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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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Looking for domestic and imported fasteners? Birmingham Fastener has you covered! Our massive inventory ensures your bolts will be shipped fast and on time! Call us or get a quote online today!

Anchor Bolts: Types and Uses

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anchor-bolts

Anchor bolts are designed to attach structural elements to concrete. In our industry, anchor bolts are typically used to attach steel to concrete. One end is embedded into the concrete, while the opposite end is threaded to attach structural support. There are four main types of anchor bolts: L-shaped, double end rods with plate, headed, and swedge. Each type has their own uses, sizes, and advantages. Let’s go over each type of anchor bolt and how they are used in structural applications each day.

L-Shaped Anchor Bolts

L-Shaped anchor bolts are used in a variety of applications including light poles, sign structures, heavy equipment and tooling. At Birmingham Fastener, we distribute L-shaped bolts in 3/8”-2.5” diameter and any length required in the following standards: A307, F1554 -36, F1554-55, F1554-105, A193 B7, 304 Stainless, 316 stainless, and any grade the customer may require.

Double End Rods with Plate

These types of anchors are double end rods with a plate washer added to one end. The plate can either be welded to the anchor bolt itself, or it can be tack welded to a nut entrenched in concrete. Plate bolts are used primarily in constructing columns for buildings, highway signs, and other applications. At Birmingham Fastener, we distribute straight with plate bolts in 3/8”-4” diameter and any length required in the following standards: A307, F1554 -36, F1554-55, F1554-105, A193 B7, 304 Stainless, 316 stainless, and any grade the customer may require.

Headed Anchor Bolts

Unlike most anchor bolts, headed anchor bolts have a forged head on their unthreaded end. It is typically a hex, heavy hex, or square head. The head is embedded into the concrete to secure a variety of constructions including structural columns, bridge railing, and light poles. At Birmingham Fastener, we distribute straight with headed anchor bolts in 1/2”-2” diameter and any length required in the following standards: A307, F1554 -36, F1554-55, F1554-105, A193 B7, 304 Stainless, 316 stainless, and any grade the customer may require.

Swedge Bolts

Swedge bolts consist of round bar steel that is threaded on one end and “swedged” on the other. “Swedged” means one end will have multiple indentions to allow concrete to flow into them. Swedge bolts are 100% domestic, as they are used to connect girders and piers. Most swedge bolts are hot dipped galvanized and come in diameters ranging from 5/8” to 4”. They are also available in other materials including stainless steel.

For an easy to read chart, view our Anchor Bolts Length Chart.

Electropolishing vs. Passivation – Choosing the Right Finish

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electropolishing-passivation

Electropolishing and Passivation

A lot can go into choosing a finish for your stainless steel fasteners. The two finishing operations most industries specify for their parts are electropolishing and passivation. Today, we’ll look at these two chemical processes, learn their differences, and discuss the advantages one may have over another.

Electropolishing

Electropolishing is a chemical process that can be performed on almost all metal to remove imperfections and contaminants on the surface of the metal. The process involves submerging the fastener or other metal product in a temperature-controlled chemical bath. A current is then passed through the bath, oxidizing the surface and causing it to shed and deburr the contaminants and smooth out any flaws. The fastener comes out to a very bright finish. Not only is the steel visibly shinier, but electropolishing has greater corrosion resistance than that of passivation.

Passivation

Like electropolishing, passivation is also a chemical process designed to remove imperfections from steel and provide a clean finish. In contrast to electropolishing, passivation does not produce a bright or shiny finish. Passivation is designed to improve corrosion resistance on stainless steel. Passivation is effective on most grades of stainless steel, but it is not recommended for certain types of alloys. One difference between electropolishing and passivation is the pre-cleaning step in passivation. Sometimes, a pre-cleaning operation is required prior to passivation, because the process alone is not completely effective. After pre-cleaning, the process of passivation involves placing the steel parts into a nitric or citric acid bath at a set temperature and time depending on the type of alloy. The free iron and other materials on the surface of the steel is then removed in the bath. The finished product has a dull, silver colored finish. On average, passivation is a third less expensive than electropolishing, making it a cost-effective option that produces good corrosion resistance.

Bottom Line

While both methods of finishing provides increased corrosion resistance, electropolishing produces a brighter finish with better corrosion resistance than passivation. That said, passivation provides a clean finish with corrosion resistance at a third of the cost.

 

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Call or contact us for a quote today to learn how Birmingham Fastener can provide you with quality fasteners with a quick turnaround!

AASHTO and ASTM Standard Conversions

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AASHTO and ASTM

As we have discussed in earlier blogs, ASTM International produces over 12,000 standards for many different types of products globally. In relation to fasteners, the ASTM provides the standards for how they are made, what raw materials can be used to make them, and what testing methods must be performed prior to installation.

The American Association of State Highway and Transportation Officials (AASHTO) is a nonpartisan association representing highway and transportation departments in the United States. AASHTO sets technical standards for all phases of highway system development, including design, construction, materials, testing, and more.

The standards for ASTM and AASHTO often overlap, and there are times when AASHTO standards reference ASTM standards. Sometimes it is important to know how one standard converts to another. Below, you will find a chart with the common conversions for ASTM and AASHTO standards relating to fasteners.

AASHTO to ASTM Conversion Chart

AASHTO ASTM Specification Description
M-111 A123 Hot-Dip Galvanized Coatings on Iron and Steel Products
M-232 A153 Hot-Dip Coating on Fasteners
M-164 A325 Structural Bolt
M-253 A490 Structural Bolt
M-183 A36 Low Carbon Structural Steel
M-222 A588 High Strength Weathering Steel
M-223 A572 High Strength Low Alloy Structural Steel
M-291 A563 Carbon and Alloy Steel Nuts
M-292 A194 High Strength Heavy Hex Nuts
M-293 F436 Hardened Steel Washers
M-314 F1554 Anchor Bolts

 

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Call or contact us for a quote today to learn how Birmingham Fastener can provide you with quality fasteners with a quick turnaround!

Anchor Bolt Length Chart

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This chart is available for referencing bent anchor bolt lengths. All sizes are in inches. For a printable version of our chart, download our Anchor Bolt Length Chart PDF. To learn more about anchor bolts, check out our blog on their types and uses.

Size Length Hook Thread Length
3/8 6 1 1/2
3/8 8 1 1/2
3/8 10 1 1/2
3/8 12 1 1/2
1/2 6 1 2
1/2 8 1 2
1/2 10 1 2
1/2 12 1 2
1/2 14 1 2
1/2 16 1 2
1/2 18 1 2
1/2 20 1 2
1/2 24 1 2
5/8 6 2 4
5/8 8 2 4
5/8 10 2 4
5/8 12 2 4
5/8 14 2 4
5/8 18 2 4
5/8 20 2 4
5/8 24 2 4
3/4 6 3 4
3/4 10 3 4
3/4 12 3 4
3/4 14 3 4
3/4 16 3 4
3/4 18 3 4
3/4 24 3 4
3/4 30 3 4
3/4 36 3 4
7/8 12 3 5
7/8 14 3 5
7/8 18 3 5
7/8 24 3 5
1 14 3 6
1 15 3 6
1 16 3 6
1 18 3 6
1 20 3 6
1 24 3 6
1 30 3 6
1 36 3 6
1 36 4 6
1 1/4 18 3 6
1 1/4 24 3 6

How to Measure a U-Bolt – U-Bolt Size Chart

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How to Measure a U-Bolt

A U-bolt is measured by four dimensions: the length, the hook, the diameter, and the thread length. In waterworks applications, you can refer to the chart below for the correct U-bolt size you will need for different pipe sizes.

u-bolt

U-Bolt Length

The length of a U-bolt is measured from the end of the bolt to the inside of the bend (see image above).U-Bolt Hook

A U-bolt’s hook is the distance between the legs of the bolt, as represented by “C” in the image above. It’s important to note that in some drawings, the hook is shown at the center or bottom of the bolt. Furthermore, some companies measure the hook from the center of one leg to the center of the other leg. Birmingham Fastener measures the dimensions as outlined in the Industrial Fastener Institute Standard IFI-136.

U-Bolt Diameter

To measure a U-bolt’s diameter, you’ll measure the diameter of one of the bolt’s legs (see “D” in the image above).

U-Bolt Size Chart

This chart is available for referencing U-bolt lengths. All sizes are in inches. For a printable version of our chart, download our U-Bolt Length Chart PDF.

Pipe Size Diameter C (Hook) L (Length) T (Thread Length)
1/2 1/4 15/16 3  1/4 2  3/8
3/4 1/4 1  1/8 3  5/16 2  3/8
1 1/4 1  3/8 3  7/16 2  3/8
1  1/4 3/8 1  11/16 3  3/4 2  3/8
1  1/2 3/8 2 4 2  1/2
2 3/8 2 7/16 4 1/2 2  1/2
2  1/2 1/2 2 15/16 5 1/4 3
3 1/2 3 9/16 5 13/16 3
3 1/2 1/2 4 1/16 6 5/16 3
4 1/2 4 9/16 6 13/16 3
5 1/2 5 5/8 7 13/16 3
6 5/8 6 3/4 9 1/2 3 3/4
8 5/8 8 3/4 11 1/2 3 3/4
10 3/4 10 7/8 13 13/16 4
12 7/8 12 7/8 16 1/16 4 1/4
14 7/8 14 1/8 17 5/16 4 1/4
16 7/8 16 1/8 19 5/16 4 1/4
18 1 18 1/8 21 11/16 4 3/4
20 1 20 1/8 23 11/16 4 3/4
24 1 24 1/8 27 11/16 4 3/4
30 1 30 1/8 33 11/16 4 3/4
36 1 36 1/8 39 11/16 4 3/4