Engineering properties of aluminium: Which of the following is a key disadvantage of aluminium as a construction material in process equipment?

Introduction / Context:
Aluminium is widely used due to its light weight, good corrosion resistance, and formability. However, when selecting materials for process vessels and structures, trade-offs between properties must be considered.

Given Data / Assumptions:

• Comparison is to common carbon and stainless steels.
• Focus on mechanical limitations versus advantages.
• General-purpose applications, not specialized heat-treated grades.

Concept / Approach:
Aluminium’s density is one-third of steel, giving excellent strength-to-weight ratio when alloys are optimized. Nonetheless, absolute tensile strength (especially in annealed or non-heat-treated tempers) is lower than typical steels, limiting use in high-stress, high-temperature pressure applications without significant design allowances.

Step-by-Step Solution:
Identify incorrect distractors: availability is not scarce; cost is not extremely high relative to specialty alloys.Strength-to-weight: aluminium actually has a favorable ratio in many alloys.Conclude the primary disadvantage: comparatively lower absolute tensile strength.

Verification / Alternative check:
Compare typical yield strengths: mild steel ~250 MPa; 304 stainless ~200–215 MPa; common Al alloys vary widely but many service grades are lower unless heat-treated, and temperature capability is also lower.

Why Other Options Are Wrong:
Very high cost: untrue versus stainless or nickel alloys. Very low strength-to-weight ratio: opposite of reality. Scarce availability: aluminium is abundant and widely produced.

Common Pitfalls:
Ignoring temper/heat-treatment effects when comparing properties; overlooking reduced high-temperature strength of aluminium.

Final Answer:
Rather low tensile strength (compared to steels)