Tank budgets at feasibility stage: what a Class 5 estimate means and what a firm offer needs

October 19, 2026  ·  Indumor

Class 5 estimate: in AACE International’s classification, the cost estimate prepared when a project is only 0 to 2% defined: an idea, a list, a first sketch. Its typical accuracy range is wide: the final cost can land 20 to 50% below or 30 to 100% above it. The opinion: it is a tool for deciding whether a project moves forward, not for signing a purchase order.

The classification was published in the late nineties — hence the recommended practice’s name, 18R-97 — and today it is used by mining companies, oil producers and engineering firms worldwide. When a project at feasibility stage asks for a price on a lot of tanks, these are the five things worth knowing.

1. A good budget states its assumptions

Without specifications, the fabricator has to assume materials, thicknesses, reference standards, wind and seismic loads, and the coating system. Those assumptions must be written down, line by line.

2. It states what is included and what is not

Typical exclusions are freight to site, erection, foundations, instrumentation, third-party inspection and taxes. Two budgets with the same total can describe very different scopes.

3. With a defined list, uncertainty shrinks

If tank sizes are already fixed, the range on a tank budget can be considerably narrower than that of the project as a whole. What moves the number most are thicknesses, accessories and finish. A budget for a lot of tanks with fixed sizes can work to a range on the order of ±30%, far narrower than a Class 5 range for a whole project; it is worth saying so in exactly those words, so nobody mistakes one number for the other.

4. Certain data turn the estimate into a firm offer

Material and coating specifications; final dimensions and nozzle lists; fluids with their densities and temperatures; site data such as altitude, snow, wind and seismic zone; inspection and documentation requirements; and logistics, above all the maximum transport width to site. An example list is in the tanks of a mine.

5. Price is not the only thing to compare

Lead time, the partial delivery schedule, payment terms and documentation — as-built drawings, certificates, test reports and data book — weigh as much as the total. For quotes in general, see how to request a fabrication quote.

One piece of advice, the same we give any engineering firm at Indumor: ask for the feasibility budget to state what it assumes and what it excludes. It is the only way to compare two numbers, and to make today’s number resemble the one on the purchase order. The full line is on our steel tanks page.

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