The cost and effort to inspect for and repair corrosion under insulation (CUI) that is routinely discovered on aging equipment is exceedingly high. Obviously, this work is crucial, but the cost remains high due to labor-intensive steps that must be performed, often in difficult circumstances. These steps include:

  • Provide personnel access to pipe and equipment of often complex geometry in locations that often exceed 100-feet elevation and exist within the congested confines of other closely spaced equipment.
  • Remove, bag, transport and dispose of old insulation (which can contain asbestos and, if so, imparts yet additional costs due to specialized handling and personnel certifications).
  • Inspect equipment for CUI.
  • Provide repairs or replacement where necessary.
  • Provide an acceptable surface preparation, which yields the specified anchor profile by a method that is not prohibited by safety-related restrictions in force because this work usually occurs within operating units.
  • Apply the specified CUI coating in an often unaccommodating outdoor operating environment to steel, which is not likely operating at an ideal temperature.

So the major challenge for the coatings and insulation specifier is:

How can we achieve the lowest possible cost without sacrificing long-term corrosion protection and long-term functionality of the insulation?

These two aspects are viewed by facilities as crucial to achieving the reliable production of on-spec products.

I believe that one way to overcome this challenge is by using proven technology where it is suitable and makes sense. Not every technology is suitable for every circumstance, but this discussion addresses certain new "where it makes sense" opportunities—where cost can be measurably reduced and scenarios are technically suitable for the products. (For more on selecting an appropriate coating, read Methods & Pitfalls in Selecting Coating Systems for Specification.)

The Challenge of Assessing New Technology

Acceptance must occur before a facility can proceed with using a technology that is new to their company. What usually has to be in place first is official acceptance of the technology at the company level. After all, much is at stake when we are talking about corrosion protection, equipment safety and reliability. A company must invest significant personnel resources to complete the vetting, evaluation and field trial process for any new technology.

Yet even after acceptance of the technology and incorporation into company standards, the decision to implement the technology is usually made by the individual facilities within a company. Often, there is legitimate hesitation because they "don't want to be the guinea pig". This is where field trials can be a good way to start. Evaluating technology that is new to a facility with a small-scale field trial makes sense, and is a necessary first step to its full-scale adoption.

Two "New" Technologies that Aren’t Really New

We will examine the pros and cons of two technologies as they pertain to cost reduction and the likelihood that functionality will not degrade over the intended performance life.

Companies can no longer afford to use products that are not likely to remain functional for their intended performance life. When hundreds of thousands of dollars are spent to install a coating/insulation system on equipment that operates in the CUI temperature range, the general expectation is that the materials will do their job for at least 20 years. So we want long-term functionality at the lowest cost.

Two technologies that have been introduced to the oil & gas industry within the last 10 to 15 years are of particular interest because they have real potential to measurably reduce the costs described above:

  • A mineralization gel coating that can significantly impact the overall cost of coating applications for both steel under insulation, and bare un-insulated steel.
  • Aerogel blanket insulation, which most people in the industry have at least heard about, and quite a few have tried.

Both of these technologies have been in existence for decades and are well proven in other industries. But because they are relatively new to oil & gas and may not be familiar to many who are struggling to manage the costs of CUI, we will briefly discuss their properties and examine the pros and cons.

Mineralization Gel Coating

Mineralization gel coating works by forming (literally growing) a very thin layer of mineralization on the steel surface, thereby passivating it. When applied to steel, components in the gel react with ferrous metal to form a glass-like mineral layer. This layer creates a corrosion-resistant barrier between the chlorides (electrolytes) and the metal.

While it takes a very tiny amount of the chemistry to form the layer of mineralization, there is obviously a need to achieve a continuous application. (Related reading: Understanding Insulation Chemistry Proven to Inhibit CUI.) As such, the recommended 20 mil thickness of the gel (new application) resides on the surface, acting like a reservoir of "standby" material, ready to provide the constituents to form a new layer at the site of any future damage. For corrosion mitigation, 30 mil thickness is recommended.

The way it works is not unlike the way stainless steel and aluminum passivate themselves, reacting with the atmosphere at the surface to form their extremely tough oxides. When stainless steel is fresh from the smelter, it immediately reacts with the humidity in the atmosphere and oxidizes. Its oxide is extremely tough, compared to that of carbon steel. The durability of the oxide that forms a protective layer on stainless steel can be compared to that of concrete—very tough and durable. A similar impervious oxidation occurs with aluminum. The weathering resistance of aluminum and the chemical resistance of stainless steel are such that neither is much affected by Mother Nature.

Mineralization technology, also called "surface conversion gel", has been well demonstrated in the naval, refrigeration and automotive industries. The small crevice at the steel surface under thermal insulation is essentially the same geometry for which the technology was originally developed. Corrosion within the tiny crevices between the wires forming a cable held within a sheath (think brake cable) was, at one time, a tremendously serious issue of huge proportion, threatening the entire transportation industry. The resounding success of this technology, which quickly made history of that corrosion problem, solidified its usefulness and sparked interest for other industries.

Because the gel activates when in contact with bare steel, the only surface preparation needed is removal of rust to a hard surface and the removal of any debris and loose coating. This coating eliminates the need for traditional surface preparation (grit blasting or power tool cleaning), which makes up a large part of the cost of any coating application job.

The abrasive blast labor-related cost savings that this technology allows includes the labor to:

  • Erect containment
  • Perform blasting
  • Collect the spent grit
  • Containerize and label the grit
  • Collect and send sample grit to test the grit for leachable lead
  • Dispose of the grit per jurisdictional regulations according to the hazard category resulting from lead test report

Additional rules apply if blasting occurs inside of the plant. Many companies do not allow grit blasting inside operating units, which significantly increases the cost of CUI remediation when power tool cleaning is required (assuming that is allowed).

Application of the gel can be by glove, by pipe-shaped gauge/trowel, or by spray. Due to the viscosity of the gel, spray application generates little overspray. No mixing or stirring is needed; it comes ready to apply.

Figure 1. Hand or trowel applied to achieve ~20 mil thickness.
Figure 1. Hand or trowel applied to achieve ~20 mil thickness.

While well-protected under thermal insulation from the external environment, exposure to boiling water (when it is present) can erode away the gel by the continuously breaking bubbles. So the gel is protected from the action of boiling water by the use of a uni-directional geotextile wrap. The wrap also serves in a secondary role to keep the insulation clean. Imagine applying Vaseline on a skin injury and wrapping a gauze bandage around it.

The pros of mineralization gel technology:

  • Eliminates the need for near-white metal cleanliness and anchor profile
  • Eliminates the risk of mixing error
  • Eliminates the requirement for precise coating thickness
  • Eliminates the need for proper conditions and coating cure duration
  • It is non-flammable, unlike most liquid CUI coatings
  • Risk of overspray is totally eliminated when applied by glove or gauged trowel
  • Coating application can progress regardless of elevation without containment
  • Spray application can occur in up to 40 mph wind without overspray
  • Can be applied to steel, which is slightly damp
  • Various versions allow for a good range of application and operating temperatures
  • One version has no minimum application temperature
  • Elevated temperature version is tested to sustain 350°F (177°C)
  • Suitable for stainless steel to mitigate stress-corrosion cracking

The cons of this technology:

  • High-temp version maximum operating temperature is 350°F (177°C)
  • The versions that remain soft are not suitable for bare-steel applications unless they receive the fabric wrap and aluminized weather jacket
  • Shop application of the gel requires covering it with insulation before transporting or applying overwrap, and requires special handling during transport

Aerogel Blanket Insulation

This insulation material first came to our industry in 2004. It’s been around for 10 years, but is still considered new and in the adoption phase because the incumbent materials have been in use for more than 50 years.

As a background, silica aerogel was invented in the 1930s but it was not until the 1990s that its use in products of high value warranted the expense of its manufacture. The silica aerogel particle is full of pores. These nano-sized pores are what primarily imparts its outstanding thermal properties. Aerogel blanket has been well proven in the aerospace industry and the military, and is currently being considered by other industries because of its excellent thermal conductivity allowing for an enhanced thermal resistance-to-volume ratio.

Figure 2. Reusable, water repellent silica aerogel up to 600°F (315°C).
Figure 2. Reusable, water repellent silica aerogel up to 600°F (315°C).

Silica aerogel is a flexible, long-term moisture repellent, non-woven "blanket". Because the material is in the form of a flexible fibrous batt, it literally cannot be broken. In fact, according to accelerated testing, there is almost no way to degrade (by temperature aging, thermal cycling or vibration) the thermal properties of the glass fiber product within its maximum temperature limit. (Testing is discussed in more detail in Third Party Long-Term Testing: CUI & Thermal Results.) Because it is flexible and unbreakable, the insulation can be installed onto equipment in a fabrication shop or at a coating shop, and transported to the job site without risk of damage.

This technology is groundbreaking for its technical properties and for constructability reasons:

  • Reduces the risk of CUI, due to through-thickness water repellency up to 600°F (315°C)
  • Allows water vapor transfer, but does not absorb liquid water, allowing hot insulation to breathe
  • Product suitable for cold service (including cryogenic) is available with integral vapor barrier
  • Eliminates need for contraction joints in cold insulation
  • Large productivity increase (especially on cold insulation) is allowed by sealing large sections of cold service blanket with butyl tape vs. the labor required to install cold service rigid insulation (i.e. full-thickness manual application of sealant around every section of rigid insulation and manual application of mastic or sheet-style vapor barrier)
  • Third-party tested to confirm blast and fire resistance
  • Third-party tested to confirm sound attenuation properties meet industry standard
  • Can be removed and reused without degradation of properties (one-time purchase)
  • Large reduction of transportation and storage footprint

The cons:

  • Lack of manufacturers to create competition
  • Confusion caused by those who are ignorant of cost impacts of constructability. Commodity (material) cost is higher than other materials, but total erected cost is less than rigid insulation when constructability aspects are considered, especially using labor rates in the U.S., Europe, Australia and offshore
  • Hesitation of insulators due to fear that aerogel powder is hazardous
  • Depending on handling and cutting practices, dust generation can be an issue; industry is still learning how to handle in a manner that minimizes dust

With rigid block pipe covering, there will always be a small gap between the insulation and the steel, a space where ingressing water can exist. When flexible batt is squeezed against the cylindrical steel shape of a pipe or vessel by the metal jacket, this space is eliminated so that there is no place for the water to go. In the CUI range, water is not absorbed by aerogel blanket, nor can water get behind blanket that is applied to a cylindrical surface and held firmly in place by traditional steel banding.

Since the cause of CUI is the long duration of water contact with steel, and because aerogel blanket insulation is both water-repellent and effective at preventing water ingress, this type of insulation is especially effective at reducing the risk of CUI. As noted in The Detrimental Effects of Wet Insulation in the CUI Range, the water repellency of expanded perlite (the other water repellent industrial insulation for which we have 40 years of case history), has been shown to be extremely effective from a CUI reduction standpoint.

In Summary

The oil & gas industry has struggled for many years with the deleterious and costly effects of corrosion under insulation. Identifying and capitalizing on technologies that have proven themselves in other industries is a key approach in reducing the massive cost of this work. Of course, any cost reduction steps must not negatively impact the expected functionality or reliability of corrosion protection and thermal insulation systems. These two materials, somewhat new to our industry, are proving to be promising cost-reduction alternatives as their adoption and field experience increases.