In piping layout and fittings selection, which component is primarily used to change the direction of a pipeline while maintaining a fixed centerline radius or angle?

Introduction / Context:
Piping systems need fittings to accomplish various functions: direction change, connection/disconnection, branch creation, and allowance for thermal expansion. Selecting the correct fitting ensures hydraulic performance, mechanical integrity, and ease of maintenance.

Given Data / Assumptions:

• Standard industrial piping following common codes.
• Fixed-angle changes such as 45°, 90°, or 180° are frequently needed.

Concept / Approach:
An elbow is the standard fitting to change pipeline direction. Elbows are commonly available as 45°, 90°, and 180° bends, with short-radius (R ≈ 1D) and long-radius (R ≈ 1.5D) variants. Other fittings serve different purposes: a union enables quick disassembly; a flange provides a bolted joint; a compensator (expansion device) accommodates movement or thermal growth rather than acute direction change.

Step-by-Step Solution:

Verification / Alternative check:
Piping catalogs and standards list elbows under directional fittings; unions and flanges are categorized under joints/connectors; compensators are flexible devices for expansion/oscillation control.

Why Other Options Are Wrong:

• Union: used for disconnection, not direction change.
• Flange: bolted connection; direction is defined by the mating flanges and spool.
• Disc compensator: used to absorb expansion, not to create a fixed bend.

Common Pitfalls:
Confusing elbows with bends formed in situ; both change direction, but elbows are prefabricated fittings with standard radii.

Final Answer:
Elbow