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How to Reapply Bolt Lubricant

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How to Reapply Bolt Lubricant

Structural bolting components, whether uncoated or galvanized, are lubricated for installation purposes. Sometimes it is necessary to reapply bolt lubricant. Though the types of structural bolt lubricant vary, both have a chance of coming off prior to installation. This is typically caused by exposure to the elements from improper jobsite storage. Reapplication of the lubricant is typically required prior to installation. Here, we’ll go over how and when to reapply lubricant on structural bolting assemblies.

Reapplying Bolt Lubricant on Uncoated Assemblies

While there are no specific ASTM requirements that uncoated bolting assemblies be lubricated, their lubricant comes from the left over water-soluble oil from production. This oil ensures ease of installation. The lubricant can wash away when exposed to condensation, or it can evaporate when their containers are left open.  If this happens, the assemblies can be difficult to install, and the bolt’s ductility is lessened due to the stress of tightening the non-lubricated bolt.

If the bolting assemblies have lost their lubrication, you may reapply an oil-based structural bolt lubricant, like stick wax or liquid wax, prior to installation. To reapply bolt lubricant, put it on the nut’s threads and inside face. It’s important that the lubricant is on the inside face of the nut, because much of the torque used to tighten the bolt is to get past the friction between the nut and washer or steel. Once the bolt lubricant is reapplied, you may be required to retest the bolting assemblies or recalibrate your wrenches prior to installation. Refer to the RCSC for more details.

Reapplying Bolt Lubricant on Galvanized Assemblies

In contrast to uncoated bolting assemblies, galvanized nuts are lubricated with a dry, wax-based bolt lubricant. Because it isn’t oily, you may not be able to feel this lubricant. The ASTM requires that the lubricant be dyed to ensure that the nuts have been lubricated (Note: the color is not specified and varies from manufacturer to manufacturer).

Similar to the uncoated bolting assemblies, if the nuts have lost their lubrication, reapply a wax-based lubricant on the nut’s threads and inner face. There is no need to lubricate the bolt or washer. Once the lubricant has been reapplied, you must retest the assembly. Refer to the RCSC for more details on testing.

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A325 Bolts vs. A490: What is the Difference?

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ASTM A325 Bolts and A490 Bolts

ASTM F3125 Grade A325 bolts and A490 bolts are two of the main types of structural bolts we sell, and they are the two you will most often see on a jobsite. The difference in grades A325 and A490 may seem simple. A490 is stronger than A325. That said, plenty of projects call for A325 bolts. Let’s take a look at why this is, what are the other key differences, and why you would use one over the other.

In a lot of ways, grades A325 and A490 are similar. Both of these F3125 bolts have a heavy hex head configuration which gives a larger bearing surface to distribute the load. These structural bolts have a specific thread length and shank length. In structural bolting applications, this allows the bolt's threads to not be in the shear plane (where the two plates meet up). The threaded section of the bolt is the weakest, thus a longer shank length makes for a stronger tensile connection. While these similarities make these grades of bolts seemingly identical, there are some fundamental differences that make grades A325 and A490 different.

F3125 Grade A325 Bolts

Grade A325 bolts are commonly used in bridge and highway construction projects. They can be made of Type 1 medium carbon steel or Type 3 weathering steel. An important distinction between A325 bolts and A490 is that it A325 Type 1 bolts can be galvanized. A325 bolts have a minimum tensile strength of 120,000 PSI for one inch or less diameters and 105,000 PSI for over one inch. This makes them weaker than A490, certain jobs do not require a structural bolt as strong as Grade A490.

F3125 Grade A490 Bolts

Grade A490 bolts can be made of Type 1 higher carbon alloy steel or Type 3 weathering steel. Unlike Grade A325, Grade A490 bolts cannot be galvanized. This is due to the potential for hydrogen embrittlement, which could happen during the hot dip or mechanical galvanizing process. As mentioned earlier, Grade A490 requires a higher minimum tensile strength (150,000 PSI), making it stronger than Grade A325. Therefore, jobs that require a stronger bolt typically use Grade A490. That said, their strength can often be an issue. Higher strengths of steel are more susceptible to stress corrosion or hydrogen cracking. Because of this, A490 bolts are not as commonly used for bridge and highway construction compared to A325 bolts.

Bottom Line

Ultimately, your engineers will specify which grade of F3125 structural bolts you will need to use, but it is important to know the distinction between grades A325 and A490. Grade A490 is stronger than Grade A325, but strength isn't the only factor in making a decision for bolts. A490 bolts cannot be hot dip or mechanically galvanized. Grade A325 is not as strong, but it is a lower cost bolt that can be galvanized to avoid corrosion.

Author’s Note: In 2016, ASTM A325 and A490 were replaced by ASTM F3125. A325 and A490 are now grades under the F3125 specification. When reading this blog, please note that when we discuss “A325” and “A490” structural bolts, we are specifically discussing the grades of F3125 structural bolts. This blog is for informational purposes only. For more information on the ASTM, visit their website.

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Understanding and Preventing Fastener Corrosion

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Fastener failures occur when the wrong fasteners are being used for a project, or the right fasteners are being treated incorrectly. Fastener corrosion is one of the most prevalent issues causing fastener failure. Let’s go over the what corrosion is, types of corrosion and how to avoid it in your project.

How Fastener Corrosion Occurs

Corrosion is the destructive alteration of metal by chemical or electrochemical reactions within its environment. Corroded parts fail for a variety of reasons including:

  • Loss of mechanical integrity: corroded areas do not possess mechanical strength
  • Fatigue: Corrosion site causes cracks in the fastener
  • Loss of surrounding clamped materials: the material the fastener is clamping erodes around the head of the fastener
  • Stress corrosion: exposure to harsh environment causing embrittlement

Types of Fastener Corrosion

There are two main categories of fastener corrosion: a direct chemical attack or electrochemical corrosion. 

A direct chemical attack occurs when the material the fastener is made out of is soluble in its environment. This typically happens in harsh environments, like the oil and gas industry. To prevent this, make sure to choose a fastener material that is unaffected by solvent, or choose the proper coating to withstand the solvent. 

Electrochemical corrosion encompasses many types of corrosion, and it results in many small electrical current flows through the fastener. This process results from the contact of two different types of metal or the presence of atmospheric oxygen within the presence of an electrolyte. Here are a few types of electrochemical corrosion you may encounter:

  • Galvanic Corrosion - caused when two different metals are in contact, resulting in pitting or erosion damage.
  • Stress Corrosion Cracking - caused when tensile stressed parts are in a corrosive environment. There is too much tension on the fastener, making it more susceptible to failure. Stress corrosion cracking can happen much more quickly than the other types of corrosion.
  • Crevice corrosion - occurs in the crevices of a fastener that isn’t properly ventilated. This happens any place dirt or moisture accumulate. This is one of the more dangerous types of corrosion, as it often isn’t caught until after the damage has occurred.
  • Uniform corrosion - occurs due to improper coating of the fastener, causing rust that makes the fastener difficult to replace.
  • Pitting corrosion - caused when microscopic holes form on the fastener. 

Avoiding Fastener Corrosion

The best way to avoid corrosion is to ensure you are using the right materials and coatings for the job. You should also make sure the fasteners are being stored properly on the jobsite, and are installed correctly. If you have any questions, always refer to your project engineer and follow the proper standards for the project.

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Type 304 and Type 316 Stainless Steel Fasteners

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One of the great things about stainless steel fasteners is the intrinsic protection within the makeup of the steel. The fastener maintains a shiny, clean finish (when electropolished) while maintaining corrosion resistance. Let’s get into the meaning of stainless steel, its characteristics, and the differences in Type 304 and 316.

What Makes Stainless Steel Fasteners “Stainless?”

The term stainless steel is used for a family of iron-based alloys that contain at minimum 10.5% chromium. This amount of chromium allows for corrosion and heat resistance due to the creation of a surface layer that prevents oxygen from penetrating the steel. Rust cannot form, thus making it “stainless.” Often, their composition also includes other alloys such as nickel, manganese, sulfur, or titanium. These alloys add extra corrosion resistance.

In the fastener world, most stainless steel is austenitic stainless steel, commonly referred to as the 300 series. While there are many compositions that fall under the 300 series, we mostly use types 304 and 316. While they both provide excellent corrosion resistance and have similar compositions, their differences lie in the ratio of chromium to nickel and the environments they are used in.

Stainless Steel: Type 304

You will often hear the term “18-8” when researching the 304 series of stainless steel fasteners. 18-8 refers to the 18% chromium and 8% nickel in the steel. While many stainless materials in the 300 series have this 18-8 mixture, their chemistries and corrosion resistance do not necessarily meet that of type 304. Type 304 is the most popular of the 300 series of stainless steel, as it provides some of the best corrosion resistance in the series.

Stainless Steel: Type 316

Type 316 stainless steel fasteners fall right behind Type 304 in terms of popularity and provides excellent corrosion resistance. Unlike 304, Type 316 does not follow the 18-8 makeup. The chromium is lowered to 16% and the nickel is raised to 10%. Type 316 also contains 2% of molybdenum. Adding molybdenum provides superior resistance to chlorides which can cause pitting.

Because of its composition, Type 316 is used in more corrosive environments where the fasteners will be exposed to chemicals, solvents, or salt water. Type 316 stainless steel fasteners are best used in applications with abrasive chemicals or direct salt spray.

ASTM Designations – Interpreting the Standards

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In other blogs, we discuss the ASTM International, what it is, and how we use them in the fastener industry. Our sales team will often refer our customers to the ASTM standards, and our team uses and adheres to them each day. For those unfamiliar, the ASTM standards may seem unapproachable, but the standards are actually accessible once you understand their organization. Let’s go over the standards, their designations, what they contain, and how you can find the right standard.

ASTM Designations

There are over 12,000 ASTM standards covering a variety of fields and industries. For our purposes, we’ll focus on the standards that relate to fasteners. The ASTM designation is a mandatory title of each standard (example: F3125 or A325). The first letter is the classification of the standard:

A - Ferrous metals and products (steel)
B - Nonferrous metals and products (coatings)
C - Cementitious, ceramic, concrete, and masonry materials
F - end-use materials and products (bolts)
G - Corrosion, deterioration, weathering, durability, and degradation of materials and products

After the letter, there is a reference number given to the standard.  From there, a grade can be added. For example, F3125 is the standard for high strength bolts. A325 and A490 are grades that fall under that standard, so you’d call a bolt F3125 Grade A325. When reading an ASTM standard, you will usually see two numbers after the standard, like A449-14. The last two numbers signify the year the standard was updated.

Reading an ASTM Standard

ASTM standards are written in a specific, organized manner. Each standard begins with the scope, which informs the reader the purpose and limitations of the standard. It then has a bibliography of referenced documents within the standard and may also include a list of any terminology used that may be unfamiliar.

From there, in regards to fasteners, you will find details on everything needed to manufacture the fastener. This includes materials, mechanical properties, chemical compositions, dimensions, appearances, and testing methods. These details can also include fastener limitations, reference tables, supplementary requirements, and notes on packaging. Referring to an ASTM standard is a great way for manufacturers and customers alike to determine the right fastener for a particular job, as well recognize the advantages and limitations of a standard.

Finding an ASTM Standard

ASTM International provides a comprehensive search engine on their website for over 12,000 standards. Standards are available for purchase in print or electronically. For specific questions on a standard, contact your project engineer or the Birmingham Fastener sales team, who are always available to answer specific questions about the products we sell.

The Electroplating Process and its Benefits for Fasteners

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We’ve discussed a few different types of zinc coatings for corrosion resistance in the past. The electroplating process is another way to coat fasteners to ensure corrosion resistance and improve the finish of the bolt. Electroplating, or electrodepositing, is covered in the ASTM standards F1941 and B633. Let’s go over the electroplating process, characteristics of an electroplated fastener, and the benefits of this type of coating.

The Electroplating Process

To begin the process, workers clean the fastener with alkaline detergent solutions before being treated with acid. This removes any rust, oils, or other impurities on the surface of the fastener. Once cleaned, the electroplating process begins through electro deposition, or submerging the fasteners into a zinc bath. There, the direct current is sent through the chemical bath, creating a chemical reaction on the fastener, thus electroplating it.

Types of Plating Processes

Most commonly, fasteners are rack plated or barrel plated. Each have advantages and disadvantages.

In rack plating, the fasteners are left to dry on a rack after the chemical bath. This allows the threads of the fastener to remain untouched, but because the fasteners are set on a rack, the fastener ends up without the coating in certain, small areas.

In barrel plating, the fasteners are dried in a turning barrel. While you get full coverage of the coating, there runs a risk of nicked threads. If the fasteners are made from steel and then heat treated to a hardness above 39 HRC, they are baked to minimize the risk of hydrogen embrittlement. Once this process is complete, the fasteners are tested for coating thickness, corrosion resistance, and embrittlement.

Electroplating Characteristics and Benefits

Electroplating allows for a thinner coating with a clean finish, particularly compared to the hot dipped galvanized fasteners where the coating is much thicker and requires overtapping of the nut. Electroplated fasteners are typically plated in yellow or clear zinc. The yellow zinc produces a yellow/muted gold finish, while the clear zinc produces a bright, silver finish on the bolt. The benefits are mostly aesthetic, as this finish is smooth and even while still providing corrosion resistance. It is also less expensive than some other types of coatings.