Cost scaling in process design — six-tenths factor rule The six-tenths factor rule is commonly used for estimating which of the following?

Introduction / Context:During conceptual design, engineers frequently estimate the cost of equipment at a new capacity based on a known cost at a different capacity. The empirical “six-tenths factor” provides a quick capacity exponent for many equipment types.

Given Data / Assumptions:

• Known equipment cost C1 at capacity Q1.
• Need to estimate cost C2 at capacity Q2.
• Use a capacity exponent n ≈ 0.6 (the six-tenths factor) as a rule of thumb.

Concept / Approach:The capacity scaling equation is C2 = C1 * (Q2 / Q1)^n. For many process equipment categories, n lies between 0.5 and 0.8; 0.6 is a common default when specific data are not available. This captures economies of scale, where cost increases slower than capacity.

Step-by-Step Solution:Identify base data (C1, Q1) and target capacity Q2.Apply exponent n = 0.6 to compute C2 = C1 * (Q2/Q1)^0.6.Use for quick screening estimates before detailed vendor quotes.

Verification / Alternative check:Compare results with vendor budget quotes or historical cost curves; deviations indicate the need for equipment-specific exponents.

Why Other Options Are Wrong:

• Installation, piping, and utilities each follow different estimating bases and factors; the six-tenths rule specifically refers to equipment cost versus capacity scaling.

Common Pitfalls:

• Applying 0.6 universally; some equipment requires a different exponent.
• Ignoring time escalation, material cost swings, and pressure/temperature class adjustments.

Final Answer:Equipment cost by scaling (capacity exponent method)