🔍 Key Concepts

• Boiler furnace construction and how the furnace arch is supported • The role of refractory materials and shapes inside water‑tube boilers • Difference between a shape that supports brickwork and hardware like bolts or coatings

💭 Think About

• Think about what physically supports or forms the furnace arch inside a water‑tube boiler: is it usually a metal fastener, a shaped refractory piece, or a deposit? • Consider which option describes an intentional, structural part of the furnace design rather than a by‑product or a minor filler material. • Ask yourself where you would most likely find a corbel: in structural brickwork, as soot, as a simple fillet, or as an anchoring bolt?

✅ Before You Answer

• Eliminate any choices that describe unwanted deposits or by‑products of combustion rather than designed components. • Focus on options that could be a supporting projection or shaped piece used in brick or refractory construction. • Check which option best matches something that would physically carry or support the furnace arch in a water‑tube boiler.