Tungsten Carbide Versus Villains: Is it Rust or Corrosion?

Q: “We have tungsten carbide insert surgical devices, and some of them look like they are rusting on and around the tips. I thought tungsten carbide is not supposed to rust at all because it doesn’t contain iron. Can you explain?”

A:

First, without pictures I will share my thought process on what might be taking place.

Some basic facts about tungsten carbide (WC) inserts:

There are two grades of tungsten carbide: industrial grade and jewelry grade.¹ It is important to know the quality of the tungsten used on your instruments. Most tungsten carbide inserts placed on surgical instruments are generally identified by gold on their ring handles (if they have ring handles).

Tungsten carbide should not rust when autoclaved because it contains no iron; although, it can still be damaged and even tarnished.² Damage can be caused by exposure to acid solutions (oxidizers like acidic glutaraldehyde product and hydrogen peroxide [like Plasma sterilization]). A process called leaching can take place where the bond between the stainless steel and the tungsten carbide inserts break down (metal dissolution).

Some questions that should be asked to help determine whether it is rust, corrosion, or something else:

• Where is this taking place?
  • On the tips only?
  • Between the bond?
• What is the color of the stain?
• Do you have any pictures of the affected area?
• Other areas of the surgical instrument?
• Has it been repaired?
  • By whom?
  • When was the last repair done?
• Does it have a Unique Device Identification (UDI)?
• Is it just a few or many instruments?
• Have you changed cleaning solutions recently?
• What type of pretreatment process is being used?
• Are you sure it is rust or corrosion?
• What is the policy of the department on inspection concerning detection of corrosion or rust on instruments?
  • Was the eraser test used?
  • Did you test the area of concern with a hemoglobin test to help define the area better?³
  • Did you review your instrument process and look for areas of concern?
  • Did you interview your staff for input?
• Have you contacted the Original Equipment Manufacturer (OEM) for investigational help?
• Have you reread the IFU concerning care and handling and compared it to your process?
• Have you distinguished whether it is rust or something else?

Why rust or corrosion appears on devices is always a crapshoot. There are many possible villains. Finding which one is not always possible because they can gang up, and finding the ringleader, as with any group of villains, is tough.

Some of the possible villains include a) use of inappropriate solutions, b) poor instrument handling, c) cleaning chemicals, d) abrasive cleaners/tools, e) disinfectants, f) steam quality, g) poor water quality, h) improper loading of cleaning equipment, i) mixing of metals, and others.

To me, rust can come from two major areas of concern when talking in general about tungsten carbide inserts. First, from the area between the bond of the insert and the stainless steel. Second, from the stainless steel instrument itself and migrating to other areas of the instrument. (Again, without pictures, I had to take a general approach).

Answers to my questions and others you might have may help you find out the source of concern and hopefully resolve the concern if it is rust, corrosion, or something else on the tips of your tungsten carbide instruments.

Thus, tungsten carbide inserts do not rust, but if by rust you mean “corrode,” then the answer is “probably yes,” and you do need to find the villain(s) and correct them as soon as possible.

References:

1. Alam, Mohammed. (2020). Does tungsten tarnish, warp, or rust? Quora. https://www.quora.com/Does-tungsten-tarnish-warp-or-rust

2. KDMFAB. (2024, June 3). Does Tungsten Rust – Truth about Rusting Properties of Tungsten Revealed. KDM Fabrication. https://kdmfab.com/does-tungsten-rust/#:~:text=Environmental%20Conditions,and%20oxygen%20may%20facilitate%20rusting

3. Kovach, Stephen M. (2020, December 21). Erasing instrument errors. Healthcare Purchasing News. https://www.hpnonline.com/sterile-processing/article/21202330/erasing-instrument-errors