Pressurized pipelines and water hammer: Identify the correct statements about internal pressure, hydraulic gradient, and surge (water-hammer) effects.

Introduction / Context:
Understanding pressure relationships in pipelines is essential for safe design. Internal pressure arises from static head and dynamic effects; the hydraulic gradient line (HGL) visualizes energy grade, and operational transients like rapid valve closure cause water hammer that can exceed design pressures if unmanaged.

Given Data / Assumptions:

• Closed conduits running full under steady or transient conditions.
• Incompressible liquid approximation for steady analysis; finite wave speed for surge.
• HGL and energy grade line are well-defined.

Concept / Approach:

For full pipes, piezometric head at a point is the vertical distance from the HGL to the point. At rest, pressure equals static head. Transients (e.g., sudden closure) induce pressure waves that add to static pressure—water hammer—requiring surge mitigation (air vessels, surge tanks, slow-closing valves).

Step-by-Step Solution:

Verification / Alternative check:

Pipe-surge textbooks confirm that static head plus surge governs maximum internal pressure, and HGL provides the geometric visualization of pressure distribution.

Why Other Options Are Wrong:

• Each individual statement is correct; selecting fewer than all leaves out essential aspects of pipeline hydraulics.

Common Pitfalls:

• Ignoring elevation of pipe center when interpreting HGL.
• Underestimating water hammer when using quick-acting valves or long rising mains.

Final Answer:

All the above.