Tank Size

Tank size seems like a redundant question once you calculate your product tonnage per year. However, you must determine the diameter and height combination that best suites your property. If property space is tight, a taller height and smaller diameter is a good choice. If your property has ground space, but height restrictions due to wires or other obstructions, a lower height and larger diameter is a better fit.

In addition to the individual API 650 tank you intend to build, consider your future expansion possibilities. What is your 10-20 year plan in your business and the possible storage facility expansion? How will the size choice of the next tank work with the future expansion and the property available? Business planning is crucial to making choices on the tank size for the current project.


Containment is the next crucial choice and many factors contribute as to which option is best for your business. The containment choices are a double wall tank, a dike, and an internal PVC liner.

State regulations will determine whether an internal PVC liner is an option. While many states have given the green light to use of PVC liners, several states still do not permit their use. Contrary to other secondary containment choices, the PVC liner serves as the first level of containment, and then the tank serves as the secondary containment. Choosing an internal PVC liner will alter the API 650 design by requiring valve boxes. Valve boxes will contain the head pressure of the liquid product in the case of a valve leak. The benefits of an internal PVC liner are that the API 650 storage tank takes the least amount of space and is usually the most cost effective.

The other containment options serve as the secondary containment for the tank. A double wall tank is an API 650 design of another tank surrounding the tank storing the liquid product. The secondary tank traps the product if the internal tank fails and prevents environmental contamination. However, the cost is almost double that of a single tank for obvious reasons. A lined dike is more economical than a double wall tank, but usually costs more than a liner. Considerations in choosing a dike is that it has a larger land footprint and rainwater will need to be removed to ensure enough capacity for if a tank failure occurs.


The third major API 650 design choice is nozzle size and placement. Your choice in nozzle size depends on the volume of product you want to move in a certain amount of time. The more product in less time to be moved, the larger nozzle size you will need. Examples would be if you want to fill 10 railcars at once, an 8 inch or 10 inch nozzle is a better choice. If you want to fill only 4 railcars at once, a 6 inch nozzle could be adequate. The other considerations in this scenario are the horsepower, size of the pump, and pipe size used in the API 650 storage tank setup.

Another consideration in nozzle size and placement is how your API 650 storage tanks will be filled. If the tank will be filled over the top of the tank, then no additional nozzles are needed. However, many tank owners prefer filling the API 650 storage tank through an inlet nozzle in the side of the tank. This method of filling is also a great way to circulate and thoroughly mix the product. Having an inlet nozzle requires the same inquiry of how fast you want to move a certain volume of product into the tank.

Need some help in deciding what choices in an API 650 tank design is best for your business? Contact our tank professionals at 800-774-3230 or find out more.