Large-diameter tanks and vessels have unique insulation requirements and installation practices. The sheer size of these large-diameter structures introduces new challenges that simply are not as common with typical pipe insulation applications. To ensure that your tanks and vessels are set up for success, here are six key considerations you need to keep in mind when designing, specifying, and installing insulation systems for large-diameter tanks and vessels.

The vast majority of the installation will be done from scaffolding.

In industrial applications, large-diameter tanks and vessels can be anywhere from 10 feet high to more than 100 feet high. So when the insulation is installed, the vast majority of the job will be done from a scaffold or mobile elevating work platforms. Installers will have limited space to maneuver, and it will be difficult—if not impossible—to fabricate pieces on the fly. To accommodate the scaffolding, material typically will be fabricated on the ground and then put into place from the scaffold. This added step makes the process much more labor-intensive than a standard pipe insulation installation.

For this reason, it is preferable to use flexible, lightweight, blanket-type insulations like mineral wool boards and pipe and tank wrap, fiber glass boards and large-diameter pipe and tank wrap, and microporous thin blanket. The size, weight, and maneuverability of these materials make them easier to work with from a scaffold than other materials. Additionally, each of these insulations can be pinned to the vessel, rather than held on by banding, making them easier to install. That said, if it is not possible to use weld pins to install the insulation, metal bands can be used. Using bands also allows for the use of other types of more rigid insulations like calcium silicate and expanded perlite.

Insulation support rings are critical.

Tanks need to be insulated on all sides; and on vertical tanks and vessels, that means the insulation will be stacked on top of itself (as shown in Figure 1, from the Midwest Insulation Contractors Association’s North American Industrial Insulation Standards manual.)

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If insulation support rings are not welded to the tank, the insulation on a vertical piece of equipment will start to sag or slip downward. Insulation support rings are typically specified by the engineer and can be placed every 10, 12, or 16 feet. These support rings are critical to ensure the entire system remains insulated as designed.

It is important to note that while insulation support rings are necessary, they also create areas that are highly prone to corrosion under insulation (CUI). Water can seep beneath the jacket and pool on top of the support ring beneath the insulation. The longer the water sits against the metal of the tank or vessel, the more likely it is that corrosion will occur. To avoid this, designers usually specify that support rings should be installed at a slight downward angle or with slits to allow for drainage. A robust maintenance plan will account for this potential weakness in CUI defense, and it will ensure that insulation support rings are an area of focus for regular inspection and maintenance.

There will be many cutouts.

Tanks and vessels frequently require a multitude of cutouts to accommodate manways, nozzles, and anchors. At each of these locations, the insulation will need to be carefully cut and fitted to allow for the various appendages. More importantly, however, the area also will need to be carefully weatherproofed. Every single cutout is a potential Achilles’ heel for water penetration, and installers need to take the time to properly seal the cutout with a high-temperature caulk that can withstand the demands of the application.

It also is important to remember that because large tanks and vessels require scaffolding to insulate and inspect, they are more costly to inspect than pipes that are lower to the ground and easier to access. Large-diameter tanks and vessels may therefore end up on longer inspection schedules. With this in mind, careful weather sealing should be a top priority for all cutouts and joints to ensure the system is built for long-term durability and limited CUI risk.

Thermal expansion and contraction are significant and must be accounted for in the design.

The sheer size of large tanks and vessels, when compared to standard pipes, creates an environment where expansion and contraction must be considered during the design phase. The system should be designed to accommodate the expansion/contraction, using tools like expansion springs that will allow the entire insulation and jacketing system to flex with the expansion or contraction of the tank or vessel beneath it. Additionally, all the insulation should be double-layered, and the layers should be staggered so there is never a direct pathway from the surface of the tank to the metal jacketing as the expansion or contraction occurs.

People walk on the tops of tanks.

If the top of the tank will be insulated, it should be insulated with a material that has high compressive strength, like calcium silicate or expanded perlite. Both materials have excellent compressive strength (>100 psi and 80 psi, respectively) that stands up against the rigors of applications where plant personnel walk on the insulated systems. If a softer insulation is used, such as mineral wool, it could buckle under the weight of the personnel, creating gaps in the jacketing and increasing the likelihood that water will enter the
system and contribute to CUI.

Pre-engineered paneled systems are an easy solution for some applications.

Some companies fabricate and insulate sheet metal jacketing with fiber glass or other insulations in offsite fabrication shops. These products are called pre-engineered paneled systems. While not appropriate for every application, in certain cases, this solution can be a faster and easier alternative to applying the insulation and jacketing independently.

As with most industrial applications, large-diameter tanks and vessels require more detailed consideration than simply insulating for thermal or acoustical performance. To appropriately protect and insulate these types of applications, designers and installers need to consider everything from thermal performance to CUI and whether or not plant employees are likely to walk on the insulation. By keeping these details in mind, and scheduling a rigorous inspection and maintenance plan, you can keep these large structures in excellent operating condition for years to come.

References:
1. MICA National Commercial & Industrial Insulation Standards, 7th Edition. Page 154: Large Diameter Vertical Vessels Block and Blanket Insulation.