Horton sphere storage for liquid ammonia: identify the incorrect statement about dimensions, support, working pressure, and service conditions.

Introduction / Context:
Horton spheres are spherical storage vessels widely used for liquefied gases (e.g., ammonia, LPG). Their geometry gives favorable stress distribution and minimum surface area per unit volume. This question checks practical knowledge about their dimensions, supports, and pressure ranges.

Given Data / Assumptions:

• Spherical storage for ammonia and similar volatile liquids.
• Conventional carbon steel construction with standard supports.
• Moderate pressures for refrigerated or ambient storage.

Concept / Approach:
Spheres use columns/legs for support and commonly range from a few meters to a few tens of meters in diameter. Because of uniform membrane stress, required thickness is lower than for a cylindrical shell at the same pressure. Operating pressures for such storage are typically moderate; extremely high pressures (hundreds of kg/cm2) are not used for bulk storage spheres, especially at sub-zero conditions where low-pressure refrigeration is favored.

Step-by-Step Solution:

Verification / Alternative check:
Industry practices for ammonia storage employ refrigerated low-pressure tanks or pressurized spheres at modest pressures—far below hundreds of kg/cm2.

Why Other Options Are Wrong:

• (a) Typical size and supports are correctly described.
• (b) Spherical shells indeed need less thickness and insulation than comparable cylinders.
• (c) Moderate-pressure service is a standard application for Horton spheres.

Common Pitfalls:
Confusing transport cylinders (high-pressure) with large fixed storage spheres (moderate-pressure). Also, assuming low temperature always implies high pressure.

Final Answer:
Used for storing liquids at sub-zero temperature at very high pressure up to 200 kg/cm2.