Welded vs. Bolted

The experts seem to agree that the debate over welded tanks vs. bolted tanks will never be resolved. There are certainly pros and cons to each type of tank. As a contractor, SCCI has installed and will continue to install both welded and bolted tanks.

However, if pressed for our opinion, we do have a preference for welded steel tanks, which is based on the following list of reasons culled from our experience in the field:

• Welded tanks are inherently more resistant to earthquake damage than equivalent-capacity bolted tanks with the same dimensions. On a bolted tank, every bolt is a potential point of weakness. Consequently, there have been more catastrophic failures of bolted tanks than welded tanks from seismic activity.
• Welded tanks can be built in any size and capacity up to 20MG. Bolted tanks generally come in standard sizes, which are dictated by the manufacturer, not the customer.
• For two tanks of equal capacity, the welded tank is made of thicker/heavier steel, adding years to its useful life.
• Welded tanks can be easily and cost-effectively adapted for cathodic protection systems, which extend the useful life of the tankís steel and its coatings. Because bolted tanks are gasketed, expensive jumper connections must be used to bond together every stave of a bolted tank.
• Welded steel tanks are easy to recoat. Because bolted tanks have so many inaccessible areas that are subject to corrosion, they must be disassembled, recoated, regasketed and then reassembled.
• With proper maintenance, the useful life of a welded tank is between 75 and 100 years. The lifespan of a bolted tank is between 25 and 30 years. So even though bolted tanks can be less expensive initially, this cost advantage disappears over time. Bottom line: The cost benefit per year of useful service is lower for welded tanks.

In the interest of fairness, we should point out two specific advantages of bolted steel tanks:

• A bolted tank is made of smaller sections, which allows them to be erected more easily in locations where limited access prevents the use of the larger cranes required for welded tank installations.
• Bolted tanks are typically erected more quickly than welded tanks. However, since this is a website for SCCI, it is important to point out that we have developed a project management system that can let us to go from order to completion of a welded tank as fast or faster than a bolted tank. (Keep in mind that the average time between order and delivery of a bolted tank to the site is six to eight weeks.)