Cost index application (CEPCI): The present cost of a plant = original cost × (current index / past index). In the Chemical Engineering Plant Cost Index (CEPCI), the most heavily weighted component is:

Introduction / Context:
Cost indices allow quick escalation of historical capital costs to current prices. The Chemical Engineering Plant Cost Index (CEPCI) is widely used for process plants, combining weighted subindices to reflect equipment and material cost trends.

Given Data / Assumptions:

• Present cost = Original cost × (Index_now / Index_then).
• We focus on CEPCI composition by weight.
• We assume standard CEPCI category weights used in practice.

Concept / Approach:
CEPCI aggregates several categories. Historically, the dominant weight belongs to fabricated equipment and process machinery (pressure vessels, exchangers, tanks, reactors, large rotating equipment). Because these items represent a major portion of installed cost and track key commodity and fabrication cost trends, this subindex drives overall movements more than smaller categories.

Step-by-Step Solution:

Verification / Alternative check:
CEPCI documentation and textbooks in plant design consistently show equipment and machinery as the most significant weight.

Why Other Options Are Wrong:

Common Pitfalls:
Applying a single index to projects with unusual content (e.g., instrumentation-heavy plants); consider custom weighting when atypical.

Final Answer:
fabricated equipment and machinery