Boiler classification: A “high-pressure” boiler is commonly defined as one that generates steam at pressures exceeding which threshold value (use kg/cm² as the unit)?

Introduction / Context:
Boilers are categorized by pressure level because materials, safety valves, drum design, and water–steam circuitry depend strongly on operating pressure. Recognizing the conventional boundary for “high-pressure” helps in selecting codes and standards, and in anticipating efficiency and superheat levels.

Given Data / Assumptions:

• Conventional textbook/industry classification for stationary boilers.
• Pressure unit is kg/cm² (approximately bar).
• Focus on threshold commonly cited in competitive exams and practice.

Concept / Approach:
Traditional classifications consider boilers with steam pressure above about 80 kg/cm² as “high-pressure.” Examples include Benson, Lamont, and Loeffler types. Below this, units are often termed low- to medium-pressure with simpler drum and circulation arrangements.

Step-by-Step Solution:

Verification / Alternative check:
Standard boiler engineering texts list high-pressure boilers as those exceeding roughly 80 kg/cm², consistent with the given choices.

Why Other Options Are Wrong:

• 10, 30, 50: Typical of low to medium pressure ranges; not the usual “high-pressure” designation.

Common Pitfalls:
Confusing “supercritical” classification (beyond critical pressure) with merely “high-pressure”; these are distinct categories.

Final Answer:
80