Difficulty: Easy
Correct Answer: 0.85
Explanation:
Introduction / Context:
Welded joint efficiency is a factor used in the mechanical design of pressure vessels and storage tanks to account for the quality of welds versus base metal. In chemical process equipment design, this factor directly influences required thickness and allowable stress, ensuring safe operation under internal pressure.
Given Data / Assumptions:
Concept / Approach:
The joint efficiency E scales the required thickness: lower E implies thicker walls for the same pressure. Typical values used in design handbooks: E ≈ 1.00 for fully radiographed welds, E ≈ 0.85 for spot radiography or standard shop welds, and lower values when quality control is minimal. Many textbook problems and preliminary designs adopt E = 0.85 as a practical, conservative default when full radiography is not mandated.
Step-by-Step Solution:
Step 1: Recognize that design thickness t increases as joint efficiency E decreases.Step 2: Identify common reference values: E = 1.00 (full radiography), E ≈ 0.85 (spot radiography/typical), E ≈ 0.7–0.8 (older or less controlled cases).Step 3: For routine chemical equipment design without full radiography, standard practice assumes E ≈ 0.85.Step 4: Select the closest option representing this conventional assumption.
Verification / Alternative check:
Compare with code tables and typical design examples: preliminary sizing examples often tabulate E = 0.85 when radiography is not specified, increasing required thickness modestly while staying practical for fabrication and cost.
Why Other Options Are Wrong:
0.55: Unrealistically low for modern shop welds; would over-penalize thickness.0.75: Possible in some legacy contexts, but not the most common assumed default.0.95: Implies near-full radiography quality; not standard unless explicitly mandated.1.00: Reserved for fully radiographed joints; not the assumed norm here.
Common Pitfalls:
Using E = 1.00 by default can dangerously under-estimate thickness when radiography is not performed. Conversely, choosing an excessively low E inflates cost and weight without proportional safety benefit.
Final Answer:
0.85
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