Locomotive Boiler — Practical Upper Limit of Steam Pressure Select the nearest practical limit of maximum working steam pressure for a classic locomotive fire-tube boiler.

Introduction / Context:
Locomotive boilers are mobile fire-tube units with an internal firebox. Their allowable pressure is constrained by shell design, materials, and safety considerations. Typical historical working pressures help anchor order-of-magnitude intuition for MN/m^2 (MPa) units.

Given Data / Assumptions:

• Conventional riveted/welded locomotive boilers, not modern water-tube or supercritical units.
• Standard steel shells and stayed fireboxes as historically used.
• Working pressure rather than test or burst pressure.

Concept / Approach:
Typical locomotive boilers operated around 1.0–1.6 MPa, with many later designs achieving roughly 1.6–2.0 MPa. Converting MPa to MN/m^2 (1 MPa = 1 MN/m^2) makes option 1.8 MN/m^2 (≈ 18 bar) the realistic upper working range, while 18 or 180 MN/m^2 are far beyond fire-tube shell limits.

Step-by-Step Solution:
Translate units: 1 MN/m^2 = 1 MPa ≈ 10 bar.Check historical ranges: many locomotives ~12–18 bar (1.2–1.8 MPa).Choose the closest practical maximum: 1.8 MN/m^2.

Verification / Alternative check:
Design codes and preserved locomotive data commonly cite working pressures from 1.2 to about 1.8 MPa, with hydrostatic test pressures higher but not relevant to “maximum working” values.

Why Other Options Are Wrong:

• 0.18 MN/m^2: Only 1.8 bar, too low for mainline service.
• 18 MN/m^2 or 180 MN/m^2: 180 or 1800 bar, impossible for fire-tube locomotive construction.

Common Pitfalls:
Confusing MN/m^2 with kN/m^2; always convert to MPa or bar to sanity-check.

Final Answer:
1.8 MN/m^2