3D Printed Inconel Sleeve Protects Critical Valves from Thermal Shock

The 3D printed thermal sleeve looks simple, but the double-walled design is filled with complex lattice structures that enable this monolithic part to provide insulating protection to valves in high-temperature applications. Source: Velan

Montreal-based valve manufacturer Velan had been watching additive manufacturing for nearly a decade before the company saw just the right way to jump in.

“We connected all the dots on this part,” says Luc Vernhes, director of business development.

The product, commercialized as Hexashield, is a thermal sleeve used within valves for ebullated bed (e-bed) hydrocracking. This process “upgrades” residues from oil refining into distillate products, using an ebullated bed reactor. Ebullated bed hydrocracking operates at high temperatures and pressures, with the oil inside the reactor reaching up to 850°F and over 3,000 psi. When that oil exits the reactor, it subjects the valve it travels through to this high temperature, potentially inducing thermal shock and stress.

“This is a severe service application,” explains Duke Tran, executive vice president of product innovation and technology. “The valve changes from very hot to room temperature repeatedly. That thermal cycling puts a lot of stress on the valve body.” Over time, the stress can lead to cracking of the valve body, causing leaks and unscheduled plant shutdowns.

Velan now produces a 3D printed thermal sleeve that sits inside the valve to insulate it from temperature extremes. The 3D printed component helps reduce cyclical stress and risk of thermal shock, and represents Velan’s first significant intersection of the right design, application and price point for additive manufacturing.

The Hexashield thermal sleeve sits inside the valve; its role is to protect the valve from the extreme cyclic temperature varietions of the oil passing through. Source: Velan

A One-Piece Metal “Thermos”

Existing thermal sleeves for ebullated bed valves achieve their insulating properties through microscale porosity created with a ceramic coating. These sleeves are machined from metal and then covered with a special ceramic thermal barrier coating (TBC). While effective and economical, the TBC can be brittle and prone to cracking, and the manufacturing process for these sleeves is complex because of the necessary coating step.

Velan’s 3D printed Inconel 718 sleeve (left) uses interior lattices for its insulating properties rather than the thermal barrier coating (TBC) applied to the conventional machined sleeve on the right. 

But despite potential manufacturing challenges with the existing TBC-coated product, Velan recognized the need to innovate beyond this insulating option. The company developed a unique thermal sleeve concept that delivers superior thermal insulating performance using a different strategy, while setting itself apart in the market. 

Refractory bricks are laid in an offset pattern, partly so that heat traveling from the interior of the pipe to the exterior is forced through a tortuous path. Source: Velan

In developing a different solution, Velan considered the types of insulation options already available for pipes and valves. Fully ceramic thermal sleeves are used in some high-temperature applications, but are not suitable for coping with the elevated temperatures of e-bed processing. Refractory bricks are sometimes laid in pipelines to provide insulation, but this solution would be too bulky for e-bed valves.

To create a thermal sleeve that would fit the desired form factor and meet the demanding environment, Velan instead developed a fully 3D printed metal sleeve that uses geometry to provide the insulating performance. Taking inspiration from the labyrinthine structures of bricks with offset seams and the microporosity of TBC and ceramic, the team landed on a double-walled sleeve design with lattice infill.

Similar to a Thermos, the double-walled design creates a gap that heat must cross, with the lattices forcing it through a tortuous path that slows its progress. As a result, less heat reaches the valve body and it does so more slowly, keeping the valve body cooler and resisting dramatic fluctuations.

The sleeve can be 3D printed as one monolithic piece through laser powder bed fusion (LPBF). It is manufactured from Inconel 718, and unlike machined metal sleeves, requires no TBC application.

Physical Prototyping and Testing

Developing the monolithic thermal sleeve posed a number of challenges, not least of which was identifying the proper lattice geometry. The team experimented with parameters including infill percentage, lattice pattern, and even the thickness of the inner and outer shells of the sleeve.“We started with conceptual design, and we used thermal finite element analysis to simulate the concept,” explains Fadila Khelfaoui, Velan corporate engineer, metallurgy. But the complexity of the design quickly outstripped the reasonable capabilities of the software.

“It’s a hell of a challenge to mesh a mesh,” Vernhes says, referencing both the computational mesh and the mesh lattice geometries under consideration.

“The software used was not capable of accurately modeling the complex lattice,” Khelfaoui says. “One simulation lasted for many days. Those limitations led us to rely on physical testing.”

Velan worked with a supplier to print mini sleeves using various lattice infill designs, and then built a test rig to thermally cycle each one (as well as conventional sleeves) to capture thermal profiles. The testing procedure involved injecting high-pressure steam at 900°F into a valve equipped with the test sleeve, and then rapidly cooling it. Thermocouples in multiple locations monitored the temperature of the sleeve and the valve body to create a thermal profile.

In testing, the inner diameter of the valve body without any sleeve hit peak stress in just a few seconds and rose to nearly 600°F within a few minutes. With the 3D printed sleeve, however, the valve ID maxed out at less than half the peak stress and around 550°F.

With the 3D printed thermal sleeve, the valve body reached peak stress less than half what it would see without any sleeve in use. Source: Velan

Additionally, the body ID with the AM sleeve saw a more gradual temperature rise. The lower final temperature and less drastic heating are beneficial to the ongoing operation of the reactor system, helping to insulate the valve body and also prevent cracking and fatigue of the thermal sleeve itself over time.

With the AM thermal sleeve, the valve temperature rose more slowly and reached a lower final temperature compared to no sleeve. Source: Velan

Through this physical testing and feeding data back into a simulation model, the team was able to identify the best lattice geometry for the interior of the sleeve. The exact design selected is proprietary, but cutaways of some rejected lattices can be seen below:

Velan varied the size and shape of the lattice struts, the infill density, the thickness of the walls, and more variables to arrive at the correct lattice. The complexity of the geometries slowed simulations so much that the company quickly moved into production and testing of physical prototypes instead. Source: Velan

Commercializing the Solution

After studying and demonstrating success with the small-scale models, Velan scaled up and moved the 3D printed Hexashield thermal sleeves into production through LPBF, again through a supplier. With its location in Montreal, Velan has access to a number of service providers familiar with 3D printing of Inconel for the aerospace industry and says it has no plans to bring additive manufacturing internal.

3D printed sleeves arrive at Velan post printing, depowdering and heat treat. They require minor finish machining and the application of a coating on the interior before they are ready for installation. Source: Velan

“The technology is evolving so fast, I don’t think we need to print in-house,” Khelfaoui says.

When the sleeves arrive at Velan, they have been 3D printed, depowdered and heat treated. From there, they require only finish machining and the application of a coating (not TBC) on the inner diameter. Compared to a machined metal sleeve, the 3D printed product can be manufactured in fewer steps, without the necessity of sending parts to a specialized supplier for TBC.

More than 100 3D printed Hexashield thermal sleeves have been sold so far, ranging in size from 1 to 6 inches inner diameter.

A Velan employee inserts the Hexashield thermal sleeve into a metal-seated ball valve. Source: Velan

Commercializing a 3D printed valve product is not completely straightforward, as the valve industry has been slow to issue qualification standards around parts made this way. However, the role of the thermal sleeve has made it somewhat easier to qualify than other types of valve components.

“It is not a pressure boundary product,” Khelfaoui explains, which means that the thermal sleeves are not beholden to pressure vessel standards. Instead, Velan evaluates the 3D printed sleeves against quality requirements it has established internally.

“We have still done qualification to confirm compliance with our own standards for mechanical strength and corrosion resistance,” Vernhes adds.

The 3D printed thermal sleeve is more expensive to produce than a machined version, but was shown to provide better performance in terms of thermal insulation in testing. At the end of the day, however, the Velan team says the cost to manufacture the sleeve itself is less significant compared to the criticality of its application.

“The valve costs a whole lot more than the sleeve,” Tran says.

About the Author

Stephanie Hendrixson reports on 3D printing technology and applications as executive editor for Additive Manufacturing. She is also co-host of The Cool Parts Show, a video series that highlights unique, unusual and weird 3D printed parts, and co-host and creator of the AM Radio podcast. SUBSCRIBE HERE