Coatings World interviewed a number of major coatings manufacturers on the topic of corrosion control. The respondents were Viktoria Slattery, technical lead packaging coatings product development, AkzoNobel; Peter Guest, group technical manager, EMEA liquid industrial coatings, Axalta Coating Systems; Robert Wong, group director, head of protective & industrial, Hempel A/S; Steven C Matthews, technical sales & operations manager – Americas, PPG Protective and Marine Coatings; Dr. Jeffrey David Rogozinski, global product director and Bruce Towes, global market director – oil and gas for Sherwin-Williams Protective & Marine Coatings.

Coatings World: Protecting a substrate from corrosion is one of the most important functions of coatings. What types of products does your company recommend to protect high-value assets (pipelines, outdoor structures, oil rigs, etc.) from corrosion?

AkzoNobel: The particular product will always depend on the specific end use, but some examples include high film build coatings based on epoxy technology or multi-coat systems including an anti-corrosive pigment containing primer combined with a functional top coat. At AkzoNobel, we believe in sustainable coatings and through decades of real-life case studies have successfully proven that chrome-free primers can perform equally when compared to carcinogenic chrome VI containing primers, dependent on the environment the product is exposed in.

Axalta: Coatings need to be considered as ‘barriers’ applied to assets to extend their working lives. A secondary application, certainly in heavy-duty protection, is to provide an acceptable finish. Selecting coating products and systems are specific to each asset and are dependent on a number of factors, including construction material, the method of preparation, working environment, life expectancy, asset value, the budget for protection, appearance required, application process, VOC limits, and so on. Appropriate coating products can then be selected, usually a range of product options which will offer different positive and negative impacts. We offer a wide variety of ecoat, liquid, and powder coating products, which can be used in combination to fulfill all requirements for coaters. From the industry-leading heavy-metal-free ecoat (EC6100) to zinc-free or zinc-rich primer systems in liquid and powder coatings, to high solids topcoats, we have a product system to meet any customer requirement.

Hempel: Protecting any asset, high value or not, against corrosion involves selecting the appropriate system from the outset which usually consists of two or three coats of paint. The first coat normally involves a zinc silicate or zinc epoxy-based primer, followed by a high build epoxy mastic intermediate coat (for added barrier protection) and completed with a polyurethane cosmetic top coat. If a higher performance top coat is required, then a polysiloxane-based coating should be selected.

PPG: Multi-coat highly advanced technological solutions like zinc-rich epoxy primers, high-solids epoxies and polysiloxane topcoat technologies (should be considered).

Sherwin-Williams: In the oil and gas pipeline market, a multi-layered coatings approach is advised to prevent pipeline corrosion, protect anti-corrosion coatings and preserve fusion-bonded epoxy (FBE) coatings before pipes are buried in the ground. For example, the ideal base coating layer is an anti-corrosion FBE coating designed to prevent corrosive elements from reaching the steel pipe substrate and working synergistically with cathodic protection systems. Next, a protective, abrasion- and damage resistant FBE coating layer is advised to resist the scratches and scrapes a pipe may encounter from transportation to installation. Such scrapes could otherwise expose the bare steel below and increase corrosion potential. Finally, it’s helpful to consider a preservation layer as an optional topcoat to protect the lower FBE layers against prolonged UV exposure in oftentimes inevitable cases of pipeline installation delays. When building this sort of pipeline protection one layer at a time, remember that all three coating layers will work synergistically and should be selected based on the most stringent performance needs to ensure success.

CW: What are the main factors to consider when selecting a corrosion protection coating?

AkzoNobel: When selecting the right coating to protect your assets, for instance, a metal roof or a metal garage door, it is very important to understand the environment your asset is exposed to. The corrosion severity in rural areas is lower compared to industrial and coastal areas due to variance in factors such as temperature, humidity and salinity in the air. When we evaluate corrosion performance we always test “fit for purpose” through appropriate accelerated and natural corrosion tests, for example, prohesion or seaside exposure. We use exposure sites around the world and compare the behavior of our products in various environments.

Axalta: The asset and its environment, substrate and pretreatment, life expectancy requirement, finish expectations, ease of coating application, environmental requirements
and budget.

Hempel: There are three main key considerations: the aggressiveness of the environment – industrial, coastal and marine environments being the harshest and most challenging; durability – what is the expected lifetime of the coating system required and in-service performance requirements – for example high heat; fire protection; chemical resistance; maintenance/production performance during the application of the paint process.

PPG: Managing customer expectations as they relate to budget constraints, access to asset, surface prep, aesthetics  – whether/not they’re important and environmental conditions within which the asset exists.

Sherwin-Williams: On the fuel storage end of the oil and gas chain, tank owners are looking for longer-performing lining materials to help reduce operating costs. Currently, the American Petroleum Institute’s API 653 tank inspection guidelines require 10-year inspection intervals for tank linings, with the expectation that a 20-year life would be acceptable. However, tanks lined 20 years ago with single-coat epoxies are showing no signs of lining failure and are being recertified for another 10-year inspection period. With these coatings offering the potential of at least a 30-year interval between lining applications, it’s possible that inspection intervals will eventually expand to, say, 15 years, which would enable owners to eliminate one complete inspection cycle over 30 years, an efficiency that would add up to significant savings.

CW: How important is substrate preparation as opposed to choosing a higher-end coating?

AkzoNobel: Both are equally important and have an impact on performance. Adhesion and substrate preparation is critical for corrosion protection. Corrosion and application field failures are often due to loss of adhesion and in many cases, poor surface preparation and therefore lack of performance are identified as the root cause. Unfortunately, a high-end coating will not overcome the lack of bonding to such surfaces but choosing the right coating system based on end use is also crucial. For example, high UV exposure climate areas require durable coatings which will withstand degradation and therefore protect against delamination.

Axalta: Surface preparation is one of the most important factors, whether using a simple air-drying primer at $5 per liter or a fluoropolymer-based coating at $200 per liter, if applied onto an inadequately prepared surface the coating system will ultimately fail prematurely. Any coating system selection should be considered inclusive of pretreatment.

Hempel: Substrate preparation is always critical to ensure that the coating system performs to the optimum. Even when applying the highest performing coating system, if there has been inadequate surface preparation then this will undermine it.

PPG:  It depends on the asset and the application. {There needs to be a] balance between customer expectations and desired outcome. Substrate prep is critical, however, there are coatings that make up for poor/minimal surface prep. [Another consideration is] long-term performance versus economics of proper surface prep.

Sherwin-Williams: Completing surface preparation to an established standard is the foundation for the successful long-term performance of a coating system. However, applicators sometimes encounter substrates that can’t be prepared for the proper standard before applying coating systems. In these situations, the substrate may have a marginally prepared surface that’s far from the recommended surface preparation for the coating’s intended service. Yet, such surfaces can be coated successfully – and deliver long-term performance – when applicators appropriately address two critical factors: the maximum achievable surface preparation and the proper coating system selection.