Fabrication choice: lap joints are generally preferred for plates having what thickness range?

Introduction / Context:
Joint selection in plate fabrication balances strength, ease of manufacture, fit-up tolerance, and leakage risk. Lap joints are simple and economical but are best suited to thinner plates due to alignment and stress considerations; thicker plates typically use butt joints with full penetration welds for structural continuity.

Given Data / Assumptions:

• General fabrication in tanks, ducts, and low-pressure fabrications.
• Standard carbon steel plates with typical shop tolerances.

Concept / Approach:
With increasing thickness, lap joints become harder to align, and eccentric load paths cause higher bending stresses at the overlap. Below about 12.5 mm, lap joints remain practical and economical; above that, butt joints are favored to maintain alignment and reduce stress concentrations.

Step-by-Step Solution:

Verification / Alternative check:
Fabrication guides and codes commonly reference lap joints for sheet and thin plate; butt welds dominate in heavy plate construction and pressure parts.

Why Other Options Are Wrong:

• > 3 mm or > 5 mm: Too broad; does not reflect the practical upper bound.
• 5–10 mm: Overly narrow and not the commonly cited cutoff; laps extend up to about 12.5 mm.

Common Pitfalls:
Using lap joints in cyclic or fatigue-sensitive locations; not sealing laps in corrosive service which can trap fluids at the faying surface.

Final Answer:
< 12.5 mm