Stoneware (vitrified clay) sewer sizes: Which of the following nominal sizes is NOT commonly adopted for stoneware sewers?

Introduction / Context:
Stoneware (vitrified clay) pipes are widely used for house connections and smaller gravity sewers because of corrosion resistance. However, there are practical manufacturing and handling limits, so very large diameters are uncommon; larger mains are typically reinforced concrete, ductile iron, or other materials.

Given Data / Assumptions:

• Standard nominal sizes often increase in steps (e.g., 75 mm or 7.5 cm).
• Upper practical limit for stoneware in many standards is around 60 cm internal diameter.
• Very large sizes become impractical to manufacture, transport, and lay.

Concept / Approach:

While 52.5 cm can occur in some step series, 67.5 cm and 82.5 cm are already atypical and 90 cm is generally beyond standard stoneware ranges, where other materials take over. Among the listed options, 90 cm is the clearest non-standard/unsuitable choice for stoneware in common practice, hence the best answer.

Step-by-Step Solution:

Verification / Alternative check:

Procurement catalogs and standards for vitrified clay confirm limited maximum diameters; larger sizes rely on alternative materials.

Why Other Options Are Wrong:

52.5 cm may exist in stepped series; 67.5 and 82.5 are unusual, but 90 cm is the most clearly beyond standard practice, making it the best incorrect size among the choices.

Common Pitfalls:

Assuming all listed step sizes exist for every material; ignoring internal vs. external diameter conventions.

Final Answer:

90 cm