Materials of construction – Relative cost for pressure vessels: Among the following common choices for pressure-vessel fabrication, which material is typically the costliest per unit mass?

Introduction / Context:
Material selection for pressure vessels balances corrosion resistance, strength, fabricability, availability, and cost. Exotic alloys can drastically raise capital cost, so understanding relative pricing is essential.

Given Data / Assumptions:

• Typical market conditions and standard grades.
• Comparison is qualitative (relative cost ranking) rather than exact ₹/kg.
• Titanium is considered in corrosion-resistant service (e.g., chloride-rich media).

Concept / Approach:
Low alloy steels are inexpensive mainstream materials. High alloy steels (stainless) are costlier but still far below titanium for most grades. Lead is inexpensive per kilogram but is heavy, soft, and used for specific linings, not general vessel shells.

Step-by-Step Solution:
Rank by typical market price: low alloy steel < high alloy steel < titanium.Lead is low cost but unsuitable structurally; used selectively for lining.Therefore, titanium is the costliest option among those listed.

Verification / Alternative check:
Vendor quotes and historical cost data consistently place titanium well above stainless steels and carbon/low-alloy steels.

Why Other Options Are Wrong:

• Low alloy steel: economical structural choice.
• High alloy steel: costlier than low alloy, but cheaper than titanium in most cases.
• Lead: cheap but not a vessel shell material; used as lining where needed.

Common Pitfalls:
Choosing titanium solely for corrosion resistance without evaluating cheaper alternatives (e.g., rubber-lined steel, FRP, or specific stainless alloys).

Final Answer:
Titanium