Understanding the Importance of Oxidized Inconel Lockwire in Aerospace Safety

Lock wire: the most underappreciated safety device that has indirectly saved countless lives and makes flying safe. A lock or safety wire is a simple device that keeps nuts and bolts from backing off after being appropriately torqued. However, simple does not mean easy; if the lock wire is installed improperly, it will not work effectively. Creating a good, tight braid of lock wire is as much art as it is technique, and using the right Oxidized Inconel Lockwire is the key ingredient in a nice, tight, safety wire in anything that needs wire locking tension. 

We carry and supply Oxidized Inconel lock wire in one-pound rolls to keep you in the fight for a long time. 

Safety Wire: Keeping You Safe For Millions of Flight Hours

The aerospace industry relies heavily on safety wires, also known as lock wires, to secure fasteners and prevent them from loosening due to vibration and other forces. The lock wire is pulled tight against another fastener or against a tab that is built into the component. Both methods are standard, although the techniques are a little different.  

Safety wiring is critical to ensuring the integrity of aircraft and spacecraft systems. While there are other locking mechanisms, nothing is more tried, accurate, and proven than a simple oxidized lock wire. 

It always works, is cost-effective, and is easy to use. You only need a pair of diagonal cutters, your hands, and PPE. Safety wire pliers make the job a little easier, but are not a requirement. The most basic toolbox has all the items you need to safety wire anything on the aircraft. 

Oxidized Inconel lock wire is a popular choice for safety-critical applications due to its high strength and resistance to corrosion. There is more than one diameter to choose from, but the most common is 0.032”. 

Properties of Oxidized Inconel

On to the salient characteristics of safety wire. 

Oxidized Inconel wire is known for its high strength, corrosion resistance, and ability to withstand high temperatures. It is used for everything from wheel hub retaining bolts to drain plugs to bolts used in the engine. It is vital that these bolts do not come loose in operation because this will lead to catastrophic failure. 

It is commonly used in high-stress applications where other materials may fail, so a safety wire is used where flight safety is paramount. The list of applications is a mile long. The properties of oxidized Inconel make it an ideal material for lock wire products in the aerospace industry.

The name Inconel is the alloy used for the safety wire. Here are some of the key characteristics of safety wire, as it is commonly known:

  • Color and Identification: The wire undergoes an oxidation process, giving it a characteristic dull gray or gray-blue finish. This finish is intended explicitly for easy visual identification, distinguishing it from stainless steel and Monel wires.
  • Material Composition: Inconel 600 is a nickel-chromium alloy, sometimes called Chromel C. Its composition provides excellent resistance to corrosion, oxidation, and carburization, and strong mechanical properties across a wide temperature range.
  • Temperature Resistance: Oxidized Inconel safety wire is suitable for use at temperatures up to 900°F (482°C), and the base alloy can withstand even higher temperatures in some applications. However, tensile strength may begin to decrease between 800°F and 900°F (427°C–482°C).
  • Corrosion Resistance: The high nickel and chromium content provides exceptional resistance to chloride stress corrosion cracking, acids, seawater, and other corrosive chemicals.
  • Mechanical Strength: The wire maintains high strength and fatigue resistance even under extreme stresses, vibrations, and environmental conditions. It is not precipitation-hardened but gains strength through cold work.

Applications of Lockwire

Although aerospace is the most prolific, Lockwire is used in various applications, including aerospace, automotive, and industrial equipment. Anywhere there is a high vibration, fasteners tend to loosen or lose contact with the components they are attached to, so it is a good fit for a lock wire. 

The most common use for lock wire is to secure fasteners in safety-critical systems, such as engines, gearboxes, and landing gear.

  • Schrader valves, commonly used on landing gear struts, centering cylinders, and pressurized hydraulic fluid reservoirs, are always safety wired in place.

Benefits of Using Lockwire

We could not state this as a benefit because using a lock wire is mandatory, but it certainly has benefits. Lock wire prevents fasteners from loosening over time, which can lead to equipment failure and accidents.

Packaging and Storage

Lock wire products are typically packaged in one-pound spools in a plastic canister. The typical best practice is to keep the packaging in which it was manufactured because it keeps the sharp ends of the wire covered and protected. It also keeps the wire in a spool so it does not unravel with use. 

Stocking lock wire products in a cool, dry place is important to prevent damage and degradation. The toolbox is usually perfectly fine, but it should not be stored long-term in anything made of leather or other materials that retain moisture. 

Maintenance and Inspection

Routine inspections are critical to ensuring the safety and reliability of lock wire products. The standard pre-flight, through-flight, and post-flight inspections should include looking at Schrader valves, system drain plugs, wheel hubs, and anywhere else that uses safety wire to secure fasteners. There is not much in the way of maintenance; if the wire is broken, you need to replace it, and you should inspect and probably re-torque whatever it was securing. 

Regulatory Compliance

Several regulatory bodies, including the Federal Aviation Administration (FAA) and the European Aviation Safety Agency (EASA), regulate using lock wire products in aerospace. The military also mandates the use of safety wire in all fleet airframes. 

The FAA regulates and describes safety wire usage in its comprehensive manual, FAA Advisory Circular AC 43.13- 1 B. All acceptable methods of civil aircraft maintenance, repair, and construction are in the A/C 43.13-1B, so it is definitely the definitive guide. 

The military regulations are a little harder to track and follow because there are several. The regulations specify the materials that can be used for lock wire products, such as oxidized inconel and stainless steel. Different compositions are used for other applications, which is very important on tactical aircraft. The most common MIL-SPEC lock wire specifications are M22759 and M25038. 

Companies that manufacture and supply lock wire products must comply with these regulations to make sure their safety wire products are safe and reliable, and can be marketed to the aerospace industry. 

Installation Best Practices

Here is a simple and definitely not complete list of best practices for safety wiring aircraft components

  • Installing lockwire products requires careful attention to detail to ensure they are used effectively. It is EASY to do it wrong and think you did it right. 
  • The wire should be threaded through the fastener hole and twisted to secure it in place. Sometimes it will go from bolt head to bolt head, other times it is a tab to a drain plug. They are all different. 
  • Using a single strand or multiple strands of wire depends on the specific application and the type of fastener being used. Generally, it is a best practice to keep strands and sections as short as possible.
  • Fasteners and bolts must be torqued appropriately FIRST before they can be safety wired. 

Final Thoughts on Safety Wiring

We cannot overstress how important this simple component is. Getting the lock wire right is as much an art form as a science. The correct rate of twist, the right direction from item to item, and securing it correctly are all critical maintenance skills. 

Greenwood Aerospace is your go-to stop for oxidized inconel safety wire spools, a common staple of the standard shop consumables list. If your maintenance shop is running low on safety wire, give us a call, and we will get you set up with what you need. 

Greenwood Aerospace is U.S. Department of State ITAR-registered, allowing us to partner with large defense contractors on various military initiatives for exporting ITAR-controlled items.

  • UEI: KVSUYYSJS174
  • DUNS: 604006874
  • Cage Code: 2Y735
  • ITAR DDTC Export Compliant
  • AS9120B QMS Certified
  • NAICS: 488190, 336413, 332722, 336411, 336413, 481212, 532411

If you have any questions about what we offer or stock, call us at (580) 762-2580 or email us at contact@governmentprocurement.com.