptability of readings, inspection plans and other important aspects of DFT measurement. This paper describes DFT measurement and compares the requirements of the IMO performance Standard with those described in other Standards. It also provides examples of typical readings and how they can be analysed and suggests some important areas that must be examined to remediate inconsistencies and inefficiencies in DFT specification, measurement and analysis of results.

Long-Term Corrosion Rates: Guide Values in Codes Compared to Actual Results

Australasian Corrosion Association Conference, Perth November 2023 – Paper number ACA2023-19921, 2023

This paper looks at long-term steel corrosion rates for atmospheric, immersed and underground env... more This paper looks at long-term steel corrosion rates for atmospheric, immersed and underground environments as advised in standards and compares them to actual figures available in the literature. Atmospheric corrosivity can be quantified by measuring the first-year corrosion rate of steel. According to ISO 9224, the long-term corrosion rate can be determined if this first year rate is known. The results of a number of investigations into longer term corrosion in a range of environmental corrosivities have been compared with the suggested long-term rates given in the ISO 9224 standard. For immersed and underground environments, a comparison has been made between actual long-term loss measurements in these environments from the literature and the suggested losses given in the piling standards, AS 2159 and Eurocode 3 Part 5. These comparisons show that, while the standards can give realistic loss figures in some situations, in other cases the suggested losses due to corrosion can be quite erroneous.

Fillers or Extenders in Zinc-Rich paints

Australasian Corrosion Association Conference, Perth, November 2023 – Paper number 0023-19838, 2023

Fillers or extender pigments have been added to protective coatings over the years, mainly to eco... more Fillers or extender pigments have been added to protective coatings over the years, mainly to economically increase the solids content of the paint. Such additions have often been added to commercial zinc-rich paints, but their effect on durability has not been widely discussed. This review evaluates investigations that have looked at the effect of such additions on the durability of zinc-rich paints, both organic and inorganic. It looks at the different extenders of various shape and sizes that have been used. The review shows that most such additions are not detrimental to performance and, in fact, are often beneficial. Nodular, inert extenders that are relatively coarse such as silica, with a particle size somewhat larger than the zinc particles, appear to be most effective. A possible explanation for these findings is given.

So How Long Will It Last? Understanding the Corrosion Rate of Structural Steel

Steel Construction, Vol 20, No2, June, 2020

This paper looks at the factors influencing the rate of steel corrosion in the atmosphere, how it... more

Zinc-rich paints: Exploring protection mechanisms

ACA Conference, Newcastle, Australia Paper 326, 2022

Zinc-rich paints are the protective coating of choice as primers and single coat systems for many... more Zinc-rich paints are the protective coating of choice as primers and single coat systems for many aggressive environments. They provide sacrificial protection to the steel substrate and it is this property that sets them apart from other coating types. There must be some sort of alternative protection to explain their performance for long-term protection when cathodic protection may be lost, but there have been many differing opinions and theories provided over the years. This paper reviews some of the field exposure, accelerated testing and electrochemical investigations that have been carried out on zinc-rich paints over the years to attempt to provide a clearer understanding of how they provide protection.

Laboratory testing of zinc-rich paints: What can you learn?

ACA Conference, Newcastle, Australia. Paper 286, 2022

Investigations into the performance and protection mechanisms of protective coatings will typical... more Investigations into the performance and protection mechanisms of protective coatings will typically require accelerated exposure or electrochemical tests or both to be carried out. A number of such tests have been developed over the years which range from quick and simple exposure tests to complex electrochemical investigations. This paper reviews the most popular tests used in investigations, specifically into the performance zinc-rich paints, mainly directed at coating users and specifiers rather than researchers. A brief description of the methods, how the results may be presented, examples and advantages and limitations are given.

Ten Years’ Experience with the Australian Corrosivity Standard

ACA Conference, Adelaide, Australia, Paper 13, 2018

AS 4312 (Atmospheric corrosivity zones in Australia) has been in use for ten years and is still t... more AS 4312 (Atmospheric corrosivity zones in Australia) has been in use for ten years and is still the only standard of its kind in the world. It enables the user to identify the important factors which influence atmospheric corrosion and determine the ISO corrosivity category for a given geographic location in Australia. This paper describes some new information now available, how it relates to AS 4312 and how it can be used to update and improve the standard.

Understanding and monitoring photodegradation

JPCL, 2023

The primary purpose of a protective coating is to prevent corrosion of the substrate, but it is o... more The primary purpose of a protective coating is to prevent corrosion of the substrate, but it is often important that the structure looks attractive, especially when visible to the public. Even when the coating is sound, if the appearance is poor, then it will often require repair and maintenance. This article looks at the main causes of poor appearance, concentrating on color loss, along with how changes in color can be quantified. The CityLink Gateway structure on a major highway into Melbourne, Australia, provides a case study showing how such how such color change can be minimized and monitored.

Comprehending Pull-off Adhesion Testing

JPCL, 2020

Pull-off adhesion testing of coatings is increasingly being specified and used by coating inspect... more Pull-off adhesion testing of coatings is increasingly being specified and used by coating inspectors. Is this increased interest based on the its ability to provide useful information on the performance of coating systems, or is this a case of a test method being more attractive because
it can produce a number— even if that number has little meaning? This article looks closely at pull-off testing— specifically, what is measured and what the results mean.

format_quoteDifferent pull-off testing devices affect results significantly, impacting reliability and validity.format_quote

A Close Look at Visual Surface Cleaning Standards

JPCL, 2015

Visual cleanliness of a steel surface is perhaps the most important requirement influencing coati... more Visual cleanliness of a steel surface is perhaps the most important requirement influencing coating durability. However, there are arguments, confusion and disagreements regarding both cleanliness levels and correlation between the various industry standards. Furthermore, new methods of power tool cleaning are being introduced, which claim to provide cleanliness levels approaching those of the higher classes of abrasive blast-cleaning. This article discusses visual cleanliness for blast-cleaning and hand and power tool cleaning, with a view on clarifying requirements for the specifier, contractor and inspector.

format_quoteThe highest blast-cleaning standard (SSPC-SP 5) requires complete removal of all contaminants for optimal coating durability.format_quote

Relining Potable Water Tanks: Research and Field Work

JPCL, 2012

The steel floor plates of a number of Melbourne Water’s potable water tanks have suffered severe ... more The steel floor plates of a number of Melbourne Water’s potable water tanks have suffered severe corrosion and perforation because of chloride salts in the limestone bedding material. One method of remediation is to apply a reinforced organic lining to the steel base. Candidate lining and reinforcement types were investigated and are described in this article.
A review of repair options concluded that installation of a reinforced epoxy lining, which provides mechanical strength in addition to corrosion protection, was the optimum solution. This article looks at the issues involved in selecting a lining that provides the required strength and flexibility as well as resistance to and compatibility with potable water, including a discussion of candidate glass reinforcement materials. Also described are practical issues involved in applying the lining and the
results of a follow-up inspection.

Francis JPCL Dec 2009 Dry Film Thickness Measurements - How Many Are Enough

JPCL, 2009

Dry film thickness (DFT) is probably the single most important measurement made during inspection... more Dry film thickness (DFT) is probably the single most important measurement made during inspection or quality control of protective coating application. Even the most basic protective coating specification will inevitably require the DFT to be measured. The thickness of each coating in a system, and the total system thickness will have to be measured and recorded to show that the specified system will meet the desired durability. The number of readings that will be taken is important to all parties involved in coating works. The contractor and inspector obviously need to know how many readings to take as part of their inspection or QA work. But the owner and specifier also need to be aware of such requirements because this will greatly influence the cost and time required for inspection. This paper looks at the requirements regarding the number of readings that have to be taken described in recent DFT standards. There are many other important aspects of DFT measurement, including adjustment of gauges and effect of surface profile but this paper concentrates on the required number of readings.

Corrosive effects of micro-environments and design features

ACA On-line Conference. Paper 015, 2020

The recently updated standard on Australian atmospheric corrosivity zones, AS 4312, concentrates ... more The recently updated standard on Australian atmospheric corrosivity zones, AS 4312, concentrates on identifying macro environments or macro corrosivity zones, largely based on proximity to the ocean and whether the seas are rough or relatively quiet. However, it is well known that the corrosivity in such macro-environments can be significantly modified by the presence of micro-environments such as local pollution sources or by design features such as ponding areas. While the standard recognises the impact of these on corrosivity, very little information is provided on the actual quantitative effect they may have. This paper looks at the corrosion effect of these features on structural and other metallic objects largely from the literature and gives some guidance on how they may affect corrosivity of a given site and structure.

The treatment of rusted steel with mimosa tannin

Corrosion Science, 1978

Tannin treatments for rusted steel have been in use for some years now but their mode of action i... more Tannin treatments for rusted steel have been in use for some years now but their mode of action is poorly understood. Investigations including the use of scanning electron microscopy, electron probe analysis and i.r. spectrophotometry, have determined some fundamental aspects of the behaviour of tannin when protecting steel. It was found that the tannin reacted with the steel to form a crazed outer layer of ferric tannate. About half the rust was impregnated with the ferric tannate or unreacted tannin. Some of the rust was apparently converted to protective magnetite over a period of time. Excessive moisture caused breakdown of the film by removing the unreacted tannin and causing regrowth of the existing rust.

When colour matters: Resisting photodegradtion of coatings

ACA Conference, Melbourne, 2019

Many paint coating systems will provide good corrosion protection for years but achieving long la... more Many paint coating systems will provide good corrosion protection for years but achieving long lasting aesthetics is more challenging, especially for high profile structures exposed to harsh Australian UV conditions. Degradation of the appearance of a coating by chalking, loss of gloss or differential colour fading or some combination of these is caused by exposure to UV radiation and weathering. This paper focuses on the mechanisms of colour change and how such degradation can be measured. It looks at how Melbourne's CityLink Gateway red colour degraded and how this has since been minimised. Monitoring colour change of the structure has shown only minor fade after seven year's exposure.

Comprehending coating adhesion: Part 2– Pull-off adhesion testing

Corrosion & Materials, 2019

Pull-off ‘adhesion’ testing of coatings appears to be more regularly discussed and specified in r... more Pull-off ‘adhesion’ testing of coatings appears to be more regularly discussed and specified in recent years. Is this increased interest based on its ability to provide useful information on performance of coating systems, or is this a case of a test method being more attractive because it can produce a number, even if that number has little meaning? This paper looks closely at pull-off testing, what is measured and what the results mean.

The Morphology of Corrosion Products on Steel

Key Engineering Materials, 1991

Chloride Contamination Measurement to AS3894 part 6

Corrosion and Materials, Nov 2018, pp30-31, 2018

The method for determination of soluble salts (chlorides) according to AS 3894.61 Method A allows... more The method for determination of soluble salts (chlorides) according to
AS 3894.61 Method A allows two methods of extraction of the chlorides,
the swabbing procedure and plastic patch procedure, commonly known as the Bresle patch. One method of analysis of the solution is given, the use of chloride titrator strips, commonly known as Quantab strips. Although these methods, and newer developments, have now been in use for many years, there is still some confusion regarding the results and comparison between the methods. This note discusses some issues regarding the measurements obtained using the two analysis methods.

Francis C&M 201811 Comprehending coating adhesion Part 1

Corrosion and Materials, 2018

This paper looks at the factors that determine whether or not a given coating will adhere to a su... more This paper looks at the factors that determine whether or not a given coating will adhere to a substrate. After some adhesion fundamentals, it compares adhesion of epoxy to steel to the lack of adhesion to polyethylene. It looks at the effect of abrasive blasting and adhesion of low energy surfaces.

$Figure 5: Relationship between peel force and viscoelastic properties. speeds, the adhesive acts like a liquid and very low peel strength is measured. However, as the peel rate increases, the adhesive becomes more viscous and the forces are now used up in pulling the adhesive apart. The adhesive fails in a cohesive manner and the required peel force increases. At very high strain rates, the adhesive acts largely as a glassy solid and easily fractures, resulting in much easier removal.$