Cast iron (spun) water pipes: choose the incorrect nominal internal diameter (mm) from the list of typical standard sizes.
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A300 mm
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B400 mm
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C500 mm
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D550 mm
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E600 mm
Answer
Correct Answer: 550 mm
Explanation
Introduction / Context:Standardization of nominal diameters simplifies procurement, inventory, and fittings for cast iron (and ductile iron) pipe networks. Non-standard sizes complicate jointing and spares.
Given Data / Assumptions:
- Typical nominal sizes progress in standard steps (e.g., 80, 100, 150, 200, 250, 300, 350, 400, 450, 500, 600 mm, etc.).
- Question asks for the incorrect (non-standard) size.
Concept / Approach:Identify the odd size that does not belong to the common standardized series used in municipal systems and catalogs for C.I. spun pipes.
Step-by-Step Solution:
Scan listed sizes and compare with the standard sequence.300, 400, 500, 600 mm are common nominal steps.550 mm does not typically exist as a standard C.I. nominal diameter.Verification / Alternative check:Checking fittings and valves catalogs also reveals the absence of 550 mm as a usual nominal size.
Why Other Options Are Wrong:The remaining options correspond to standard sizes commonly available in pipes, valves, and specials.
Common Pitfalls:Assuming any intermediate number could be ordered; network components must align with prevailing standard sizes.
Final Answer:550 mm