The power grid in the United States is complex, made up of generating stations, substations, transmission lines, as well as step-up and step-down transformers. Each of these is designed by the utility industry to fit within the larger power system, with the goal of moving power safely with as little loss over the greatest distance to the most people as possible. No easy task.
For example, consider just one part of the system: latticed transmission towers and power lines. These span the roadways and stretch across the fields everywhere. There are nearly 360,000 miles of transmission lines in the United States alone, carried by six different styles of transmission towers, each designed for a different voltage of line. Transmission towers are so common, they become a taken-for-granted part of the horizon. We forget that they require constant repair, and in many cases, replacement.
The utility industry maintains steel transmission towers according to ASTM International or the American Society of Civil Engineer (ASCE) standards, many of which overlap. This means that there are specific criteria depending on where a fastener will go based on what stresses it may face. Some of the cross-bars in a given tower are solely for the purpose of tension. Others are meant to hold the lines. Some are more likely to face the brunt of wind shear.
ASTM has specific standards for the hexagon and square-headed bolts used in these towers. ASTM defines the use for Type 0 bolts, which include hot-dip, zinc-coated bolts made of low or medium carbon steel; Type 1 bolts, which are different in that they are made of quenched and tempered medium carbon steel; and Type 3 bolts, which are bare, quenched, and tempered bolts made of weathering steel. ASTM even outlines the processes by which the bolts must be made, the allowed additives, and the quenching medium. They also argue for the necessity of testing bolts for hardness, tensile strength, and shear strength. And this is only the bolts: there are similar standards for other fastening products: guyed wire, hex jam pals, links, rigging hardware, step bolts and step bolt clips, and turnbuckles.
The standards are complex for a simple reason: the repercussions of a failing tower – or any part of the utility system failing – is too significant to the safety and operations of the country.
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