Coatings that don't cost the earth

Tony Collins, EonCoat, USA, explains how the shift towards sustainability has seen an increase in support for LNG storage assets protected by non-toxic coatings.

The 21st Century demands solutions that sustainably meet the economic needs of society, but also protect the environment in the face of climate change and pollution. LNG is the right energy solution for an environmentally conscious society: it is the cleanest-burning fossil fuel and has numerous environmental advantages, providing operators a smart, safe, and affordable way to meet regulations.

LNG releases 45 – 50% less carbon dioxide (CO2) than coal, 30% less CO2 than fuel oil, dramatically reduces nitric oxide emissions, does not emit soot, dust, or fumes, and produces insignificant amounts of sulfur dioxide, mercury, and other particulates compared to other fuels.

Safety

LNG is inherently safe because it is not flammable in liquid form. Another huge safety factor is that LNG vapours are not toxic. In addition, LNG spills do not damage the waterway or harm aquatic life in any way.

So where do the operators of this safest, cleanest, and most environmentally-friendly fuel turn when they need to protect the steel assets that store and transmit their product? Many of them choose the safest, cleanest, most environmentally-friendly and completely non-toxic coating of chemically bonded phosphate cement that protects steel from corrosion for decades, typically the life of the asset. In addition to being safe and environmentally-friendly, chemically bonded phosphate cements are not flammable – making them even safer for use around fuels.

Cement as coating

So, what are chemically bonded phosphate cements? They are acid/base cements, similar to dental cements, and were pioneered by Argonne National Labs to shield radioactive waste in the

mid-1990s. In 2010, while working on cement for structural applications, EonCoat (based in North Carolina, the US), observed that this cement would stop the rusting of carbon steel better than any known protective mechanism – including superior to cathodic protection and all known corrosion coatings.

How can it be that a cement could be so effective? Simple: it has no resin.

Coatings have four things: z Binder (or resin). z Pigments. z Additives.

z Solvents.

This fundamental assumption is why no coating engineer would have considered the technology created by EonCoat. Technically, chemically bonded phosphate cements are not coatings because they do not have a resin as the binding agent, but rather bond to steel through an acid/base reaction. Oddly, the absence of a resin is exactly why chemically bonded phosphate cements are so effective. Coatings can contain only a limited amount of pigment because of something called critical pigment volume concentration. Exceed this volume percentage and the resin cracks. There is a practical limit of approximately 20% inhibitive pigment in resins. These inhibitors are what enable coatings to prevent corrosion by providing something for steel to bond with. An inhibitor is something that has a lower energy state – called Gibbs energy – when bonding with steel which has lost an electron. In order for steel to protect itself when it loses an electron, it must be offered something with a lower energy state than oxygen. Otherwise, the steel will bond with the oxygen and form rust.

An additional downside of resins is that they are sticky, and the inhibitor must work its way out of that resin to get to the metal where it can protect the steel.

Instead of using a resin, the inhibitors in chemically bonded phosphate cements bond to each other, and to steel, via an acid/base reaction. The cement can be a 100% inhibitive pigment, and this can be bonded chemically to the metal. Chemically bonded phosphate cements enable a pigment loading five times the maximum loading of inhibitor for most polymers, and an easy way for the pigment to reach the steel because it is chemically bonded with it. There is no resin to impede access to the metal.

Why is this important? Corrosion comes down to a simple fact – corrosion is the result of an iron atom losing an electron and bonding with oxygen. Iron will choose what it bonds with based on what creates the lowest energy state and what negatively charged ion is physically closest to it. The goal as corrosion engineers is to provide a large volume of inhibitive pigment – such as phosphates and silicates – that have lower energy states when bonding with iron than oxygen does.

So how much volume is required? If a blasted steel panel is placed in a glass of salt water, it is possible to see the rust begin to form. Once the phosphate ion has been added to the solution, the rate of corrosion slows down when it reaches 0.5 moles of phosphate/l of water. Upon reaching a 1 molar concentration, or practically exceeding the molar concentration of the salt, the rust will completely stop. With a chemically bonded phosphate cement, it is possible to reach a 4 moles/l concentration at the coating/metal interface. At that concentration, rust is just not possible. Embedding inhibitors in a resin limits the molar concentration to well under 0.5%. This is the inherent limitation of polymer technology. It is not possible to get enough ammunition to the battlefield.

Figure 1. Sameer Patel, Lead Scientist in developing EonCoat, safely applying EonCoat with minimal PPE.

Applications of the coating

Within a year of discovery of the corrosion resistance, EonCoat had figured out how to spray the cement like a coating. Shortly after, the first large oil company began using EonCoat to protect tanks. Today, many energy companies across the globe use EonCoat on tanks, pipelines, and offshore platforms. This protection mechanism is not only 100% effective, even in corrosive environments, but enough phosphate can be added to last the life of the asset.

Over time, two new coatings have been developed using similar chemistry. In 2015, a high-temperature product was developed that is primarily used for corrosion-under-insulation. And most recently, EonCoat developed the weldable tank bottom coating – soil facing side. This product will not burn or otherwise be compromised when the tank plate it is on is welded from the other side. Customers use this coating to protect the soil facing side of tank bottoms. No longer will tank bottoms rust out and need to be replaced.

As great as the protection is, perhaps the most significant impact of this technology is that it gets rid of the safety and environmental impacts of polymer coatings. Volatile organic compounds (VOCs) cause so much harm to the health of painters who apply them and to the environment in the form of greenhouse gas. Now it is known that employees who are exposed to VOCs suffer a loss of 10 – 15 points in IQ. The other health hazards are too numerous to list here – but VOCs are likely to be the next asbestos. When the public did not know better, everybody had an excuse, but now the public does know. EonCoat have painters wear a PF-100 mask that filters down to 0.3 µm. The implication is that the staff are safe from toxins, yet painters suffer cognitive decline and a host of unpleasant illnesses that take their lives too soon. The company now knows that VOC molecules, because they are gases, are approximately 1000 times smaller than what the PF-100 filters can capture, with dia. in the scale of picometers. One picometer is a million times smaller than a micrometer. It is a reasonable assumption that PF-100 masks do not adequately capture VOCs.

The LNG industry, the beacon of clean and safe fuels, is embracing chemically bonded phosphate cements, the clean and safe way to protect its carbon steel assets. It is a leadership example to all.