Archive: Jun 2021

Passivation Methods to Preserve Stainless Steel Products

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What is the Passivation of Stainless Steel?

Untreated stainless steel has a chemically reactive surface and can rust over time. However, the process of passivation — chemically washing the body of a stainless steel part — protects the surface and results in a longer-lasting item that better resists corrosion and rusting. Passivation removes free iron from stainless steel surfaces, which is highly advantageous for newly machined and manufactured parts. Some of the benefits of passivation include:

  • Resistance to the elements: The iron in stainless steel is the reactive component in the alloy. Chromium and nickel (the other metals in the alloy) are much less reactive to air, moisture, and water. Because the acid wash removes the surface iron, only the passive chromium and nickel oxide layer get exposed to air.
  • Reapplication: Stainless steel parts can undergo the passivation process multiple times without weakening or adverse reactions, allowing operators to deal with iron exposure from physical impact or damage. Regular passivation processes extend the lifespan of the item.
  • Reduced maintenance costs: Passivation reduces the risk of broken parts, contamination from rust, and unscheduled downtime.

The Passivation Process

Passivation is a three-step process that can happen immediately following fabrication and machining. 


  1. Technicians thoroughly clean the stainless steel part to remove grease, dirt, debris, and shavings. This step ensures that the acid wash reaches every inch of the surface to dissolve any unwanted free iron. It also reduces the risk of flash attacks—dark spots and deposits that stain the passivated surface.
  2. The parts are placed in a passivating bath of either nitric acid or citric acid. The components sit in the bath until all of the iron in the surface layers has dissolved.
  3. Testing verifies the removal of all iron from the surface, after which passivation is complete. Different grades of stainless steel may undergo slightly different testing methods. The most common test involves swabbing a test part with copper sulfate to see if plating copper develops.

Considerations for Tank Passivation

Passivation experts can carefully balance different factors to tailor the passivation process for each batch of stainless steel products. Some of the unique characteristics that can change between batches include:

  • The chemical composition of the passivation bath: The bath will use nitric or citric acid, depending on the stainless steel grade, the application specifications, and the environmental concerns of the company.
  • Submersion duration: Different parts need to be submerged in the acid for different lengths of time to ensure all iron gets dissolved.

These factors and others will play a role in the efficacy of the free iron removal process and the final surface quality, which affects the service life and aesthetic appeal of the final product. 

Choose Highland Equipment for High-Quality Stainless Steel Passivation

At Highland Equipment, we specialize in thorough passivation processes that result in high-quality, aesthetically pleasing stainless steel components. We offer a full suite of passivation surfaces to meet the finishing needs of numerous product types. Contact us or request a quote to see how our passivation services can support your project. 


Factors That Determine High Shear vs. Low Shear Mixing

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Processing plants need rotating mixers that can handle different compositions and materials to meet a desired endpoint. When mixing impellers rotate in a batch, they generate shear, or stress, on the materials, to mix them together. The viscosity and other properties of liquids, as well as the presence of solids, determine the force needed to combine the materials. The amount of shear is dictated by the blade design and rotational speed. Mixers can use either high shear mixing or low shear mixing to incorporate the disparate materials into one mixture, depending on your needs.

High Shear Mixing

High Shear Mixing

Shear forces are caused by one force pushing part of a mixture while another force pushes a different part of the mixture in the opposite direction in a parallel field. The higher the shear force is, the better the materials can incorporate together, even mixtures with viscous liquids and solids. 

High shear mixers have a high-speed rotor that forces the mixture outward against a stator to generate shear. These mixers mix, rotate, and agitate the batch. One particular type of high shear mixing, called dispersion, uses high levels of horsepower to create even higher levels of shear. In addition to combining the mixture, high shear forces also ensure the materials are evenly distributed within the batch.

Low Shear Mixing

Low Shear Mixing

Low shear mixing is a gentler, less forceful mixing process. This process is ideal for miscible materials that don’t need a lot of energy or force to combine. It also can handle delicate materials—including adhesives, polymers, and structured food products—and materials with large particle sizes that shouldn’t be broken down during mixing. If the shear rate gets too high, the materials can start to suffer from shear degradation.

Low shear mixing processes feature a wide variety of different rotor blade designs, and they use the flow and turbulence in the tank to help incorporate the materials. 

Applications for High and Low Shear Mixing

Applications for High and Low Shear Mixing

High shear mixing and low shear mixing each meet the needs of different applications. High shear mixing equipment uses include:

  • Emulsifying and homogenizing liquid-liquid compounds
  • Dispersing powders into liquid compounds
  • Mixing liquid-liquid mixtures with materials that have different viscosity levels
  • Dispersing and suspending solids in liquids
  • Reducing particle sizes in mixtures

Low shear mixing processes are reserved for mixtures that need gentler handling or require less force to achieve the desired result. Popular applications include:

  • Combining miscible liquids and fluids
  • Flavoring
  • Increasing the efficiency of heating mixtures
  • Maintaining suspension of particles
  • Mixing liquid chemicals

Working With Highland: Leveraging Software to Optimize the Mix

The key to optimal low and high shear mixing isn’t just the hardware—it’s also the software. High-quality shear mixing software can model the different factors that impact sanitary mixing processes, including heat transfer, reactions, and turbulence.

Using this modeling, Fluent software can present a wide range of industrial functions, such as airflow over aircraft wings, semiconductor manufacturing, and more. New iterations of software are also user-friendly, in that they can easily be used by new and experienced operators. Users follow task-based workflow guides to speedily create simulation processes with accurate results based on different meshes, different blade radius and shape parameters, and more.

Fluent also uses a Mosaic meshing technology as part of its patent-pending high-speed system. This technology combines different boundary layer meshes to create a unique mesh. This ensures faster and more accurate flow resolution based on the models.

With this software, Highland can test different mixing scenarios and blade configurations to optimize the process and time requirements for every batch, design blades with the right radii and shapes to speed up mixing, create better consistency, and create customized equipment for each of our customers. 

Contact Us Today for High Shear and Low Shear Mixing Solutions

High shear and low shear mixing processes each play an important role in manufacturing. Different mixtures may need to be homogenized, while others need consistently suspended solids. High shear, or very forceful, mixing processes uses high-speed impellers, and low shear mixing processes use flow, turbulence, and rotational force to combined miscible goods. 

At Highland Equipment, we specialize in testing and designing high shear mixing and low shear mixing equipment. Every product is customized and thoroughly modeled to create the optimal shear mixing force for each of our customer’s needs. Request a quote today to get the customized mixing tools your facility needs.

How Do Companies Utilize Borescoping to QC Fabrications?

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Borescopes are optical instruments that facilitate visual inspection of hard-to-reach spaces, such as the inside of narrow pipes or tubes. They consist of a lens or camera on one end, a flexible, semi-rigid, or rigid tube and/or fiber assembly, and a display on the other end. Industry professionals utilize them to inspect a wide range of industrial parts and products during manufacturing operations and maintenance and repair work. By detecting defects in components—e.g., cracks or leaks in welds—that need to be resolved, they help improve ROI and extend component life.

What Is a Borescope Inspection?

Borescopes are commonly used in non-destructive testing (NDT) operations involving components with hard-to-reach cavities. Some have lights on the lens end to enhance visibility within the component during inspection operations, while others (video borescopes) have a recording function that makes it easier to maintain comprehensive documentation of inspections. Regardless of the design and configuration, they serve the same function: helping technicians inspect component areas that are difficult or impossible to reach without damaging or dismantling the object. These instruments allow for fast and easy diagnosis of component issues, such as blockages, corrosion, cracking, erosion, or weak welds.

Borescope Inspection Procedure for Piping and Tubing

One of the most common applications for borescopes is the inspection of pipes/tubes and fittings. They are used to determine and/or verify the integrity of longitudinal weld joints in manufactured pipes and tubes and orbital weld joints in connected pipe and tube assemblies.

Common issues found in tube/pipe interiors include weld irregularities (which can lead to corrosion and buildup), gaps or light (which indicate an incomplete weld), and cracks or damage (which can cause malfunction). Catching these defects early on allows welders to rectify them before they cause more significant problems.

Once pipes and tubes are thoroughly inspected and approved for use, they are employed in a wide range of industrial applications and processes, including, but not limited to, the following:

  • Food Processing
  • Brewery and Beverage Systems
  • Aseptic Dairy Processes
  • Pharmaceutical Manufacturing
  • Any Piping System that is welded

Highland Equipment: How We Use Borescopes to Ensure Quality

At Highland Equipment, we are fully aware of the important role borescopes play in inspection operations. By utilizing these tools to inspect the hard-to-reach areas of our piping system fabrications, we ensure the quality of each weld and the integrity of the overall system. To learn more about how we use borescopes to ensure fabrication quality, contact us today.