The Roller Coaster Thrill Provided by Steel

For many school children in the northeastern part of the United States (and elsewhere), summers mean beaches, barbecues and roller coasters.  Many teens (and adults) believe there needs to be at least one amusement park visit before the summer ends and school starts. There’s nothing like a ride on a steel roller coaster that has a top speed of 77 mph and a drop of 221 feet to give one a thrill of a lifetime. I’m referring to the Superman hypercoaster, located about two hours west of our corporate headquarters in Massachusetts. But that’s just a toddler compared to New Jersey’s Kingda Ka hydraulic launch rocket coaster that boasts a 418-foot drop and speeds of 128 miles per hour. The United States is not the only country with a fondness for mind-numbing speed and perilous drops; Japan’s Steel Dragon boasts the world’s longest coaster at over 8,000 feet.

That’s a lot of steel for one amusement ride.  And a lot of potential danger.

In addition to hoping that the engineers got the loops and drops right so one does not go airborne while sitting on the coaster, thrill riders should also consider the manufacturing of the coaster’s pieces, especially the metalwork.  There are a lot of metals and alloys used in these steel coasters that can cover over a mile’s distance. The Minerals, Metals & Materials Society reported that among its responsibilities, the crew at one Ohio amusement park is in charge of maintaining 13.4 km of steel and wood track.

And the metal better be made up of the correct materials — the kind that can withstand heat and the outdoor elements, daily wear and tear, and the friction of cars zipping along their tracks faster than a motorist is allowed to drive on the highway. The roller coaster manufacturers keep their specifications pretty close to the vest, but we can surmise that alloy steel, factory-formed tubular steel, and carbon steel make up the bulk of the materials. And those materials better meet the engineer’s specifications.

As we learned in a previous article, steel is widely-used for its strength, but it must also meet certain requirements for stiffness, depending on the end product it is used to make. A material can have high strength and low stiffness. If a metal cracks easily, it has low strength, but if it has low stiffness, it can deflect a high load.  All steel has approximately the same stiffness, but comes in many different strengths depending on the alloying metals used.  Stainless steel comes in more than 100 grades which are created by adding alloys such as chromium, silicon, nickel, carbon, nitrogen, and manganese to impart properties such as heat resistance, strength, flexibility, and ductility. Martensitic or semi-austenitic steels are the strongest due to the addition of elements such as aluminum, copper and niobium.

Metal alloy material verification for quality assurance and quality control (QA/QC) is critical to product integrity, and can affect the safety of the final product. Incorrect or out-of-specification metal alloys can lead to premature and potentially catastrophic part failures, which can be expensive, damaging to your reputation, and, sometimes, result in loss of life. X-Ray fluorescence (XRF) analyzers are usually the technology of choice for positive material identification to verify incoming or in-stock raw material and their alloy grade, and since the technology is completely nondestructive, it can be used for a final quality check of finished products without concern. This “double-check” process helps ensure that the incoming raw materials and the outgoing finished parts meet the expected engineering requirements.

Even wooden coasters that utilize steel for their trusses and tracks needs to make sure they are using the correct materials.  According to Coaster101,

Tubular roller coaster track is typically formed by heating and then permanently bending steel pipe into the desired shape. However, this process can cause significant fatigue in the material of the pipe. The roller coaster track needs to support static loads during construction and installation and dynamic loads as a coaster train travels along it. During the lifetime of the roller coaster, the stresses due to the aforementioned loads along with the initial manufacturing stress results in the pipe needing to be replaced- a very costly endeavor….

The other drawback for using bent steel rods or pipes is the resulting shape is not always one-hundred percent accurate, which can potentially become a large issue when you are dealing with thousands of feet of pipe. Metal typically bends at either its weakest point or where the strongest force is applied over a span. Manufacturers then attempt to fix the pipe by bending it again or end up settling for a less-than-perfect piece.

For the right bend, it needs to be made of the right materials. Small, maybe even minute, ‘extra’ elements – sometimes known as trace or tramp elements — may be contaminants and adversely affect the alloyed products.

These situations just reinforce the idea that to keep their rides safe, parks need to have regular inspections of the ride components as well as the rides themselves. The Ohio park workers use nondestructive testing methods to examine the rails regularly, looking for parts that need to be replaced. The National Association of Amusement Ride  Safety Officials (NAARSO)  administers a certification program for amusement device inspectors which recognizes that the individual possesses a certain level of knowledge required to perform an amusement ride inspection. Formal training consists of “NAARSO approved amusement ride seminars, conferences, and/or local training on related subjects such as welding, NDT, hydraulic, operations, electrical or mechanical systems.”

Positive Material Identification and Inspection with XRF

To keep riders safe, however, park owners are not the only ones who need to implement NDT and inspection programs.  The manufacturers of all the steel and metal components also need to put into practice their own metal and alloy verification procedures, all along the manufacturing floor.

That also includes verification of nuts and bolts. Metal fasteners, such as screws, nuts, bolts, and clamps, are universal components of many machines and assemblies. In critical applications such as aerospace (and roller coaster) manufacturing, fasteners made with the wrong alloy can result in costly or even catastrophic consequences, as evidenced in documented cases of counterfeit fasteners in industry.   If fasteners used in critical applications such as in the manufacture of airplane parts are not made with the precise alloy required, they cannot support the weight and stresses they are designed to bear. (You can read more about quality assurance of critical fasteners in this article.)

With all of these potential safety hazards, it seems peculiar that, according to this article, there are no federal regulations or oversight of the rides and inspections differ from state to state.  So I guess we have to have as much faith in the park’s established inspection procedures, and the manufacturer’s alloy identification methods, as we do in the engineering that will keep us safely seated in the fabricated car that is careening corners at breakneck speed and plummeting down a very steep hill.

By the way, the world’s tallest roller coaster — The Skyscraper at Skyplex, with a 570 foot drop — is scheduled to open in Florida in 2019.

Start screaming now.

Additional Resources:

• Download our free eBook: A Practical Guide to Improving Steel Manufacturing Processes and Production Methods
• Visit our center for Improving Steel Manufacturing Processes and Production