While these coatings are valued for their corrosion control, customers also require an aesthetically appealing finish.
AkzoNobel has a wide range of products to provide corrosion control. “Many of our products are based on 2 pack epoxy resin technology and are applied direct to metal (e.g. Intershield, Interseal, Interplus, Interzone, Intergard),” said Ian Fletcher, regional marketing manager – Europe, Protective Coatings, AkzoNobel. “We also have zinc rich epoxy or inorganic zinc primers (Interzinc) that provide excellent corrosion protection; these are typically part of a 3 coat scheme that contains the zinc primer, an epoxy intermediate and, for example, a polyurethane (Interthane) or isocyanate-free top-coat (Interfine). Where abrasion or impact resistance is a particular issue we provide high build epoxy coatings that contain lamellar glass flake pigmentation.”
“A combination of zinc rich primers, epoxies, urethanes and specialty topcoats can be used to provide corrosion protection,” said Jake Ojeda, PPG’s global petrochemical segment manager. “It is important to consider the type of service (immersion, atmospheric, etc.), substrate (ferrous, non-ferrous, concrete, etc.), environmental conditions (temperature, humidity, etc.) and turnaround time (hours, days, weeks).
There are various factors to consider when selecting a corrosion protection coating.
“Factors such as abrasion, impact and chemical resistance are important,” noted Fletcher. “Also compatibility with cathodic protection is critical for e.g. some offshore structures and pipelines applications. Another factor that has to be considered is the operating temperature of the coated steel as only certain technologies are suitable for use above 120˚C. And also the coating appearance; some end-users want a coating to maintain its color or gloss to a certain level so depending on the end use they are often top-coated with more durable finishes. Other factors can include, drying time, the volume solids/volatile content, hold-up and brush/roller application properties.”
Substrate preparation is critical when applying corrosion control coatings. These types of coatings are usually applied by specially trained applicators. They can be applied as part of new construction or during routine maintenance to provide continued asset protection from wear and tear and deterioration.
“A high-end coating will not perform well if the substrate preparation is poor,” said Fletcher. “The quality of the surface preparation will determine how long the coating will last on the steel. Ideally, steel should be degreased, mill-scale and rust removed and abrasive blasted to create a sharp angular profile. Other surface preparation methods like wire brushing and power tool cleaning are available but the coating performance on the steel will not be as good as abrasive blasting to e.g. Sa2.5.”
“Substrate preparation is the key to ensure proper adhesion and removal of any contaminants that could impact the coatings performance,” said Ojeda. “However, there are products that are surface tolerant and allow for minimal surface preparation and can still provide adequate protection.
Customers are looking for a variety of performance attributes when selecting corrosion protection systems. “All customers want the time to first maintenance to be as long as possible,” said Fletcher. “Typically major maintenance expectations are at least 15 years after coating application during new construction but for maintenance applications customers accept around five years depending on the level of surface preparation before maintenance needs to be done again.”
“Owners are looking for products and systems that can extend the life of their assets as well as prolong the time between regular maintenance schedules,” agreed Ojeda. “Applicators want products that are cost competitive, easy to apply and can increase their throughput.”
“We are seeing new developments in primers that provide cathodic protection as well as epoxies that are more robust,” said Ojeda.
“Most technology tends to be based on new formulations using e.g. existing epoxy technology,” said Fletcher. “There have been some new amine curing agent technologies. Polyaspartic is one example of a new chemistry providing fast curing low volatile organic content technology for e.g. OEM applications.”
An innovative coating approach is providing a long-term solution to fighting corrosion in petrochemical coastal assets
In the oil and gas industry, protecting massive carbon steel assets from corrosion is a continual challenge around the world, including China, particularly along coastline exposed to high humidity and salty air near oceans or other bodies of water.
The problem is worsened by the fact that many refineries and petrochemical facilities – including tanks and process equipment, as well as above ground pipeline and railcars – are located near ports to facilitate the storage and transport of both raw crude and processed products.
The typical preventive measure is to use barrier type coatings that are commonly reapplied every few years in these high-risk coastal areas. This can be costly and disruptive to oil and gas facility production, requiring blasting off the old coating, cleaning the surface, and reapplying multiple coatings. Despite this costly maintenance, excessive corrosion of such carbon steel assets can lead to leaks, fires and accidents, as well as accelerate premature replacement.
Now in these petrochemical coastal assets, an innovative coating approach is providing a long-term solution to fighting atmospheric corrosion, while minimizing production downtime and increasing safety.
Protecting Coastal Assets from Corrosion
The Chinese port city of Ningbo, bounded on the east by the East China Sea and on the north by Hangzhou Bay, has a very wet, humid climate, as well as salt laden air, that make the corrosion of petrochemical assets in the area a particular problem. For decades, the region has received an annual average of over 56 inches/1,440 mm of rain, along with over 157 precipitation days, and 80%+ average relative humidity – not to mention a monsoon season.
In these trying conditions, Ningbo Xingang Fuel Storage Company sought to protect its assets from corrosion. However, the corrosion on their carbon steel equipment is quite severe. The company faced a particular challenge in protecting two firewater cannons and the auxiliary fire lines on the east and west side of a 50,000 ton crude oil terminal located in the Beilun District of Ningbo.
Traditional methods of protection, such as applying polymer paints and rubber type coatings, have been ineffective and lose their effect soon after application.
While these methods can create a physical barrier to keep corrosion promoters such as water and oxygen away from steel substrates, this only works until the paint is scratched, chipped, or breached and corrosion promoters enter the gap between the substrate and coating. Then the coating can act like a greenhouse – trapping water, oxygen and other corrosion promoters – which allows the corrosion to spread.
Due to these harsh conditions the company looked for a better solution and turned to EonCoat, a spray applied inorganic coating from the Raleigh, North Carolina-based company of the same name, for use on a corrosion protection project to extend the life of the firewater cannons and auxiliary fire lines. EonCoat represents a new category of tough, Chemically Bonded Phosphate Ceramics (CBPCs) that can stop corrosion, ease application, and reduce production downtime.
In contrast to traditional polymer coatings that sit on top of the substrate, the corrosion resistant CBPC coating bonds through a chemical reaction with the substrate, and slight surface oxidation actually improves the reaction. An alloy layer is formed. This makes it impossible for corrosion promoters like oxygen and humidity to get behind the coating the way they can with ordinary paints, the company reported.
Although traditional polymer coatings mechanically bond to substrates that have been extensively prepared, if gouged, moisture and oxygen will migrate under the coating’s film from all sides of the gouge.
By contrast, the same damage to the ceramic coated substrate will not spread corrosion in oil and gas facilities because the carbon steel’s surface is turned into an alloy of stable oxides. Once the steel’s surface is stable (the way noble metals like gold and silver are stable) it will no longer react with the environment and cannot corrode.
Visible in scanning electron microscope photography, EonCoat does not leave a gap between the steel and the coating because the bond is chemical rather than mechanical. Since there is no gap, even if moisture was to get through to the steel due to a gouge, there is nowhere for the moisture to travel. This effectively stops atmospheric corrosion of coastal tankage and other petrochemical assets.
The corrosion barrier is covered by a ceramic shell that further resists corrosion, fire, water, abrasion, impact, chemicals, and temperatures up to 400 °F. Beyond this, the ceramic shell serves a unique role that helps to end the costly maintenance cycle of replacing typical barrier type coatings every few years.
“In coastal petrochemical assets, such as refineries and storage tank farms, if the ceramic shell and alloy layer are ever breached, the ceramic shell acts as a reservoir of phosphate to continually realloy the steel,” explained Merrick Alpert,” president of EonCoat. “This ‘self heals’ the breach, depending on its size, and stops the corrosion if necessary. This capability, along with the coating’s other properties, enables effective corrosion protection for the life of the asset with a single application.”
The Ningbo Xingang Fuel Storage Company project has been successfully coated with the spray applied inorganic coating, and a topcoat added. EonCoat is compatible with a wide range of commonly used topcoats.
Because of the ceramic coating’s multiple layers of corrosion protection, and the ability to “self heal” breaches, the coastal facility is on track to see long term protection of its equipment, effectively breaking the costly cycle of blasting and repainting every few years.
Oil and gas operation managers or corrosion engineers looking to reduce costs are finding additional advantages to CBPC coatings like EonCoat beyond corrosion resistance.
For instance, one of the ways the Chinese government is working to mitigate the negative effects of air pollution is by turning to green alternatives such as CBPC coatings, which are inorganic and non-toxic, so there are no VOCs, no HAPs and no odor. This means the non-flammable coatings can be applied safely even in confined spaces.
Such coatings consist of two non-hazardous components that do not interact until applied by a standard industrial plural spray system like those commonly used to apply polyurethane foam or polyurea coatings.
One of the greatest additional benefits is the quick return to service that minimizes facility downtime. The time saved on an anti-corrosion coating project with the ceramic coating comes both from simplified surface preparation and expedited curing time.
With a typical corrosion coating, near white metal blast cleaning (NACE 2 / SSPC-SP 10) is required to prepare the surface. But with the ceramic coating, only a NACE 3 / SSPC-SP 6 commercial blast cleaning is typically necessary.
For corrosion protection projects using typical polymer paints such as polyurethanes or epoxies, the cure time may be days or weeks before the next coat of traditional ‘three part systems’ can be applied, depending on the product. The cure time is necessary to allow each coat to achieve its full properties, even though it may feel dry to the touch.
With traditional coatings, extensive surface preparation is required and done a little at a time to avoid surface oxidation, commonly known as ‘flash rust,’ which can require re-blasting.
In contrast, a corrosion resistant coating for carbon steel utilizing the ceramic coating in a single coat requires almost no curing time. Return to service can be achieved in as little as one hour. This kind of speed in getting an asset producing again can potentially save hundreds of thousands of dollars per day in reduced downtime in oil and gas applications.
With atmospheric corrosion a perennial problem for oil and gas facilities with massive carbon steel structures, the utilization of CBPC coatings that can control corrosion for decades will only help the bottom line.•