Building a Better Tank Car

DOT-111 tankers like the one pictured here were not designed to carry oil when they entered service in the 1960s.
DOT-111 tankers like the one pictured here were not designed to carry oil when they entered service in the 1960s.

In the wake of a deluge of oil tank fires and train derailments, the old industry standard DOT-111 oil tanker hasn’t maintained a good public image.

With over 300,000 DOT-111s in the North American fleet, the non-pressurized rail car with a 20 to 30 thousand gallon tank has long been a popular choice for shipping hazardous and non-hazardous material.

Then the fires came, and everything went off the rails.

A boom in crude oil from North Dakota’s Bakken Shale reserves was followed fast by alarming numbers of railway accidents. Experts discovered that Bakken crude oil is more volatile than other crude oil and ignites at significantly lower temperatures.

In short, the tankers simply weren’t thick enough to handle the volatile oil. The DOT-111’s thin skin would suffer oil spilling ruptures that then exploded once exposed to a spark. Even the fittings and valves were completely torn off during a derailment.

The DOT-111, intended as a non-pressurized tanker, also lacked any kind of pressure relief device to prevent various natural gas liquids found in North Dakota oil from expanding into explosive vapor. The higher the pressure those gasses created, the more likely the tank was to rupture.

Building the CPC-1232 CLICK TO ENLARGE
Building the CPC-1232

Because of this, a voluntary new standard was used to create a new thicker-skinned tanker called the CPC-1232. The standard was introduced in October 2011 with plans to have the DOT-111s completely replaced by 2025.

The new tanker’s features, including half-height head shields (reinforced tank ends that offer extra protection against heat and rupture) and a ½” thick steel shell, should have prevented further explosions. However, the slow adoption and transition to the new standard means many DOT-111 cars that are either partially adapted to the new standard or completely unchanged are still on the rails. If one of these older cars ruptures, it puts the whole train at risk, regardless of standards.

CPC Safety Features

It is still not clear what part, if any, the CPC-1232 tankers played in the recent series of derailments. However, lingering doubts have resulted in a call for a newer, sturdier standard, the DOT-117.  The new standard would make full-height head shields mandatory, require 9/16-inch steel shells, extra thermal protection, removal of certain protruding parts on the lower side of the tank that are easily torn off during derailment, and electronically controlled pneumatic brakes. Additional reinforcements designed to make the tanker near impervious are also under consideration, including increased puncture resistance.

The hope is that this standard will further improve the safety of tankers but also be adopted as a federally enforced standard that would make transition to the DOT-117 mandatory. The faster a uniform standard is adopted, the less likely an accident is to occur.

Tank Car Differences        CLICK TO ENLARGE

It’s still unclear whether or not a government enforced standard will be approved, but we’ll be sure to report on it here. In the meantime we welcome you to visit AWS Learning, where you can find online courses, virtual lectures and other digital tools to help you expand your welding career.

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