In the fastener industry, “high strength” typically refers to any medium carbon or medium carbon alloy steel that is quenched and tempered (heat treated). The heat treating process increases the strength of the raw material to the parameters defined by the ASTM or AASHTO specification in question. In the case of highway barrier pins, this most commonly comes into play in the case of headed connection pins called out to ASTM A449 or AASHTO M-164.

According to the American Institute of Steel Construction, quenched and tempered bolting material cannot be welded or heated. Applying heat to steel that has already been quenched and tempered will alter the mechanical properties of the steel in the area that has been heated. This compromises the integrity of the product and exposes both the supplier and the end user to potential liability due to these pins failing in the field. To avoid this problem, the correct way to manufacture a high strength barrier pin with a welded plate and/or nut would be to take “as rolled” medium carbon or medium carbon alloy steel round bar, cut it, weld the washer, and then send the entire assembly out for heat treating after performing the welding operation. The pin would then need to be tested in a finished condition to ensure that the mechanical properties are within the parameters of the applicable ASTM/AASHTO specification. If not manufactured and tested properly in this way, the manufacturer, as well as the contractor using the barrier pins, could be exposing themselves to a tremendous amount of liability.

Due to this potential for improper manufacturing, several states have approved headed pins that are heat-treated after forging as an acceptable alternative to designs that required welding to high strength steel. This option helps to avoid some of the potential pitfalls surrounding welding to high strength steel. If you have doubts about which type of barrier pin is required or approved for your particular job, please contact me and I may be able to help you sort out the correct barrier pins that are needed for your project and avoid any potential liability issues.

Question: What is charpy impact testing?

Answer: The Charpy impact test, also known as the Charpy V-notch test, is a standardized test which determines the amount of energy absorbed by a material during fracture. It is specified for some barrier pins to ensure the material is strong enough to prevent the barriers from moving on impact.

A v-shaped notch is cut into a rectangular sample of the steel, then the sample is cooled to a specified temperature (-20°F in the case of F1554 Grade 105). A specialized pendulum is then swung at the notch in the sample. The pendulum will cleave through the steel and the results of the test are determined based on:

• The distance the pendulum travels past the steel test piece, and
• The way the material fractures

Typically, the only barrier pins that will be subject to a Charpy impact test are parts made to ASTM F1554 Grade 105. For this test, 3 sample pieces are cooled to -20°F and the amount of energy absorbed by each piece is measured. The three samples must show an average absorbed energy of 15 ft-lbs. Additionally, at least one of the sample pieces must show a minimum absorbed energy of 12 ft-lbs. Watch a Charpy impact test here.

There are two main types of barrier fasteners: connecting pins and anchor pins.

• Connecting pins can also be called connection pins, connection bolts, or connection rods, depending on the state. Connecting pins connect two barriers by sliding into loops on the ends of each barrier to prevent them from pulling apart.
• Anchor pins can also be called stabilization pins or anchor bolts, depending on the state. Anchor pins go through a hole in the base of the barrier and into the ground to prevent them from moving.