Controlling hot process corrosion

The press release describes HCTC as a coating manufacturer – and we are – but we think of ourselves as a technology company. Back in the company’s infancy, the founders had a very good understanding of this particular market. They had both been in this industry for several years before branching out on their own. And during that time they saw a market that was plagued with failures. They saw that clients were using antiquated technology – and that failures were commonplace. Even though industrial heat resistant coatings only constitute a small percentage of a plant's overall coatings requirements, these applications have accounted for a high percentage of the site's overall coatings failures.

Failures
In the beginning, we targeted 10 problems that clients saw with generic high temperature coatings. The objective was to formulate a product line that corrected all 10 of these deficiencies. These problems vary ­– from very limited color availability to very thin film coatings (resulting in pin point rusting) to ambient-only apply coatings.

Ambient apply coatings
These are coatings that are applied to equipment that is not in operation – which includes almost all currently available heat resistant coatings. Historically, there would have to be a scheduled shutdown for clients to apply a heat resistant coating – there were no coatings that could be applied to hot, operating equipment. We formulated a line of coatings that can be applied directly to hot, in-service equipment.

How hot can the surface be when applying our coating?
Hi-Temp 1027 can be applied to carbon or stainless steel that ranges in surface temperature from ambient, all the way up to 260°C.

Hi-Temp 1027 can be applied to a unit that is in operation, directly to a hot surface.I don’t mean to suggest that this technology is new. Hi-Temp 1027 has protected over 6 million square feet of carbon and stainless steel over the last 5 years – with a significant portion of that being applied to a hot surface.

Hi-Temp 1027 was specifically formulated for the prevention of corrosion under insulation. Corrosion under insulation (CUI) is a unique problem. A CUI protective coating needs to be able to withstand multiple abuses that occur in this environment and also have certain application characteristics in order to make it a viable solution.

When I am conducting a training session, I often ask the following question, “Why does CUI exist?” And typically I’ll receive numerous responses – all of which focus on some sort of moisture as the fundamental cause. And they are right – to a degree.

But the simple fact of the matter is that the problem of CUI exists because there has not been a coating that has been able to withstand the extremely harsh conditions that exist under insulation. Engineers, contractors, and clients had no choice. They had to use coatings that were not up to the task simply because they were the only coatings that were commercially available at the time.

What are these harsh conditions?
There are two conditions that a CUI coating must be able to withstand; boiling water and prolonged heat. A n insulated piece of equipment can have trapped moisture by two means: condensation (due to cyclic equipment) and rain. Rainwater will eventually enter weak points in the system and pour onto the surface under insulation. In the case of an insulated hot pipe or vessel, the trapped water lays upon a surface that is over 100°C and subsequently boils.
Therefore, an effective CUI coating must be resistant to immersion in boiling water. However, almost all the products being used today are NOT resistant to boiling water. When this wet/dry cycling occurs your corrosion cell will begin and continue to worsen over time. These surfaces are out of sight and the damage can progress undetected. The idea of corrosion going undetected does not sit well with the people who are responsible for protecting that particular piece of insulated equipment.

Almost all of the generic CUI products available today use older technology and are epoxy based. These include phenolic systems, novolac systems, phenolic/novolacs, flake filled products, etc. And as we know, epoxies become brittle and crack when exposed to prolonged high temperatures. Once cracking begins, water is able to penetrate and corrosion will begin.

Simply put, CUI is a problem today because the coatings that were typically used were not able to withstand wet/dry cycling and prolonged heat. Hi-Temp 1027 was specifically formulated to resist boiling water and to withstand prolonged heat.

Unfortunately, one can’t easily determine if wet/dry cycling has compromised the coating because the pipe is insulated and jacketed. You also can’t determine, simply by looking at the vessel, if the coating is now cracking due to prolonged heat. In 5 years, there hasn’t been a single failure under insulation with Hi-Temp 1027. Since CUI is such a pervasive problem, I would imagine that, over the years, there have been plenty of engineers and owners who have had difficulty sleeping at night not knowing if they still have a functioning coating underneath that insulation and jacketing. We basically offer peace of mind to engineers and plant owners.

Hi-Temp 1027 is not an epoxy. What type of coating is it?
The specific technology itself is proprietary but it falls in the general category of inorganic modified polysiloxane. 7 years ago, we wrote down a list of the characteristics that we felt an optimal CUI coating should possess. As a starting point, the coating needed to be resistant to wet/dry cycling and it should not become brittle when exposed to prolonged heat. Also, the CUI coatings available at the time were thin filmed and usually were unable to even cover the blast profile. This typically resulted in pin-point rusting that started almost immediately after the coating was applied. We therefore wanted to be able to apply the coating at a higher than normal dry film thickness. This was not an easy task since conventional wisdom suggests that a heat resistant coating needs to be thin at these elevated temperatures – otherwise, when the steel expands, the coating would crack. It was doubly difficult since another one of the desirable characteristics was thermal shock resistance to 700°C.

Since the older technology could not withstand the harsh conditions that exist under insulation, we needed to create new technology.

Hi-Temp 1027 is unique
Generic heat resistant coatings require some sort of post complex heat cure in order to provide the recommended corrosion protection. This typically involves slowly ramping up the equipment to a specific temperature and keeping it at that temperature for a specified period of time. This is expensive, time consuming, and quite frankly unrealistic. Often times it is impossible to slowly ramp up the unit and keep it at a certain temperature. Clients therefore, might simply turn on the unit and hope for the best. This is an example of the industry’s low expectations of heat resistant coatings. We’re trying to elevate those expectations – to raise the bar. None of our products require any sort of heat cure. This makes Hi-Temp 1027 very user-friendly.

Also, it is single component. No mixing, no ratios, no plural components. It does not require any special equipment to apply – simply use either airless or conventional spray. It has no recoat window. As long as the previous coat of Hi-Temp 1027 is clean, you can apply an additional coat(s) any time later. Our goal was to create a high performance coating that could withstand the harsh conditions under insulation, but we also wanted the coating to be more versatile than the older technology. For example, Hi-Temp 1027 can be applied to hot steel so that clients could avoid costly shutdowns. As you could imagine, this has been especially helpful for offshore platforms.

Testing that confirms these claims
All of this was confirmed by one of the world’s largest petrochemical companies. A few years back, they were searching for a coatings solution to their ongoing worldwide CUI problem. Their Coatings Division asked paint manufacturers to submit CUI coatings for testing. It was an accelerated test which conservatively projected a 5-7 year life span for any coating that passed. The test itself was extremely harsh. Coated panels were subjected to 16 consecutive hours in a heated oven and this was immediately followed by a quench into cold water. The quench into cold water demonstrates a coating’s ability to withstand thermal shock – a quick and dramatic drop in temperature. After the quench, the panel was then placed into 109°C water for 8 hours (boiling water) and this also was followed immediately by another quench into cold water. This process went on 24 hours a day, 7 days a week – for 16 consecutive weeks. After 8 weeks, all of the epoxies, modified silicones, and inorganic zincs that were submitted were removed from testing. Those coatings had failed catastrophically by that point and there was no further reason to continue testing them.

Hi-Temp 1027 passed the entire test and was thereby approved for use on their facilities worldwide to prevent corrosion under insulation.

Although this approval is terrific, the real proof has been in the field. After 5 years and 6 million square feet, there has not been a single failure associated with Hi-temp 1027 for the prevention of corrosion under insulation.

A dvantages of Hi-Temp 1027 over modified silicones for the prevention of chloride induced stress corrosion cracking
First and foremost, a coating that is used under insulation, whether it is carbon steel or stainless steel, needs to be able to withstand wet/dry cycles. Moisture will inevitably be present at some point and the coating that is used must be able to withstand this cycling. As demonstrated by the independent wet/dry cycling test mentioned earlier, modified silicones cannot withstand the introduction of moisture whereas Hi-Temp 1027 can. Secondly, modified silicones are also applied at very thin films whereas Hi-Temp 1027 can be applied at very high dry film thicknesses. Saudi Aramco has used Hi-Temp 1027 extensively on their LNG facilities to provide protection of austenitic stainless steel against chloride induced stress corrosion cracking under insulation. In addition to protecting stainless steel under insulation at elevated temperatures, Hi-Temp 1027 is ideal for cryogenic equipment – offering resistance from minus 185°C to plus 540°C.

Is Hi-Temp 1027 only used under insulation?
Hi-Temp 1027 is also a high build primer used to protect exposed steel. As expected, it retains the same characteristics: high build, ambient or hot apply, no heat cure requirement, no recoat window, UV resistant, single component, etc. HTC has a full line of topcoats to compliment Hi-Temp 1027 when it is used as a primer. In addition to our 12 standard colors, we can custom match any color and these products have excellent color stability. To further compliment Hi-Temp 1027, we have color topcoats that can also be applied directly to hot steel. Although Hi-Temp 1027 was initially formulated as a CUI coating, it has since become the standard of excellence for elevated temperature primers in the United States. HTC is the sole supplier of heat resistant coatings for The Sherwin Williams Company in North America. Clients ranging from the world’s largest petrochemical companies to local hospitals and schools have used the HTC line to solve their corrosion of elevated steel problems.