Securing the integrity of rail tank car supply chains

Article 1: The importance of rail tank car liners for sulfuric acid transportation

Sulfuric acid is one of the most widely used and produced chemicals in the world, as well as being one of the most-produced industrial chemicals in the United States by tonnage. Those facts carry significant weight for anyone working across fertilizers, steel, mining or battery manufacturing; all industries that depend on steady, reliable access to the material at high concentrations and in large volumes.

Due to its extensive and widespread use, plus health and safety considerations owing to its corrosive nature, there are well-established processes for the safe, efficient movement of sulfuric acid from producer to end user. In the US, rail is the dominant mode of transport for bulk quantities of acid and the integrity of the tank cars carrying it - especially the linings protecting their internal steel surfaces - has a direct bearing on supply chain reliability, cargo quality, and commercial outcomes across the sector.

A chemical at the heart of industry

The range of industries that depend on sulfuric acid is broader than most people appreciate; so much so that its consumption is used as an index of industrial development. Phosphate fertilizer production accounts for more than half of global consumption, but the acid is equally essential to petroleum refining, copper smelting, pulp and paper production, and a range of chemical synthesis processes. Battery manufacture is another rapidly growing end-use, driven by demand for energy storage across other sectors. Each of these applications places distinct demands on supply, from the acid concentration grade required to the volume and frequency of delivery.

The complexity of rail transport

A batch of sulfuric acid can pass through multiple legs of the supply chain before it reaches its final application. From the production plant, it may travel to a storage terminal or directly to an industrial customer. Once used and diluted, spent acid can be transported again to a regeneration facility, purified, and returned to the supply chain at commercial concentration. Unit trains of 36 to 56 tank cars, each holding around 15,000 gallons, are the backbone of this distribution network, moving acid between production sites, terminals and end-users at scale.

Ownership and operational responsibility

The ownership and operational structure of this fleet adds a layer of complexity with implications for how rail cars are built and maintained. Tank cars are typically built and leased by manufacturers who carry responsibility for the external condition of the asset. The shipper, by contrast, takes on responsibility for the internal condition, including the lining, and is contractually required to return the car in its original state, meaning that the service life, repairability and turnaround time are not technical considerations, but carry measurable financial consequences. 

The critical role of coatings

Concentrated sulfuric acid is a severe test for any containment system. At the concentrations used commercially, it rapidly attacks unprotected carbon steel, and even localised lining damage can compromise both the structural integrity of the car and the purity of the acid cargo. Contamination or discolouration of the acid can bring commercial implications that extend well beyond the immediate cost of repair: the affected product may be rejected and the car taken out of service at precisely the moment when demand is high.

The internal linings of sulfuric acid rail tank cars are therefore a critical component of industrial supply chains, operating largely out of sight, but underpinning the flow of materials that reach some of the most essential manufacturing sectors in the economy. As demand from those sectors grows, particularly in battery production and the broader energy transition, the performance requirements placed on the transport infrastructure that serves them are also growing.

Rethinking traditional lining technology

Against this backdrop, the coatings technology that has been relied upon by sulfuric acid supply chains is also being re-examined. For decades, the industry has relied upon a traditional solution based on baked phenolic technology and there are considerable benefits to this technology as the industry standard, not least for its ability to maintain the purity of the cargo, with minimal contamination or discolouration. In addition, asset owners are understandably comfortable with a solution that has a proven track record.

However, there are also considerable drawbacks to this solution, which are becoming more and more apparent as performance expectations and industry standards rise, and the pressure to improve availability and repairability of these high-value assets increases.

In response, a new generation of rail tank car linings are coming to the market that can deliver the same standards of sulfuric acid purity, while driving up standards of safety, application and lifecycle costs. 

Coming next

In the next article in this series, we will take a closer look at how old assumptions about rail car lining technologies are being challenged, and how new solutions, such as Ceilcote 4098 from International®, can provide enhanced protection for the assets that underpin sulfuric acid supply chains through a new approach – one that looks beyond traditional baked phenolic technology in favour of a next-generation low bake solution.