Pressure in sewers: Identify the correct statements about internal pressure and its structural implications for pressure sewers.

Introduction / Context:
Sewers are commonly gravity conduits, but some reach segments or rising mains operate under pressure. Understanding internal pressure and corresponding stresses is crucial to material selection and structural safety, especially for ductile iron, steel, or pressure-rated PVC/HDPE pipes.

Given Data / Assumptions:

• Pipe runs full and is pressurized (e.g., a rising main).
• Internal pressure acts radially on the pipe wall.
• Pipe design follows tensile (hoop) stress criteria.

Concept / Approach:

For a thin-walled cylinder, hoop stress sigma_h ≈ p * D / (2 * t), where p is internal pressure, D diameter, t wall thickness. This tensile stress governs pressure rating. Materials and joints must resist tension; thrust blocks or restrained joints resist axial forces at bends and fittings.

Step-by-Step Solution:

Verification / Alternative check:

Manufacturers provide pressure classes tied to allowable hoop stress; design checks verify safety under surge and steady-state pressures.

Why Other Options Are Wrong:

Options (a), (b), and (c) are each correct; thus the comprehensive correct choice is (d).

Common Pitfalls:

Ignoring surge/transient pressures; underestimating axial forces at bends; using non-pressure-rated joints in pressure segments.

Final Answer:

All of the above