Extend boiler tube life

Extend boiler tube life with laser metal deposition

One of the harshest operating environments in the power generation industry is within the boilers at waste-to-energy (WTE) facilities.  Between high temperatures, high pressure, and fuel that is highly corrosive and erosive, WTE boiler components like superheater tubes and platens need to be replaced regularly – at a significant cost for the energy producer.

The conventional solution for minimizing erosion and corrosion on boiler components is to use an overlaying alloy of Inconel 625.  While Inconel can be effective, one of our customers found that it fell short of their desired component lifetime performance goals.  Their typical superheater lifespan was 16-24 months, at which point they were replacing the entire primary and secondary superheater at significant cost.

Working together, we developed a solution using the laser metal deposition (LMD) process along with a powdered alloy that improved both corrosion and wear-resistance. The result? Five years later, these tubes are still in operation.

In addition to extending the life expectancy of boiler tubes, the laser metal deposition process resulted in improved thermal efficiencies, reduced maintenance costs, and production costs per linear foot that were equal to or less than traditional Inconel 625 overlays.

These results have applications in other industries that burn harsh fuels, including the biomass and pulp & paper industries. To learn more about this project, download our case study or contact us to talk to an expert.  

Is laser cladding expensive?

Think laser cladding is expensive? Think again.

We hear this one quite often:  “I’m interested in laser cladding, but it’s too expensive compared to other processes.”  Not true – laser cladding can be very cost competitive.  Let me explain why.

First, to compare apples to apples, I’ll discuss laser cladding in comparison to Plasma Transferred Arc (PTA), TIG, or GTAW welding.  Let’s use the example of a typical valve that is common in the power generation industry. It will probably be coated with Cobalt 6, also known as Stellite 6 by its common trade name.  Cobalt 6 is one of the most prominent alloys used on valve seating surfaces to protect against galling and wear.  If the valve is coated using traditional methods like PTA, the coating is applied very thick to overcome problems caused by dilution.

The advantages of laser cladding became obvious during a recent quote for a large valve company.  The valve manufacturer came to us with a print asking us to apply a coating of Cobalt 6 to a thickness of 0.160” on a set of ball valves. We pointed out that the coating did not need to be this thick and was actually counter-productive.

We then showed the customer cross sections of the valve laser cladding process and explained that we could achieve full material properties in as little as 0.015” to 0.030”. They agreed to redesign the ball since it would need to be slightly larger without the thick coating.

The advantages of laser cladding for this application include:

  • Lower powder costs: In this example, the thicker coating required 64 pounds of powder, compared to our laser clad coating which required only 25 pounds. Since powder can sometimes account for 40 to 50 percent of the cost of a job, this can result in significant cost savings, especially with expensive Cobalt or Nickel alloys.
  • Improved metallurgy: The metallurgy is generally better with laser cladding, since the heat source can be controlled more precisely. In the laser process, the weld pool solidifies quicker so the material hardness is generally higher.  It is not uncommon for the laser cladding process to achieve a hardness of 50 to 54 Rockwell C when depositing Cobalt 6.
  • Less stress: Less stress is induced into the component due to lower heat input.
  • Shorter process time: In many cases, our process time is actually shorter than using PTA.

What are the disadvantages?

Capital equipment costs can be one disadvantage.  Yes, laser cladding equipment can be expensive. However, laser cladding can allow you to use less filler material. Also, in many cases we can deposit filler material at a higher feed rate and still get superior results. These advantages can generally offset the higher cost of equipment.

Another disadvantage can arise when component prints are not revised to take advantage of the technology.  We still receive numerous prints with RFQ’s that require the traditionally thicker coatings to be applied.  We’ve seen prints that call out 0.380” – 0.500” coating thickness.  This can be problematic due to the higher-than-usual hardness values that are achieved with the laser application.

We also try to prepare customers for the fact that their first couple of parts are always the most expensive, due to programming costs and tooling costs.  However, once past these steps, laser cladding can be equal to or less than the cost of more traditional methods, and usually with better results.

This blog post just scratches the surface of this topic, so talk to an expert to find out more about how laser cladding can be a very cost-effective option for your process.

Laser cladding extends the life of soot blower lances

After repairs to the coaxial nozzle (above), our testing shows a fully aligned stream of powder exiting the nozzle.

We just wrapped up another successful project: repairing a coaxial nozzle used for laser cladding at a reduced cost and lead time for our customer, who previously had to ship the nozzles to Europe for repairs.

In laser cladding, a stream of metallic powder is fed through a nozzle and combined with a laser beam to apply a protective coating to a component. Over time, the powder causes wear to the nozzles.  In addition, if the inside and outside cones of a coaxial nozzle are not perfectly aligned, the powder stream is choked, the velocity drops and the powder comes out skewed, resulting in inaccurate and inefficient application.  If the powder wear is extensive, it can also blow a hole through the powder tube.  

In this project, we refurbished the inside cone of the nozzle and aligned the inside cone to the outside cone to make them concentric. We also replaced the three powder tubes using brazing.

After completing the repairs, we conducted trials to measure the powder efficiency before and after the repairs and provided a report to the customer. We also aligned their nozzle to a reference nozzle for a specific application and documented these test results for the customer. 

If you’d like more information about this project or want to discuss how this type of repair could be helpful for your project, get in touch with one of our experts here, or give us a call at 860-413-3098.