Engineering Discipline Knowledge
The Engineering Discipline Knowledge section checks whether you can apply first principles from your applied branch-Mechanical, Electrical, Electronics, Civil, Chemical, or Metallurgy-to plant-level problems. BHEL supervisor work involves fabrication, assembly, testing, erection and commissioning, so questions often combine units, material behaviour, machine ratings and process control rather than isolated definitions.
Core rules and concepts
- Use SI units consistently: force N, stress N/mm² or MPa, power W, pressure Pa; convert mm² to m² by 10^-6.
- Mechanical: stress = load/area; strain = change in length/original length; factor of safety = ultimate stress/working stress.
- Electrical: Ohm’s law V=IR; three-phase power P=√3 V_L I_L cos φ; rms and peak values differ by √2 for a sine wave.
- Electronics: diode forward bias, transistor switching, logic gates, and signal grounding.
- Civil: bending moment, shear force, concrete grade, soil bearing pressure.
- Chemical/Metallurgy: pH, molarity, hardness, heat treatment, alloy composition and corrosion.
Worked example
A 20 mm diameter mild-steel bar carries a tensile load of 50 kN. Area A = πd²/4 = π(20)²/4 = 314.16 mm². Stress σ = F/A = 50,000 N / 314.16 mm² = 159.2 N/mm² ≈ 159 MPa. If yield strength is 250 MPa, the factor of safety is 250/159.2 ≈ 1.57. The reasoning matters: use force in newtons and area in mm² to get MPa directly.
Traps
Mixing gauge and absolute pressure; using diameter instead of radius in area; treating nominal pipe size as exact bore; confusing peak with rms voltage; ignoring power factor in AC power; and using ultimate strength when a design code specifies yield.